texts:
I have just received my first microcontroller, an Atmega8. I will soon be making a voltage regulation circuit for it to run at 5V, but I don't have all the parts yet.

Instead, I have a 5V DC 1000mA adapter, and thought there's no reason it shouldn't work just as well. Is this a good/bad idea?

Furthermore, I checked and it is actually outputting 5.48V. So I checked the Atmega8 datasheet, and it says that it will operate between 4.5 - 5.5V. I am quite close to the upper limit, so am I taking a risk with this?


texts:
Not sure it's a 100% appropriate forum, but we're having a project at school in which we faff around with noise measurements. The problem is we haven't really been given proper instructions on how to use the meters - just a slip listing some settings. I was wondering if anyone could help me interpret it:

"1) RMS, fast, Leq
2) Peak, Imp, SPL
3) RMS, Slow, SPL"

We were instructed to measure the noise level in various enviroments (silence, extreme noise, somewhere inbetween for example a class room) using both A- and C-filters, but not really when to use what setting, or how to interpret the results.

For example, when using setting #2, this meter told me that when my daughter dropped a crayon about a meter away, she emitted an 80dB noise. It doesn't even seem reasonable to me. Maybe there's something about the SPL setting that I'm missing?

Can anyone help me with deciphering the instructions?


texts:
I'm trying to design a servo control board to be a daughter card for DE0-NANO, but run into a problem where all the servos (18 for hexapod) get to the end position on power up.
The initial idea was to implement 'power on reset' circuit, but i was told it a bad idea.

Im looking for some suggestion as to how i can achieve a sequential start up for each leg of the robot. I was thinking maybe some digitally controlled relays or a separate little micro-controller or maybe somebody has a better idea?????


texts:
It's an 0402 sized component. Measures about 50 milliohms out of circuit. I also measured it with a cheap LCR meter and it shows -47nH. Capacitance measures 350mF. So I'm pretty sure it's a jumper.  It's weird that it's on an antenna GPS feed line coming in from the middle right.

It looks like it's shorting the signal to ground. The component is half green half black and there are a few others of these on the circuit.

If it is a jumper why is it shorting the signal to ground?


texts:
Writing a value to RAM is a small part of my project, everything is working, but I cannot explain one thing related to RAM/digital timing.

I will write a description in regards to picture I added.

macc_out goes to data_in of the RAM
address_ram is the address of the RAM cell
out_temp is the output of the RAM
write_en_ram is write_en of the RAM

As far as I had the idea of RAM, it writes straight on the rising edge of the clock. So data seen on data_in on the rising edge of clock will be written to the RAM. Even if data_in changes on the same clock as write_goes high, the the old data will be written.

Then why in my case RAM writes -36 and not -10.

Now I tried to change data_in value with a clock value (0/1) and now it does as it should do. What's happening? ram_in is data_in of RAM in this case.

macc_out == ram_in == data_in


texts: How to stops flickering in high current draw Circuit

texts:
I have 6v DC circuit that quickly pulses high current LEDs on and off at a fast rate (10ms or less).

When the high current LEDs cycle, the low power 5mm LEDs used for power on indication and voltage monitoring will flicker.  They are directly attached to the battery source. I figure its because of a drop in current from the battery.. ?

Can someone give me a hint as to how I can keep the current from dropping to these 5mm LEDs when the draw goes up as a result of the high current LEDs turning on ?

Will using an Inductor help resolve this ?

Thanks in advance.
Bob


texts: how to verify truth table of MAX485/RS485

texts:
I want verify 2nd case of the below truth table of MAX485 IC (RS485). Please see in red color.
Is my circuit correct ? I have connected RE,DE and A-B to GND for making it LOW.I have connect DI to GND also just to avoid floating connection. However LED still unexpectedly blinks. why?

simulate this circuit – Schematic created using CircuitLab
what is wrong in my cicuit?
thanks


texts: Where to find a belt for my REVOX B77 MKII reel 2 reel?

texts:
I am totally conscious that this is an Electrical Engineering forum, but I would welcome any input on where to ask for this request.

Please take a look at the pic below :

The belt whom dead parts you see on the pic in black is used to move the 0000 counter.

The problem is that I don't know at all where to attach theother side of the belt ! Please help.

Thank you.


texts: How any one achieve sinusoidal back emf in PMSM and Trapezoidal back EMF in BLDC ? What is the winding differences?

texts:
How any one can achieve sinusoidal back emf and trapezoidal back emf in the motor.
What is the winding differences in those motors.
I have take an In-wheel BLDC exterior motor which is used in e-bike. I get sinusoidal shape instead of "Trapezoidal shape".
In this case how can I calculate back emf constant.


texts: Battery powered, wearable, non line of sight, short range metal detector?

texts:
I want to build a circuit to detect when people bring their hands close to their mouth. This could be used to warn chronic nail biters of impending nail biting for example :)

The idea I have is that a person can wear a metallic ring on their finger (iron/gold?) and a necklace with a small sensor near the neck. A heavy pendant counters the sensors weight and keeps it on top near the neck. Now the circuit's job is to detect proximity of the metallic ring within a 3 inch radius and I am looking for ideas.

I couldn't find anything like this on adafruit et al. Also there is another question that asks about short range metal detector but the solution doesn't fit my constraints.


texts: Budget alternative to fancy linear slide

texts:
I have been checking out nice 1D linear slides such as this and this and this.

Especially the first one is really nice since it has a built in encoder and a controller with RS232 interface. However, the downside is that these have a starting price around $1,700.

The specs should be something like:

100 mm travel
1 mm precision
Encoder
RS232 / USB interface
Speed is not critical
The load will not be large (<5N)

Does anyone have any suggestion how you could do this on a budget of say $500?
Or does anyone have a suggestion for something completely different with the same function?


texts:
I want to interface MQ-135 air quality gas sensor. Sensor have 5V output interface. However my mcu work at 3.3V. I can basically put a voltage divider. But sensor itself is a voltage divider with a specific resistor range at output.

So in this case I need opamp or something like that. But what would be the easiest way interface this 5V to 3.3V.


texts:
I've always struggled with some really basic questions around amperage. Like, if you're plugging a 2 amp device into a wall socket, but that circuit is a 20 amp circuits why doesn't it blow up?
Then I realized, and want to ask this question:
In reference to circuits in a building, like a standard 20a 120v circuit, is that referring to amperage capacity and the amperage on my phone charger is referring to actual amperage drawn? If so, why is it never explained?? I know that is really simple but I've never understood it and wish somebody had said that to me years ago.
Basically, a 20a circuit can provide UP TO 20 amp, and a device draws what it says it requires.


texts: RS-422 for pseudo-multipoint bus topology?

texts:
I have been trying to get a definitive answer on the possibility to use RS-422 for connecting one master and several slaves in a pseudo-multipoint/bus fashion, with slaves being able to send some data back to the master.

My intended usecase is:

1 master
4 slaves
one Tx pair driven by the master, connected to all slaves (i.e. RS-422 multi-drop topology)
one shared Rx pair driven by (all) the slaves, back to the master
only the master would initiate communications.
full duplex communication is not required.
the master would include a target slave address in the messages broadcasted on the Tx bus, so that only one specific slave processes it, others would discard it.
the targeted slave sends back some data to the master over the single/shared Rx bus

Now, I do know that RS-485 would be more appropriate, but would still like to understand how far I can push RS-422. I only have 4 target nodes, well below the limit of 10 allowed by RS-R422. The only problem I see is with having all slaves permanently connected to/driving the Rx bus, even if they only talk one at a time: will this work ?
I also understand that should any slave fail, my Rx bus is gone for good.

I have read conflicting statements about what RS-422 cannot/should not be used for (with a gray area about using RS-422 for the usecase above), so any enlightment would be appreciated.

Regards,
Julien


texts: Help with the design of a rectangular loop antenna for the PN532 controller for NFC communication

texts:
I am currently designing an NFC reader in the context of my PhD thesis. The NFC reader will use a PN532 chip from NXP (which is one of the requirements of my circuit). I plan to draw a rectangular loop inductor on the PCB (which is often referred to as an NFC antenna in wireless design) which would approximately occupy a 3x3 cm square (up to 4x4 cm). There will be other components on this PCB such as an LED driver, some LEDs, etc. The main micro-controller will stand on a separate PCB and will communicate with this board through an SPI link. Space is the main constraint: the volume occupied by the PCB has to be minimized as much as possible.

I read this document quite carefully (NXP Antenna Design Guide) and I have very specific questions related to the design of the PCB that will carry the NFC controller and antenna:

Could it be acceptable to put the components (NFC controller, LED driver) on the same PCB as the NFC antenna?
What would be the "best" position relatively to the antenna in this case? (i.e. one that would limit eddy currents and inductance increase)
How to efficiently shield the main controller board? Will a sheet of copper do the job (instead of ferrite)?
Is there an advantage to have different length and width for the antenna?


texts: We're trying to setup rotary phase converter, and we're getting some differences in line voltage. The black reads 350 to ground while red and white read 120 to ground. This is all from a 220 input. Red to white reads at 240 volts. Any thoughts on the problem? I don't imagine this is normal.


texts: If Voltage determines current , a transformer regulate current?

texts:
Well , a transformer can regulate the voltage , increasing and decreasing it .

And , if the voltage increase , the current too .

So... a transformer regulates current too right?

Sorry if its a very basic question , but after lot of searching in google im getting more and more confused ...

Thanks.


texts:
I could use some help on finding a replacement Transistor. One of the depth finders on our boat has failed and shows a dead short on the power input lines. The problem may be a shorted Transistor in the power supply section. I haven't removed it yet because i wasn't sure i could get a replacement. It has a Motorola logo on it and the numbers 734 and J31. It is a SOT23(?) surface mount package.

My Internet searches couldn't find the Mot part,  but found a FMMT734. I'm not sure that is the correct match.  Can anyone give me some information this component and where i might be able to purchase one?


texts: Switching between series and parallel battery connection

texts:
Previously I made same scheme (attached) but with two relays and it worked pretty well. Now I want to rebuild it with transistors (MOSFETs).

The main purpose as I mentioned in the subject is to switch battery connection type, from series, which I need to power my scheme, to parallel, for charging with USB. (Arduino will switch MOSFETs states.)

