texts: Are ultraviolet LEDs used in consumer lights? (xmas lights)

texts:
I took apart a bulb on this strip of purple christmas lights and was surprised to find that the LEDs inside are actually purple 3mm LEDs. Naturally, I looked into some replacements but then the thought crossed my mind of whether or not these are UV emitting, or some mixture to make purple. Looking around online, it seems sort of difficult to find purple LEDs that are "non-ultraviolet". Here's a picture:
Edit: I am also choosing a purple LED to replace the bad lights but am concerned about the health risks. The lights are encased inside of a tinted “globe”. I’ve seen LED’s on amazon around 395nm wavelength.


texts: I would like to control the motor direction using an LM324(as a window comparator) & an L293D. the two output pins of my LM324 go to the Logic input pins of the L293D. The output voltage of the LM324 is 10.58V. According to the datasheet of the L293D the maximum input voltage to the logic pins should be less than equal to 7V. I cannot seem to understand the current requirements of the L293D using the datasheet. I wish to find the correct value of resistance wish is to be connected between the LM324 output pins to the input pins of the L293D.


texts: Digital IN + Multiplexer OUT for a keyboard. Is this a solution?

texts:
Introduction
I'm asking for help to validate following schema. I'm a nob in electronics, this project is not a professional project, just for fun. Please, be kind to me. Thanks.
My Goal
I would like to connect a piano toy keyboard to Arduino to get MIDI notes through USB connector.
Details
The keyboard has a matrix layout like this:

Example 1: When power flow is set to P23, if pushbutton 1 is pressed, the power flow arrives to P30. If, also pushbutton 9 is pressed, power flow, also, arrives to P31. Please check "On/off switches board pinout labels" for piano keyboard details.
Notice that I only can to send +5v from one pin (from P10 to P23) at a time. On Example 1, If flow is sent from all the pins at a time, we can't know witch pushbutton from 1 to 8 was pressed.
What I have thought
Because the keyboard has a lot of pins I guess I need to use a multiplexer. One multiplexer for 5V output (only output one pin at a time).
This is the schema I have in my mind:

For me, looks like a solution, to connect P30, P31, ... P40 to Arduino digital inputs and multiplexing with +5v one pin at a time from P10 to P23 using the multiplexer module.
Materials
This is what a have:

Arduino Leonardo
5 multiplexer module
600 Resistors

Question
I would like to know if my solution is right, or they are a more clever/elegant solution.
Disclaimer
I'm not an electronic hacker guy, I'm looking for a project I can do with my daughter and have a bit of fun. Please, be kind. This is not a module for a nuclear power plant, just a summer side project. Any help is welcome. Also, sorry about my poor English, if some part is confused, please, let me know to try to write a proper explanation.


texts: Will my zener diode work again with a polyfuse after a overvoltage?

texts:
I am trying to make a simple overvoltage & current limiting circuit for my PCB.

I made the following circuit.

The zener will break down and conduct current to ground. Since its resistance has broken down after reaching its breakdown voltage and it is now conducting, its voltage drops dramatically, so the load in parallel does not receive this excess voltage.

So my question is will the zener diode work again after the polyfuse has been cooled down?

Or do I have to replace it with a new one?
Or are there other options?

Because I really don't wan't to replace a zener diode, not that its much of a work. But I am making this for a friend of mine and he does not have basic knowledge of electronics.


texts: A question related to threshold voltage in relation with the body effect in MOS

texts:
I've just begun the MOS-level study of a MOSFET. So, pardon the naivety.

A very brief backstory:
The Strong Inversion occurs in a MOSFET, particularly NMOS, when the silicon surface reaches a voltage value which is twice the Fermi Potential(ϕ). For p-type silicon, ϕ= -0.3V. Hence, for the inversion to occur the silicon surface voltage should reach -0.6V, given that voltage between source and body (Vsb) = 0V. The Value of Vgs (gate-to-source voltage) where strong inversion occurs is called threshold voltage (Vt).

My question:
Please refer to the figure, which is mentioned in the same context as above. It says at Vbs = 0V, the value of Vt = 0.45V. So, at a gate voltage of 0.45V, inversion occured, which essentially means that the silicon surface potential has reached -0.6V.

With just an external gate voltage of 0.45V, and all other potentials (Vsb) at 0v, how did the silicon surface manage to attain a voltage of -0.6V. Where did the extra voltage come from? My question might be wrong as well, owing to the feeble intimacy to the topic; I tried others books but couldn't find a clean answer. Please enlighten.


texts: how to convert synchronous generator field voltage from per unit to voltge

texts: I've been working in PSCAD and in this time I'm struggling with synchronous generator in PSCAD. As you know synchronous generator in PSCAD, working in per unite so I have to change its amount to Voltage and Ampere. Therefore it's been for a long that I'm exploring on the internet how to convert synchronous generator field voltage from per unite scale to voltage scale, but unfortunately i couldn't find. If there is someone who had worked on such an issue before, could you please give me some introduction or any other help?


texts: Choose between Bluetooth Low Energy advertizing and connection for low-power small-data application

texts: I have several sensors running on coin batteries, which are supposed to send data to a central device periodically. The data size is small: the meaningful data should be a few bytes excluding the BLE packet overhead. The transmission period is long: it can be once per hour or even per several hours. I am using a Bluetooth Low Energy (BLE) module (BL600 from Laird) which has a nRF51822 SoC inside. The goal is to minimize the average power consumption since the sensors are supposed to run from battery for a long time (a year or so?). Obviously the BLE peripheral can send data either by advertizing or connection. I am not sure which is the way to go, and what factors I should consider in making the choice. Could anyone please advice?


texts:
I am new to electronic design (textbook taught hence practical experience limited), and upon reading the BOM of an EMI filter I noticed an asterisk *. Is this indicating that for CX1 there are eight capacitors in parallel, or does the asterisk indicate something else I am missing? I have not found a parallel of this on other EMI filter designs (design + BOM) with other DC DC Converters.

The DC DC converter is Delta Electronics'E48SC32009NRDH - https://www.mouser.ca/datasheet/2/632/DS_E48SC32009-1385692.pdf

I apologize in advance for the rudimentary question, and thanks for taking the time to read through.


texts:
Why is it safer for ground to be connected to the chassis for an electronic system?

For example, the ground on the mains supply of an AC motor in a box fan is connected to the outer chassis of the fan?

My only explanation would be that in the event of something accidentally shorting to the chassis, its shorted to ground as opposed to the chassis now being a live voltage?


texts: Why is there a solder mask opening over a microstrip line?

texts:
I have always wondered why there is an opening in the solder mask whenever a microstrip line is laid out on a PCB.
For reference consider the following board:

There is clearly a large opening in the board around the microstrip lines and stubs.
Does it have something to do with avoiding to change the characteristic impedance of the line, or does the solder mask somehow effect the propagation in the microstrip line?
I have searched but could not find a clear enough answer.


texts: Why is Atmega324pb pin change interrupt not firing even though input is changing?

texts:
For some reason my pin change interrupts are not triggered on my Atmega324PB. To test, I'm using an eval board and connecting an output pin to a pin configured to trigger a pin change interrupt. Is there something I'm missing?

volatile uint16_t motorCount = 0;

// Configuring pin change interrupt on A7.
// A7 pin change interrupts are handled in
// "pin change interrupt request 3"
PCICR |= (1 << PCIE3);
PCMSK3 |= (1<<PCINT31);

// Interrupt routine
ISR(PCINT3_vect)
{
  motorCount++;
}

To test, I've wired it to an output pin, A2. I have verified with a multimeter that pin A2 and A7 are changing from low (0V), to high (~3.6V). This change doesn't trigger the interrupt. It doesn't trigger when changing back to low either.

// main.c
...
__enable_interrupt();
uint8_t test = 0;
DDRA |= (1 << DDRA2);   // A2 as output

while (1) {
    if(kbhit())  // Wait's for serial input character (configured separately)
    {
        if(('\n' == tmp) || ('\r'== tmp))
        {
            test ^= 1; // Toggle first bit.
            test &= 1; // Mask to only first bit.
            if (test == 1) {
                // output high on A2
                PORTA |= (1 << PORTA2);
            }
            else {
                // output low on A2
                PORTA &= ~(1 << PORTA2);
            }
        }
    }
}
...


texts:
I am having some problems with an active rectifier (AFE unit) that produces a 8 kHz and a 50 Hz component on my DC.

