texts: DMX: What should I do with ground and shield?

texts:
I'm currently developing a DMX interface (master interface) with USB and Ethernet connections. The power for my device I'm retrieving from the 5V of the USB connector.

The shield of the USB connector and the Ethernet connector is connected with each other but hasn't any connection with the signal ground. I'm not sure if this is correct, so please correct me if I'm wrong!?

The DMX interface is decoupled with a DC-DC converter (CRE1S0505SC) and a digital isolator (SI8422AB-D-IS).

I'm now wondering what I should do with the shield of the XLR plug? Should I just connected it with the shield of the USB and Ethernet connector? Or isn't the device galvanically isolated anymore if I do that? The pin 1 of the XLR connector is connected with the ground of the DC-DC converter. But I think this should be correct.

The case of my device is plastic.

I know there are many threads in the internet about this. But I haven't found anything which describes my problem exactly. So I would be very happy if anyone could help me!

Edit: I have attached a simplified schematic.


texts: What would be a good use for a memristor?

texts: I am an electronics hobbyist and I found something that I hadn't heard of before, named Memristor. I found some information about how memristors work on this site and I want to know that how it can be used. In which type of application are these components used?


texts: Mesh Analysis has failed to solve this circuit

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I built the following circuit in LTSpice and found each mesh currents to be (which also matches the answer sheet provided by my professor):

  i1: 9A
  i2: 8A
  i3: 11A
  i4: -6A

However, I am unable to solve each mesh current using Mesh Analysis following the sign conventions.

Here's my approach:

  Mesh 1: i1 = 9A
  Mesh 2: R1*(i2 - i1) + i4*3 + R2*(i2 - i3) = 0
  Supermesh: R2*(i3 - i2) + R3*i4 = 0
  Also: i3 - i4 = 17  ===> i3 = 17 + i4

  where R1=6ohm;  R2=4ohm;  R3=2ohm

If I substitute in mesh current from the spice simulation, the supermesh matches where Mesh 2 doesn't. However, I checked many online sites and followed the sign conventions, but I am not able to get it to work, where did I do wrong?


texts: Bipolar transistors that only connect via base to emitter

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I am trying to understand how to use this configuration of the LTC2992 power measure IC and the only part I am confused with so far is the two transistors which I have circled.

What I know so far about this part is the ORGND will change between being rather ground or a maximum of -95V. The GPIO pins are set to input they are both open drain. I don't understand the point of these transistors even after going through the datasheet unless I have missed something. I only theory is that they are acting as diodes so far. Heres a link to the datasheet

https://www.analog.com/media/en/technical-documentation/data-sheets/ltc2992.pdf

The IC itself is meant to be able to sense the power across the sense resistor and then send this data to a master.


texts: Multiplexing a 16 button keypad to an 8 button remote control module

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I am wanting to multiplex a 16 button keypad to an 8 button RC transceiver so that I can have remote control over 16 functions instead of the standard 8.

The transceiver I am using is the 900MHz HumPRC from Linx Technologies. https://linxtechnologies.com/wp/product/humprc-series-remote-control/

I am getting hung up on a couple of things:

Which would make more sense, use eight 2:1 MUX, use two 8:4 MUX, or one 4x4 matrix keypad and a PIC microcontroller?
The radio only has 8 status lines and transmits the image of these status lines across the wireless link. On the receiver side how do I know that a button greater than 8 was pressed?


texts:
So I'm implementing an analog control scheme, and one important component is a first-order high pass filter.

The source signal is the output of a shunt monitor (INA138 - in the circuit below the current source).

In order for the output of the filter be in the range of 0-12V. I've used a 5.6V zener as bias.

simulate this circuit – Schematic created using CircuitLab

As I was measuring with an osciloscope, with no load on my shunt (so Vsource=0V) I've noted a very strange behaviour:
While the zener bias and the op-amp output was at 5.6v RMS, the output of the filter was at 4.6v!

How is that possible? Could it be that the probe is drawing current - thus the drop? This would mean that the probe has a 575K resistance, but  normaly it should be of Mohms of magnitude. Am I missing something else?


texts: For given circuit, does the current "io" through the branch equal zero after short circuit ? [2-port network]

texts:
The circuit is;

simulate this circuit – Schematic created using CircuitLab

For given 2 port network, Im shorting V1 to solve for y22 and y12 and apply a current source at V2.[Y-Parameters]

This is the circuit we get;

simulate this circuit

Now my question is; what will be io (current through 3-ohm resistor branch) will be equal to? Will it flow through 6-ohm resistor ? Or will it be equal to "zero"?


texts:
I've been designing a board for manufacturing with JLCPCB. I've finished all the design and created gerber files etc. Now I'm at the step of creating a BOM from KiCad that works with JLCPCB (I need to use this house since my boards contain a lot of components that come pre-soldered from this house). There is a custom plugin that allows KiCad to generate a BOM in the format that JLCPCB wants. But when I try to use that plugin, I get all kinds of errors. The first error I got was this:

Then I tried a few different things (including getting another such plugin which works using Python), none of which worked for me. I'm not an expert in KiCad, so don't know how to fix these deep errors. I need to send this design out for manufacture ASAP, so if anyone knows how to help, please tell. Thanks.


texts: What is the advantage of putting capacitors in parallel with glass fuse tube

texts: I have seen a board and I wonder to know what would be the advantage of having capacitor in parallel with fuse.


texts: VL6180x sensor breakout stays on despite removed VIN

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I'm experimenting with a couple of VL6180x distance sensors on breakouts (http://www.ebay.com/itm/172823051918, the blue ones).

Because the sensor resets its i2c adress when the power is removed, and because I want to use more than one, I need to be able to set the desired adress after boot.

My idea to solve that was to simply turn on the VIN to the sensors one after the other, and set the adress before the next one turns on. Unfortunately it seems like the sensors get power somehow even without any VIN connected. I'm guessing it's through the pullup resistors on the i2c bus.

How can I solve this? Do I have to add something to break the i2c bus connection together with VIN, or are there other better ways?

(Since the project they're intended for have limited free space, I'd prefer a solution with a low component count)


texts: Thevenin equivalent and maximum power transfer theorem question

texts:
I want to find a load resistance's value so that it gets the maximum power transfer, and thus I am using Thevenin's theorem by finding the equivalent circuit's resistance.

By doing so, I got 2929.28 Ω.

The problem is that one of our classmate's claims that the resistance labelled as R4 doesn't have to be taken into account when calculating the equivalent resistance, with no further explanation as to why or how.

The question would be, does that...statement make any sense? Wouldn't all the resistances need to be grouped together in order to get the Thevenin/Norton resistance?

Below is the circuit and my solution:

Thanks!


texts: Power supply: How to diferentiate current source and voltage source

texts:
I found a power supply in my workshop that is marked as 12v@2A it is the typical Chinese power supply to drive leds so it is supposed to be Current Source, but I'm not sure at all, so I would like to know if there is any simple test I can do on the power supply unit to determine if it is a constant current source or a voltage source.

Thanks in advanced.


texts:
simulate this circuit – Schematic created using CircuitLab

There are two buffers made with the TL084CN, which is part of the conditioning of an LTS25-P transformer. Currently, I have put a 100ohm resistor in the non-inverting input, and the feedback is without the resistor.

Is it advisable to add a resistor in feedback? Will the reading be influenced if I do not?


texts: I'm designing a circuit using Logisim that I will later physically implement.  Unfortunately, the gates provided to me in the physical implementation do not include one of the gates I used in my design, namely a 4-input NAND.  I do, however, have access to both 2- and 3-input NANDs.  Is there any way I can take the inputs to the 4-input NAND and use only 2- and 3-input NANDS to achieve the same functionality?


texts: Multiple output Flyback - Stacked transformer - Cross regulation - TL431

texts:
Suppose I have the following output stage of a flyback:

simulate this circuit – Schematic created using CircuitLab
The schematic is a bit simplified but the idea is here. Do not pay attetion to the values of the different components. They are not right. What I wanted to show is that the feedback is function of Vout1 and Vout2. The reference pin of the TL431 is about 2V5. When the reference pin is exceeded, the LED of the optocoupler begins to conduct as a rough approximation. In any case, there are many solutions on Vout1 and Vout2 for having 2V5 to the reference pin. So how could be define Vout2? or Vout1? At a certain point an equilibrium between the two outputs will be reach, but this equilibrium could be unstable? How does it work?
As the transformer is stacked, the ouput voltage Vout1 is function of the output voltage Vout2. Actually suppose there is the same number of windings between the two outputs, Vout1 is equal to 2 times Vout2. Then an equilibrium could be reached  as there is only one unknown parameter into the previous equation for determining  Vout1 (2Vout2) and Vout2 with the reference voltage of the TL431. Nevertheless if Vout1 = 2Vout2. Why do we need to add Vout1 to the feedback? As it seems that Vout1 is regulated through Vout 2? And this what we supposed by remplacing into the previous equation for determining Vout1 and Vout2 with the reference pin voltage.
The flyback is working in DCM.
Thank you very much and have a nice day!


texts: PIC32MX795F512H + DP83822I Transmit Error Signal

texts: I am using PIC32MX795F512H with DP83822I  as the Ethernet PHY transceiver. On the PIC32MX there is a pin for Transmit Error (ETXERR) but no Transmit Error pin on DP83822I. What should I do with the ETXERR pin since I can't connect it to to the DP83822I?


texts: how can I check battery health in an embedded system

texts:
I'm working on an IOT system powered with 30Ah battery (from 4.2 volt to 3.1 volt). I'm checking battery charge level by measuring the battery voltage.

now I'm looking for a way to measure battery health over time. what should I measure to determine the battery health???.


texts: Memory-mapped I/O and Peripheral-mapped I/O in 8085 microprocessor

texts:
In the book it is given that:

  "to identify the I/O devices these devices can be interfaced using address from memory space: MEMORY-MAPPED I/O. Another option is to have a separate numbering (addressing) scheme for I/O devices. The 8085 has separate 8-bit addressing scheme:
  PERIPHERAL-MAPPED I/O."

When the 8085 microprocessor has fixed 64kB of memory which it uses for addressing the different memory locations then how it can share that memory with the I/O address (i.e., for any external peripheral) in memory mapped and how can it use "separate 8-bit addressing scheme" when it has fixed memory in it.