But I have some questions:

Is it okay to use M1 or should I use NPN BJT to drive M2?
How to pull up M2 gate?
Will M3 be closed by default or I should use scheme like on the second attachment. (M1, M4: N-channel MOSFET; M2, M3: P-channel MOSFET)


texts: How to choose between Mealy and Moore state machine

texts:
I know the basic differences between Mealy and Moore FSM (Finite state machine). What I want to understand is the following:

Pros and cons of using Mealy over Moore and vice versa
In which situation Moore is more suitable than Mealy and vice versa

The figures of merit for comparison could be latency, throughput, area (state encoding FF's), power etc.


texts: what happens when both anode and cathode voltages are same for a diode?

texts: In a circuit if the ideal diode has both the cathode and anode voltage same, will it conduct or not? Similarly, in a constant drop model if the voltage drop is exactly equal to 0.7 will it conduct or not?


texts: UART read consistently missing half of the transmitted bytes

texts:
I have setup a simple UART test on my SAML21 and believe I must be misusing the library due to the behavior I'm seeing

uint8_t testData[8] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06}

void broadcast_test_data(void)
{
    usart_write_buffer_wait(&usart_instance, testData, sizeof(testData))
}

void serial_data_handler(void)
{
    unit16_t rxInt;
    if (usart_read_wait(&usart_instance, &rxInt) == STATUS_OK) {
        printf("RX %d", rxInt);
    }
}

int main(void)
{
    struct usart_config config_usart;
    usart_get_config_defaults(&config_usart);

    config_usart.baudrate = 1000;
    config_usart.mux_setting = USART_RX_3_TX_2_XCK_3;
    config_usart.pinmux_pad0 = PINMUX_UNUSED;
    config_usart.pinmux_pad1 = PINMUX_UNUSED;
    config_usart.pinmux_pad2 = PINMUX_PA24C_SERCOM3_PAD2;
    config_usart.pinmux_pad3 = PINMUX_PA24C_SERCOM3_PAD3;

    usart_enable(&usart_instance);

    while (1) {
        // run-loop
        SYSTEM_RunTasks();
        serial_data_handler();
    }
}

I verified that the TX data is transmitting the entire testData array via Putty.

The issue is that when I tie the RX and TX together to test receiving, I am only ever getting bytes (0x01, 0x02, and 0x06).  Is polling for RX data via the while loop not the way I should be doing this?  Do I need to somehow mark data as read before UART moves onto the next received byte?  Should I be asking for more than 1 byte at a time?

Thanks for any info you can provide


texts: The S parameters of an attenuator--but what is actually wrong with it?

texts:
I have measured S parameters of an 10 dB attenuator on hand--please see the attachment.

In my view, this attenuator is not performing as expected, e.g., |S12| / |S21| is not giving 10dB attenuation but rather it is giving ~20 dB attenuation (but varying over frequency).
the reflections, |S11|, are just too high.  Also |S22| are just too high in low frequency, but high frequencies it is low.

But my question is, if you are asked to describe the characteristics of such an attenuator, then what else would you say?

Thank you


texts: ESP32 output pin - internal pull-up/pull-down resistor

texts:
When configuring a pin as output on the ESP32, does it set an internal pull-up or pull-down resistor?

I am connecting a bus buffer  to an output pin, and I am not sure whether I should use a pull-up or pull-down resistor on the bus.

EDIT - Schematic:


texts: Problem with a circuit of an controlled variable voltage source

texts:
I have this circuit, it should regulate the output voltage between 15V and 0V. But the output I get when I simulate it is between 2V and 3V, and when I implemented, I burned zener diode 1N4734A. Anyone know the problem?

Some components:

4 transistors NPN BC548
1 potentiometer (linear) 10[K ohm]

The input voltage is 220V/50Hz and the transformer goes from 220V to 15V.


texts: Creating a small range, small baseline varying resistor

texts:
I am doing a design project on making a passive varying resistor device. I have a flex sensor that increases in resistance when you bend it. It has a 10k ohm nominal resistance and increase to 110k when it is a 90o degree bend. HOWEVER, I want my device to have a nominal resistance of 100 ohm and increase only 2-3 ohm instead.

My initial approach:
I made parallel-resistors circuits but when I get to the right nominal resistance, the resistance change is not what I want when I bend the sensor.

ONE of my important design criteria is that I want my device to be passive, so that my device will still have a desire resistance range even with it has different resistance source.


texts:
I'm learning about the construction of Peltier tiles from Wikpedia. However, some of the statements in the article are not at all clear.

Here's the extract:

  Two unique semiconductors, one n-type and one p-type, are used because
  they need to have different electron densities. The semiconductors are
  placed thermally in parallel to each other and electrically in series
  and then joined with a thermally conducting plate on each side. When a
  voltage is applied to the free ends of the two semiconductors there is
  a flow of DC current across the junction of the semiconductors causing
  a temperature difference. The side with the cooling plate absorbs heat
  which is then moved to the other side of the device where the heat
  sink is. Thermoelectric Coolers, also abbreviated to TECs are
  typically connected side by side and sandwiched between two ceramic
  plates. The cooling ability of the total unit is then proportional to
  the number of TECs in it.

What does "thermally in parallel to each other and electrically in series" mean for semiconductors? Also, why should they be arranged in this fashion?
Why does flow of DC current across the junction of semiconductors cause a temperature difference? Which "junction" are they talking about?


texts: Can a bad cell cause excessive heat in charging circuit?

texts:
Something I have noticed and am curious of. I had a cases where a lithium ion cell, is bad or dead and it seems to cause overheating in the IC chip on the charging circuit

Today I was having issues with a device that runs a touch display and power supply + battery for my raspberry pi . So I opened up the case to try and do some simple diagnostics. Noticed IC is getting hot.

I know this can happen when a power supply is short of amperage to supply the circuit too, and the port on my device is very loose so maybe it's possible it isn't receiving enough amperage? But is it also possible for a bunk cell to cause excessive heat in a charging circuit?


texts: PSU charging / USB charging with data transmission - LiPo cell

texts:
I am designing Rev.2 of my Geiger counter trying to squeeze in more functionality in it and make it portable.
I decided to go with single LiPo cell 3.7V, STM32 microcontroller and step-up converter 5V with regulation to +3.3V. I wanted also some leeway in future expansion of project regarding communication and connectivity so I added USBMicro connector with CP2102.
As I would need to charge battery I designed this section to acquire power from both USB connector and external PSU rated for +5V. I wanted to power up device when charging as well. There are 3 states this section can be:

Ext. PSU connected, USB VBUS disconnected, battery charging, Device powered up

In this state VIN is a positive rail +5V, hence IC12 (P-MOSFET) is open disconnecting V_USB. IC11 is getting 5V and charges Battery through pins 9 & 10 of IC11. Q2 is closed, max. current allowed is 1000mA. VDD is +5V as well since IC13 (P-MOSFET)  is open disconnecting battery during charge. Step-up converter IC9 is disabled since Q1 is closed and pulling EN pin down to GND. +5V is flowing through L3 to +3.3V regulator. Device is powered up.

Ext. PSU disconnected, USB VBUS connected, battery charging, Device powered up

In this state VIN is disconnected, hence IC12 (P-MOSFET) is closed allowing current from V_USB to flow. IC11 is getting 5V and charges Battery through pins 9 & 10 of IC11. Q2 is open, max. current allowed is 500mA. VDD is +5V, since IC13 (P-MOSFET)  is open disconnecting battery during charge. Step-up converter IC9 is disabled as Q1 is closed and pulling EN pin down to GND again. +5V is flowing through L3 to +3.3V regulator. Device is powered up.

Ext. PSU disconnected, USB VBUS disconnected, battery connected, Device powered up

In this state VIN and V_USB is disconnected. IC11 is not charging up and IC13 (P-MOSFET) is closed due to  lack of voltage on gate. Battery is connected to VDD supplying 3.7V to IC9 step-up regulator with Q1 open and EN pin pulled up to VDD. Once again +5V is flowing to +3.3V regulator. Device is powered up.
As this is first try of mine when powering device from battery that you can charge I am quite careful. There are many thing to consider with lithium batteries, specially ones you hold in you hands.
My questions are:

Is this a good solution to implement for conditions described above (3 states)?
Is it safe? OVP and OCP are on cells' PCB itself
Will I be able to communicate with MCU through USB when charging?

Answering in advance - yes I checked here for similar questions and I read few application notes (including AN1149 and AN0046 I found here). Any suggestions regarding schematic and layout are welcomed as I am still learning.


texts:
I unfortunately shot two Transistors of my Commander Pro because I drew to much current when I connected a pump to the fan-connector.
Now I want to desolder these two transistors, but I can't figure out the exact part number. The only markings are a "Y2" on top of the transistor (see picture). I couldn't find where the transistor is connected to ground. I also couldn't find a circuit diagram anywhere.
How can I find out which type (pnp or npn) it is?
Can I hack it anyway so that I can connect a pump to the port in the future, like buying a beefier transistor?
PS: I wrote an e-mail to corsairs support, but have little hope.


texts:
When I have a lightning protection system installed on a building roof top , what is the best way to bond the electrical equipment on the roof? Is it ok to directly bond it to the down counductor of the LPS? or different measures should be taken?

Lets say I have multiple air-condition units on the roof, how can I safely bond them to the lightning protection system. With bonding here I mean bonding the metalic body of the units.

Lets say if I bond the body directly to the down conductor, in case of a lightning strike will current pass through the unit and destroy the electronics inside it or will it only follow to the down conductor and to the ground?


texts:
I'm using the MSP430 SD16_A 16 bit Sigma-Delta ADC (page 843) for bipolar differential ADC measurements in a +/- 0.6V range. While the inputs can handle +3.3V, on the negative side the absolute maximum input voltage is -1V. The input seems to be a switched capacitor input with an input impedance of about 200Kohm. The driving opamp, an AD8475, though, can produce +/-4V outputs. I'd like to protect the ADC inputs from overvoltage. I'm considering :

(a) Regular 0.7V forward drop Silicon diodes between each input and Ground (in both directions, or 4 diodes per ADC input pair)

(b) TVS Suppression diodes between each input and ground, though these seem to hard to come by at low voltages.

(c) ESD Suppression Diode structures on each input line, though there isn't a +/-1V rail to clip the signals to.

(c) Some form of 1.8V Zener Diode (a pair in anti-parallel) between A+ and A- to prevent the inputs from going beyond that range. 1.8V seems to be the lowest Zener voltage available. I'm not sure if the AD8475 output common mode voltage will be able to follow the 0V given to it at VOCM when it's outputs are being forced by a Zener Diode, in which case ensuring that the negative voltage remains less than 0.9V becomes difficult. Also, the Zener forward conduction is likely to make this unviable in any case.