We have bult in a normal standard Low-pass filter that deals with the 8 kHz, so no problems there.

But we still have the 50 Hz problem (its a software issue in the AFE inverter itself, and therefore not easily solved fast).
Its not much, 600mA rms when charging with 50A@600VDC but apparently still enough to mess up the battery that it is charging.

The problem is that the battery that the AFE is charging can be considered a capacitive load. So the dampening effect on the low pass filter for it to take care of the 50Hz is quite much.

We solved it with putting in a standard power resistor in series before the load, so with a normal power resistor on 1 ohm we can filter the 50Hz signal also. But that is not so economical, just burning off a cupple of hundreds of watt.
So the the next step is to get a 3,2 mH inductor to create 1 ohm of resistance@50Hz and that will we test this week.

But what I am thinking about is the voltage spike from this inductor,
we have capacitors that is sitting between + and - before and after the inductor. Approx 1 mF on each side.

Since a capacitor is a low inductance on rapid voltage changes, they should take care of the voltage spike.
The voltage spike can be simply calculated with E=I x R.
Since the capacitor is the resistance here, it is frequency dependent of course but we can still say that the spike will se the capacitor as a low resistance.

But am I correct in my thoughts here, that capacitors between + and - will take care of the spike?

And how do i calculate the amount of current/energy, that will go into the capacitor?


texts:
Due to space constraint, I wanted to set up two coils over each other. (So one coil is wound on a spool, then I want to wind the other coil over it (not necessarily touching it.))

However as it will cause them to effect each other (as it behaves like a transformer), I was looking for a solution to isolate the two.

Do you guys have any suggestions to achieve the same?


texts: cascade of boost converter and an inverter

texts: i am designing DC to AC converter. The first phase of the converter is a boost converter that will boost voltage from a 12 V battery into 30 V. Then the 30 V is fed to an inverter that will invert 30 V into 30 Vpk-pk AC signal. The ultimate  output voltage of  the system was required to be 230 Vrms. So i included a transformer rated 20/230V rms. When i simulate the cascade of a boost and inverter with a load, on simulations it works fine. then  I designed and built and tested my boost independently and it worked properly. I also designed and built the inverter, it also worked fine. But when i test the cascade of both subsystems with a load of 77 W( overall system is rated at 120 W). the problem i am encountering is that when the load of 77 W is connected on my system the systems output voltage drops to 135 Vrms, i am not sure what might be the problem because on simulation it works fine and i a getting 230Vrms?


texts: Why is it like that if we increase the speed of the induction motor, its core losses decrease and stray, windage losses increase?


texts: FPGA Data Collector - What Specs Should I Look For?

texts:
I'm working on a high-speed data collection device for an ADC running at 80 Msps. After digging through resources on MCUs and asking several questions here and in other forums, I've turned my attention to FPGAs. From what I understand, an FPGA-based circuit would be the fastest method to collect data from a series of inputs and store that data. The event I'm trying to capture will be relatively short and can be set up with a trigger, so I'm thinking of sending data to SDRAM during the event and extracting it later via USB or some other interface. The ADC I'm using is the MAX1448, which provides a 10-bit parallel output with each clock cycle at 80 MHz (with a pipeline delay of ~5.5 cycles).
When looking at MCUs, I gathered that for each input pin, instruction cycles were needed to send that bit from the GPIO to DMA or other peripherals. So just to execute one instruction for each bit, I needed a clock speed at least 10x my ADC sample rate. From what I understand, FPGAs get around this bottleneck by programming the data path beforehand. My question though, is what should I be looking for in a FPGA in order to store ADC data at a specified rate with a set number of bits/inputs? How does the clock speed of a FPGA determine the data transfer rate, or what clock speed do I need to look for to achieve 800 Mbps (or 10 data paths at 80 Mbps each)?


texts: What does this PNP transistor + OPAMP circuit does?

texts: I can solve the circuit for given DC input voltage with transistors Ies and alfa values. It amplifies the input signal for like 13 times. (Not linearly). But i couldn't understand the purpose of this circuit. Could you help me with that? Thanks in advance


texts: Adding ripple to a voltage signal in ADS

texts:
I'm simulating an FMCW radar in ADS and to control the VCO I use a ramp generator. I tried the ideal case, now I want to add a ripple to my ramp voltage so I can analyze the effect of a ramp voltage with voltage noise. I don't know how to add ripples to a voltage in ADS. I put a voltage noise source in series with my pulse generator but it shows only the noise in the output and not the noise coupled ramp signal. Could someone help me please on this?

Thanks,


texts:
I have thought about the below question a lot but i can't understand how to go ahead. The question appears to be wrong to me. Any help or even a comment will be appreciated thank you.

A Zener regulator has an input voltage in the range 15V to 20V
and a load current in the
range of
5 to 20 mA . If the Zener voltage is 6.8V, the value of the series resistor
should be ?


texts:
I want to use a stepper motor in place of a hobbyist servo that I am currently using to actuate a throttle. The motor is to turn from 0 to 90 and modulate engine speed between these two positions using a PID algorithm implemented on an Arduino Mega microcontroller.

I am having difficulty with the control logic. I have purchased a BigEasyDriver circuit but cannot work out how to get the motor to return to the "0 throttle angle" position upon being reset. The servo was simple to control in this regard - one would simply write servo.write(0) and it would actuate back to the right throttle position. However the stepper does not have an "absolute" starting position?

Can anyone give some advise in this regard? Thanks


texts:
I'm trying to find the input resistance, output resistance and gain of this circuit.

simulate this circuit – Schematic created using CircuitLab

My textbook only has the simpler case when \$R_1 = 0\$ and \$R_2 = 0\$, wich are

\$ R_{in} \approx  \beta \left [ R_L+ (r_{eN}||r_{eP}) \right ] \$

\$ R_{out} = r_{eN}||r_{eP} \$ (I'm not sure if this one is exact)

\$ \frac{v_o}{v_i} = \frac{R_L}{  R_L + r_{eN}||r_{eP} }\$


texts: PIC IOC vs INT and the interrupt function

texts:
I am using PIC18F26K83 and I want to use interrupts for a switch that will be connected to one of the pins of my PIC. So I have some related questions:

There are 2 interrupt options in PIC18F26K83: IOC vs INT. What is the difference? I heard that is quite easy to miss edges with IOC though. Can I use both of them at the same time?
Other question is related to interrupt function. If I have 2 interrupt functions : interrupt i1(void) and interrupt i2(void), in case of any interrupt, does the software enters all the interrupts one by one? If not how does it get which function is related to coming interrupt? For example I am using CANBus interrupt, I2C interrupt, timer interrupt and one external interrupt coming from a switch. If I press the switch, how will software know which interrupt function is related to switch? Thanks beforehand.


texts: Determine total current in a darlington transistor

texts:
I'm trying to figure out what will be the total current consumption of a TIP120.

Looking at the internal schematic I see that the second BJT's base is following the emitter of the first one so it will consume current proportional to the base current of the first one but I'm having a hard time determining the exact values. The ones given in the datasheet are for the entire pair, right? How can I determine what current will be consumed by the base-emmiter paths with a 500mA load on the collector of the pair?

Additionally what is the role of the voltage divider? If current follows the path of least resistance then this must mean there will not be any current going through the resistors? (which is certainly not the case)


texts: What is the proper term for downgraded NAND Flash ICs?

texts:
In the manufacture of NAND flash (to my understanding):

Wafer is produced
Dies are probed for testing
Dies that pass testing are configured as Tier-1 chips, then packaged.
Dies that fail Tier-1 testing are modified (if possible) so they have reduced capacity, for example a 128 gigabit die has defective sections configured as unavailable yielding a die with 64 gigabit capacity.
Successfully downgraded dies are packaged (for example in TSOP-48) but not marked with the manufacturer logo, part number or serial number.
Finished ICs are sold to manufacturers for use in inexpensive USB Flash Drives.