I am unable to understand this. If anyone knows this please explain this in detail or tell me where it is explained in detail.


texts: Finding the supply voltage, knowing the resistance and current

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I am learning the basics of electrotechnics. I had this task for my university that I failed doing and I want to learn how to solve it anyway. Thanks for assistance! :)

Here is the exercise task:
I assume I need to find the \$U\$. Knowing the \$I = 14 A\$ and \$R = 8 Ω\$

This is how I calculated this:

\$ U = IR_{z} \$ where \$ R_{z} = R_{123456}\$ (equivalent resistance)

\$ R_{12} = R_{1} + R_{2} = 4 Ω + 4 Ω = 8 Ω \$

\$ R_{123} = \frac{R_{12}R_{3}}{R_{12}+R_{3}} = \frac{8 Ω * 8 Ω}{8 Ω + 8 Ω} = 4 Ω\$

\$ R_{1234} = R_{123} + R_{4} = 4 Ω + 4 Ω = 8 Ω \$

\$ R_{12345} = \frac{R_{1234}R_{5}}{R_{1234}+R_{5}} = \frac{8 Ω * 8 Ω}{8 Ω + 8 Ω} = 4 Ω\$

\$ R_{123456} = R_{12345} + R_{6} = 4 Ω + 4 Ω = 8 Ω \$

\$ R_{z} = R_{123456} = 8 Ω \$

\$ U = IR_{z} = 14 A * 8 Ω = 112 V \$

Yet somehow 112 V is wrong answer. Any clues, hints? Where did I do an error?


texts: Creating Li-Ion charger with step up to 700mA from 500mA?

texts:
Canon apparently hasn't ever herd of something called USB-charging. The factory AC adapter for this battery(NB-5L) output's 4.2V's at 700mA. Most standard USB chargers output 5V at only 500mA. Would it be feasible to step up 500mA to 700mA for this application? Because it's a Lithium battery I also need some sort of IC to protect from over-charging, I haven't worked much with micro controllers, what kind would I need? I also need to add a IC that can access the batteries communication terminal to light up the LED when the battery is fully charged.

This is one of my first projects of this complexity, and I'm not sure where I should start. Thank you for any help you can provide!


texts: Finding node voltages in a MOSFET circuit

texts:
simulate this circuit – Schematic created using CircuitLab

Considering Vdd=5v I want to calculate the node voltages at P,Q and R.


texts: External to internal antenna setup doesn't increase signal power

texts:
For a larger project where I basically want to boost phone signals indoors using an external antenna I have devised a small experiment to make sure I get the basics right before I expend a lot of energy.

Basically, I have made an enclosure to reduce signal strength in which I put a cell phone displaying the current RSSI or dBm and a small-scale version of the external and internal antenna setup. Basically just two small antennas connected by a wire.

The idea was that I should be able to measure a difference in signal strength inside of the box when putting a small antenna connected to another antenna outside of the box. This would then validate the feasability of using the bigger antennas.

Step 1 was to make an enclosure that would block (some) signals. A card board box wrapped in aluminium foil was no true Faraday cage, but when closing the lid it managed to reduce the signal strength by 15dB, which is noticable.

Step 2 was then to verify that these antennas would boost the signal inside of the box. This is where I fail, somehow. While closing the lid of the box made the signal go from -90 to -105 on the dBm scale, putting the antenna in there made absolutely no difference - no matter how long I waited.

I suddenly realized that I might be reading the wrong figures, as I still had 4G enabled (the antennas are both for about 900 MHz, while 4G is 1800 and 2100 MHz in Norway), but disabling 4G and strictly running on 2G made no real difference.

So this leaves me wondering: what am I doing wrong? Are there some basic assumptions I have made on how this should work that are just plain wrong?

Debugging steps:

I have verified that there's no short in any of the links from the black whip up until the N-connector using a voltmeter (0.6 V reading).
I have turned off 4G
I have verified that I lose 12-15dB of signal when closing the lid
Tech specs on the long whip (900 MHz range)
Tech specs on the stick antenna (900 MHz range)
The splitter box used to connect the two male cable connectors seems to be fine too when checking using a voltmeter.


texts: Problem with a Butterworth filter in stereo to mono audio input

texts:
Stereo to mono is simple to apply to a signal that came from audio jack. But I've encountered problems with the Butterworth filter.

There is an example circuit what I've done, first, the two channel were summed into one, then is applied the filter.

The filter type should be an high pass, the cut should be at 106Hz 12dB/oct.

R1 & R2: 1kOhm
C1: 220nF
R3: 68kOhm

Only the filter: works correctly.

Only the mono: works correcty.

The problem: mono + filter is only (almost) 1/6 of the maximum volume. Why? Please correct me if I've done a mistake.


texts:
I have 31 digital inputs (each is high or low) and want one digital output which is high only if at least 16 inputs are high.  How can I implement this "majority" function (which is also the most significant bit of the sum) with the fewest MOS transistors?

As a bonus, I'd also like to know the fastest-in-worst-case implementation.


texts:
I'm going to be using an 8 MHz crystal to run my microcontroller at 16 MIPS (PLL 4x, 2 cycle instructions.) However, 8 MHz doesn't divide into any UART frequencies AFAIK... so how critical are these frequencies? I plan to use 115,200 baud.

Can UART run within ±1%? If this doesn't work, what frequency should I use? (I would like to get as near to 16 MIPS as possible, for maximum processing speed.) If it matters, I'm using a PIC24FJ64GA004.


texts:
I'm  trying to do some reverse engineering and  want to know if there is a way to reprogram the controllers of a board like this one. I know usually the manufacturers have some pins on the boards which are used to program, fix and debug boards but this one looks quite complex, at least for me.

I have this device for learn more about electronics and my main goal is reprogram with some basic functionalities.

Based on the documentation of the main controller, i need a JTAG port to program it. This board have a ton of test points so i think maybe some of then are used to interact with the board and not only for test.

1  MSP430F149 datasheet
2  K4M56163PG datasheet
3  256M29EWH  datasheet
4  K4M56163PG datasheet
5  MC9328MXLDVM20 datasheet

I know this is a abstract question but any help or suggestion will be very helpful.


texts: voltage fluctuation observed in two parallel Li-socl2 battery

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Application:

our device working is like it wake up 5 times a day wake up period is nearly 30 sec and during this time take measurement from sensor and send data on zigbee and go to sleep.active mode current is nearly 80ma and sleep mode is 1.6ma.we are using two new Li-socl2 non rechargeable battery in parallel configuration(reason is that continuous current of one cell is 50ma so we use 2 cell in parallel to counter this situation).cell name is LS 14500 shaft battery.what we observed is,

1-in some device for particular time(for ex on some day during we voltage of this parallel battery pack is down to 3.0v compare two normal working day which is 3.6v,and during this time some time micro controller board restarted(teensy 3.6).after some time voltage again switched to normal condition 3.6v and continue to work normally.

2- we are also measure voltage for our reference of this cell pack using bq35100 ic.in here we used practice to meassure voltage between wake up and powering on all other module(so only teensy micro controller board is on) to avoid fluctuation in voltage.but here same thing observed for some hours or day voltage is drooped down from 3.6v to 3.2v or 3.3v and after some time again switch to normal 3.55v.

so i am not able to understand why for some days voltage is stable and for some day its drop down and after that again go bake to normal.

NOTE:i recently received one such battery pack from site and for checking purpose i open its plastic coting and check both parallel battery separately one is showing open circuit voltage 3.6v and running voltage is drooped to 3.0v.Other battery showing 2.4v in open circuit and same on running(here i think board is not powered on properly in this condition).so we can say that in-spite of parallel condition one cell is discharged more than other(both are new cell when first taken in use).

can some one help to understand this situation??


texts: Why signal coming out of a Constant K filter takes 0.5ms to stabilize?

texts:
I made a simulation of an audio amplifier with an input signal of 200 microVolts.

The question is why my filter does not deliver the desired output, which operates between 512 Hz and 2048 Hz.

From the Bode plot, I get a gain of -7dB which I assume it's from the matching impedance from input and output which is later corrected with an amplifying op-amp.

With the values from the schematic, running a transient analysis, I get the following data:

The larger signal is the input and the smaller one is the output on R24.
We can see that at 0.5 ms the signal is not perfect, why does that happen and how can it be corrected?


texts:
I have a few questions about transformers and isolation.  I will describe my understanding (maybe wrong) and questions about them.

Transformers provide safe isolation by disconnecting two circuits electrically. So now instead of touching one hot wire on the isolated circuit, you must touch both to get shocked.
Why don't my wall outlets work this way? I know there are many transformers used in the power distribution network.  Is this because they are referenced to ground (with a center tap or something)?
If the power lines are referenced to ground, why? Wouldn't it be safer to keep the power lines floating w.r.t. ground, so that for a shock to occur a person would have to touch two wires?
Could I provide this protection at my home by putting a 1:1 isolation transformer between the power grid and my house?


texts:
I'm creating a box that let's you turn on and off a power source using a button.
The setup

Power Supply converting 230AC to 12V DC
12V goes to power the LED on the button
12V goes to a protoboard converting 12V to 5V 1.5A
5V goes to protoboard with an Aurdino, controlling a 2 Relay Module

The problem
If I give the Aurdino power through the micro USB, it works as it should. One click on the button, and the Relay is turned on (light goes on and gives off a clicking sound).
But when I remove the USB and try to give the Arduino power from the converted 5V, through the pins, it goes into some kind of loop when I press the button. I can hear/see that the Relay is turned on/off quickly in a continuous loop.
The question
What's going on here? My guess would be that there is an issue with the protoboard with the Arduino, but I can't successfully debug the problem.
Documentation
Video of the problem
int ledPin = 13;    // choose the pin for the LED
int inputPin = 7;   // choose input pin 7 for the push button
int relay = 8;

void setup() {
    pinMode(ledPin, OUTPUT);  // declare LED as output
    pinMode(inputPin, INPUT); // declare push button as input
    pinMode(relay, OUTPUT);
}

void loop() {
    int pushed = digitalRead(inputPin);  // read input value

    if (pushed == HIGH) { // check if the input is HIGH
        digitalWrite(ledPin, HIGH);  // turn LED OFF
        digitalWrite(relay, LOW);
    } else {
        digitalWrite(ledPin, LOW);  // turn LED ON
        digitalWrite(relay, HIGH);
    }
}


texts: Can I implement addition and subtraction in different operations using a MUX?

texts:
I'm building a 16-bit ALU that needs to be able to perform logical AND, OR, add, subtract and rotate one bit to the left.
I need to have addition and subtraction operate with different op codes through a mux. Right now I have my addition and subtraction going through the same output in my full adder.
Here's my 1-bit ALU slice. I'm wondering how I can alter it so I can have subtraction be it's own operation.


texts: Using same DB9 port for RS232 and RS485 (selectable) - looking for IC

texts:
Do any of you know of any transceiver ICs that can switch between RS232 and full or half duplex RS485? I'd like to be able to select which type of communication is used with either a jumper or input pin.

Basically I just want to have a port than can toggle between RS232/RS485 to give the user more flexibility since I'm limited on UARTs.


texts: Controlling mains frequency to keep it at a steady 50Hz

texts:
I run a number of mains clocks, but the frequency of UK mains over the last few years has become more unstable (apparently due to the rise of unpredictable supplies from wind farms). It 'evens out' over time, but there can be a few days in a row where the clocks are as much as 1.5 minutes slow.
Would it be possible to design something to ensure the frequency is a constant 50Hz?


texts: Why the frequency of single-core CPUs has stopped increasing?

texts:
I wonder why CPU vendors stopped producing CPU with frequencies above 3.0 - 3.6 Ghz and switched to using multi-core CPUs?