Which of these is likely to cause the least distortion to the signal? I expect diode capacitance is likely to mess with bandwidth, but is this likely to ve a problem at, say, 10-100KHz signal bandwidth (but with 1 MSPS 1 bit Sigma-Delta conversions). I'm planning on having and RC anti-aliasing filter in front of this as well. Are there any 'standard' methods to protect ADC inputs of such a low voltage, that preferably don't require the protection voltage to equal the ADC supply rails?


texts: Power amplifier, does this circuit work?

texts: I found that circuit for a power amplifier. Does it work? I want to build one for myself.


texts: Timing Improvements to Silicon Photomultiplier Transimpedance Amplifier Circuit

texts:
I'm designing another Silicon Photomultiplier circuit. Right now, it is in the theoretical stage. My team and I have made numerous circuits, and the basic template is below:

simulate this circuit – Schematic created using CircuitLab

Below are some links to the main parts used:

https://www.digikey.com/product-detail/en/texas-instruments/OPA656N-250/OPA656N-250CT-ND/431967

http://sensl.com/estore/microfj-60035-tsv/

The amplifier is the Texas Instruments OPA656 op amp. It contains a slew rate of 295 V/µs and a bandwidth of 500 MHz.

The Silicon Photomultiplier (SiPM) is a SensL MicroFJ-60035-TSV, the 6 mm version. It contains a PDE of 51%, and it has a gain of 5.3*10^6 from the anode to the cathode, and a typical dark current of 4.1 µA, with a rise time of 300 ps, and a max current limit of 15 mA.

The resistors and capacitors can be adjusted as needed, but this is what my team is working with so far. We have two channels, each independent of each other in this configuration, and the team is trying to measure coincidences between the two. Now, my training is as an electrical engineer, not a nuclear engineer, so this is all new to me, but from what the team has told me briefly, between measuring the time between the two detectors, we are getting around 400 ps. Now, I'm not sure if this is the time difference between the two channels or if this is the rise time of one individual channel, but when I find out more information, I will update this accordingly.

The timing is good, but because the amplitude was smaller than what we require, we had to use an external amplifier to 'boost' the signal. From what I was told, the external amplifier did not affect the timing, but we can't rely on it forever. Thus, I was wondering what I could do to improve the timing of this circuit while achieving a larger amplitude? We are hoping to try and achieve a coincidence timing of 300 ps.

The amplitude can be adjusted by adjusting R1 and C1, so I'm not entirely concerned about that. The one thing that I don't really know how to adjust is the speed. My first thought was to switch out the OPA656 for another amplifier with a faster slew rate, but it feels like just swapping it out might not be enough. Obviously, there are other considerations to take into account when picking a new amplifier, but how can I pick a better one taking into account the parameters of the op amp? If we're talking about just the schematic below, putting aside the board layout for now, what else can I do for the timing?

EDIT: My team gave me some values for what they want out of this circuit, so I added them below, and I also adjusted the circuit to showcase the current board schematic. I apologize for not making it clearer, but with the current comments they gave me, I felt it was imperative that I highlight the change.

Currently, our board uses a single set of power supplies (-30 V, +5V, -5V, and GND) to power the entire board. This is shared amongst all SiPMs and op-amps with just one set of decoupling capacitors. For the next design, I'll make sure to power them independently of each other.

We achieved a signal rise time of 6.5 to 9 ns using a 25 ohm resistor. Initially, our feedback resistor was 470 ohms, and while that provided a high gain, it was too slow for our needs. We played around with various feedback resistor values, and we found that 25 ohms gave a really fast time. However, the issue with this value is that the gain is very low, with the max amplitude being around 160 mV, so we needed a second amplification which was done through a NIM module. For my next design, we would like to keep the timing as low as possible while hopefully achieving a 600-850 mV output voltage, a rough gain of 5.5x, so that we can take advantage of the dynamic range of our ADCs. What would be the best way to go about this, keeping the speed the same while increasing gain? Assuming that we power each channel independently in the future, the only other major change I can think of is swapping out the op-amp for another one with faster slew rate and step time.


texts: Trying to identify this resistor, it's from a 240v mains 12v battery charger,

texts: Trying to identify this resistor, it's  from a 240v mains 18v battery charger for Black and Decker drill.


texts: Why does a simple circuit drain a battery slowly?

texts: OK, so if you directly connect the two terminals of a battery, there is very little resistance in the circuit and you will drain the battery very quickly. However if you have a very simple circuit, for example a light bulb connected to the battery, the battery will drain slowly based on the watts used by the light bulb. My question is, if this light bulb provides only a little resistance, wouldn't a lot of current flow through and therefore drain the battery quickly?


texts:
I've been making a few hobbyist PCBs at home and note that the photoresist developer and ferric chloride etch solutions are both pretty nasty chemicals that come with all kinds of warnings.

So I've been extremely careful

Wearing safety goggles while dealing with them.
Wearing disposable gloves at all times and throwing them away afterwards.
Wearing old heavy clothes so that a splash won't immediately touch skin.
Rinsing everything with large amounts of water afterwards.

My question is just how much of this is needed and how "nasty" are the chemicals?

I shall continue to wear goggles as they are no trouble and there seems no point risking eye damage however unlikely.

But what about the rest? If I get a single drop of the photoresist developer or feric chloride on me (and wash it off quickly) is that likely to be a huge problem? If I've rinsed something badly and there is still a trace of diluted chemical on there is that harmful? For example I'm throwing away my disposable gloves every time. I don't believe I get significant amounts of either on there but I'm not taking any risks. I could always wash them and use them again but they are cheap so I don't. But what risk is there that a few drops were on there and didn't get entirely removed by washing and they touched my skin?

I'm of course not looking for someone to say go ahead, it's fine :) I'm just looking to know what the risks actually are so I can be an appropriate level of careful rather than over the top careful which I am now, which frankly can be a pain.


texts: AC current sensing using micro-controller and suitable circuit

texts: I'm working on the project in which I need to measure AC current. The main problem I am facing is small current amplitude. I have to obtain the current waveform(I need complete waveform not just RMS value) of amplitude ranging from 100\$\mu\$A to 600mA and frequency ranging from 500Hz to 10KHz. But, I can't afford to have voltage drop more than 4V across sensing resistor. Do I have to use relays and set of different sensing resistors? Any other better alternatives to relays?


texts:
If relay coil is specified for AC power we have to take into account thar the magnetic force applied to the moving contact will drop to zero each 10 milliseconds (or 8.3 in case of 60 Hz supply) and stays low for several milliseconds.

So the question is: what forces contacts to stay in 'closed' state during this time?


texts: System verilog: check if logic signal changes at posedge

texts:
I'm relatively new to SV. I'm building a testbench in which I want to monitor a signal and take some action if it value changes @ clock posedge.
I’m looking for a compact way to this (I.e. not using a register).

logic [31:0] var_signal

Inizialmente
begin
  for(i=0; i<max_cles; i++) begin
      @(posedge clk_i);
      //check if var_signal changed and do something
  end
end

I searched the web and found threads on assertions but it is not what I want to do here.
Any hints?


texts:
circuit idea:
    // note -> times I specify in further text are symbolic

 IDEA:
-cap gets charged to full and is not currently connected to power supply
-it starts to discharge throught paralel LED + resistor over next 2 seconds
-when cap has too low voltage or capacitance to run an LED
transistors base reads LOW from LED and using a NOT gate, CAP gets connected to the
oower supply

here is a pic:

TRICKY PART
  i want the last step (battery charging the capacitor)
  to be 0.2 seonds long no matter what, how could I do it?

 WHAT I DO HAVE :
 I have all basic elements for breadboard, timer NE555 chip, a RaspberryPI

Sidequestion:
When capacitor is empty and transistors base reads low at ONE POINT
is there any way I could make that point variable
ex. Transistor reading LOW when CAP is 1/2 charged or 3/4 ?

tyvm:))


texts: Problem with glue logic/memory decoding on a 6502 project

texts:
I have a problem understanding the following schematic, specifically the "Glue Logic(Memory Decoding)" section in the lower half middle:

This is a simple breadboard computer based on a 6502 CPU with RAM, ROM, and a D-Latch that serves as IO(seen on the lower right corner driving a single LED). The memory map is

$0000 - $3FFF: RAM (16K)
$4000 - $7FFF: I/O (16K)
$8000 - $FFFF: ROM (32K)

The one signal I don't understand is /RAMSEL. As shown in the schematic A15 and A14 are used to address the three chips(U2, U3, and U7). /RAMSEL feeds into /CE(chip enable) of the RAM chip(U3) which is active low, so if I what to read or write from RAM /RAMSEL has to be low(0).

Suppose I want to read the value located at $1000 in RAM(e.g., LDA $1000 in 6502 assembly). I expect the address bus to be $1000 which in binary is b0001000000000000. As can be seen the signals A15 and A14 are both low(0) making /RAMSEL high(1) through the glue logic. Therefore the signal on /CE is high, making the RAM chip not readable since it will be in high-impedance mode.

On the other hand, if I want to read from a ROM location say $F000/b1111000000000000, A15 and A14 are both high(1) and through the glue logic /ROMSEL will be low(0) (so the ROM chip can be read since its /CE pin is low) and /RAMSEL will be high(1) rendering it unreadable. Same applies for the IOSEL signal.

So as I understand this schematic, the signals for reading/writing to ROM and I/O works fine, but not for the RAM chip. Am I reading the glue logic wrong?

EDIT: This schematic is taken from this book, in case you wonder.


texts: Two-Port Model: "What is the amplitude of the input signal?" Solution Misunderstanding

texts:
I cannot understand the solution to the following problem:

The specific maths I can't understand are outlined in the following figure, along with what I thought the answer was. Is \$P=\frac{V^2}{R}\$ as the power dissipated over a resistor correct? So why isn't it the case in the solutions?

If someone could meticulously explain the second bubble, that would be great as well, since I don't get it based off of my understanding. Should it just be \$\frac{(45.3mV)^2}{1}\$?


texts:
I have a very simple circuit and want to see the current in the inductor.
But I do not know why switch is behaving like that...

Actually, I supposed to get KA range current. but it gives me very small values.

Following I added the same circuit with 5s delay for clafication.


texts: How can I rotate a part in Altium without an collision error?

texts:
When I select a component when its rotated 0 degrees, 90 degrees or anything that is a multiple of 90 degrees, I get get a selection like seen below with C62. Notice how the selection highlights the component perfect.

Now when I rotate that component by 315 degrees, the selected component is actually much larger. It doesn't fit the component as tightly as the previous image.

When I move the rotated component near another rotated component, I get a collision error. It's violating the default collision rule of 10 mils.

If I change the rule such that the horizontal and vertical collision value is 0 mils, my error goes away, but I notice that I can move components onto each other without triggering a violation. Which is not what I want.