My question: What is the proper term for these downgraded NAND Flash ICs?


texts: Findout output voltage of an opamp when given input voltage and open loop gain

texts:
Just in theory, please ignore the values...

Given the open loop gain of an opamp and its input voltage and a circuit similar to the figure below, how would I find the output voltage?

]

My thoughts were to just do nodal analysis and avoid the open loop gain all together since the circuit given is closed loop, I thought that it was irrelevant and just given to throw you off.
Or would the correct steps be to assume:
v_out = A(v_+ - v_-)
v_out = A(-v_-)


texts: High current over 5V on PCB panes instead of track

texts:
I have leds running for around 600 Watts of 5V leds (120 amps).
The source of the power are three 48V to 5V converters which each can handle 200 watts.

If I would run this amount of Amps over my PCB I would need a 110mm wide track to carry all the load. The complete location for it on my PCB is only around 100mm. Can I just use 2 planes to connect everything together or should I worry about a short circuit?

current solution: Made the converters not parallel and made them connect with 1/3 of the connectors so that the amps would fall to 40. In this way the track could be much less wide but of course I need to count leds so I do not put to much power on one converter.

Datasheet 48V To 5V DC DC Converter: Scroll down to CHS300


texts: IIR filter concerns in PID control systems

texts:
The following diagram represents the system:

Here comes some more description:

The system input (ref or reference is zero). And actually the goal of the controller is to maintain the output of the system at zero.
In this system, there are also disturbance and noises. The disturbance has the shape of roughly a ramp, however by nature more like random events. The noises are band limited with bandwidth around 10Hz.
So the controller strives to compensate the influence from disturbance while get rid of noises.
As the noises are from sensors and I add a filter before the controller.

My questions are:

I was using simple FIR filters. The filter wait for, say, 5 seconds to get a batch of data and process them and pass the output to controller. The the controller controlls at 0.2Hz.
However, the bandwidth of 0.2Hz still brings too much noise to the system. If the controller waits 20 seconds for FIR, the system will be too slow. I was advised to use IIR, since it is online, instead of FIR for the filter to further reduce noises.
My question is: since IIR contains information of the past measurements, would the controller output still be accurate? It is supposed to adjust only for current errors! IIR brings past errors to the system!

Any other advice to reduce the noises further? Thanks!


texts:
As a part of a controlled power supply for hardware-in-loop testing for a student driven project, I had to develop a current buffer (voltage follower) which could source up to 1 A.

I had the (bad) idea of trying to implement this simple circuit:

The PMOS inside the feedback loop acts as an inverter (more V_gate, less V_out), and that's why the loop closes in the POSITIVE terminal of the opAmp instead of the negative.

In the lab I set VREF = 5V and VIN = 7V. I should get then 5V at VOUT, but I obtain this out-of-control output VOUT:

And this is the control signal (output of opAmp, connected to the gate of the MOSFET)

I find similar behaviors under different VREF, VIN and Rloads. Also note that the output of the opAmp is not saturated to any of the rails.

My assumption is that the gain of the loop is too high for keeping the opAmp in stability.

I have some background in control systems and opamps, but I don't know how to apply it to solve this situation...

Is it possible to apply some phase shift network to stabilize the loop?

I would appreciate both "quick hacks" or educational answers!


texts: Altium Designer: for some reason I can't use vias

texts:
AD version is 16.0.6.
I have a simple 2-layer PCB. I'm trying to go to the second (bottom) layer, but everything I tried - did not work: "L", "+", "-", "*", etc. Just nothing happens.
Even Place -> Via produces nothing.
For "L" I can hear the Windows sound which usually appears when user trying to do something prohibited and there is a zoom out on "-" press.
I have set up the via layer pair and via rules. So I can not understand what can be wrong with my Altium.


texts:
Can I connect a 12 volt DC regulated switch mode power supply (good voltage control) in parallel with a 12 volt DC car battery (great amp supply) to supply the extra current need to run my RF-amplifier?

This seems to me, a lot like the design in a running automobile. Instead of an engine turning an alternator, I have an AC to DC switch mode power supply.


texts: BJT: why does Ic increase when temperature increases?

texts:
When the temperature of an BJT increases, the thermal voltage
$$
V_T = \frac{k_BT}{q}
$$
where \$k_B\$ is the Boltzmann constant, \$T\$ is the absolute temperature of the junction, \$q\$ is the elementary charge,
should increase. Therefore collector current which is equal to
$$
I_C=I_s\exp(V_{in}/V_T)
$$ should decrease but it does not. Why is this?


texts: This is regarding thermal properties of MOSFETs. Most data sheets show a property called Rj  (thermal resistance) measured in C/W (celcius per watt). Suppose I want to derate power in MOSFET ,in order to get W/C, is it the reciprocal of C/W ? Is such a relationship so straightforward ?


texts: Basic Question: Why does this Short cause Blown Fuse?

texts:
I recently re-did some wiring connections for the horns in my car and accidentally shorted the wires out at the green wire in the picture below. This causes the 20 Amp fuse to blow, but I do not understand why. Specifically, when I press the horn, the horns beep then the fuse immediately blows.

https://imgur.com/a/i3Z50m8

The battery is a 12 V car battery. I would think that since the battery is both the source and ground for the high current, switched circuit, that the fuse would usually see higher currents. So why would shorting at this location cause it to blow?

Thanks!


texts: Which current ripple equation should I use? (Boost converter)

texts:
I am designing a boost converter for a microgrid as an university project. It is supposed to interface a 2.4kW 120V solar array (using MPPT) with a 380V DC bus. There will be other sources and loads connected to the bus.

My professor have told me to have 5% current ripple regulation for the converter. Therefore I am trying to choose a suitable inductor value, but I am stumped as there seem to be 2 equations to use.

Equation 1:

versus

Equation 2:

As you can see, I would very much prefer to use the values of equation 2 since they are much smaller than equation 1. My supervisor also told me not to overrate the inductor.  But I think I do need to confirm and understand the equations to use when interfacing between a bus and a solar array, which is why I am seeking advice from the experts here.


texts: Why offline regulator output diodes have a high voltage rating?

texts:
I am currently having a look at AC to DC offline buck regulators - regulators which convert AC mains voltage to smaller DC, without any isolation transformers. Two examples are AP3917 from Diodes Semi, and FSL336 from ON Semi. Here is an example application circuit:

Both of these IC's have design spreadsheets to help with the calculations. However they both calculate the minimum reverse voltage ratings of output freewheeling diodes as 500'ish Volts. What is the reason, since the output should be 24V? I was planning to use a 40V Schottky Diode for my output for better efficiency.


texts: What components or circuitry exist that can provide extremely high speed, accurate clocks?

texts:
I've been curious for awhile now about doing some high speed projects, such as measuring time differences of radio wave reception, and was wondering if there exists components that provide clocks much faster than a typical CPU can, such as up to 10 GHz or higher. The fastest of clocks I have used is the CLOCK_MONOTONIC in linux, accurate to 1 nanosecond.  This also makes me wonder why there isn't a clock accurate to the actual speed of my processor, churning along at over twice that speed.

Further expanding on that, what approach is used to create such clocks? And how can these clocks be interfaced with other circuitry? Are there really digital or analog circuits that can operate that fast?


texts: Effects on motor encoder by over-volting

texts:
I'm using Maxon RE-max 17 4.5W 12V DC motor with encoder attached for my research. Currently I'm using up to 18V for the voltage input to get a better rotation speed and torque.

My questions: Is this likely to affect the lifespan of the encoder/motor? If not, why?

Thanks in advance.

p/s: For reference, this motor and this encoder is the closest versions currently available.


texts: How to calculate thickness of cable based on material and current?

texts:
How thick copper cable should I use for 16A current? How thick it should be if I use aluminum wire? Is there any generic equation which I can use?