What was the reason behind this step? Was there a physical constraint or the new approach came up being more feasible?


texts: Why double synchronizer alone is not enough for multi byte transfer between two clock domains?

texts: When one bit information is transferred between two different clock domains, we use 2 Flip-flops or double synchronizers. But when we transfer multi bit signals across two different clock domains, why is it that, just double synchronizers alone aren't sufficient? Why is it that in this case we need special hand shake signals/ gray code etc along with the double synchronizing flip-flops that complicates the entire setup?


texts: What are the practical problems for designing low freq. chokes or EMI filters

texts:
The power line filters like commercial RFI or EMI filters usually composed of  R L and C passive components and they don't usually work below under kHz frequencies.
What makes it difficult or a challenge to design such filter with 200 Hz cut off for instance?


texts: How do crystal oscillators work with feedback consisting of CMOS inverters?

texts:
For a crystal oscillator to work, there must exist a feedback path with properly designed specifications in order for all to work as expected. Broadly, the basic form of this control system is as follows:

Where the transfer function of this control system is:

$$\frac{Vout(s)}{Vin(s)} = T(s) = \frac{G(s)}{1+k(s)G(s)}$$

The theory of this type of oscillating circuit is such that if we make

$$k(s)G(s) = -1$$

Then we will have

$$T(s) = \frac{G(s)}{0}=\infty $$

And with zero input to the system (i.e. self-contained feedback only)

$$Vout(s) = 0*\infty$$

Which is undefined and together with the -1 feedback we find the system to be unstable and oscillatory in nature. What practical circuits do is design such that we have a phase-shift of 180 degrees and a gain of 1 equating to the -1 requirement. Namely, the feedback path k provides the 180 degrees phase shift and the forward path, G, provide the unity gain.

All of this together (with the crystal oscillator and phase-shifting load capacitance) give a circuit that is unstable and will oscillate at the resonant frequency of the used crystal.

tl;dr

Now, the point of all of that was to setup for a simple question. Knowing that the gain in the forward path must be unity, it makes sense that we would use something like an op-amp configured as a voltage follower, or equivalent. Since the oscillator will oscillate in a sinusoidal manner, it makes sense that we would use an amplification method that would track the input. However, what I've found is that these circuits tend not to use op-amps but rather high bandwidth CMOS inverters (like CD4049). Of the type:

How could it be that we are able to use an inverter to provide this unity gain with no additional phase shift?

The datasheet for the CD4049 cites that low voltages is anything below 1V, while high voltages are defined as being greater than 4V. That said, how can this be considered sufficient as a unity-gain amplifier when the output is either HIGH or LOW and not actually tracking the input as one would expect with something like a voltage follower?

I have actually constructed and measured this circuit; here are the results.


texts:
I need to build a power supply that delivers high currents of 2500 Amps or greater. A common circuit design that has been used to deliver this high current is shown below.

This circuit design works by charging regular capacitors (only one is shown, but there would really be 10 capacitors- two parallel sets of 5 capacitors in series) and discharging them with a trigger pulse and SCR. Protection diodes are used to make sure the capacitors are protected from current going the opposite way. A system of relays (only one switch is shown) can also be used to charge and discharge the capacitors effectively.

However, I was wondering if this design shown below would be an alternative that could provide just as high currents. It would be easier to build this design as I would not need the SCR and trigger pulse circuit. The SCR is hard to get without spending a lot of money, since it needs to have a rating of at least 5kA for a single pulse or 1000A continuous.

In this circuit it is similar with the Variac and full-wave rectifier to produce DC output current. The DC output would be smoothed with a regular capacitor if necessary for charging the supercap bank. I would keep a voltmeter across the supercapacitor bank to know when they are fully charged. When the supercaps are fully charged, a switch would be closed and the high current would enter into a low resistance circuit with protection diodes to prevent from current flowing the opposite direction. I already have a Variac with a output of 30A anywhere between 0-100V. I would probably turn the voltage lower to not hurt the supercaps which will be rated at lower voltages. I also have the rectifier with high current diodes rated well above the Variac input.

Is this circuit design feasible? I read that supercapacitors can discharge high currents and are not damaged by it, nor would they need the SCR trigger pulse component to get the high current discharge. Would this design be feasible?

*Note the Polywell is what this power supply is being used for; it is essentially just inductor coils used to create strong magnetic fields.


texts:
I'm new to electronics, so forgive not using official terms.

I want to make a MIDI project with an Arduino (Mega) and want to have 3 MIDI input channels. Currently on my breadboard I use 6N137 optocouplers which seem to work.

However, I also see schematics using a 6N138 or 6N139 optocouplers... Since I'm not so good at reading datasheets, let alone comparing them (since they use somewhat different terminology).

Since I need to use 3, maybe I thought I can use a so called multiple-optocoupler like this 4 channel optocouper

Also I found LTV847

However, is it comparable to a 6N137? And would I still need to use a diode and resistors as in the schematic of e.g. the MIDI In of this?

Or should I use a 6N138 or 6N139 or another since the 6N137 has disadvantages?

Or are there even better/more suitable multiple channel optocouplers than the one I found?

(the reason is want to check if I can save some space by using a multi channel optocoupler instead of 3 separate ones, including resistors/diodes etc).


texts: Robotics Experts: How to do trajectory planning for a robotic arm

texts:
I have a homemade 3D printed prosthetic robotic arm similar to the picture below

Right now this is completely open loop control system. The elbow, wrist and base can only rotate in around its primary axis. I enter the angle that the base, elbow and wrist should rotate and it performs that action - nothing else happens. Each of the finger is actuated by a motor and that enables grip and release of each fingers and this is controlled by an entirely different control system at a much lower output voltage than the wrist, elbow and base motors.

But I do not feel that very sophisticated. I wish modify this arm so to make it more "industry" purpose.

What should I do to get started in developing a control algorithm for the trajectory of this arm?

Some thoughts: maybe add some "sensors" that provides angle information of the arm in space? Can someone who is familiar with robotics provide me with some information as to how this is done?


texts: How can the 2.4GHz ISM band have 130+ channels?

texts:
I am a relative beginner regarding wireless communications protocols and I am looking into the protocols used by toy helicopters, in particular the Hubsan X4. According to more experienced people who have done similar work the X4 uses "an A7105 transceiver chip".
Now according to the A7105 specification (pages 1 and 5), the A7105 runs on the 2.4GHz band, and is suitable for "2400 ~ 2483.5MHz ISM Systems".
Returning to my original source, he describes the binding mechanism of the helicopter:

First the Tx scans the RSSI on the following channels and picks the best one:
14 1e 28 32 3c 46 50 5a 64 6e 78 82 [HEX]

I was under the impression that the 2.4GHz band had only 14 bands (Wiki), so how can there be 130(+) channels for the helicopter to search through?


texts:
I'm driving a small, benchtop vibe table (shaker) with two Crown DSI-1000 PA's, and also cleaning my signal with a DBX 231s EQ. Currently running the system at 6.8 GRMS, but I'm looking to increase my overall driving level.

With the test article mass/ test levels I'm shooting for, I'm conflicting with the specified peak capability of my shaker.

To be more precise, I would like to drive a ~5.5 lb object to ~10 grms (random vibe). According to my back-of-the-envelope calcs (Eqn 1), I don't think there is much I can do besides purchasing a larger shaker. This shaker tops out at 200 lbf. However I figured it would be worthwhile to probe the community for ideas in case there is some sort of electrical engineering voodoo I can employ. Will also post in engineering SE.

TL:DR, Is there any way for me to increase the peak driving force/ capabiltiy of my shaker table without the risk of damaging it?

My PA's and EQ are also getting close to their maximums, at just 6.8 grms.

Desired profile: NASA GEVs STD-7000a:

Eqn 1: GRMS = [PEAK_SHAKER_FORCE / (ARTICLE_MASS + ARMATURE_MASS)] / 2 . --> GRMS = (200 lbs/ 13.5 lbs) / 2 ...................................................................... --> GRMS_MAX = 7.4


texts: Unexpected results from voltage mulitplier

texts:
I needed a high voltage (500VDC) source in order to test a circuit. To achieve this, my mentor instructed me to build a voltage doubler, which I would power with 250VAC. I chose to use a simple half-wave rectifier as shown below.

The diodes are 1N4007's. The only high-voltage capacitors available were 2.2nF 2KV non-polarised caps. 2.2nF is not much, but I don't have any other options here. I built it in the formation above, with the nodes a few centimeters apart.
When it came to testing, however, the results were not what I was expecting. I put 29VAC on the input, but got only 35VDC out. I did some testing, and this is what I found:
I then built a quadrupler in order to do some more testing, and this is what I got:
Much surprised, my mentor and I did an LTspice simulation of the circuits, which behaved as originally expected. Here are the screenshots:

As you can see, I am testing voltage at the input and output.

Why didn't my circuits work?
I understand that SPICE models use ideal components, but even so, why does the simulation differ so much from what I have in real life?


texts:
I've got a Roland TD-11 drum module that I want to power from a battery.

I only need to power it for 2 hours at a time.

Can I please have some recommendations how to achieve this?

SPECS:

Output Impedance: 1.0k ohm
Power Supply: AC adapter (DC 9V)
Current Draw: 350 mA


texts: ENIG or HASL for prototype with small pitch and expectation to need rework

texts:
I have a project where I'm about to order the PCB's for a first prototype, and I'm staring at the option of HASL vs. ENIG on the website. I will hand solder it with an iron, the smallest pitch part is 0.5mm (which I've succesfully soldered before, though with some difficulty, on a board with HASL finish). My skills with the soldering iron are not especially good, although as mentioned, I have succesfully soldered similar parts before, and I'm learning to be better all the time.

Now based on this question, I suppose an ENIG finish might save me some headache at these pitches. On the other hand, based on this website, one of the disadvantages of ENIG is "not reworkable".

Since this is a prototype, I will certainly have to swap around some 0603 resistors and maybe capacitors, once I get to evaluate the device in action, to find the right values, and test if some noise-reducing RC -filters are even necessary in the first place.

The question is: is ENIG so bad for rework that, considering I know for sure I will have to replace at least some resistors, I should go for HASL and just deal with the HASLle of soldering the fine pitch parts there?

In terms of price, the difference in the board house I'm using is 25$ for 10 PCB's between HASL vs. ENIG, which is not prohibitive, although if it's a close match, the price might be a tie-breaker in favor of HASL.


texts: Version control system for KiCAD which can deal with merge requests

texts: When working on a project with a group of people it is often required to merge changes someone else has made into a master version of the project. However my EDA of chocie, KiCAD, does not seem to support this. I've seen alot of people doing version control in git. However after trying this the merge conflicts are horrifying. Altium seems to have a nice tool to do this however I would like to stay with KiCAD. I am trying to find a way to do a diff on revisions of a board and schematics, can KiCAD do this?


texts: Charge pump vs. boost converter for high current LED driver

texts:
I am designing a high current LED driver circuit to power a matrix of pulsed IR LEDs.  The LEDs will operate at 5A; 4.6V; 0.1ms pulses (~10 pulses at this frequency, wait 300s, repeat.)  The device is powered off a 3.3V Li-Po battery.