How I can rotate a part and not generate errors collisions error (when in reality, there is no collision) ?I believe its something to do with that highlighted box it, because the error only happens at the intersection of those boxes.


texts: Circuit analysis with an LED and a voltage divider

texts:
First, I know its not particularly useful to use a voltage divider for an LED, especially with such a big drop, but this circuit is for educational purposes particularly for voltage dividers. It hass been a couple years since I've had circuit analysis so I'm just refreshing myself.
I created this voltage divider circuit with an LED as the load. The top schematic is the calculated circuit, and the bottom is pure measurements. I find I get a big difference between the 2.
**I just noticed a mistake in my calculated currents right off the bat, IA = .0225A, IB = .005A, and IC = .022A. I used 12V instead of 7.2V.
Besides that, my theory on the difference is that the voltage divider will normally end up with a Vout of 4.8V. However the LED has a forward voltage of around 2.84-2.94 V, this extra voltage has to go somewhere so the rest of the voltage will get dumped into R1, which of course will change everything.
Is this a correct assumption? In that case LEDs would be analyzed always as having there forward voltage drop over them (which depends on the current running through them), and calculations go from there (this would further reinforce the idea that voltage dividers are not ideal for LEDs.)
If that is the case, then I could (and probably should) add another resister in series with the LED to soak up the rest of the voltage and set my current correctly.
So to sum up, is my assumption of what's happening correct? If so, is this how it works with just LEDs, or how does actually using voltage dividers with a load work, as most articles only tell you about the voltage divider with no load?


texts:
Through the fantastic help of one viewer, I was able to set up a diode chain with LTspice and view it's I-V curve. However this led to 2 very interesting issues.

What I need to know is:
1) Does this I-V curve look reasonably correct? As I wanted to know how a mixture of reversed and forward biased diode would react, I probed in the direction of the diode chain's ground.

2) I cannot locate the spice models of the actual diodes that I need to simulate. How can I manually generate one?


texts: PNP transistor base voltage acting weird

texts:
I'm afraid I forgets something in my circuit about PNP transistor use.
I try to use the transistor to supply current to 2 small screens back light.
For that I'm using this transistor- https://www.fairchildsemi.com/datasheets/MM/MMBT2907A.pdf
And this is they way I connect it:

Screen_backlight net connects directly to the MCU (which is limited to 20mA source current). When I give it "1", I see its is really 3.3V as it supposed to be, and when I give it "0" it, for some reason, goes to 2.4V and backlight is working. So for functionality- it works fine, but why I'm seeing this strange behavior?

Is it related to the VCC I give directly to the Emitter? Is it related to series resistor I should put on the base net?

Please advise.

Thanks,
Dudi


texts: Which mosfet description (pictures provided) is more accurate?

texts:
I was reading my physics book and found a description of mosfets that was different than the one I'm used to.
Here is the picture from the physics book:

In summary the physics book describes it's operation as this:

Gate = OFF = No potential difference applied to gate. This allows electrons to drift through the n channel (which is already there at the beginning). Current is maintained because of applied potential difference between source and drain.
Gate = ON = Potential difference is applied to the gate, in such away that repels the electrons in the n channel into the p substrate. This reverse bias causes the depletion zone between the p-n junction to increase, causing the n-channel to decrease, and the current to stop due to a low amount of charge carriers.

mosfet that I'm used to (taken from a digital design book)

Gate = OFF = No current due to no conduction path.
Gate = ON = Electrons attracted to the gate, forming a n channel path for electrons to drift through, so current flows.


texts: Why use triac when opto-coupler can already handle mains voltage

texts:
I have recently seen a opto-isloated triac driver circuit. The Gate terminal of triac is connected to a live wire through physical switch. So when the physical switch is turned on, triac conducts and gives the signal to opto-isolator which then trigger gpio on the Microcontroller.

Now my question is:
As far as I know opto-isolator used in the circuit can handle the mains voltage also. What is the necessity of triac here. Why can’t I directly connect the mains voltage to opto-isolator and skip the triac all together?

Let me know if the question is not clear. I will try to come up with circuit diagram soon.


texts: 555 astable - frequency not linear with discharge resistor for smaller resistor values

texts:
I'm trying to use a 555 timer to create a variable frequency from a resistance, the output frequency should be about 1 kHz up to 300 kHz. I'm using a TS555CN CMOS version, which can oscillate up to 2.7 MHz or so.

When using different values for R2, I see a linear relationship between the output frequency (measured using a scope) and 1/R2 for larger values of R1, but the frequency goes up less than expected for resistances below about 1k, and this effect gets progressively worse as the resistor values go lower, down to 10Ω where the frequency is just 1/3 of the expected frequency.

I've wired the 555 using the output as control, this as I need a 50% duty cycle. In earlier tests I noticed that, especially at lower resistor values, the duty cycle goes up more and more until it's about 70% and the output was far from a square block wave. This is of course an effect of the output not going to Vcc (3.3V for me), plus the internal resistance of the output. To solve this I put a non-inverting buffer on the output (U2 - actually two of them, as it's a dual package). That solved the duty cycle problem, and I'm getting perfect 50% square wave at all resistor values.

When trying the same with a ceramic cap instead of a film cap I got a less precise result (expected) but the linear part continued down to 470Ω, before the frequency really started to lag.

Changing the capacitor from 33 nF to 10 nF didn't make a change. The frequency itself of course changed, but the effect on linearity was the same, implying it has to do with the current. But here it ends... I don't understand why, as at 1k the peak charge current is no more than about 2 mA, while the buffers can supply some 20 mA each. Disconnecting one of the buffers did not make a difference.

(edit for additional info)
The purpose of this circuit is to measure the resistance of a liquid - so the resistance is a given, and can not be changed. This will have to go down to about 50Ω...


texts: Nema17/A4988 + LED display pump, 5v circuit not complete?

texts:
I'm trying to build a pump from Instructables, with no experience at all. I appear to be pretty close but the 5V line from the Arduino does not power the driver or LCD screen via my perfboard, it works fine on a breadboard. See the complete schematic here:

The arduino is powered without USB, so the 12 current flows as intended, but the driver and LCD is not powered (via the 5v). The schematic is a bit confusing to me, I made a connection in the red highligted area in the next pic, but it isn't drawn as connected in the schematic?

And on the arduino, the two gnd pins by the 5v are greened out, what does this mean?

I also haven't tested the encoder yet, but it looks like it is not powered? Can it be powered by the data pins directly?

Appreciate any advice.

EDIT: I checked some ground connections with the multimeter, the following are connected:


texts:
For Arduino there are VS1053b-based MP3 shields and I do not understand some points. I asked for MP3 format but it can be generalised for other formats as well.

When a sound is recorded and encoded as MP3 and saved in SD card, why do we need a VS1053b encoder-decoder chip? Can't we just use a D/A converter to play it?

It seems to me we are just sending the sound file from the SD card to VS1053b chip over SPI and that chip is feeding that data to its own D/A converter.

So:

What is the purpose of this VS1053b chip if we are just playing a file from an SD card?
When we send hex values (samples of an MP3 file) from the SD card to VS1053b over SPI, is it processing those samples to recover the unencoded data (basically decoding)? If so, is this for better quality since we get rid of some data from file during MP3 encoding?
Are these chips more meaningful if we, for example, record our voice with a microphone and let VS1053b encode that recording so we can take data over SPI and save it as an MP3 file?

Any help is appreciated.


texts:
My car's dashboard lighting uses six B9 base incandescent bulbs .  The brightness of these bulbs is controlled through a wire-wound variable-resistance potentiometer with an output of 0-12VDC.  This is an antique vehicle with basic, non-modern, non-electronic wiring.

I want to replace the incandescent bulbs with LED bulbs also having B9 bases without having to add an additional control, just using the present controller.

Is there a device I can add to the potentiometer output that will convert the variable (0-12VDC) voltage to PWM to drive the bulbs?  It would go in the green wire in this diagram:


texts: How data transfers to micro-controllers memory?

texts:
I have been working with Arduino for a while now i thought of using AVR micro-controllers in the bread-board . I saw several tutorials on how to transfer .hex file to the AVR micro-controller . They showed how to use the USB programmer to transfer the .hex file but if i say i want to know how to make a USB programmer works , what is the structure of a USB programmer ? I found nothing , can anyone give me a good answer of how the .hex file is transfered into the micro-controllers memory , i.e code-segment in the memory .

Thanks,


texts: How to get two buttons to work with the 16f628a - C, Hi-tech comp, mplabx

texts:
I'm just began exploring my new hobby - mcu electronics. I have bought an 16f628a after reading some forumposts suggestion that is a good mcu for beginners.
I have download mplabX, the hi-tech compiler and the isis program for simulating my circuit and code. I have some knowledge from c# and java development, so I like working with their "mother language" C. I have allready created the "hello world" and "blinking led" project.

Now I want to add two buttons to my blinking led prosject (one for each led. One pin for each led and one pin for each button, everthing happening programmatically), I have been searching the Internet and found some examples and tutorials but not any that I got to work.

If any got some links to tutorials / examples, code snippets with schematics or anything else that will help me create this I would appreciate it. I can post my blinking led code and schematics if that would help. thanks


texts: Stabilizing opamps - am I doing it right?

texts:
I'm designing a high current linear regulator and learning about real opamps as opposed to ideal ones described in tutorials all over the net as I go.

My initial voltage regulation design was stable enough under the resistive load, but oscillated under capacitive load. So as I've learned on the net, I had to isolate opamp output from external capacitance and add a capacitor on negative feedback - C7. At first I've tried adding a cap from output directly to IN-, it worked, but I've noticed that when i add feedback after MOSFET output, it works better.

When I've added current limiting, the output would oscillate heavily when in current-limiting mode and the only way to stop that was to add RC network R13, C8 and a feedback cap C6 - this one worked only when I connected it on transistor output.

What I'm concerned about is that negative feedback caps are rather big, way bigger than anything I was able to find on the net as examples.

Am I doing it right?


texts: Other active component principles of operation

texts:
Besides valves and transistors...

On another question, someone talked about magnetic amplifiers, but they are slow.

Are there any other kind of "would-be" transistors out there ?