I am using direct current with 12V but as far as I know it doesn't matter.


texts: How do I derive \$(i_x)/(V_A-V_B)\$ in this circuit?

texts:
I have this circuit below:
http://qph.is.quoracdn.net/main-qimg-a5380479d6b436dcfb9a36252ac3f1c1?convert_to_webp=true

Can I make the small signal equivalent circuit as shown below and when doing the KCL equation, When I pick the node above $$g_mV_A$$  can I simply assume $$g_m*V_A-g_m*V_B-2*i_x=0$$?

http://qph.is.quoracdn.net/main-qimg-20c87843bd57823b4c4489e360000033


texts:
I have a shielded twisted pair running from one device polling several devices in an RS 485 loop. The conditions:

The devices are in parallel as they should be.
The termination resistors are in place as they should be.
The communications are half duplex.
There is no GND wire running with the twisted pair data lines.
The shield is connected to the Chassis ground on the various devices in the loop - and not at the 'master' end - no ground loops.
The Signal ground is connected to the chassis ground within the devices with 1nF 500V caps.
The transceiver in all the 'slave' devices is isolated in terms or power supply (galvanically) and signals (optocoupler).
The data is being sent over a relatively slow baud rate of 19.2K. The total length of the 485 loop is less than 500m.

The issue: The 'slave' devices are blowing up - no visible blowing of components but the tranceivers are failing after some time. The probable causes identified are surges being injected into the shield - I am pursuing this; and common mode noise being coupled into the data lines, which are exceeding the acceptable voltage levels of 15V.

For the latter, I am planning to add some zener diodes to limit the voltage levels on the transceiver pins from the external connection. Since we do not have a signal ground with the data lines (which should be the reference for the zeners - so all the three (Tx+, Tx- and SGND) can float, is it okay to connect the zeners to chassis ground with some current limiting resistors?
The chassis ground was tested and found to be quite stable and low potential. This is the only ground to the receivers and all internal ground are connected to it through caps.

Bottom line:

Will connecting the zeners to chassis ground work, and save the data lines from dangerous voltages?
Will this scheme interfere with the data integrity?
Or should the zeners be connected to SGND (internal to the system)?
Should the SGND and chassis ground be connected with 1nF caps, or should i remove that connection to have the SGND float freely?

Apologies for the long question, please let me know if you would like any more details - sharing of schematics would not be possible though.


texts: Arduino serial communication fails when stalling/loading a DC motor controlled by PWM

texts:
I'm using the following circuit (from http://luckylarry.co.uk/arduino-projects/arduino-control-a-dc-motor-with-potentiometer-and-multiple-power-supplies/) to control the speed of a 6V DC motor powered by a separate power supply:

When I put a heavy load on the motor or stall it, serial communication between my Arduino Uno and my PC (over USB) fails.  Data stops coming over and I need to disconnect the Uno, close the IDE, connect the Uno again, and then start the IDE in order to get the link back up.

Not sure if this is a grounding problem (I took care to make sure all grounds go to the same rail), a load problem (even though the Uno and the motor have separate power supplies) or a back-emf problem.

Any help would be appreciated.

Thanks,

-Rob


texts: Does changing wire gauge change output of a thermocouple?

texts:
So I've been experimenting creating thermocouples with copper and constantan wire, just by twisting them together at one end and heating the junction with a candle and using a voltmeter to measure the emf at the other end. I thought that changing the gauge of the copper wire might change the emf output, and it appears that the smaller the diameter of the wire the larger the voltage is, but I'm not sure why this is. From research, it looks like the thermoelectric efficiency is determined by the Seebeck coefficient, the thermal conductivity, and the electrical conductivity, as well as the temperature difference.

Since the conductivities are intrinsic properties of the copper and I'm keeping the temperature constant, I'm not sure why the output of the thermocouple is changing. I thought that I might be changing the conductivity in some way by changing the gauge, but is this possible?


texts: Is this a H-Bridge, why are the two ICs there?

texts:
I would like to know if this is a H-Bridge:

Why is there IC3 and IC4? Is it because you can't use the MOSFETs with as low voltage as 3.3V? This motor is probably driven with a STM32 and PWM.
I have a general understanding of PWM, but why do I need to give the IC3 and IC4 a inverted signal of my PWM flank? Can't the IC just assume, if there is no high on the HI pin, there is a high signal on LI?
Can you tell me something of the overall "quality" of this circuit?


texts: Correct way to measure a wall wart voltage

texts:
I got a full drawer of second hand wall warts which I'm planning to use for powering arduino projects (mostly 5V "pro mini" or "nano").

I'm using a voltmeter to check that they are still working, however most of them seem to output a far greater voltage than what is printed on the case.

For example the Arduino pro mini accept up to 12V so I've been looking at 9V wall warts, but they often give more than 12V.

Example (but typical reading):

written specification: 9 V 300 mA
Measured voltage: 12.37 V
Measured voltage while powering a led (through a 300 ohms resistor): 11.2 V

I tried to add a led because I've read that measuring a voltage with no load may give a wrong result, but perhaps that's not enough to get a proper reading...

My questions are:

Is there a way to measure the correct voltage that will be issued in "normal usage conditions"?
Can I safely use a "9V wall wart" to power a "12V max" device if I measure more than 12V?

PS: So far I've use 6V wall warts which are giving about 10V, but I don't have any left so I'm trying to use 9V ones


texts: can't press two buttons simultaneously on infrared sauna curcuitboard

texts:
I have an infrared sauna at home that I'd like to hook up to a wifi-controlled outlet and control via the internet.  It's a pretty basic made-in-China kind of a cabin, so I'm going to have to implement all the bells and whistles myself.

I've taken off the piezo speaker (so it doesn't beep at me for pressing buttons) and I am able to bridge the connection so the "add more time" button is always being pressed down.

The problem is that the circuit board apparently can't listen to more than one button being pressed simultaneously.  If I'm pressing "add more time" I can't press "power on".  Every time I reconnect the sauna to power I have to re-press the power button.

Are there any heuristics to take the power button on the circuit board out of the equation, to make the sauna always be "on" if it's getting electricity?  I really think that's the shortest path to success here.

I recognize this question doesn't have all the details you need.  I don't know what those are.


texts: Need to charge a lithium power pack from USB

texts:
I need to charge a small lithium power pack from a device that was originally charged using a 5v USB connection. The connector on the device is damaged so I need to charge the power pack directly.
I'm not very experienced with electrical stuff so I am not sure what kind of connection it has? I've taken a photo of it with a sharpie pen for scale.

I'm assuming a need something like this?

http://www.ebay.co.uk/itm/NEW-5V-Mini-USB-1A-Lithium-Battery-Charging-Board-Charger-Module-WST-for-Arduino-/251447228883?pt=UK_Sound_Vision_Battery_Chargers&hash=item3a8b6c39d3
The power pack has 4 wires. 1 Yellow, 1 Red, and 2 Black.
I don't want to strip or cut any wires so I ideally need to find a female connector of that type with wires I can solder to the USB charger.
Can anyone help with pointers on things to search for and which wires I need to solder to the + and - points?


texts: What LED PWM controller has marking AT508CS?

texts:
I have an LED worklight with low- and strobe-functions.

One click: On - full Power
Two clicks: half Power
Three clicks: strobe
Four clicks: Off

The controller is circled:

No markings on the top so I desoldered it and found the markings on the bottom.

AT508CS (might be AT50BCS, but I don't Think so)
RBFKG1000
1904 X

Tried to identify the pinout:


texts: Maximum frequency for a FPGA-based square wave signal

texts:
I have an understanding problem what is the maximum possible frequency for a square wave signal that can be generated.

I am currently experimenting with a FPGA board (Red Pitaya), which has a 125Mhz Xilinx Zynq FPGA. When I am connecting the clock signal via a Binary Counter and Slice (Xilinx IPs) for the bit #0 and to an output pin, I measure about the half frequency (62,5Mhz).

Here is the Xilinx Vivado block diagram
(32bit Binary Counter in UP-mode, 1bit Slice Din From + Din Down To are both 0):

I would have expected that I will see exactly the clock frequency on the output port.