In order to deliver sufficient power, I need a DC-DC converter as part of my driver circuit.  I would have assumed that a boost converter would be a no-brainer for this application, however doing some reading seems to suggest that for such high-current applications, the size of properly rated inductors would start to become prohibitive, and so I am wondering if it is worth looking at charge pumps instead.

I've done some reading on it (https://www.maximintegrated.com/en/design/technical-documents/tutorials/7/725.html) and while the losses would be much higher than a boost converter, would the size and cost savings be significant enough to support the use of a simpler charge pump?  Are there any drawbacks from a charge pump that makes it unusable for a battery-powered device?


texts: Choosing the right power cord for my PC adapter

texts:
I need to replace the euro power cord on my new PC with a UK one.

The power adapter for the PC has the following rating:

Input: AC100-240V - 50-60Hz, 3.5A
Output: 19.5V (direct current) 11.8A

The original (european) power cord plug is 250V with a 16A fuse.

Looking online I can not find a UK power cord with a 16A fuse, best I can find is a 13A fuse 250V power cord.

I'm assuming the 13A fuse is enough, but would I get away with a 10A fuse too? The input for power adapter is 3.5A as mentioned above but output is 11.8A so I'm a little lost here.


texts: MXR Distortion + guitar pedal schematic - meaning of +4.5V

texts:
I found this schematic of the "MXR Distortion +" guitar pedal.

I am trying to rebuild it, but I have some doubts about this +4.5V in the bottom left corner.
What does it mean?

I mean, I have only 1 power source: a 9V battery, so how should I add a 4.5V?

So basically my question is what is this 4.5V, and how can I add it to my circuit?
And I don’t understand exactly the same thing in the power supply stage right.


texts: Sharing a common schematic among multiple boards in Altium

texts:
Is it possible to share a single schematic among multiple boards in Altium?
In the old days when schematic capture and PCB layout were more separate, it was more obvious how to do this. How about now?
This is a design that over time there may be a dozen variants of the PCB, which differ only in the number of driver chips and shape.  Thus:
Power Supply Schematic + CPU Schematic + Driver Schematic for L shaped board  => L Shaped PCB
Power Supply Schematic + CPU Schematic + Driver Schematic for Z shaped board  => Z Shaped PCB
Power Supply Schematic + CPU Schematic + Driver Schematic for circle shaped board => Circle Shaped PCB


texts: STUSB4500: Unable to negotiate USB-C PD voltage higher than 5V

texts:
for my project, I have decided to use STUSB4500 for negotiating 20V for powering external remotely controlled LED lighting.
My circuit design comes from the minimum implementation in the datasheet, but I've decided to get rid of the p-Mosfet as I don't need on/off switch on the sink. I believe that the negotiation is happening on the CC lines, so hopefully, this decision shouldn't interfere.
A very similar circuit is used in the fpx module, as well as in the SparkFun Power Delivery Board. Both of them have the p-Mosfets included, however.
Here is the relevant part of my schematic:

The whole schematic is available here, if needed.
I am unable to negotiate any voltage above 5V. I've tried to use both factory settings of the chip and also programming the NVM contents by myself.
The SparkFun board is working as expected with the same USB adapter. The schematic looks pretty similar apart from the mentioned p-MOSFET:

According to the datasheet, the VBUS_EN_SNK pin is an open-drain which I believe could even be left unconnected.
The NVRAM content I tried is the following (default configuration in the Sparkfun library):
uint8_t sector[5][8] =
{
  {0x00,0x00,0xB0,0xAA,0x00,0x45,0x00,0x00},
  {0x10,0x40,0x9C,0x1C,0xFF,0x01,0x3C,0xDF},
  {0x02,0x40,0x0F,0x00,0x32,0x00,0xFC,0xF1},
  {0x00,0x19,0x56,0xAF,0xF5,0x35,0x5F,0x00},
  {0x00,0x4B,0x90,0x21,0x43,0x00,0x40,0xFB}
};

As a guide for understanding the NVRAM content, the relevant parts of the SparkFun library could be used.
I've already inspected the board for soldering problems and tried four different pieces. Any ideas on what could be wrong or how to debug power delivery communication?
Is there any other purpose for the original MOSFET, other than switching on and off the external device?
Thanks!


texts: Schematic Critique: Phy interface with RJ45/Magnetics

texts:
I'm working on my first major schematic design and would really appreciate some feedback on the analog side of the 1000BASE-T Ethernet interface. I'm mostly concerned about the analog line termination and the isolated supply of the analog signals and separate ground plane.
This is the analog side. I've used the same center-tap voltage as the phy analog in, and isolated the gnd using a ferrite-core inductor.

Here's the analog power into the PHY (enough decoupling caps? I used as many caps as input power pins):

I'm a bit concerned about the fact that the phy (88e1111) doesn't have a dedicated analog GND, so I would assume that the analog outs are relative to the global gnd. Doesn't this mess up my ground isolation external to the device?

I would also appreciate it if you could critique my schematic layout, a client is going to see this and I want it to be perfect!


texts: Why voltage in capacitor lags behind the source voltage in RC circuit?

texts:
Voltage across the capacitor lags behind the current through capacitor as we know. But why the voltage across the capacitor lags behind the source voltage in this circuit ? Similarly it is found that voltage across the inductor leads the source voltage in RL circuit.
Why this happens when the resistor between source and capacitor in RC circuit & resistor between source and inductor in RL circuit has no effect on the phase of the voltage and current in these circuits? Shouldn't the source voltage apear across the Capacitor and Inductor although with less amplitude but with the same phase angle across capacitor/inductor in these cases ?


texts:
I need to implement a frequency counter (pulses per minute) of a DC circuit that goes up to 20 volts. A little background, I am building a linear power supply 0-20 volts, 0-3 amps for my relative who is a tattoo artist. He wants me to help him build the supply but he has the need to know what frequency the tattoo machine (just a basic doorbell circuit) is operating at. His specialty tattoo machine power supply has this feature and I guess it's helpful for something.

I have found several schematics for DIY frequency counters, I really like the  Weeder Tech auto-ranging unit but I cannot figure out a reliable way to interface one with a DC power supply. I have looked into preamp circuits for low voltage signals, but that still presents a question about feeding it up to 20 volts. I am quite certain the full 20 volts will fry the IC's, and honestly I am uncertain if it'll even measure DC pulses because of the capacitors in the signal path of the frequency counter. I have looked into Hall effect current sensors, Zener diodes, voltage dividers and all of that, but I'm lost as to how to simply count how many times a second the circuit is closed by the machine and providing current. I just need a low cost reliable way of making a 0-20 volt DC circuit a logic level signal. Even if it was as simple as an IC or op amp that would go high when any current is flowing, that would seem perfect.

I know this is a rather odd request as usually only AC is interesting frequency wise, but really appreciate any help in finding a solution to this one.


texts:
Update: I found the solution...
There is a wrong resistor assembled in the VFB circuit. R12 is unequal to 108k.

I have this power supply circuit to drive an application over a battery:

The circuit is taken from the official device datasheet but it seems that the DC/DC converter isn´t running. I power the circuits DC/DC LT3873-5 with 5 V and I measure a 5 V input voltage for the L4931 hence the 12 V rail.
The layout looks like this:

And I measure the following voltages:

Pin 1 (IPRG): 0 V
Pin 2 (ITH): 0.53 V
Pin 3 (VFB): 2.7 V
Pin 5 (NGATE): 0 V
Pin 7 (RUN): 3.8 V
Pin 8 (SW): 4.7 V

So what is wrong here?


texts:
I'm using these Mean Well LDD-H DC-DC constant current step-down LED drivers to drive these LEDs.

What I'm seeing is that when the -Vout terminals of the drivers are connected together, both LED strips start being driven in sync (as if the PWM inputs are connected).

If is use a separate ground for each driver-strip pair, it works as expected.

Why is that happening?

Closely related to this question, but with more specifics.


texts: Is this Thevenin equivalent circuit correct?

texts:
I am asked to find the equivalent Thevenin circuit between nodes A and B of the following problem, removing R1. I have attached my work because I have no idea if this is completely correct or totally wrong. Can someone please take a look at it? I would really appreciate it.

Also, if they had asked me to calculate the Thevenin circuit between the nodes that limit R6, could this have been a good starting point, or would it be incorrect?

I am not sure if I am removing the resistances properly in both cases.

Thank you for any help!


texts: uC -> wire -> LED in metal enclosure. ESD/EMI protection

texts:
I need to blink a LED with a LPC micro-controller. Enclosure is solid aluminum. LEDs will be on a separate PCB 20cm away from uC PCB and protruding from the metal enclosure. What would be the simplest reliable ESD/EMC protection strategy? I am considering transient suppressors, ferrite beads, resistors, but I am not sure whether all is necessary and at which side of the cable (maybe at both sides?) I should be protecting.

Thanks in advance!


texts: laptop batteries charging myths - Long life OR short life

texts:
I'm very conscious about the life of battery.

  Some people say that don't keep plugged-in laptop all over the time and remove battery charging at 70% and again charge at 40% so your battery cells don't charge or discharge at their full position, and battery cells will keep at their optimal voltage rate.

VS

  Some of says keep your battery plugged-in all the time so that your battery will not be used by laptop and battery's life cycles will not drain and important this is laptop will stop battery charging automatically when it reached to 100%

Which is true?


texts: Thermal calculation in case of duty cycle for a mosfet

texts:
For a multiplex LED matrix, I am intending to use two ULN2803's as sink source for 16 times 20 mA per column (channel).

However, maybe I will try a test with 100 mA LEDs (10% duty cycle). For that I have IRLZ44Ns (see Datasheet IRLZ44N.

See the circuit below (simplified because of the circuit maker area restriction and somehow some connections are connected which should not, but the idea is clear I hope).

simulate this circuit – Schematic created using CircuitLab

Below is the thermal resistance table on the first page:

Parameter                                Min. Typ. Max. Units
RθJC Junction-to-Case                    –––– –––– 1.4  °C/W
RθCS Case-to-Sink, Flat, Greased Surface –––– 0.50 –––– °C/W
RθJA Junction-to-Ambient                 –––– –––– 62   °C/W

If I'm right the calculation is as follows:

16 (leds) * 0.1 (A) = 1.6A

For the voltage, I'm not sure. I intend to use a 9V adapter, however the UDN2891 source driver's reduce it with about 1 V, and I also have to remove the forward voltage of a LED. I'm using different colors, but let's say in worst case it's 1.8V, so I have a total voltage of:

9 - 1 - 1.8 = 6.2 V

This results in a power of

P = V * I = 6.2 V * 1.6 A = 9.92 W

With the RθJA value it would mean

Temp = P * RθJA = 9.92 * 62 °C/W = 615 °C

So I would definitely need heat sinks.