A transistor that does not work on semiconductor principles, nor thermionic emission principles, does another principle of operation exist?


texts: Setting maximum opamp input voltage by zener diodes with respect to supply voltage

texts:
When I was about to implement a circuit with a 24V supply voltage I noticed that the comparator's inverting input in the part below receiving 24V with respect to ground when the input signal goes high. I was investigating hysteresis and I also add 2Vpp noise to the input signal which makes the input voltage higher than supply voltage. So the non-inverting input goes at least up to 24V in the circuit below:

As a remedy to limit the input voltage less than 24V just after the C1 I added to 15V zener diodes back to back as in the below schematic(I think I have to set R1 R2 again in this case):

Is my concern correct? What should be the max input voltage to an opamp comparing to the supply voltage Vcc? I used zeners to limit the voltage which works in simulation. Is that doable?

eidt:

I just learned opmap input could exceed Vcc depending on the opamp:


texts:
I am still a beginner with electronics and amidst hours of reading I am attempting to diagram out a simple circuit board from a cheap Mario Kart RC car toy that stopped responding to the remote. The toy doesnt work anymore so my main objective is just trying to understand the electronics, i consider it a bonus if I figure out what is wrong with the thing and am able to fix it.

I cannot seem to identify any of the IC components either because the label is faint or datasheets simply dont exist, or because they are unmarked.

The 16 pin IC looks like a microcontroller of some kind with no marking other than a small dot signifying pin 1.  It seems to be connected to a 16Mhz oscillator on the other side of the board.  There are three identical 8 pin IC's that are marked with what appears to be an MX prefix (Mitsubishi?), but this doesn't seem to match any manufacturer I have seen thus far.  I wonder if they are flash memory of some kind storing firmware.  One of these three ICs seem to have two pins soldered together for some reason.  There are two motors attached to M1 and M2, as well as a third smaller motor control for tilting the wheels down for hover mode.  There is a connector on the back for Try Me mode that connected to the remote while still in the packaging with a three way slide switch that turns it from Off -> Try Me -> On.

Any tips for identifying an unmarked IC or one that doesnt seem to have a datasheet?


texts: How can I solve atmega328p-pu resetting while it is supplied from power supply

texts:
Currently I am using a dip Atmega328p-pu with a breadboard built circuit. The problem is when i am supplying the circuit from Arduino Uno's 5V it is working perfectly fine, but it's not working when I supply it from power supply. When I mean not working, it has the typical blink code in it and it works perfectly fine with uno's 5v, but it keeps resetting or freezing in one part of code -the led just lights instead of blinking-

The circuit has 10k resistor in first pin, 16 mhz crystal, 2x22 pf capacitors near it and all power connections are also connected

Thank you


texts: What's the use-case for gain selection on a DAC?

texts:
I'm looking at the datasheet for an MCP4921 12-bit DAC (PDF), which describes the following feature:

  Selectable Unity or 2x Gain Output - The user can configure the full-scale range of the device to be VREF or 2*VREF by setting the gain selection option bit (gain of 1 of 2).

This doesn't give me much of an idea as to why anyone would need such a feature. It seems to me that one could just increase VREF, instead of using the gain selection. So I read further into the sheet:

  In some applications, precision digital control of the output range is desirable. Example 6-4 illustrates how to use the DAC devices to achieve this in a bipolar or
  single-supply application. This circuit is typically used in Multiplier mode and is
  ideal for linearizing a sensor whose slope and offset varies. Refer to Section 6.9 “Using Multiplier Mode” for more information on Multiplier mode.

And, from section 6.9:

  The MCP4921 uses an external reference, and these devices are ideally suited for use as a multiplier/divider in a signal chain. Common applications are: (a) precision programmable gain/attenuator amplifiers and (b) motor control feedback loops. The wide input range (0V – VDD) is in Unbuffered mode, and near rail-to-rail range in Buffered mode. Its bandwidth (> 400 kHz), selectable 1x/2x gain and low power consumption give maximum flexibility to meet the application’s needs.

This seems pretty vague - I don't see how having the output range go to 2*VREF would be a common enough requirement to warrant making it a feature of the device.

What am I missing? Is there a common use for DACs that makes such a feature useful / beneficial? Why wouldn't we just set VREF to a higher voltage if we wanted that increased range?


texts: How can I adjust my IC placement further to route properly?

texts: I've been trying to place my ICs properly to allow the autorouter to route the ICs with no success, I'm a total beginner at this and I tried routing manually with no success, any hints? The board is 1 layer only.


texts: 4-20ma 3 wire linear transducer and arduino connection problem

texts:
I am trying to connect a 24 volt 4-20ma 3 wire resistive linear transducer to arduino with 4-20ma to 0-5 volt converter (https://www.amazon.com/Isolation-Current-Transmitter-Converter-Transformer/dp/B07ZCPGDG9)

The converter needs two cables like +,- but transducer has three wires.
i couldn't figure how to wire them together, please help.


texts: Circuit to create X levels of brightness for a LED

texts:
If I'm here today, it's because I need some help for something that is, I think, easy for you. I am quite a newbie in EE but I am trying to improve myself :).

Here is the thing, I'll try to be as clear as possible with what I am dealing with. I am trying to figure out how I could create some level of brightness for some LEDs connected to an Arduino knowing that I can't use PWM.

Here is what I did since then :

I have three LEDs and I would like to have 3 levels of brightness for them. The LED I have are 3.02V / 15mA. So if I am not wrong, with a 3.3V power supply, I need a 20 Ohm resistor to bright one of them fully. With a MOSFET properly chosen, I will be able to drive it, am I right ? If so, with the above schematic, will I be able to have my 3 levels of brightness ? Since for each MOSFET, I have a different resistor value.

Are there others ways to achieve what I am trying to do without PWM ?

Thank you in advance for your answers !

(sorry if my English is not perfect)


texts: why do rectified voltage boosts after adding a capacitor?

texts:
So I found this 9V 1A AC power supply laying around and decided to make a DC source.  I rectified and added a capacitor to make things a bit even. After adding a capacitor my voltage boosted from 9V to 14V. Can somebody explain why this happened for me? (maybe this has something to do with frequency?) According to theoretical graph I should get aprox the same voltage even after adding the capacitor. And voltage varies depending on how much capacity the capacitor has (aprox. from 12-16V). Maybe there's some sort of equation to determine the actual output voltage depending on caps? It would be great to get 12V out of this thing.

P.S.: Personally I find this boost weird because this circuit doesn't have any switches and coils to boost the voltage, so I need an explanation, thank you in advance!


texts: Voltage drop if power draw is too quick: Does it happen naturally or regulated?

texts:
If a laptop forced to drag out more current than the power supply can provide at the given voltage (i.e. 20 volts), the voltage does decrease, usually approximately anti-proportionally if I am correct.

For a 100W (20V 5A) power supply, it is U[V]=(20×5)/I[A] starting at 5 ampères:

5A 20V
6.25A 16V (voltage dropped to 16V)
8A 12V
10A 10V (might be unrealistic if the conductors of the cable are not strong enough. Maybe it's just 10V 8A or even 10V 5A if 5A is the supplier's ampèrage limit despite voltage drop).
20A 5V (again hypothetical, just for the anti-proportional concept.)
40A 0V (by that time, the short circuit protection should kick in, thus 0V and testing if the short circuit has already vanished by sending short power impulses every few seconds.)

If the limit of 5A at 20V gets exceeded, the voltage will drop for one of these reasons:

Voltage drops naturally and the laptop power supply just keeps on supplying 100W.
Laptop power supply reduces voltage deliberately instead of naturally, to avoid exceeding 100W of output power.

Which one is the correct reason?

Which one is the reason for the drop of the voltage?


texts: How to improve a high frequency square wave for laser imaging

texts:
I am trying to create a current source for laser direct imaging and I have a problem in the circuit I cannot solve.
The laser is a 120 mW 405nm diode and I use it in a laser module from a laser printer. The circuit for the BLDC motor with the hexagon mirror works fine but the circuit for the laser is designed for a 100mA infrared laser diode. This is too much for my UV diode, I have destroyed one diode already. Also the 405nm diode has a common cathode where the infrared types have a different connections.
I am going to modulate the laser with a STM32 microcontroller with the SPI MOSI signal at 18 MHz SPI clock. I have tested that already and this work fine too. This may be a much to high frequency but I have to start somewhere. Don't want to scale down the specs at the beginning of the project.
The problem I encounter is a spike at the beginning of the pulses. See the attached pictures. I have already tried to reduce this effect but I am an embedded software programmer, not an electronics engineer. I hope to find someone here who can tell me what I need to add to reduce the current spike during the start of a pulse.
The bias current is required to calibrate the optics for a sharp image.
The images below show a LTSpice simulation with the minimum and maximum currents set.
With a resistor I try simulate the internal photo diode (PD) in 10 steps between 10k and 100k

I can provide the LTSpice simulation file when someone wants to give it a try in the simulator.
@Andy aka,
Is this what you meant with using a high side driver?
I cannot connect the cathode of the PD to ground completely as the base of Q2 will not receive enough voltage to start. Now I had to add a resistor (R1) to make Q2 work. I am pleased with the shape of the wave although it is not a square.


texts:
I am building a cheap bench top power supply for my bread board prototypes using a LM7805.

I want to know based on the above diagram could I just change in a LM7812? I would like to be able to flick a switch to change between voltages if so. Could the switch just change the input switch or would I need to remove all three connections?


texts: Where can I find 20-pin IC Socket for the PIC16F690 in eagle ? which lib.?

texts: Where can I find 20-pin IC Socket for the PIC16F690 in eagle ? which lib. ?


texts: Derivation for average value input current in buck-boost converter

texts:
I am struggling with the derivation of average value of input current as below.
The image is from the lecture here (page 26).

Here is what I got so far.
How did the lecture derive the final step here?

$$ \langle i_g(t)\rangle_{T_s}=\frac{1}{T_s} \int_{0}^{T_s} i_g(t) dt =\frac{1}{T_s} \int_{0}^{dT_s} \langle i(t)\rangle_{T_s}  dt = d(t)\langle i(t)\rangle_{T_s} $$


texts: Verilog modulus operator for wrapping around a range

texts:
My background is in software and I'm new to (System)Verilog so when tasked with implementing a caesar shifter (shift each letter in a string by N letters, wrapping around if necessary e.g. ABCXYZ shifted by 3 becomes DEFABC), I wrote the following, hoping to be able to reduce code duplication, like I would in software:

  /* every variable except 'direction' has the type 'byte' */
  always_comb
  begin
    shifted_char = fresh_char; /* don't touch bytes that aren't letters */
    is_lower_case = "z" >= fresh_char && fresh_char >= "a";
    is_upper_case = "Z" >= fresh_char && fresh_char >= "A";
    if (is_lower_case || is_upper_case)
      begin
        unique if (is_lower_case)
          alphabet_start = "a";
        else if (is_upper_case)
          alphabet_start = "A";
        alphabet_position = fresh_char - alphabet_start;
        if (direction == "f") /* direction is a module parameter: f for forwards results in a shifter, any other value results in an 'unshifter' */
          new_alphabet_position = (26 + (alphabet_position + shift_by)) % 26;
        else
          new_alphabet_position = (26 + (alphabet_position - shift_by)) % 26;
        shifted_char = new_alphabet_position + alphabet_start;
      end
  end

My question is (assuming it's a forward shifter): regarding the "% 26" part, can I expect the synthesizer to deduce that the range of possible values it's going to get  at that point is [26, 26+25+25] ([26, 76]) and so there's only 2 cases the logic needs to distinguish between (>26 and >52), rather than [whatever is the smart call when having handle all possible 256 different inputs - (would it be to consider the cases >26, >52, >78 etc...? Or is there a better way? I digress...)]?