Can someone please explain me why the frequency got halved and what is the maximum square wave frequency that can be created by a FPGA?


texts:
My mini lathe motor has a sort of clicking sound when there's pressure on the shaft from the side.
Link to 35 second movie with sound.
Is this normal? Does something needs to be replaced? Thank you!


texts:
I'm trying to make an ATMega328P to send serial data to my computer and print onto Putty using an arduino board to do the USB to serial conversions.  The data that's printed, however is garbage data.  I've tried changing the number of stop bits, checked the serial communications in putty, checked the Baud error rates, and have also added a delay so that the computer can read the serial data easier. Here's the code:

#include <avr/io.h>
#include <stdio.h>
#include <util/delay.h>

#define USART_BAUDRATE 9600
#define F_CPU 7372800
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)

void printString(const char myString[]){
    uint8_t i = 8;
    while(myString[i]){
       while ((UCSR0A &(1<<UDRE0)) == 0){}//do nothing until transmission flag is set
          UDR0 = myString[i];
          i++;
    }
}

int main(void)
{
    //--------------init usart----------------//
    UCSR0B = (1<<RXEN0)|(1<<TXEN0); //Enables the USART transmitter and receiver
    _delay_ms(10);
    UCSR0C = (1<<UCSZ01)|(1<<UCSZ00)|(USBS0<<1); //tells it to send 8bit characters (setting both USCZ01 and UCSZ00 to one)
    //now it has 2 stop bits.

    UBRR0H = (BAUD_PRESCALE >> 8); //loads the upper 8 bits into the high byte of the UBRR register
    UBRR0L = BAUD_PRESCALE; //loads the lower 8 bits
    //----------------------------------------//
    _delay_ms(10);

    for(;;){
    printString("Hello World!\r\n");
    }
return (0);
}

And the data that's displayed in putty is as follows.  First there's a bunch of this:
  àà  àà  à   à àà  àà  àà  à.     Then there's a bunch of this:
   f,Mün$M´M,M´M$M´M,M´M,M´M,M´M
and other similar characters.  I don't know why these are getting printed.  Thanks.

edit: here's the datasheet


texts:
I think this a simple question but I can't find the answer ! I try but ... that don't came out !

I have an USB connector. In one case, I want to powering myself with my batterie (if I use it with a device and I'm the host). In the other case, I will have Vbus powering by an external host (so I want to cut the power by the battery) -> So the schematic case

I don't want to use a power switch CI.

I found a solution with a simple diode but I lose some voltage power ... I wanted to use a Mosfet for switching power. I can command this mosfet with an MCU. So when I detect vbus power 5V, I cut the battery power ...

How i can do this with a mosfet ? (P or N ...) ?

simulate this circuit – Schematic created using CircuitLab

Thanks you very much


texts: How does an ADC with an unequal split supply work?

texts:
I'm having some trouble verifying my thought process for how a differential-input ADC works, especially when done in a case when run off an unequal split supply. I'm hoping to get some clarification here. For example, if I have a differential-input ADC running off a -5V/+10V supply, with an internal reference of 2V, how is the analog data converted and what is it referenced to?

The way I'm thinking of it is this. With a -5V/+10V supply, the 'center' is at +2.5V. I'm feeding a differential output voltage from a sensor (also powered from -5/+10) into the ADC, with the CM at +2.5V. Let's say that this sensor momentarily has the differential outputs equal to each other, meaning both are exactly +2.5V.

Would the ADC read this as 'zero'? I believe it would, based on the fact that the difference between AIN+ and AIN- is exactly zero. However, since the internal voltage reference is 2V, and both my inputs are above 2V, would this cause an issue? Or, would the 2V reference be referenced to the 'center' of the supply voltages (+2.5V), meaning that the full-scale range of the ADC is then from 2.5-4.5V (referenced from the supply voltages -5/+10V)?

Lastly, how does an ADC compare a differential signal to a voltage reference? Is it correct to say that the differential signal is converted to the single-ended signal by taking the difference between V+ and V-, and then doing the comparison then?

Thanks for the help everybody!


texts: RS-232 interface chip problem - why is the voltage level so wrong?

texts:
1. What I want to do:

I have a PCB with an AVR microcontroller (ATmega16U4) on it. I want the microcontroller to communicate with my computer through an RS-232 cable.

2. What I did:

I added an interface chip (Analog Devices ADM3202) between the microcontroller and the RS-232 9-pin connector. I know that the RS-232 works at a voltage level between  -15V and 15V and I know that the most popular chip that people use is the MAX232. However, on my PCB, I only have +3.3V available to use. That is the reason that I chose ADM3202.
In the datasheet of ADM3202, I see that this chip can fulfill my requirement:

We can see that given input from 0 to 3.3V, it is outputting a range from -5V to 5V. So I used it!
I connected the chip in the circuit like the picture below. Just in case that there is a problem with my circuit connections.

3. What is the problem I'm facing:

The problem is that I got nothing in my Tera Term in my computer. Then I checked the voltage level of certain points in my circuit. The picture below shows the waveform when I am trying to send data (0x75) from the microcontroller to the computer. The baud rate is 9600.

Here, CH2 is connected to the TXD pin of the AVR microcontroller and CH1 is connected to the pin14(T1O) of the ADM3202 chip.

First, I think the TXD pin voltage behaves wired. I think it is supposed to give me a voltage level from 0 to 3.3V according to the digital values. But, it is giving me from -3.3V to 0.

Second, the output of the interface chip is problematic. For the computer to recognize '1' and '0', the voltage level should look like the picture below: it needs a wider range than (-3V, 3V). Apparently, my circuit is not working correctly.

However, I cannot find the reason why I am wrong. I think I built the circuit correctly based on the datasheet. Can you tell me where the problem exists? Thank you!

========================================================================
Reply to Peter Bennett:

You are correct, it was AC coupling. This is what it looks like after using DC.

=============================================================

Reply to TimWescott:

After I disconnected the cable from the PC, I got the waveform below:

It looks much better! Then, what is the reason I cannot get any data from the Tera Term terminal?


texts: Are DC-DC converters designed with fixed output or fixed output/input ratio?

texts:
When I was learning DC-DC converters, I think they are a "DC version" of transformer (which is for AC-AC). So when I was designing a 100-30V flyback converter, my suggestion is: if a user inputs a DC 100V source, he gets a 30V output; if he inputs a DC 50V source, he gets a 15V. Just like how transformers act with AC, which have a fixed output/input ratio.

And someone then told me: no. If he inputs a 100V he gets 30V output; if he inputs a 50V, he should still get a 30V; even if he inputs a 15V, he still have to get a 30V. (We were talking about flyback converter. I'm not sure what about buck/boost converter. ) This is like a DC power supply (or it is), with which you want a fixed output.

So I'm curious and a little confused now about the actual situation. Do manufacturers always make DC-DC converters with fixed output voltage? Or with fixed output/input ratio? Or both are possible? In this case, is one of them are more often to use then the other?

The "someone" was like "How dumb are you! How can you even don't know this! " while telling me the story. I think it's more possible what he said makes more sense, because I'm really stupid. But what confused me is: if the actual situation is we never design DC-DC converters, like buck or boost or flyback or any other DC-DC converters, with a fixed output/input ratio, then how do I do if I want a "DC transformer" which give me output = f(input) = input * 3? Or, I don't know, maybe we will never want a DC transformer like this?


texts: Solving a series RLC DC step response circuit

texts:
I got two different answers to this RLC problem when using a method shown in class. What am I doing wrong?

Edit: I graphed each answer. I'm assuming the answer for Vc on the right is correct, as the response looks nromal, but I still don't know why my diff.eq. method is wrong.


texts: Drive a resistive heater from a low power IC

texts:
I'd like to drive a resistive heater using an IC operating at 3.3 V. The heater may need to dissipate up to 18 W, and will be powered by a 28.8 V battery. The IC is able to generate PWM signals, but driving the heater should be as little noisy as possible. Finally, the driver shouldn't dissipate too much energy.

To prevent switching the high current flowing through the resistor, and thus EM noise emission, I thought about putting a simple RC low-pass filter before the actual driver, which would smooth its input signal.

Now, for the driver itself, using a MOSFET would be easy, however they dissipate more power than bipolar transistors, so a Darlington pair might be more appropriate. Then, the issue of the high base-emitter voltage arises, since the PWM signal will have a 3.3 V amplitude.