However, because of multiplexing, I only use a duty cycle of 10%, 100 Hz (per IRLZ44N). Does this mean, the current is (on average):

16 (leds) * 0.1 (A) * 0.1 (duty cycle) = 0.16 A

And the thermal calculation is:

Temp = P * RθJA = 0.16 A * 6.2 V * 62 = 61.5 °C

This means I do not need a heat sink; the absolute max rating is 175 °C.

Or does duty cycle have less impact on temperature this way?


texts: can I use a board that has resistor ladder buttons on raspberry pi?

texts: I have a clock that has a circuit board with a resistor ladder setup for the buttons. I want to (disconnect the clock and) put a pi inside and use the buttons to control the pi. In normal use the board is supplied with voltage and the buttons connect to ground. The clock measures the voltage somehow (I dont think its from the ground side because If I connect the ground side of the board direct to ground it still works as expected.) If I connect the gpio pins to the buttons after the resistors but before the buttons the voltage gets backtracked through the resistor to the next resistor also. The result is that the pi detects more than one button being pushed at a time. This happens because the high side of the voltage ladder resistors are tied together. How can I wire this up to the raspberry pi without removing the resistors?


texts: What is this part in my Royal Enfield motorcycle speedometer unit?

texts:
My bike meter got stuck after replacing my battery with a new one. I think due to new battery something burned in the circuit. I have images of the same.
I have an electrician who can fix televisions etc. I thought he could fix the speedometer. He says the black chip (I think it's a diode, I am not sure though) got burnt. I am not able to find the part as I don't know what it is.
I am not an electrical engineer (just a computer programmer.) I would like to know what the issue is, though. So please pardon me for my half-knowledge (rather zero-knowledge.)
What does the symbol on it mean (one with the mirrored C and H without the horizontal line.) Is it a company symbol or scientific symbol - and what is this part? If I can get a replacement he says that he can fix it.


texts: Can I use an h-bridge as a changeover circuit?

texts:
I have solar controller which outputs battery voltage when available.
I also have a switching psu as backup.

What I would like to do:

Use an h-bridge, connecting its battery negative terminal to my load and the two motor terminals one to psu negative and the other to solar controller negative.

The idea is:
When solar controller is active, feed a voltage to the h-bridge direction input so that I can select my power source.

Can this work?


texts:
I'm struggling to increase duty cycle in the controller. I'm using SG3525 on control PCB. As can be seen below, R12,R22 and C12 components are selected for 58kHz frequency.

However, I can't get duty cycle more than 45%. Typical duty cycle is given 47% in datasheet. Does the max. duty cycle limited by frequency?


texts:
Is there a difference between doing binning on a Bayer sensor before or after the ADC with respect to spatial information lost?

How the debayering works should not matter, Assuming the same method is used for both ways.

A:

Horizontal 2x1 binning before ADC by adding up pixels of same color
debayering of the binned Bayer pattern.

B:

Debayering
Binning by adding adjacent pixels horizontally.

Is there any advantage of A over B except lower noise?

In the end, I think the same spatial information is lost. Meaning information from the same originally neighboring sensor pixels ends up in any given final image pixel.


texts:
Does anyone know what a 201-1 package size is, and how it might differ from a 'normal' 0201?

I found it in a MacBook schematic.

Thanks in advance for your help.


texts: Way to get high voltage from a watch battery

texts:
I'm creating a vary small device that need an high voltage around 50v. But because the device is really small like a pistol bullet, I can only use very small batteries like watch battery or button cell. But I cant use Transformer, also because of the size limitation.

Is there any other way to do that (may be electronically). But the solution need to be small as much as possible and the light weight as much as possible.

Appropriate your helps


texts: Op-amp with compensation has positive feedback with over-unity gain

texts:
I am looking at the following figure (Maxim APPLICATION NOTE 5129
Stabilize Your Transimpedance Amplifier):

I just can't understand the following: in the region half-way between fF and fi, the slope difference indicates a 180 degree phase shift between open-loop and the external network, albeit the gain is larger than unity (it is 1 only at the intersection). So, what prevents this compensated op amp from saturating to one rail in this case due to the positive feedback and over-unity gain in some frequency range ? Thanks.


texts:
Here is a simple circuit that I have built which takes as input a DC voltage and gives out a sinusoidal output varying from -V to +V. It has three parts: (1) A LC circuit, (2) a buffer to isolate the LC circuit from the rest of the circuit, and finally (3) the differentiator. I expect to get an output of the form V*cos(wt) where w is the angular frequency of the wave. I'm not sure whether this circuit actually does the job it's supposed to do. Any idea is appreciated.

EDIT: The third part is actually a subtractor and not a differentiator.

simulate this circuit – Schematic created using CircuitLab


texts: SN74LS181: The comparison function, A=B, not operating

texts:
I have six SN74LS181N-B circuits for arithmetic functions. I intend to utilise the A=B output, which is the comparison function. Sources have indicated that this function operates, if subtraction is acted, and the output word, (F), is 1111.

However, this does not seem to occur; I tried both situations of equality and inequality to observe if the pin is inverted; I even tried when the whole output word, (F), is 1111.

Additionally, I found that the Carry pins, (Cn, Cn+4), are inverted and thus suspect the output and input words are inverted. However, if I use normal averted inputs, it operates proficiently. Do I have to utilise external inverters?


texts: How to use capacitor as battery in razor?

texts:
I have an old razor machine Philips 1304, it's circuit is broken, all I have is motor, housing ,blades and AC Adaptor.

So the question is how to use it just via power ? I can use capacitor only and don't have access to battery, according to the cover it's 4.4v AC

via AC Adaptor it's too weak, maybe because the lack of backup power like capacitor or battery.

so any help will be appreciated.


texts:
Description

I am designing a system in which there's a circuit that controls the power applied to a micro SD card (enable/disable).

The circuit is the following:

The power control circuit is done by a P-MOSFET that is deactivated by default.

MICROSD_PWR_EN signal is connected to a pin of a microcontroller configured as open-drain.

Issue

The measured voltage on the pin VDD of the micro SD card should be 0V by default. However, this voltage is near +1V, which is neither a logic "0" nor a logic "1". The voltage measured on node "+3.3V" is +3.288V and the one measured on the gate of Q5 P-MOSFET is +3.285V.

Do you have any idea regarding this issue?

Could that be related to the 3mV difference between the source and the gate of the transistor?

Firmware solution

Firstly, thank you all for your answers.

It seems that I solved the problem by firmware: by configuring the SD card GPIOs as output open-drain and by setting them to logic "0", the voltage on the VDD pin of the SD card is now near 0V.

As everyone pointed, it is probably related to protection diodes of the SD card chip GPIOs.


texts: Are plastic enclosures safe for hobby mains voltage projects?

texts:
This may seem an obvious /silly question, but bear with me because I want you to consider it from a pragmatic view point.

I have a fledgling project that will be mains powered and fit in a space roughly 200mm in any dimension.  Initially you'd think that a plastic box would be suitable.  But consider:  There will be penetrations in the form of a switch and some sort of optical indicator, both perhaps with metal bezels /lever.  And there will be a mains transformer, with a bolted attachment through the case.

What initially seemed a simple example of a Double Insulated box, now has metallic (conductive) penetrations though it, compromising the insulation integrity.  Commercial Double Insulated kit is quite complicated, with blind self tapping screws, multiple insulation layers, e.t.c that all seem a little out of reach for the typical electronics enthusiast.

It seems to me that it's safer to treat the whole thing like a washing machine,  and put it in a metal box with a good earth ...

P.S. Should I look for Aluminum or plastic enclosure for UPS touches upon these issues, but does not seem to address common enclosure penetrations.


texts: Two parallel motor under PWM now have slightly different speeds

texts:
I have a couple of peristaltic pumps to wash my cells with different conditions for live imaging with a fluorescence microscope.
I now have the two pumps with a PWM pre-assembled module. It has a timer and 3 mostfets and a poti obviously.

I need to put media from a tube to the plate with a pump AND take the media from the plate to a waste container with the other pump.

However when I was using the peristaltic pumps prior to the PWM the liquid flow was exactly the same with both pumps. (the level of water in 50ml tubes was constant in both tubes when crossing the in and out from the pumps).
However, now with the PWM signals there is a bit of a difference and one of the test tubes goes empty while the other gains volume.

I still don't know if it is mechanical or an electrical thing. I changed the peristaltic heads between motors and the same happens.

Could it be the stall start or the back EMF doing this?
The pumps are connected in parallel.

Any way to solve this? Diode to reduce the EMF or a capacitor to equalize the start of the pump?

This was my previous setup in which the liquid pump rate was exactly the same (with the same motors and peristaltic heads)

Drop the current of a couple of peristaltic pumps for a microscope use

Thanks for any help!


texts: How to change the polarity of 0~5 volts get -5~+5 volts?

texts:
I am doing a project using NI DAQ USB 6008 to control an speaker. The DAQ analogic ouput range is 0 to 5 volts and the output current drive is 5 mA. But to control the speaker I need a different range. For example, I need a range that goes from -5V to 5V to the audio amplifier which will be conected to the speaker. My audio amplifier has input impedance 30 K ohms and minimum frequency 10 Hz.

I know that if my controller calculates a negative voltage output I can multiply this value to -1 (in the control algorithm) to the DAQ card send a value between 0~5V, and then I could change the polarity of this signal after the DAQ board output (implementing an circuit to change the polarity and using a digital output of the DAQ card as switcher). So, what I need is a circuit between the DAQ card and the audio amplifier to change the voltage polarity. I do not know if this is the best/simple way to solve this problem and how to I can do this circuit in a simple way. Any ideas?

Thanks in advance


texts:
I got a shift register which I use to PWM LEDs. Since I multiplex this toggling I noticed some "afterglowing" if the next LED is not active of the same color. (RGB cathode) Multiplexing by the MOSFET and PWMing by the PNP.

I already found out, that it is not the MOSFET which is too slow. So I tried increasing the toggling speed of the PNP but I was not sure how to do so. I thought of pulling it up, so I tried it with some high resistors around 1-5k but this does nothing. After this I used smaller till I used the 20Ohms and noticed that the glowing is extremely minimal now.

So my question is, how do I do this right? Sure it does work now but I'd like to understand how to increase the speed to some kind of maximum. Is there a better solution which I can do even after soldering the 510? I can't change the 510 Ohm and 120 Ohm in front of the PNP and MOSFET since I already soldered them but I can add a line to pull them all up for example.

Down here some example how it looks:

simulate this circuit – Schematic created using CircuitLab


texts:
I have just been given a bunch of old X-10 stuff including
CM11A Computer Interface
D-shell-9-pin-Serial-connector to RJ11 (I think)
RR501 Transceiver Module
LM465 Lamp Module and several SR227 Split Receptacle Module.

I am not a newbie to computers, programming and Arduinos so would like to see if I can incorporate these into my home automation network running Arduino+nRF24LO1 and controlled by my own windows-PC software.

Can someone please point me at where to get started with the CM11A and getting it to talk to a USB serial converter? OR - can I directly access the RR501 via some form of radio? Reading the manual it says RR501 can transmit control to and from all other X-10 devices on the 110v wiring. Sounds good to me.