I could always do the following:

new_alphabet_position = alphabet_position + shift_by;
if (new_alphabet_position > 25)
  new_alpahbet_position -= 26;

/* Or, for the reverse shifter: */

new_alphabet_position = alphabet_position - shift_by;
if (new_alphabet_position < 0)
  new_alpahbet_position += 26;

...but was curious and wanted to ask that, as well as a related one (that I expect more people will be able to answer): Can it be used to make a normal non-power-of-2 counter (e.g.
    count <= (count + 1) % 6;
)? Going by hgleamon1's response to the following thread, it seems as though (at least one) VHDL synth tool might interpret it as intended: https://forums.xilinx.com/t5/Synthesis/Modulus-synthesizable-or-non-synthesizable/td-p/747493


texts: DIY car audio noise when the source device is charging from the same power source

texts:
I have a hobby in electrical engineering so I built my own car audio system given the fact that it didn't have any before. It's basically two pairs of PC speakers adapted with some resistors and regulators to work on DC 11-15V from my car. In order to eliminate any ripple and noise I have added a 4700 uF capacitor in parallel with the power wires. Like this (excuse the paint drawing)

They are low power enough (around 30W max) to work without any noise when the car is running (noise induced by the alternator) as well as when it's on battery only (of course, no noise).

My problem is when the device i'm using is charging from the SAME power lines, all the noise-filtering the capacitor is doing suddenly vanishes.

This is when my problem occurs:

My skills aren't advanced enough to figure out what's going on, so I'm asking here after 1 month of research: How do i eliminate the ripple from when my device is charging and plugged into the audio system at the same time?


texts: Help identify the discrete component in this battery pack

texts:
I am rebuilding a NiMH battery pack for a RF remote control device which can be recharged by plugging the device in.

The battery pack is connected with three wires:

black to the negative
red to the positive
BLUE through a mysterious discrete component to the negative

The component in line with the blue wire looks a bit like a glass-body diode but my multimeter cannot measure a diode voltage. (It measures infinity, not zero, if this helps.)

However, I can measure about 11.5 kOhm across the component in both directions.

Can anybody enlighten me, what this component is likely to be? I would like to verify that the component is still functional because it is unclear whether or not the device still charges properly.


texts: Analog/PWM Dimming signal for a LED driver (LIPO battery low-voltage cut-off)

texts:
I am using a 4S LIPO-battery and a commercial constant current LED driver to drive a LED setup. Data Sheet for the driver

To avoid abusing the LIPO battery, I would like to build a low-battery cut-off using the driver's on-board dimming input. The driver has both PWM and analog dimming inputs.

As for analog dimming input, the signal voltages are as follows:

0 ... 0.2V -> the driver shuts off (battery voltage 13.0 or below)

0.2V ... 1.3V -> dimming in function (battery voltage 13.0 ... 13.5V)

1.3V ... 8.0V -> LED driver in 100 % (battery voltage 13.5V or more)

What kind of circuitry would solve my case here?

Thanks!


texts:
Assumptions:

Computer architecture: Describes how the different modules of a processor interact with each other.
A computer architecture is defined using vhdl files
Computer Organization: Describes the physical layout of the processor modules on silicon.
A computer organization is defined using a set of photo masks (and manufacturing process eg chemical, that goes at each step)
Computer Organization, therefore, requires that the fab process be taken into account.
ARM is not in the fabrication business, therefore it does not sell photo masks.

My question(s):

What exactly is ARM selling to a vendor (eg: freescale)?
For a SoC (System On Chip), (eg: iMx6), which part is ARM and which is Freescale? Who did the integration?


texts: Load cell circuit does not work on circuit simulator

texts:
I want to simulate a load cell interfacing with AD620 for amplification.
- My load cell is 40 Kg max with 2mV/V sensitivity and 10 V excitation voltage with input resistance of 405 ohm and output resistance of 350 ohm as you can see.
I want an output voltage ranging from 0 to 2.5 V. Using AD620 gain equation from its datasheet, I calculated Rg to be 398 ohm, I have then used a 400 ohm resistor on the simulator.
First, my question is by how much should I vary R4 (strain resistor) to simulate the change in the real load cell because I am going to implement this circuit.
Second, is the circuit down here correct?
Regards,


texts: Altium. Multichannel design. How to specify the repeat(port) connection order?

texts:
I am doing a multichannel design with Altium. Each channel has an 2 input ports called ID0 and ID1 which are used to set the address (or ID) of each of the channels.

How do you specify the connection on the sheet entry?

For Example I would like to connect ID0 of Channel 1 to Vcc, ID0 of channel 2 to ground, ID0 of channel 3 to Vcc, etc...

I have tried as I show in the picture but it does not owrk (basically does not creat any connections at all.

Any ideas?

Thank you very much in advance


texts:
I'm learning about NPN transistors and have wired up this:

I understand some of its behavior, but one is a complete mystery for me.
First, if I tie "B" (green dangling wire) to "G" (blue dangling wire) then the LED turns off, as expected.
If I let "B" float, the LED glows faintly (leakage current?). If I touch "B" the LED turns on brightly, it intensifies even if I just wave my hand near it. Again, expected, that's why I built it in the first place, to try this.
What is a complete mystery for me, is that if I touch "G" (just touch it, not hook "B" to "G"), the LED turns off. Same thing if I hook up "G" t o the ground from a power outlet. I don't understand this, I didn't expect it to affect anything. Again, not "B", I (sorta) understand that this setup is very sensitive to any signal on the base of Q1, but "G", which is the emitter of Q2 / negative of the power source.
Note, the "battery" on the schematics is a standard USB charger. I want to try this with a 9V battery, but didn't get to yet.
So, my main question is why/how touching "G" affects anything? Why does the LED turns off?
More generally, I'd like to understand how to properly think about these things…

Update: I experimented more with it. Changed it to a proper Darlington configuration (which didn't change anything). And tried it with a 9V battery instead of a USB charger as a power source. This completely eliminated the mysterious behavior.
My conclusion is that the USB charger doesn't provide a pure DC power, and the 50 Hz noise gets greatly amplified by this circuit. And my body with its capacitance (and just being a big bulky antenna) can affect it in various ways...


texts: How can I efficiently convert the output voltage of a 3 phase generator of 700V to 12V, 24V or 48V DC?

texts:
I recently bought a wind turbine electric brushless generator rated for 3kW. I noticed that the output voltage is really high - it is around 700V at 5400 RPM. After some research on stackexchange, I found out that using a 3 phase rectifier with a DC-DC flyback is one efficient way to achieve my goal.

Is there any better solution?
Would this setup guarantee a stable output voltage with variable current or is it more common for such a wind turbine to attach 3 transformers to each phase and convert it directly to 230V AC?


texts:
I have two LEDs

The first one is directly attached to 3V3 and the other one is attacked to the SCK line on AT Mega 328P

Here's the datasheet for the led (I am using the same LED)
http://www.image.micros.com.pl/_dane_techniczne_auto/olbs.03w0800.pdf

And the schematic bits:

Is my 1K resistor too much for these LEDs? I want to be able to see them at at least 50% brightness


texts: Variable vin AC to fixed DC power supply design.. Simplest And Small

texts:
Okay, so bare with me on this one please... First post on this stack and still refreshing my memory on electronics in general.

So basically i'm working on a project which generates a varying AC voltage from as little as 15 volt to in excess of 400 volts. To make it familiar, it is very similar to a wind mill generator.. So below 15volts would be a shut off

Input: 5vac to 400vac
Output: 15vdc to 48vdc regulated
Current: at least 1amp at lowest 15vdc output

The desired output is DC and regulated between 15 and 48 volts to keep it in a workable range with simpler circuits / anything i want to power of it.

Biggest issue i have had is trying to make use of the whole range, as in the lowest AC input from at least 10 volts all the way up to 400 volts... But the lowest range being most vital with the highest still be required as well. (Rotate of the blade can vary a lot)

While electronics is not my skill in most sense, generally i have been able to build most items given time and a fair bit of googling.. I just need a little feedback and guidance to what is the most practical, cheapest, smallest design.

What i have tried / tested / using so far?

Simple full-wave rectifier (4 diodes) - Still using this mostly
78xx regulators, They would be simple if i get to the lower DC range.. not used atm
Transformers multi-tap transformers with rectifier(s)/regulator(s).. still needs control

What i currently am looking at, But i could be way of target??

PWM type control, prototyping with a arduino...
Other SMPS chips/ic's that offer a large voltage difference
Some other form of a feedback loop to regulate
Buck converters, these still have a limited v range?

While  i could simply use a AC wall socket charger rated from 110 to 240vac.. This would remove the range from 20 to 110vac and this is absolute necessary. From my understanding, using PWM i should be able to control the voltage, but this will still need current control.. But if i am not mistaken, this would be the simplest approach for the above requirements?

As for current, well ideally in the whole range at least 1 amp at the regulated DC voltage, the current generator is able to produce 15vdc @ 1.2amp using a simple 7815.

And as before, i am not asking anyone to build it for me or draw schematics.. Just to give me some general guidance with something that will suit this need?

== Sorry for the long post / question.. Just want people to be sure of the need and that i have physically tested and tried approaches with research.


texts: A novice question about 60Hz vs 50Hz frequencies in monitors

texts:
In laptop and desktop PCs monitors have parameters such as 50Hz 60Hz ect.

What is this frequency about?