What is the appropriate way to do this?


texts:
I have two regulated 12V 12A power supplies that I want to use to provide switching power to some resistive loads. I currently have them hooked up like this:

simulate this circuit – Schematic created using CircuitLab

My problem is that when I plug them into mains, the supplies don't consistently turn on. Even if the microcontroller's PWMs are set to 100% low, the power supplies click and their status lights flicker as if they are being overloaded.

The MOSFETs are working, nothing is shorted and each PSU gives 12V when not hooked up to anything. What am I doing wrong?


texts: Inamp to Measure LiFePO4 Battery Voltage

texts:
I know there are a few posts regarding the best way to measure battery voltage but I didn't see any that were focused on the most precise method possible. I am designing a battery analyzer to measure battery state of health and state of charge. The general system diagram is in the picture attached. This diagram shows 1 channel of an 8 channel system.

I have heard the most precise method would be to use an instrumentation amplifier to measure the voltage difference which also has the benefit of reducing required MCU inputs. Since I don't have much experience applying op-amps in design much less in-amps, I am not really sure if you can use it this way. From what I have read, they are normally used for amplifying small signals accurately and rejecting common-mode signal. The one I have selected seems to offer a unity gain option and also says it can be used as a difference amplifier, however.

My question is, can I use this in-amp (MCP6N11) to measure a 2-4V battery voltage? The typical application circuit in the datasheet (see attached) shows a very similar configuration only it is measure a small voltage across a current sense resistor instead of the battery voltage.

Due to the high input impedance of the amp, will there by any issue with antenna effect if the battery is connected to the pcb via 3-6 inch wires? If so, would switching the battery+ terminal to a 10k resistor to ground during ADC measurement reduce this effect?

Also, would the high charge/discharge current (up to 1A) affect the voltage measurement? What is the optimal way of probing the battery voltage (i.e trace width/length, location, etc).

I am hoping to achieve around .1-1mV accuracy.


texts: I have a thermal camera whose external shutter doesn't close when commanded to by the camera. I think it is a current issue. Something is fried or worn out within the camera's electronics. The shutter works fine as I can get it to close by applying Vcc to the correct pin on the shutter. When the camera commands pin A to go high, it goes high, but all that happens is there is a very high pitched whine heard from the camera and the shutter never closes. Vcc is 3v, and when A goes high it is also 3v. How would I make it so that when A goes high, a switch is closed connecting Vcc to A?


texts:
I'm a final year engineering student. I'm very keen to learn VHDL and FPGA synthesis. I believe choosing a final year project involving VHDL synthesis will help me a lot to learn more about it. Unfortunately, the FPGA available to me is a Xilinx Spartan 3E Basys2. It's a starter board. Do you think I can do a final year project (a project that would be accepted as a final year project) with that board?

Here's a link to the description of the Basys2:
http://www.digilentinc.com/Products/Detail.cfm?Prod=BASYS2

I have the 250k gates version.


texts: How is the impedance of a circuit calculated when non-linearity is introduced from a switch?

texts:
What is the impedance of the following circuit if the switch operates at the same frequency with the input voltage?
Since the switch introduces non-linearity to the circuit, how can I calculate the impedance?
My guess is when the switch is off the impedance is infinity while when the switch is on impedance is Z=2πfinL. However, I believe it is possible to express one impedance for all the period T.


texts: Why does PIC MCU have (and needs) duplicate registers?

texts:
I have Recently been working on PIC16F84. In PIC16F84 the RAM is divided into two bank. I noticed some of the registers have duplicates in bank1 and bank2. Examples are PCL, STATUS etc. Can any one please explain why these duplicates are needed?
 Dataset link.


texts: Drawing energy from a 3.7V LiPo battery while simultaneously charging with a solar panel

texts:
I have a 200mAh 3.7V (0.7W) LiPo battery that I am looking to use as an energy source for a large model airship.
I also have a 7.2V 100mA (0.72W) solar panel that I would like to use as a means of topping off the battery's charge when necessary to allow for a longer flight duration.
I am wondering, because this will need to provide a constant supply of energy, what the best approach might be to integrate the solar panel into the system.
Any feedback would be very much appreciated.


texts: Fundamental questions about BJT transistors

texts:
Take a standard NPN transistor. The doping of each element of the transistor is in the name. This is what is inside the transistor...

Source of image: Bipolarer - Transistor, gif

The left "slice" of silicon is doped with an impurity which makes it negatively charged (Thus "N"). The middle slice is doped with an impurity that makes it positively charged (Thus "P"). The right slice is similar to the left slice.

The middle slice acts as an insulator between the two "N" slices. When we apply a negative voltage to the middle slice that can overcome the positive charge of the "P" slice all three slices become electrically common to a certain extent, and thus current can flow through the transistor from collector to emitter.

It is my understanding that after overcoming the initial positive charge of the "P" slice, the amount of current that can flow from the collector to the emitter is proportional to how negative "P" is relative to the "N" slices. I.E., as the negative charge of "P" increases, so does the current allowed to flow. (Presumably until "P" becomes as negatively charged as the "N" slices, at which point the current through the transistor no longer increases.)

QUESTIONS:

Since regardless of polarity there is an "N" slice on either side of the "P" slice, why do BJTs have polarity? What is the difference between the collector and the emitter?
On a datasheet, where does one find the "ratio" of charge of "P" to the total current allowed to move through the transistor?
When we apply negative charge to "P" and current is allowed through the transistor, is the current being applied to "P" (minus the charge required to overcome "P"s positive charge) along for the ride? I.E is the current applied to be added to the current on the emitter?
When used in a circuit, an NPN transistor can only be applied to the current path which is electrically common with the negative terminal of your power source, correct?

If I've made an errors in my dissection of the transistor, I would be more than happy to hear about them.


texts: RC phase shift oscillator : how to give positive feedback?

texts:
why is negative feedback given in a rc shift oscillator although a oscillator requires a positive feedback?
as shown in this figure.
And as shown here positive feedback is given by connecting the positive input terminal to output terminal,which is contradicting to the earlier figure.
Please explain this disparity.
Thank You.


texts:
I need to build a programmable current source from a 8051 microcontroller.

It needs an output current from 0 to 10mA maximun.

How do i go about doing this?  what circuits do i need to build?

I was going to do a 20 steps - with 0.5mA so from 0 to 10mA is 20 steps.


texts:
A week ago I made a circuit based on a PIC16F877a uC and MAX232 ic for RS232 serial communication between PC and device. I used USB port of my laptop to power the circuit as:

Image source: bharatbalar.wordpress.com

The circuit ran fine but after almost five minutes the MAX232 ic become very hot, I immediately disconnected the circuit from my laptop.
Now the problem is that my usb port is not working although it is giving power to other devices, the area where usb port is located always remains hot even when the system is turned off and the battery of laptop completely drains in off state. I tried shorting the Positive and ground pin of USB port but instead of turning off the system a message appeaser on screen showing that the device connected to USB port is exceeding the power limit of its HUB. I visually inspected the motherboard but did not find any damaged/burned component. There are two USB port and both are not working.

What solution do you suggest for this problem?


texts:
I am working on making a drink mixer inspired by BAR2D2, I am using a gravity fed pump that is capable of running on a 9v battery. I am using a circuit with a 555 timer to control how long the pump will run. When I hook the pump directly to the battery the pump runs perfect. When I plug it onto my circuit, I get nothing. It turns out I am not getting enough amperage to run the pump.

How can I get more amperage to my pump but still have the timing controlled by my 555 timer?

This is the circuit diagram I used to hook up the 555 timer circuit:

When I put power to the circuit I want the pump to run for 4 seconds which will fill up a cup. the green LED is where I am putting the power leads that go to the pump. When I use the green LED in the circuit the circuit works perfectly. When I replace it with the pump the pump doesn't come on. When I hook the pump to the battery the pump works. My best guess is the pump needs 2 amps to run and it is not getting that.


texts: Three Phase Input to Single Phase Output

texts:
We have three phase input and the voltages in the three input is not the same always. Sometimes, one or two or three phase will be off. I would like to connect the phase to output which lies within the range (110 - 290).