Any other information will be a great help and a great start to save me reinventing he wheel with this old stuff. I am optimistic enough to think it must have already been done a bunch of times.

I have already found some stuff, but so far nothing useful with the older X-10 components.


texts: Resistor values for OpAmp circuit with dc offset applied to inverting pin

texts:
$$
\newcommand{\rth}{R_{TH}}
\newcommand{\vth}{V_{TH}}
\newcommand{\rf}{R_{F}}
$$

Asked this in the math stack exchange, who recommended asking here instead.

I'm stumped (hence posting here!) with what is probably a very simple extrapolation.

Consider this circuit:

The values supplied are based on an example that I am working with.  I need to better understand how the resistance values were derived as I need to change the reference (from 3.3V to 2.5V), the $V_{in}$ (from 0 to 3.3V to 0 to 2.5V), and the $V_{out}$ from $\pm 36V$ to $\pm 40V$.

So I'm seeking guidance on how to calculate the resistor values.  Leading up to this, I have a good understanding.

Here is the transfer function for this circuit:
$$
   OUT = IN (1 + \frac{\rf}{\rth}) - \vth \frac{\rf}{\rth}.
$$
The opamp is supplied with +45 and -45 V rails and it can safely swing between $\pm 40V$ at those levels.

The desired output will go from $-40$ to $-40V$ as the input goes from $0$ to $+2.5V$ (at $1.25V$ the output will sit at $0V$).

The gain is calculated thusly:

\begin{align}
  Gain (\text{non-inverting}) &= (36 - (-36))/3.3 = 72/3.3 = 21.81818182\\
  Gain(\text{inverting}) &= Gain (\text{non-inverting}) - 1 = 20.81818182 = \frac{\rf}{\rth}
\end{align}

The resistor values are calculated using this formula:
$$
    \vth = 3.3 V (\frac{R_2 }{ R_1 + R_2}).
$$

First, I must find $\vth$.  Here's the formula for that:

\begin{align}
    -36 V &= 0 - \vth (\frac{\rf}{\rth})\\
    \vth &= 1.729257642 V
\end{align}

In the above, $\frac{\rf}{\rth}$ is taken as an unknown, so:
\begin{align}
    -36V &= 0-\vth \frac{\rf}{\rth}\\
    -36/20.81818182 = \vth
\end{align}

Now, here's the sticky part:
\begin{align}
  \vth &= 3.3 V \frac{R_2 }{ (R_1 + R_2)}\\
  1.729257642 V &= 3.3 V \frac{R_2}{(R_1 + R_2)}\\
  1.729257642/3.3 V &= \frac{R_2}{R_1 + R_2}\\
  1.729257642/3.3 V &= 0.5240\\
\end{align}

From $0.5240$, how in blazes do I calculate the value of $R_2$, $R_1$ and $\rf$?
$$
\rf = gain * \rth
$$
( but $\rth$ is $R_2/(R_1+R_2)$ ):

$$
  \rf  = 20.81818182 * \rth
$$
Seems as if I need to choose one value out of the blue to get the others??

--

Based on suggestions I tried this circuit:

And this is the output:

Third try:

Result:


texts:
I've been using a 12V, 7Ah sealed lead acid battery for my GPS equipment, but need something lighter.

The battery(s) will be charged daily.

Does anyone have suggestions for a battery or battery combinations that could achieve this?


texts: MIP2M4 mosfet, Arduino Uno and a 12v PWM PC fan

texts:
First, I'm am new to using transistors and MOSFETs in electronics circuits.

I have extremely basic notions of electronics, and am able to setup and use "of the shelf" boards and Arduino modules, and I do know how basic electronic components work.

Now I'm trying to do the jump to start creating a bit more advanced projects, and I'm struggling to do a simple project with recycled components from some PCBs that I recycled with the help of a heat gun.

I have some PWM fans that I can control using the Arduino, but I would like to shut them down completely, which does not happen without a "switch".

Since I don't have a relay at hand, but I have some NPN and PNP transistors, photocouplers and MOSFETs, I wanted to try to do something with them.

I have this compact MIP2M4 MOSFET that supports the load that I'm going to use of 1A, since it's two 12v 0.5A fans.

I don't want the MOSFET to control the speed of the fans, I just want it to power them off when I send a "0" value PWM signal from the Arduino to the fans, and to turn them on when I send a higher PWM value to the fans.

Can someone help me understand how can I wire the MIP2M4 with the Arduino and the fans to achieve this? I tried it with a NPN C2655, but since it got only a 5v signal on the base, it only outputs 4.83v and the fan runs really slow...

MIP2M4 DS https://industrial.panasonic.com/content/data/SC/ds/ds4/MIP2M40MT_E.pdf

Thank you in advance!

AC


texts: Miller integrator dc offset ->why no gradual increase towards saturation?

texts: I made a miller integrator with a dc offset. (The initial condition of the capacitor is set to zero so initial condition is not the problem). There is a capacitor or 10-7 F capacitance and a source resistance of 10K ohms. Due to the dc offset of 0.002 V, the integrator should cause the output signals to be like a ramp and eventually saturate when the 12 v saturation limit is reached. When I make this circuit in multisim online, the output is instantly -12.something. And it is a constant signal. why am I not getting a ramp towards saturation? Here is the circuit:


texts:
I am writing a driver for mcp3421 ADC IC and I have a problem when I measure in 12-bit accuracy. That is 240 samples per second.

In the datasheet the min and max values are 176 SPS and 328 SPS. So I expect to be able to see a new measurement every:

-min: \$1sec/176 \$ -> \$5,69msec\$

or

-max: \$1sec/328 \$ -> \$3,05msec\$

In reality I poll the mcp3421 every 7 msec to be sure it gets a new measurement but the RDY flag( 0=new measurement ) is set every 50msec.

Is that normal? Why is this happening?

Here is the tree (every 7msec)

and here is the forest( every 50msec )

 * \brief Reads all mcp3421 registers.
 *
 * \bug Needs a timeout mechanism or it might hang in a loop if device hardware fails.
 *
 * It reads mcp3421 and expects either 4 or 3 bytes.
 * If it is in 18-bit all bytes are used.
 * If it is not 18-bit the lower byte is not used.
 *
 * \param[in,out]   me          The mcp3421 handle.
 * \param[out]      upper       The first byte.
 * \param[out]      middle      The second byte.
 * \param[out]      lower       The third byte(18bit) or configuration byte(12,14,16bit).
 * \param[out]      config_reg  Register is the 3rd byte(12,14,16bit) in row or the 4rth(18bit).
 *
 * \retval          0           Success.
 * \retval          1           Failed.
 */
static int mcp3421_read_all( mcp3421_t* me, uint8_t* upper, uint8_t* middle, uint8_t* lower, uint8_t* config_reg )
{
    //TODO: Add timeout_ms
    int err = 0;
    do
    {
        /* Read mcp3421 register */
        uint8_t data[4] = { 0x00, 0x00, 0x00, 0x90 };
        if( i2c_master_receive( &(me->bus), me->address, data, 4U, MCP3421_TIMEOUT ) )
        {
            /* Exit with error */
            errorHandler();
            return 1;
        }

        /* Get data */
        *upper = data[0];
        *middle = data[1];
        *lower = data[2];
        *config_reg = data[3];

        /* Wait until the next read */
        if( mcp3421_delayUntilNextRead( *config_reg ) )
        {
            /* Exit with error */
            errorHandler();
            return 1;
        }

        /* Check if registers are updated */
        if( ( (*config_reg) & RDY_Mask ) == 0 )
        {
            /* Exit with success */
            return 0;
        }
        err++;
    }
    while( err<200 );

    /* Exit with failure */
    errorHandler();
    return 1;
}


texts: How to determine length of coax to get a certain delay?

texts:
This is a follow-up to How to make a phase shifter?, it seems one answer is to simply have different lengths of coax going to each antenna. However, how do I calculate the difference in length given the desired phase and frequency? My first assumption was that the signal should move at the speed of light, and so the calculation would be:

wavelength * (phase shift in degrees/360)

But then I remembered reading somewhere that a signal does not move at the speed of light through regular cable, but rather a fraction slower (2/3? 3/4?). Do I need to take the material the cable is made with into account?

Edit: To be clear, I'm hoping for a direct equation I can use to determine how to cut the length of cable in front of me.


texts: Do line level circuits need shielded enclosures?

texts:
I made a quick volume pedal, just a button, 50k pot, input and output jacks

I used a plastic enclosure for it since it was convenient, but I realized almost all guitar pedals and other stomp boxes are metal. Not only does this help with durability, but it acts as a Faraday cage. Connected to ground, it reduces noise, just like a shielded cable. Is this necessary? I can line the inside with aluminum foil, but it would be annoying to do so, and not sure if it's necessary.

Moreover, I am curious about what is the best practice here.

Does a line level circuit like a volume pedal need a shielded enclosure? (I don't plan on ever using this for something pickup level also.)


texts: Wien-Bridge Oscillator - gain of RC network

texts:
I'm just wondering, I'm trying to find the overall gain of

I understand where the gain of the non-inverting op amp config comes from. But where does the gain of the RC network come from? Since there is technically no input in this case?

EDIT:
I tried the suggestion of V+ being the input, however I still can't seem to get the same answer that was given before in my lecture notes (that I've written out above):


texts: AC MOSFET switching without any diodes? [Low-Cost AC Solid-State Relay With MOSFETs]

texts:
Is it possible to switch an AC load using two MOSFETs in anti-series such as the picture below?

In this mode, each MOSFET is on during one half of the wave and the other's body diode conducts to complete the circuit.

Source

With some MOSFET's RDSON approaching 4mOhm, there is very little loss (heat generation) by the FET.  However, the body diode or even external Schottkey diode can easily dissipate one watt/ampere given the near 1Volt drop.

Is there a more efficient a circuit that would use just the transistors and no diodes for the typical AC wave?


texts: How is the high frequencies are found in the rise time of signal?

texts:
I have read an article from Tektronix on how oscilloscope probes affect your meausurment
here i read that:

The consequence of a large capacitance value is severe because the front edge of the signal contains the high frequency content.(page 6)

article


texts: SPI Timeout Issue with CH341A USB to SPI board

texts:
I'm trying to use the Aceli CH341A USB to SPI board to communicate with addressable LEDs, but it keeps timing out after 32 bytes. The board is unfortunately not that well documented (in English). The LEDs do work - I was able to use the SPI bus on a raspberry pi to control them (but unfortunately that's not an option for my application).

I do have it in the correct configuration for SPI mode as indicated by the red light and I'm able to successfully control up to 6 LEDs max.  One thing I tried was to change the USB Max bulk packet size in the driver C source code file, which was originally 32, and that resolved - or at least got rid of - the timeout error, but the LEDs still don't light up.

Is there just a setting I need to modify via ioctl?  I think Python is mostly set up to do that, but I could use some help if that's the case.