Is there a DC AC converter inside the computers?


texts: Are oil-filled transformers ever run at a vacuum?

texts: Larger oil-filled transformers are sometimes dehydrated by removing the oil and pulling a vacuum inside the chassis for an extended time. That requires that the chassis must be rated to hold a vacuum. If I read correctly, the dielectric strength of a vacuum is greater than that of the insulating oil. Given that, why not just run such a transformer at a vacuum all the time? Do the thermal benefits of the oil overwhelm the benefits of the insulation being perfectly dry all the time? If so, could you design a transformer that wouldn't have that property? Are there, in fact, transformers designed for vacuum operation?


texts:
I am trying to design a circular polarized antenna. We know that the criteria for a circularly polarized E-field:

The E field should have to components
The two components should be equal in magnitude
The two components should be out of phase by 90 degrees

Due to these facts, the axial ratio of the circular polarized field should be 1 ( 0 dB). However, in antennas world, it is acceptable that we can consider an antenna as circullar polarized even if its sxial ratio reaches 3 dB as a maximum. The below figure shows the designed antenna axial ratio:

As we can see the axial ratio is drawn as a function of theta and phi. I need to understand how the axial ratio is dependent on theta and phi and if the antenna is circularly polarized according to this figure or not.


texts: Applying solder paste through stencil and with a machine dispenser

texts:
I am trying to apply soldering paste to a PCB using stencil but I am having issues with S-PQFP-G80 package with 0.5mm pitch.

Whenever I try to apply the paste through the stencil I end up with paste being smeared all over the pads on the PCB. I am using eC-stencil-mate holder and I just can't make the damn stencil stay in contact with the PCB. Do you have any advice or experience with this?

Apart from that I also have a pick and place machine with solder paste dispenser but I can't seem to find the right combination of paste, needle gauge, dispensing time for this package. Since the pad width is 0.3mm I was using 27 gauge needle but the paste just doesn't go out of the dispenser. Again, any ideas or advices?


texts: Why do some electrical devices have a ground and others don't?

texts:
I noticed in my kitchen that the toast oven and the range hood had a ground fault, first by using a voltage detector pen, when getting near it the pen would activate from a distance (around 5cm without touching the case). Both of these didn't have a ground wire so I replaced the entire AC wires to put one with a ground wire that I tied to the metal chassis of both devices

The faults are "fixed", or at least gone to ground, however, I still wonder: When these devices when designed they knew both were going to be near water sources, why weren't they designed with a ground wire plug cable in the first place?

What defines when the case of a device should or should not be grounded?

What happens when a device has a fault and it's fixed like this to the ground wire in the home? Will the ground voltage go up? I'm currently sitting around 2v last time I checked (measuring neutral and GND with AC mode in a  multimeter that doesn't have RMS values).


texts: Why is the collector- emitter voltage (Vce) not getting biased?

texts:
This question is an extension for my previously asked question here:
Why is the voltage across collector and emitter pushing itself to 0.7 volts?

A colleague of mine suggested that I take a look at the stability factor for the circuit in that question. I calculated it and found it to be 284, which is very high and bad, and I thought that this is what was driving the transistor into saturation. But then re-did my calculations by assuming a lower stability factor of 10. From this, I got new values of resistors as follows:

R1 = 4.7 K ohms

R2 = 1.2 K ohms

Rc = 2.2 K ohms

Re = 100 ohms

After making these changes, when I tested the DC conditions by applying a supply voltage of 5 volts, there were no changes in the results. The Vce voltage still remains at 0.7 volts, i.e almost in saturation, contrast to my expected value of 2.5 volts. Here are the various voltage drops I get:

Across R1 : 4.6 volts

Across R2: 0.4 volts

Across Rc: 4.2 volts

Across Re: 0.2 volts

I have even tried changing the transistor. The transistor I used is 2N3904C NPN.
Please enlighten me and provide me with a solution on how to overcome this.


texts: What does pitch means in the context of the sizing of a breadboard?

texts:
I am trying to build an eagle-cad part for an Arduino Micro. (so I can make a PCB and stick the arduino on it) I was hoping to derive the distance between the two rails of pins from the fact that on a 2.54 mm pitch breadboard, there are 5 holes in between.

Pin Empty Empty Empty Empty Empty Pin

Of course, it struck me that I don't really understand what the "pitch" is. Is it the distance between the outer-most parts of two holes, or the distance between the center of two holes? In other words, is the distance I am looking for 15.24 mm (2.54 * 6) or do I need to add something to account for the size of the holes?


texts: Transmitting through IRDA as if its a native serial port. Possible?

texts:
I'm currently making a lazertag project that utilizes the standard UART data format for data I/O.

Before I go make up another circuit board that connects a photo-transistor that senses a laser beam to a PC serial port via MAX232 IC, would it be possible that I can directly send the beam to an IRDA serial port of my laptop and have the laptop correctly read the data?

If not, then I guess I'll need to change the output to infrared-only first (using an IR emitter).

Also, would the standard serial port data be accepted on IRDA natively, or do I need special drivers to make it accept standard serial input?

I want to do real-time tests of my project and if the IRDA on the computer will make results bad then I'll just go with standard serial.

For clarification, standard serial input here means data in the 8N1 format (low bit to start data, then 8 data bits of data, then high bit to end data).


texts: Calculating photodiode current based on A/W for simulation

texts:
I'd like to simulate photodiode current for a silicon photodiode, one example device the project may use has the following specifications:

Based on the above plus a guess at Rs for the moment from a similar package / die size device where it's specified I've come up with the following so far to use as a model. I'm planning to use the device in photovoltaic mode so I believe Id may be treated as zero.

However I'm unsure how to convert lux into a ballpark for the photodiode current Iph. For example Wikipedia gives 100 lux as a very dark overcast day, assuming .40 A/W which I realise is amps per watt I'd like to derive an estimate of the current. From the physical package diagram I can see the active area is 3mm2 so I believe that would give 3.0 × 10-6 lumens of light on that area.

But presumably now to convert to watts I need to know the efficiency of the photodiode and I don't seem to have been able to find any information for this or for other photodiodes. Am I missing something or is their a standard 'near enough' value for all silicon photodiodes?

The reason I'd prefer to simulate rather than just measure is that some devices under consideration are selective photodiodes with fairly long lead times and subject to an MOQ and I need to cover a few possible options for the future.


texts: I have 3.1V LED 20mA and wire 20 or more

texts:
How you calculate how much Volt battery you need?

Like:

20 x 3.1V = 62V

....or is it something else?

I want to wire them in series manner.


texts: PIC 16F877A interface with glcd LM12864DDY

texts:
I'm using the CCS C Compiler to program my PIC 16F877A to display results of a voltage measurement. I'm using TOPWAY's LM12864DDY. I used the functions that were available in the glcd.c file in the "Examples" folder of PICC.
This is my code:

#include<16F877A.h>
#include"pic_GLCD.h"

#fuses HS,NOWDT,NOPROTECT
#use delay(clock=20000000) //crystal 20 Mhz
char voltText[]="VOLTS";

void drawFrame(x,y,w,h)
{
    int i = 0;
    glcd_rect(x, y, w, h, NO, ON);              // Outline the frame
    glcd_text57(48, 57, voltText, 1, ON);       // Display "Volts"
    for (i=5;i<=w;i+=10)                        // Draw some fancy markers :)
    {                                           // horizontal
        glcd_line(i,h,i,h+5,ON);                // every 10 pixel
    }
    for (i=y; i<=h;i+=10)                        // vertical
    {
        glcd_line(1,i,5,i,ON);
    }
}

void main (void)
{
    //LCD PORTS
    SET_TRIS_C(0x00);
    SET_TRIS_E(0x00);
    //CS1,CS2,RST PORT
    SET_TRIS_A(0xD3);

    glcd_init(ON);

    drawFrame(5,0,125,51);

}

and my output is this:

Can't really figure out what is it that I'm doing wrong. Why am I getting scattered dots in my display?


texts: What happens to input character as \$V_{CE}\$ is increased?

texts:
In a NPN transistor and its study of input character, we obtain a graph (Ib vs Vbe) similar to that of PN junction diode.

Now that is same for a same potential difference between Collector and emitter (Vce). What is going to happen to the curve on a different Vce, say when increased.

According to what I have understood, as Vce is increased, that'll mean that some electrons pulled into base will be pulled by Vce once it arrives at base decreasing base current. So as Vce is increased, Ib should decrease and the curve should shift to the right (i.e. More Vbe required for same base current).
I'd appreciate insight in this matter.


texts: RS232 Splitter Capable of Transmitting/Receiving data to one device and only Transmitting to another

texts:
I was wondering if it is possible to have a RS232 splitter that is able to split the data into two RS232 connections, and allow for one of the connects to still be able to transmit data back through the splitter to the source.

So the problem that I am having which has led to this question is that I have data coming from an ECU in my rallycross car, via an RS232 cable, and I need to split this data. One device is a RF transceiver to stream the data to a laptop, this device would need to be able to receive and transmit data to the ECU. The other device is a DAQ system that then feeds into a driver display, the DAQ only needs to receive data and does not need to transmit back to the ECU.


texts: 2N2222 low side relay switch not turning off

texts:
I've been pulling my hair out over this for weeks and I can not for love nor money work out why it's not working.
I have a very standard NPN low side switch setup to turn a relay on/off from a 3.3V signal. In reality the 3.3V signal will come from an ESP8266 but on my breadboard setup its coming from a power supply.
When I push the tactile pushbutton the relay turns on, when I let the button go, the relay stays on.
The only way I can get the relay to turn off again is to disconnect the 12V power source.

Things I've tried:

I've tested all of the voltages and they're fine
I thought maybe the 2N2222 (TR1) base wasn't draining properly so I tried connecting it to ground via a 10k ohm resistor as well as the 1k ohm, no luck there
I thought maybe for some crazy reason 3.3V just wasn't cutting it so I tried a 5V signal instead, no luck there either
I tried all of the above with a 330 ohm resistor instead of a 1k (R1) to increase the current through the transistor, no luck there either
Thought I might be losing my mind and had wired the transistor in backwards. I hadn't, that transistor is now dead
Thought the relay might be fried, swapped it out for a different one then connected it directly to 12V. Worked just fine
Read through this identical question
Also read through this one

If anyone has any ideas on how to get this to work or if they notice something I've wired backwards (highly embarrassing) please let me know.
Appreciate the help!!


texts: How do I best visualize this voltage data for a science project?

texts:
I'm helping my son with his 7th grade science project. We've had a good deal of fun with our experiments with Solar Arrays and charging 12 volt UPS batteries! But, I am not sure how to interpret the data!

Our original hypothesis was that the length of the wire between the solar panel and the battery would affect the voltage charge the most. We do NOT think that was true!

We just need to get some good charts out of the data to show something that we learned!


texts:
I would like to create a software simulation of an accelerometer (MPU-6000). As part of that simulation, I need to model the noise on the accelerometer signal. According to the datasheet of the chip, the noise is 400ug / root Hz:

In C++, I can use boost:random to generate normally distributed random numbers. However, the boost function takes a sigma value as a parameter.

Question: How can I calculate the value of the sigma parameter to correctly model the noise from the accelerometer?