Some background - I'm a mechanical/controls engineer so only just getting into all this C and embedded stuff.

this has been my best resource, and the driver compiled with no problems --> https://github.com/gschorcht/spi-ch341-usb

other references:
http://www.chinalctech.com/m/view.php?aid=266

https://github.com/hpaluch/hpaluch.github.io/wiki/Getting-started-with-LC-CH341A-USB-conversion-module


texts: How do I switch between two voltages of a capacitive divider

texts:
The circuit I am building uses a capacitive voltage divider. The switches are used to toggle between the two voltages across the divider as can be seen in the schematic below. I tried it in hardware but on the output I just get voltage spikes
whenever the switch gate pulse transitions from low to high, the voltage appears to be just noise.

I don't have any problem with the voltages. as the capacitor dividor performs its job well (because of an auxillary active voltage balancing system). However the switches even if they turn on the voltage on the source side of the MOSFET doesn't appear. It just idles at zero with noise and the spikes as mentioned above.

I am using a micro-controller to provide the gate signal which is stepped up to 10V and used to drive the MOSFET gates. The switching frequency is also very low around 100Hz.

So, what is going on here. I would like to know why the circuit is failing to perform its task and how to correct it.

I can't replace the MOSFETS with BJTS because of current constraints

The Battery is 24 Volts. So I would expect voltage at the output alternating between around 12 Volts and 24 Volts.

! - The NOT gate is not present in the real design. The actual design uses a single transistor inverter.


texts:
This is to trigger a 12v solenoid (acting as a laser shutter) with 5v (JP2) thru an optocoupler.
The problem is 5v line have bit fast interruptions on a laser show, so I'd like to add a bit of delay OFF (say 0,5sec) in order the shutter remains active (energised) when this fast OFF interruptions happens (you know, to avoid click-click shutter open-close noise)
So I think I need to put a capacitor and maybe resistor+capacitor, but sorry, I don't know where on this circuit...could you help me please?
Many thanks

maybe this one?


texts: Is it bad practice to have power lines on a PCB instead of a plane

texts: I am designing a PCB and am wondering what the downsides are to having a 5V trace instead of a plane.


texts: Measuring the frequency of a 0-5V signal with DMM and no oscilloscope?

texts: I'm trying to determine whether I can use a DMM to monitor a 0-5V signal of a cam and crank sensor.  Both are magnetic.  I have a 5V ref. The sensors should vary between 0V and 5V with a short pause at 5V. I have an image of the correct waveform from a lab scope, but lack the funds to purchase one to test proper.  My DMM measures from 200Hz to 20kHz.


texts: ETH PHY Protection during "no supply" condition

texts:
My quesiton is simple: In a typical ethernet setup, the RJ-45 jack connects via some transformers (or call it magnetics if you like to) to the Ethernet PHY. (which might be internal to the microcontroll or an external PHY).

Now, if the device is not powered but the LAN cable plugged in (a very common case), there might still be packets sent über the transformers that reach the PHY whcih is not powered. As it is usually a problem when having nonzero levels on pins of unpowered ICs , why does nobody care in this case?)

Note that I am NOT talking aboud ESD protection, because latter won´t help you in this case!

Thanks!


texts: What is the red/orange coating underneath a CRT anode suction cup, and is it important?

texts:
This question is regarding a matte red/orange coating around the anode socket on a cathode ray tube which is made to be connected to via a cable with a suction cup, the coating seems to typically be a circle just a little bit larger than the suction cup, although in some images I have seen this being a much larger extended area. In my case, I found this on an oscilloscope CRT, although I have also seen this in images online appearing on CRTs from old TV sets. I have found very few mentions of what this actually is online and the information is inconsistent! The consensus seems to be between this having no purpose (which I doubt), and this being insulation which prevents arcing (which makes me wonder why it is necessary in between glass and the suction cup which are already insulators). Would anyone knowledgeable be able to tell me what this substance is and what it does?

The reason I need to know is that I accidentally removed a good part of this coating on an oscilloscope CRT while discharging the anode and cleaning the area under the cup, and need to figure out whether I need to do something to replace it. I have heard about silicone paste being used in this area to prevent arcing, however if the original coating was there for the same purpose, I wanted to find out whether whatever this substance is works better.


texts: BLDC Motors: Calculating the offset between rotor flux angle and rotary encoder Measurement

texts:
I am using an AS5147 Rotary Sensor to measure the position of a BLDC Motor. The motor is a 11 pole BLDC/PMSM. I have my own inverter circuit and right now doing a look up table based Space Vector PWM scheme to drive the motor.
For the sake of simplicity, lets assume the encoder gives me degrees (0-360, electrical not mechanical) and based on the measurement, i check my look up table (lets assume it also has 360 values, representing 1 cycle) and depending on the direction i want to drive, i get the duty cycles at the index [EncoderPosition +/- 90 ]. If i want to add a bit of field weakening, i add a few degrees.
This approach gives satisfactory results but what i described above is only valid if what I get from the rotary encoder is actually the rotor flux angle. As far as I've understood the encoder is not synchronized to the rotor flux and just gives me a measurement that has a constant offset to it.
Currently, i am finding this offset by just playing around and trying different values and this 1 SE post suggests that its not that important but for my current implementation that doesn't do current measurement, it really seems to affect the performance.
I tried to automate finding this offset by locking the motor to some position - with an arbitrary index from the look up table, take the measurement from the encoder and get the difference between them and use this as a software parameter. I was a bit lost with this approach since to my understanding, the look up table index represents the stator flux (that i generate) and the encoder measurement should represent (rotor flux + 180), since when the motor is locked, the rotor flux locks itself in the opposite direction of the stator flux. My idea was doing
Offset = (ChosenLookUpTableIndex + 180) - EncoderMeasurement
where (ChosenLookUpTableIndex + 180) is the rotor flux angle when the motor is locked.
I also had other problems such as different motor power cable orderings giving different offsets, some of them not even constant.
I would like to ask if there is a proper way to calculate this offset rather then experimenting with it.


texts:
Does anybody know the name of the cable that should be inserted in this connector? I lost it so I cannot make a picture.

I know it is a power cable where the other side is inserted in a 200-240 V (non grounded) Dutch (European) wall socket/out.

These types come in two sizes, the most generic is slightly bigger, this one is smaller (but for both I don't know the name).

The distance between the pins is about 6 mm, the horizontal distance 11 mm, and the height around 6 mm.

Brand: Philips
Type : Hair (not beard) shaver
Model: (I will add this later, not near the device)
Type : Power connector (other end of cable to ungrounded Dutch/Europen 220 V wall outlet/socket)
Marks: (I will add this later)

Update:

The model is Philips, HC3410. I could find an adapter but those are over 30 euro including shipping (more than the entire product). However, I found via AliExpress and a Dutch site a compatibility list so I hope it will work. I will not in 2 to 8 weeks.

For those who are interested:

Compatibility list: Compability list

Adapter: Adapter at AliExpress


texts: A Voltage Divider with Load Regulation and Efficiency Question?

texts:
For this question, the voltage divider splits the 12 V battery into +/- 6 V and it supplies up to 10 W total to the load, split between the two output voltage outputs in an arbitrary ration. Load regulation is intended to be greater than 1% from 0 W to 10 W. Now, in this case, the resistors, R, aren't the load resistors, the load resistors would be connected in parallel to the resistors, R

Now, what I need help on is approaching this problem. I think I managed to get the load resistors correct at 3.6 Ohms from 10 W / ((6 V)^2) but I'm not too sure


texts: Trouble getting USART working on STM32 (stm32f103c8t6)

texts:
I started working with with stm32f103c8t6 recently and I was able to set GPIO to input and output, however when I try to set USART it just does not work. I'm trying to write directly to registers, because I would like to understand how things work on the lower level, but I do realise that there are some helper libraries for working with USART.

Anyway I follow instructions from: Official reference manual on how to get USART Transmission working, but the code does not work, there is nothing in USART terminal on my PC. I do realise there is a lot of room for error. Here is my code for initializing and sending USART Transmission on stm32f103c8t6:

void initUartTransmission(){
    //1. Enable the USART by writing the UE bit in USART_CR1 register to 1.
    USART1 -> CR1 |= (0x1 << 13);
    //2. Program the M bit in USART_CR1 to define the word length.
    USART1 -> CR1 &= ~(0x1 << 12);
    //3. Program the number of stop bits in USART_CR2.
    USART1 -> CR2 &= ~(0x1 << 12);
    USART1 -> CR2 &= ~(0x1 << 13);
    // 4. Select DMA enable (DMAT) in USART_CR3 if Multi buffer Communication is to take
    // place.
    // I'm skipping this, because I'm not interested in DMA at this time
    // 5. Select the desired baud rate using the USART_BRR register.
    // I'm not certain of the clock speed I have. The board has 8 MH cristal,
    // but I'm not sure if it's enabled
    float f = ((float)(8000000/16)/9600);
    int q = (((int)f)&0x0FFF);
    int k = (float)(f - (float)q);
    k = (float)(k * 16);
    USART1 -> BRR = ((q<<0)|(((int)k&0x0F)<<8));
    //6. Set the TE bit in USART_CR1 to send an idle frame as first transmission.
    USART1 -> CR1 |= (0x1 << 3);
    //Enable clock for USART1
    RCC->APB2ENR |= RCC_APB2ENR_USART1EN;
}

void void writeUart(){
    while(!(USART1 -> SR & (1<<7))){
        USART1->DR = 'c';
    }
}

I've been trying different configurations, but I just couldn't get it to work. I am confident in connections between the board and my USB USART adapter, because I have experience with Atmega328p.

I would appreciate any help.


texts: Simple transistor switching example should show LED off

texts:
UPDATE

So even when I remove the switch, the LED is still on (see image below). I.e. there's nothing connected to the base; only to the collector. I'm using the same 2N2222-331 transistor that's in the book (I actually got all my components from the Kit sold separately at http://www.makershed.com/Make_Electronics_Components_Pack_1a_p/mecp1.htm).

I also tried another transistor (of the same type) to make sure that the one I was using wasn't faulty but to no avail.

Is it possible the author messed up the transistor type? In at least 90% of these kinds of cases it's my error an not the author's.

Reading "Make: Electronics". Trying to implement Experiment 10 on Transistor Switching. Diagram shown below:

Problem I'm having is that my circuit always has the LED ON when in theory the LED should be off when the button is not pressed because there is no voltage applied to the base of the transistor.

What am I doing wrong here? I'm sure I have the right components (except possibly for the push button) and that I'm using 12V DC. My guess is that I've got the orientation of something wrong but I'm not sure.


texts: Alternatives to screw terminals, breadboards for prototypes?

texts:
Often I want to connect components that operate at less than 5v (I mention this as it may have a bearing on the gauge of the wire?) But have an easy way to disconnect.

Screw terminals are nice but they can be slow when there are multiple wires.

Breadboards are too fragile for field testing.

I was thinking of using RCA audio video jacks and plugs, but they seem so big... Is there something similar but smaller?