Update:

If a normal distribution is inappropriate, how can I model the noise in software?


texts: Powering microcontroller from 24V lines with variable duty cycles?

texts:
Firstly I should say I'm not sure how feasible this is, and that if someone has a better solution I would love to hear it.

I have the following situation. I have a microcontroller which draws an average of about 80mA (could be up to 300mA for a very short time during boot). It operates on 3.3V. I'd like it to read the state of several 24V DC lines. No more than one line will be on at a given time. Said line may blink on and off, however.

I'd like to power my microcontroller from these same lines I'm reading. Here's a very rough solution I thought of. I'm not an EE so please point out any glaring errors. :)

Is this a reasonable approach or am I going down the completely wrong path? I'm also considering adding a lithium ion battery, but I worry I'd stress it a lot by not being able to provide a constant charge source and instead I'd be charging in really small increments at semi-random intervals.

Edited for clarity.


texts: How to protect/enhance an LDO so that it can sink current in the event of an external wiring fault?

texts:
Background

I'm designing a signal acquisition board and one of its parts has several differential op-amps which are not very good from PSRR standpoint. So they need a very clean power supply, and since my main power rails (5 and 12V) come from a SMPS, I slapped a LM2931 LDO to get a clean 3.6V rail for the op amps.

Now I'm tempted to use this same rail for the supply of some 4 temperature probes. They are wired like this:

simulate this circuit – Schematic created using CircuitLab

The problem

The thermistors are changeable/pluggable and are moved around often; therefore it's not impossible that external wiring fault gets me +5V or +12V in the "To ADC" node.

The ADC itself is protected, so it won't be toast.
I've added a TVS parallel to the thermistor to guard against short transients (ESD as well).

However in a sustained +12V scenario, assuming the TVS fails open, current will overflow through R1 and potentially raise the +3.6V rail, since the LDO won't be able to sink that ~6mA of incoming current, ruining the other 3 temp sensors, and potentially damaging the LDO.

Desired effect

I want the acquisition board to be rugged against such faults. The wiring would get corrected eventually, but I don't want this to be an immediate show-stopper for the other measurements.

Proposed solution

One way would be to add a low-value resistor on the +3.6V rail to provide ample sinking capability, should it be needed.

However, I'm also thinking about adding an op-amp buffered second +3.6V rail, which would be capable of sinking current:

simulate this circuit

The idea being that

The LM358 serves as a kind of isolation between the important +3.6V rail (that I really care about), and the thermistors power supply (not that high-priority).
The buffered 3.6V can sink current, if external faults arise.

Questions

Is the op-amp buffered idea worthy (would the second +3.6V line still be clean from noise), any caveats I might be missing?
Some other approach entirely?


texts: Circuit for squaring (raise to power 2) signal

texts:
I have a voltage signal and I want to design a circuit that can do squaring of this signal ( raise it to power 2).
For example when I read the output, instead of having 2 V I get 2^2= 4 V.

Is there a way to achieve that?

Thanks


texts:
I am using an STM32F401 microprocessor
I understand that for a regular STM32F4 I don't need a pull-up for USB

However I don't know what happens for the case of OTG
Do I need a pull up on the D+ line for OTG? Can I make this switchable?


texts: An IC to manage Solar, USB and Battery supplies

texts:
I've been looking for an IC to manage my Solar and USB input to charge my LiPo and power my circuit and I found this IC. It seems to be able to automatically switch between USB and Vin to charge the battery as well as power my circuit.

My question is, do I need another IC to manage the voltage/current fluctuations of the Solar output before I connect it to Vin of this chip?

I know there are other IC's that manage Solar power and charge batteries, but they all lack the USB switching and functionality.


texts: How do I enable/disable a running 555 astable oscillator with a control signal?

texts:
I am going to control a fan using PWM signal. PWM is generated by a 555 IC. The duty cycle rate of the PWM is controlled by a PTC thermistor. And an NTC thermistor decides when to turn on and off the fan by generating a digital signal by using a comparator.

How do I interface the comparator output and the 555? I feel like it will be done through the "control" pin of the 555, but I can't find how to.

Note: The resistor and capacitor values have not calculated yet. Please ignore those all 100k\$\Omega\$ values.


texts:
I'm doing an MTBF calculation for a system. Basically I calculated or searched for the MTBFs / FITs of every component. Then added up the FITs and got the total MTBF.

My first question would be the following: in many calculations and handbook (217F), only FIT ie. MTBF values are accessible. In case on a non-repairable system such as mine, can I safely assume that MTTF = MTBF?

My second question revolves around an example.

Now I some components are parallel, and I'm not sure how to compute the FIT for it.
Anyhow, let's assume components (let's say they are resistors) A and B are in parallel (let's assume they share the same load in normal operation) the system fails only if A and B fail at the same time.
I would like to write this but I'm not certain:

MTBF(system) = MTTF(system) = 1/FIT(A) + 1/FIT(B) - 1/(FIT(A) + FIT(B))
             = 3/ (2*FIT(A))

I'm basing this calculation on this  link pages 15-16.

Is this calculation correct?


texts: Logic gates - Creating a Digital counter

texts:
I'm wanting to create the following digital counter using only basic logic gates (AND, OR, NOT, NAND, NOR, etc):

I've done some searching and the answers provided are much more complex than what I'm actually after.

I'm just wondering if it would look something like this?


texts: How can I make a cheaper, more modern UHF RFID reader board?

texts:
I just began working on a new project that involves reading RFID tags, especiall UHF RFID tags. After doing some research on the available solutions, I came across the Cottonwood reader board. (here's the wiki: http://linksprite.com/wiki/index.php5?title=Cottonwood:_UHF_Long_distance_RFID_reader_module)

I found the schematic for the board and was shocked to see that:

The AS3992 costs $65 on digikey and seems to be older, and less available.
The coupler, RCP890A05, is so old that I can only find it on aliexpress. And it costs $8 or so.

I have done a few PCB design projects in eagle in the past few years, so I think I can lay out a design, but I'm looking for pointers that would help me reduce my cost to $50 for the components on this board and strip it down to the bare minimum.

It looks like there is another chip on here that acts as a generic microcontroller. At this point I plan to use a different chip so I can use wifi/bluetooth with this device, so that part is basically eliminated.

So I guess this all boils down to, what I can switch out to reduce costs and make parts more available?

Cheers,
David


texts:
I am doing PSpice CAD by simple schematic generation(not using netlist), I need to apply coupling and for this I need Coupling Component, but I do not know how to use that in schematic, I mean in netlist we have
K L1 L2
but when I try to do that directly in CAD I get
"Part L1 has no L1 property"
"Part L2 has no L1 property"
can somebody please tell me the real way to use this component directly through schematic (not using netlist)?


texts:
I want to build a high gain directional antenna for the 915MHz frequency band.
I have been looking into waveguide and yagi antennas, which seems to fulfill my gain a directional requirements but these antennae are quite large.

I know that the antenna sizes in general are dependent on wavelength, and it possible is a trade off between gain and size.

But what high gain directional antennas are generally smallest?


texts: Why for setup check AND gates use rising edge, while OR gates use falling edge and vice versa for hold check in clock gating?

texts:
I have two questions on set_clock_gating_check SDC command.

Why for setup check, AND, NAND gates use rising edge, while OR, NOR gates use falling edge ?

Why for hold check, AND, NAND gate use falling edge, while OR, NOR gates use rising edge ?


texts: How does an audio transformer work with DC in this circuit?

texts:
From my knowledge, there needs to be an alternating current for the transformer to be able to create magnetomotive force throughout the core.

Various nerve testers (say for standard school projects) include an audio transformer ran on a 9V DC circuit though, with nothing looking like it would create an AC.

Now I see a pushbutton? over an SCR, however in simple thinking that should not do too much, just act like transistor switch?

What on earth makes the circuit work to have a high enough voltage?

Something has popped in to my mind actually, tranformers actually do work with DC, only for a miniscule period of time when power runs through it, is that why it shocks? And why an audio transformer? Cheaper?


texts: What are the wires of headphones made up of?

texts: Of what material are headphone wires made up of? Are they made up of copper? Can can replace the wires in it with copper wire?


texts: Does phased array antenna beam rotates 360 degrees?

texts: I wonder what happens when the beam shifted. I mean, is it being blinded for a while at first direction (i.e 0 degree) when it goes to second direction (i.e 45 degree)? Or it complete the whole cycle so quickly to not fail?


texts: Problem communicating with UART1 with Python on Beaglebone Black

texts:
I am having issues communicatong to UART1 of my Beaglebone Black with python
My code on Python3 is as follows:
import Adafruit_BBIO.ADC as ADC
import Adafruit_BBIO.GPIO as GPIO
from time import sleep
import Adafruit_BBIO.UART as UART
import serial
ser = serial.Serial(port = "/dev/ttyO1", baudrate=9600)
print("Open")
ser.write(("Hello").encode)
print("message sent")
ser.read()
However, the beaglebone is sending me back:
Open
Traceback (most recent call last):
File "GPIO60.py", line 14, in
ser.write(("Hello").encode)
File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 518, in write
d = to_bytes(data)
File "/usr/lib/python3/dist-packages/serial/serialutil.py", line 66, in to_bytes
return (bytes(bytearray(seq)))
TypeError: 'builtin_function_or_method' object is not iterable
I have searched solutions for this type of error but have found nothing.
Any help would be appreciated!
Thanks


texts: Which way will I place a momentary Tactile switch in a solderless breadboard

texts:
Well I am a beginner in electronics. So, I have some 4 pin tactile switches and I am confused about placing them in the breadboard. Here is the poorly drawn photo of the two ways of placing by me. Forgive me for such shitty kind of photo.

So,when I place the switch in the way (A)(follow the image) , the switch is so loose . I am adding another image.

So, In A type, When I connect one upper end to +ve of a battery , direct flow of current is seen on one lower end (IMAGE 2) but the other lower end doesn't flow current , only if I push the switch and hold it, the other end also flows current.

now, go to type B. here, I am placing the tact switch horizontally (B), and connect any of the 2 left side pins to the +ve of battery , the other left side pin also gets charged , because of the vertical hole lines (vertical with respect to the images) of breadboard. so , if I connect that, the right side two ends both gets charged . even if I push the switch, still the right end pins get charged. I've seen many comples circuit tutorials on youtube where they used a tact switch and placed it in type (B) , and they pushed the switch once but did not hold it, and the current started to flow. they pushed the switch again , and the circuit broke , How can I properly use a tact switch as a proper switch by placing it in type (B) and I want to use it a a proper on-off switch . Please help. If there are mistakes in my description , then you are welcome to re-edit it or comment. Please do help. I know that I dont know much of the electronics terms and I just started everything as beginner. Please help.