I'm looking to connect things like sensors and breakout boards.


texts:
TLDR:
What are possible failure sources for a schottky diode? Overheating, overvoltage, overcurrent (leading to overheating) anything else?
Long version
I am currently measuring our new prototype device. It works fine, does not draw more current than expected and stays relatively cool (hottest point on the PCB is 50°C at the buck converter.)
In front of the buck I have a schottky diode for reverse voltage protection:

I left the device running for some minutes, current draw on the 3V3 rail was below 500mA, 24V current must have been below 100mA. Then I saw a small lightning, like ESD, and the device stopped working (no current draw).
On closer investigation I found a small hole in the middle of the schottky diode package, and the diode was open circuit.
I would rule out ESD, as the device was lying on the desktop and nothing touched it. The device was powered by a lab power supply. Any ideas why the component failed?


texts: Electrolytic capacitor polarity voltages

texts:
What happens if we feed an electrolytic capacitor only positive voltages while keeping the negative pin voltage lower than positive. for example positive pin 20V and negative pin 5V.

Does it affect capacitor life?


texts: Handling inferred clocks during RTL Synthesis

texts:
I am trying to synthesize a design in VHDL into a ProASIC3 FPGA using the Synplify Pro tool. The synthesis report gives me the following warning on inferred clocks.

@W:MT420 :  | Found inferred clock counter_unit| pstate_inferred_clock[1] with period 10.00ns. Please declare a user-defined clock on object "n:bcu_ins.ctr_ins.pstate[1]"

I traced back to the part of the code where the warning is being generated and the same is reproduced here for reference.

p_fsm_clk : process(reset_n_in, clk_25mhz_in)
begin
    if (reset_n_in = '0') then
        pstate <= s0;
    elsif rising_edge(clk_25mhz_in) then
        pstate <= nstate;
    end if;
end process p_fsm_clk;

p_fsm : process(pstate,restart_ctr,enable_ctr2,sys_fail)
begin
    start_ctr1 <= '0';
    start_ctr2 <= '0';

    case pstate is
        when s0 =>
        --Reset state. All counters are reset
            if (sys_fail = '0' and restart_ctr = '1') then
                nstate <= s1;   --move to start counter1
            else
                nstate <= s0;
            end if;

        when s1 =>
            start_ctr1 <= '1';  --Initiate counter1
            if (restart_ctr = '1') then
            --restart the counters
                start_ctr1 <= '0';  --reset counter1
                nstate <= s1;
            elsif (enable_ctr2 = '1') then
            --move to start counter2
                nstate <= s2;
            else
                nstate <= s1;
            end if;

        when s2 =>
        --Save the counter1 value and start counter2
            start_ctr2 <= '1';  --assert flag to start counter2
            if (restart_ctr = '1') then
            --restart the counters
                nstate <= s1;
            else
                nstate <= s3;
            end if;

        when s3 =>
            start_ctr2 <= '1';
            if (sys_fail = '1') then
                nstate <= s0;
            elsif (restart_ctr = '1') then
            --restart the counters
                nstate <= s1;
            else
                nstate <= s3;
            end if;

        when others =>
            nstate <= s0;

    end case;
end process p_fsm;

--counter1
p_ctr1 : process(reset_n_in, clk_25mhz_in)
begin
    if (reset_n_in = '0') then
        ctr1 <= 0;  --value on reset
    elsif rising_edge(clk_25mhz_in) then
        if (start_ctr1 = '1') then
        --flag is asserted to start counter1
            ctr1 <= ctr1 + 1;   --increment counter
        else
        --flag de-asserted
            ctr1 <= 0;  --reset the counter
        end if;
    end if;
end process p_offset_cnt;

--save the value of counter1
offset_val <= ctr1 when pstate = s2;

The logic contains two counters – ctr1 and ctr2. The counters are run when there are no system failures. In the first phase ctr1 is run, which is then followed by ctr2. ctr1 stops counting when ctr2 is enabled. The value of ctr1 determines how much later is ctr2 started (in terms of 25MHz clock period), referred to as the offset. This offset value is stored to a signal vector, as can be seen in the last line of the code. The state s2 is used for capturing the value of ctr1 before it resets to 0.

offset_val <= ctr1 when pstate = s2;

I realised that this assignment statement is causing the inferred clock in the design (but don’t know why). When I put the same statement inside a clocked process, the inferred clock warning disappears. However, my logic doesn’t work correctly.

I am looking for a few clarifications in this regard.

Why is there an inferred clock on pstate[1] in this design?
Is it alright to have such statements in the design? Does the presence of inferred clocks indicate a bad design practice?
If it not ok to have inferred clocks in the design, how can I fix this by coding the logic differently?
If it is ok to have inferred clocks, how can I let the tool know of it? What period constrain can I provide for such inferred clocks? How can I determine a meaningful period for such inferred clocks?


texts: Not getting input on STK600 with ATmega8515

texts:
I recently had a written exam for a class and one of the questions was to write a program for the ATmega8515.  I wrote down this:

#include <avr/io.h>
#define F_CPU 4000000UL
#include <util/delay.h>
#define Delay 5000

int main(void){
DDRB = 0xFF;    //set to output
DDRA = 0x00;    //set to input
PORTB = 0xFF;   //turn off all LEDs

while(1) {
    if (PINA == 0b11111100){    //if SW0 and SW1 are pressed
        for(uint8_t i = 7; i<=0; i--){
            PORTB &= ~(1<<i);   //Turn on led at location i
            _delay_ms(Delay);   //Delay
            PORTB |= (1<<i);    //Turn off led at location i
            _delay_ms(Delay);   //Delay
        }
    }
    else if(PINA == 0b11111110){
        for(uint8_t i=0; i>=7; i++){
            PORTB &= ~(1<<i);
            _delay_ms(Delay);
            PORTB |= (1<<i);
            _delay_ms(Delay);
        }
    }
    else if(PINA == 0b11111101){
        for(uint8_t i = 7; i<=0; i--){
            PORTB &= ~(1<<i);
            _delay_ms(Delay);
            PORTB |= (1<<i);
            _delay_ms(Delay);
        }
        for(uint8_t i=0; i>7; i++){
            PORTB &= ~(1<<i);
            _delay_ms(Delay);
            PORTB |= (1<<i);
            _delay_ms(Delay);
        }
    }
    else{}
    }
}

For some reason this does not work.

The expected outcome is that if the first two switches are pressed (SW0 & SW1), it'll scroll the leds from left to right.
if the first switch is pressed (SW0), the LEDs will scroll from right to left.
And if the second switch is pressed (SW1), the leds will scroll from left to right going back and forth forever

As of now, I know the for loops work, I've tested them in other programs.  It just seems like I'm not getting and input from the switches.


texts: How realistic is this model for an inductive spike?

texts:
I want to model a real-life scenario when a mechanical switch is rapidly opened when passing current through an inductive load. Below is a model and corresponding plots for the switch control (Vn001), switch current I(S1) and a plot to observe the voltage spike occurring at the inductor terminal V(vspike). Initially the switch is ON and after 0.2 seconds the switch is turned OFF.

I set the switch on resistance to 1 Ohm and the off resistance to 10Meg.
According to the theory I can understand why the inductor current causes such huge voltage spike when the switch is opened.

But in real life I don't think this crazy voltage makes sense and goes that high.

What happens in reality that we never see like 10 MegaVolts?
Or how can we model this to make it more realistic?

edit:

Adding some capacitance for the switch resulted more realistic results:


texts: Half-Duplex Twisted Pair ethernet - which pair?

texts:
Which ethernet pair is used for half-duplex signaling?

In full-duplex ethernet, 1,2 does TX; while 3,6 does RX.

In half-duplex, in theory, only one of them is needed - which one?


texts: 24v dc High current variable speed Voltage regulator

texts:
I’m in need off a high current voltage regulator. I know a little about electronics, but not on an engineering level of designing stuff. I have a few stuff on scrap boards that I can use that lying around my garage.

I have 24v dc input driving motor rated at 24 V, 25 A.
I need to operate the motor at somewhere in the 12 to 24 v range in order to get the right rpm to spin a PMA (Permanent Magnet Alternator).

The parts I have on hand are :

10-Lm317
50-Lm7805
4-2sc5200
5-Tp122
10-d2390
Big heat sink
10-10k resistors
Uc2842N
Uc2854
cny17-3
kia555p
8-5Watts 0.22ohm ceramic resisters
ST UA741cn


texts: Mosfet transconductance in the saturation region

texts: what happens to the transconductance of a MOSFET in the saturation region if the gate-source voltage is less than the threshold voltage? Will the transconductance be negative since the equation is given by


texts: Role of the output capacitor in buck converter in terms of frequency

texts:
I am using this DC-DC buck converter - buck converter.
Schematics :

Buck Converter Specifications :

Input Voltage - 18V to 32V
Switching Frequency - 300kHz
Output Voltage 9V
Load Current - 0mA to 200mA Maximum.

I have 2 questions:

What does it mean when a design recommendation states - "The output capacitor ESR and capacitance form a zero = 1 / (2 x π  x Cout x ESR). This zero can move significantly if an aluminum output capacitor is used. Aluminum output caps ESR can change 10x over temperature."

Can someone explain me a little intuitive on what this recommendation states and why should I take care when designing a buck converter? How to test it or verify this recommendation?

Why should we care about the output aluminium electrolytic capacitor's frequency vs impedance graph while selecting the output capacitor of the buck converter (in this case the 47uF?)

Can someone explain to me a little intuitively the answers for the above 2 questions?


texts: Does power delivery over ethernet always have to use isolated DC/DC converters?

texts:
I am examining the possibilities for building a cheap ethernet device that would be powered over ethernet using PoE technology. I came across this article which shows the generic block diagrams:

Looking around, I always find the DC-DC converters used in PoE applications to be isolated. I am trying to understand whether that is always necessary. Assuming that the PoE RJ45 cable would be the only cable connected to my device, is there really any reason for me to isolate from the input voltage? This is also assuming that the data lines are already isolated, so the only potentials without isolation is the power lines.

Edit:

To clarify more: I still want the TX and RX lines to stay isolated via transformers. I just want to skip the DC-DC part isolation (just graetz bridge, bulk capacitor and a DC-DC converter without isolation.) I don't mind being not compliant with the standard here. As for the shielding, I would leave it disconnected.


texts: Using a varactor diode to tune a resonance frequency

texts:
I think this is a question is some very elementary circuit design but...
I want to use a varactor diode to tune the resonance frequency of a resonator I have built.

I understand that a varactor is a voltage dependent capacitor, but I can't get my head around the correct configuration of using them.

Usually if I want to tune my resonator I insert a capacitor between the hot end of the resonator and the ground this will obviously shift the resonance frequency according to
$$\nu_0 = \frac{1}{2\pi \sqrt{L(C_p+C_{capacitor})}}$$

I want to do the same but with the Varactor diode, my current thinking feels very wrong as the DC voltage source is surely just going to go straight through the resonator and into ground.

I know this is basic but I am a little stuck!

simulate this circuit – Schematic created using CircuitLab