Below will be the example,

Phase 1 (290v), Phase 2 (245v), Phase 3 (190v)

I need to select Phase 1 in this case.
Ampere rating would be 40A on the selected output.

Did searched in google for single device (circuit / IC) which can does this, not finding one. Any direction would be helpful.

Voltage Reference: (Added)

Voltage reference is to the neutral line.
It would be a

4-wire input to 2 wire output with a common neutral line.

Circuit Thoughts:

Thought 1:

http://www.cy-sensors.com/CYVS14-xnS3.pdf

Compare the voltage on each phase with a voltage comparator, connect the output with a solid state SSR in the output.

I would need a power supply now that can input from magic three phases and generate DC output. Not finding the right one.

Will that work?

Thought 2:

This seem to be a cheaper and reliable solution, without inductive circuits.
Please suggest if I have missed something to consider. SMPS - Switch Mode Power Supply (5V).

Thought 3:

This is the cheapest solution, if the input voltage is constant. With the varying voltage, the coil does not seem to take a varying voltage. (100-300V).
Help from https://electronics.stackexchange.com/a/71066/24465 . Thanks to the community. If you think something can be improved, please share your thoughts.


texts: What difference do blocking and non-blocking assignments have on a single-line assign statement?

texts:
always @(posedge clk)
       count = count+1;

and
   always @(posedge clk)
           count <= count+1;

what difference do the above codes have in simulation? I get that the synthesis will yield the same result, but what changes occur for one-line assignment simulation when using blocking and non-blocking assignments.
A similar question was asked some while ago here. But I am not satisfied with the answer there, and since I am low on reputations, I could not comment there.
Please note that I know the difference between blocking and non-blocking assignments. I just need to know the difference when it comes to one-liners.


texts: powering multiple servos from 12v controlled by arduino

texts:
I am trying to control 8 servo's with an arduino uno using ROS.
The diagram below shows my current configuration to power the servos.  I have a buck regulator in between the 12v battery and the breadboard.

The arduino is powered thru a barrel plug which goes into a 12v regulator which connects to the 12v battery.

This does not seem to work when I have many servos. Strange things happen when I try to manipulate all 8 servos at once, a few respond but most do not.  Also they all seem to get jitters and wobble while plugged in.

Why is that?  Also what is the best way to power up and use many servos?
I planned on using the arduino mega 2560 to manipulate up to 30 servos.

buck 5v:

  Module Properties: Non-isolated step-down module (buck).
  Rectifier: Non-Synchronous Rectification.
  Wide Input voltage: DC 4.5-40V.
  Output Voltage: DC 1.2-37V (Adjustable) (output voltage from the USB = output voltage from the output port ).
  Output current: rated current 2A, 3A MAX (Additional heatsink is required).
  If you need its output power greater than 2A/10W, please add with heat-sink.
  Short circuit protection: current limiting, since the recovery.
  Operating temperature: Industrial grade (-40 to +85 )
  Load regulation:±0.5%
  Voltage regulation:± 2.5%
  No CC, current display function

each servo:


texts:
I would like to generate the following beep patterns using a piezo buzzer:

Single long beep
Two short beeps
Single short beep

Is there any specific chip I can use for it. Any simple automatic circuit which can do this is highly welcomed.


texts: For a thick film resistive element does the surface area of electrical contacts affect resistive value?

texts:
I am learning about film-based heating elements and they are challenging my understanding of electronics a bit.  I am used to thinking about resistors and wires on a schematic and I am not used to thinking about the contact area at the interface between a resistor and a wire.

Generally these heating elements consist of a carbon-based resistive ink that is first printed on a substrate, and after this a silver based higher conductance "wire" is printed over this, forming a circuit.  You can see an example of such a circuit in the image below:

What I am wondering is for a given film resistor element, does the amount of contact area of the "electrode elements"/wires affect the resistance value of the element?

If you want some numbers to think about this, the resistance value of the carbon resistor ink is 1700ohm/sq (at 25um) and the rectangular element I'm thinking of might be something like 0.5mm width and 3mm length.  If the wire/electrode overlap is 0.1mm, 0.5mm, 1mm, 1.49mm, is the resistance value affected?


texts: Need to intercept USB data stream going to printer

texts:
I have a label printer connected to a PC via standard USB 2.0 A to B cable. What I need in terms of functionality is a USB Y cable that would send the print data stream down both cables simultaneously. I know.... I know... these cables don't exist, and due to the characteristics of the USB com protocol, it's not as simple as splicing in another cable. However, I know there must be a way to create a redundant data stream.

REQUIREMENT: The printer must still generate a label and the 2nd data stream will be routed to a PC and captured for logging purposes and further processing.

Due to security issues, I wont be allowed to touch the computer or printer, therefore whatever solution I use must reside between the PC and Printer.

References:  Present question is similar to this previous one.


texts: Will a Tesla coil work with a square wave inverter output, used as input?

texts:
I wanted to try an unusual thing, I couldn't find enough resources explaining this approach.
Few days back, I built a fairly simple CFL inverter using a TL494 IC and a couple of power transistors. It's fed with 12V DC supply from a battery and it generated ~ 220v high frequency square wave AC output which can drive a CFL Light or similar load of approx 35 watt. It uses a 12-0-12 4 amp transformer.
I also created a Slayer exciter using my hand made 1000 turn secondary coil which is working ok. The problem is - the slayer exciter runs on 12V input and thus I have not been getting a super high output voltage on secondary and naturally the sparks are short in length. I wanted to amplify this.
I was wondering, if I can feed the output of my inverter into the primary side of the Tesla coil and get a larger output voltage at secondary or not. Theoretically I do not find a problem in this, except the power limits. 5-6 turns of primary coil will try to draw a lot more current than 40 watts is my assumption. But I can work on the current limit somehow and not overwhelm the power transistors or the inverter transformer. I am also not worrying about the lack of an interrupter right now, I can work on perfection if it works.
I want to know if the Tesla coil would work if powered this way. Where should the non-open terminal of the secondary winding of my Tesla coil  be connected to, in order to achieve this? I am just asking this in reference to the Slayer exciter design. It won't have to contribute to the oscillation of the input signal unlike Slayer exciter, because the input signal, i.e. 220v AC is already a high frequency square wave. I am assuming it has to be grounded to make it work. Is that correct?
Sorry if my question sounds silly, I am not an electronics expert. I am just a newbie hobbyist.


texts: How to choose value for unusual digital input signals

texts:
My question is theoretical in it's essence, so it may be closed as being too broad.
The situation
Suppose that a logic expression (to simplify let's say 2 parameters, \$a\$ and \$b\$, and a result) only makes sense for some combination of the parameters.
There is then \$ 2^n\$ possible, non equivalent expressions satisfying the truth table (Each having a different set of results for the forbidden value(s)).
The question
Assuming no difference of operation in the domain of definition whatsoever (such as propagation delay, price/availability of the parts,  etc...), and assuming that a result of 1 corresponds to doing something and 0 to not do it (Active high signal). Which expression to choose ?


texts: SPI Communication with multiple slaves: Problem on MISO line when both slaves are connected

texts:
----SETUP DESCRIPTION----
I'm running SPI Master VHDL code on an FPGA (Spartan 6 - XC6SLX9-3TQG144) with 2 slaves (both ADC122S021). I have one main board onto which I connect the FPGA. The first ADC (ADC1) is on a separate board that is connected to the main board but can also be detached from it. The main board can also work when this other board is detached. The signals from this ADC pass through a digital isolator (Si8641BA-B-IU). The second ADC (ADC2) is on the main board. This one does not have an isolator as the analog input to the ADC is from an isolated current sensor. Both ADCs share the SCLK, MISO and MOSI lines and have separate CS lines. The code is such that when the value received from the ADC is between a certain range (2.45-2.55V analog in this case), an LED on the FPGA board should glow. I'm also observing the signals on an oscilloscope. Schematics for the Main Board:

Schematics for the detachable board:

----PROBLEM DESCRIPTION----
When I detach the board which houses ADC1 and try to read from ADC2, the values I get on MISO are close to what I expect and the LED glows brightly. Waveforms below:

When I try to read from ADC1 (with the board attached ofc), I again get the expected values on MISO and the LED also glows brightly. In this situation the CS on ADC2 (CS2) is pulled high. Waveforms below:

The problem occurs when I try to read from ADC2 when the ADC1 board is also connected. CS1 in this case is pulled high. The MISO readings are now garbled and the LED glows very faintly. Waveforms below:
I don't understand what's going on with the MISO readings in the third case. The ADC datasheet says that the ADC is disabled when CS is pulled high. When I pull CS2 high and read from CS1 it works fine (This is the only way to read from ADC1 as it connects to the FPGA via the main board). So when I try to do the same for the other ADC, i.e. pull CS1 high and read from CS2, this should work too, but it doesn't. Also, ADC2 works fine when it's on its own (ADC1 board disconnected), so it doesn't seem to be a problem with the ADC2 itself but rather connecting them together.
Has anyone run into such a problem before or have any idea what I might be doing wrong here? I'm new to VHDL and it took me some time to get the SPI code to work properly, but I'm stuck on trying to read when multiple slaves are connected. Any help would be much appreciated!
----THINGS I'VE TRIED----
I thought the problem might be with the digital isolator since that's the only part of the path that is different for ADC1 vs. ADC2. I found this question on another blog and added a pull down resistor of 10k for the MISO line on the ADC1 side, but the results are the same.


texts: What is the use of the diode connected anti parallel to the gate resistance in the general MOSFET/IGBT gate driver circuit?

texts: From my limited knowledge, the only advantage of providing a parallel path through diode with a lower resistance across the main gate resistance is the high speed turn off of the power electronic device. Is there anything else behind this kind of design?


texts: Primary current zero at no load? Transformers

texts:
I'm doing a revision on transformers and I read on a textbook that when there is no load connected, current in the primary winding is 0.

How is this possible? I mean we are still connecting a wire to a voltage source. We have the basic inductor circuit.


texts: Simplest circuit that flashes and fades color LEDs synchronized to music?

texts:
This is about designing a circuit that can control multiple LEDs synchronized to music or sound, as simply as possible. I am looking for some conceptual ideas to start out with, not a complete circuit design or anything.

My question is inspired by this YouTube video
(now those are heels to kill for!)

I have read the question Flash an LED to music
but it does not begin to address a requirement like those shoes.

I realize that there are many different and increasingly complex ways of achieving the desired result, but I am looking for the simplest approach, even if it is not the cheapest, and not the most precise. Also, I am not looking for a ready-made pair of shoes that has this (though if there are any, would be interesting to know about them).


texts: Reduce interference over 3.5 mm to cassette tape adapter

texts:
I have one of those cheap 3.5mm > cassette adapters, to use in my car.  I've purchased high-end ones (around $40) and I've purchased cheaper ones like this ($20) but I always get static/feedback from these things, no matter the cost (think of that noise you would hear when a mobile phone was about to ring around a tv/radio).

I did notice that if I hold the wire with my hand, as pictured below, the noise is drastically reduced, usually eliminated completely.

I assume it's EMF/RF interference from my phone's antenna causing the noise.  If I'm wrong, maybe someone can point me in the right direction. I am technologically and mechanically savvy, but by no means an EE. I was thinking maybe I could wrap a section of the cable with aluminum foil (picture below), creating a bit of shielding, but the noise is still there.

Does anyone have any better ideas as to how I can go about [cheaply/easily] creating my own shielding or eliminating the noise?  Or maybe you know of a company that makes one of these adapters, which isn't prone to interference.


texts: How to resolder a broken connection for an LCD component

texts:
I'm new to electronics and I would like to learn how to attempt to repair a board like this.  As you can see in the image, it looks like someone has attempted this repair before, but the right connection has simply broken off.
I had the newbie intuition that I could just resolder this back on. Could anyone advise if this is a good option repairing this board?  Perhaps just applying a blob of solder?  Is there a more professional way?


texts: One step-down regulator 24 V to 1V or two step-down regulators with lower steps?

texts:
I am trying to design a working principle scheme to step-down the input voltage from 24Vdc ---> different low voltages (1.8 V, 1 V, 1.5 V, 3.3 V with ripples ~ 1%).

Could you kindly explain me the the pro and cons of considering a single step-down converter (replicated for all the requested lines)?

...or differently, you suggest me to implement two different steps (e.g. 24V --> 5V and then 5V ---> other lines?)?

What are the pro and cons of this latter solution?


texts: I'm trying to find out if I can run an appliance of mine can off the grid, completely on solar power and a battery.  The appliance uses 4.91 amps and uses 110 volts on the power cord.  The solar panel produces 45 watts of power.  The battery is a 12 Volt, 35 Ah Sealed Lead Acid Battery.  Now, I live in sunny FL, so sunlight shouldn't be an issue as it is sunny most of the time.  Will a single solar panel and battery be able to run it 24/7, without fail?  Meaning it must be able to run even when it dark out, cloudy, etc.  If my setup won't work, how many solar panels and batteries will I need?  Thank you in advance for your answers and advice.


texts: Solid-state relay - Integration in circuit

texts:
I have an MCP4921 DAC that is controlled by a Raspberry Pi.

Then, I have built a Howland current pump circuit that is able to regulate current depending on the input voltage:

Both of these work beautifully in the lab. I am also able to use the DAC to control the V3 voltage source on the circuit. Again, this works fine.

The last piece of the puzzle was to be able to pulsate the output current to have it look like a square wave at a given frequency. To do this, I have decided to try and use a CPC1150N solid-state relay.

I am able to use the PWM module on the Raspberry Pi to control the relay. What I tried to do was put the solid-state relay in between the DAC and the R2 resistance. However, this did not work. For some reason, I have a 4V voltage drop across the solid-state relay. Setting one end of the optical relay to 2V with the DAC, I measure 6V at the other end.

I am not very knowledgable with solid-state relays to understand why this is happening. My question is: Why is this happening? Would it even be possible to use a solid-state relay at that location and if not, what are the alternatives?

I have thought of purchasing a new DAC with switching capabilities, but wanted to know if there was another way before doing so.


texts: measuring current drawn from a 3-phase AC induction motor using a digital circuit

texts:
My background:

I have some experience with digital circuits and microcontroller programming but no prior experience with or knowledge of industrial equipment like motors/pumps. All in all, a newbie.

My requirements:

To continuously monitor the current drawn by a water pump connected to a 3-phase AC induction motor and if the current drops below a certain threshold, trip the motor. Need to figure out a simple, elegant and cost-effective way to accomplish this task.

My research results:

I found two ways to implement AC current sensing:

1) Current transformer
2) Hall-effect sensors

Both provide DC voltage proportional to the sensed AC current which can be measured in a digital circuit. I have decided to go with hall sensors for reasons of size and accuracy.

Decided approach:

To connect the three phase wires to hall sensors. The sensors will produce voltages proportional to the sensed currents. These voltages will be fed to a microcontroller via ADC and the controller will operate relays based on the voltage reading i.e. it will trip the motor if sensed current is below a pre-defined value for the motor.
I understand that I could do away with the controller and get my work done with comparators that drive those relays, but I want to keep the "threshold" configurable, so going with a controller instead. And also there is the scalability factor.

My questions:

Is the choice of hall sensors over current transformers justified, given my requirements?
Does the decided approach pack promise?
Is there a better, more generally accepted way of doing this that i am oblivious to?
Can the duo of input hall sensors and line tripping relays be replaced with a single such device which can not only measure the current but also break the circuit?


texts: What exactly fries the chip when you invert power supply?

texts:
From my own experience, burning microcontrollers is quite easy. Put the 5V at ground, GND at VCC and in an instant your chip is burned.

What exactly goes on internally that causes it to stop functioning entirely? For instance, if I were magically able to open a chip and rearrange all its semiconductor connections and fix it, where exactly would I need to look, and what would I need to do?

If this is chip-specific, please choose any that could answer my question or give me an idea at least.


texts: Why did this "backwards" power jack pass ERC in EAGLE?

texts:
As will become obvious, I am new to Eagle and PCB layout. I set out a simple design, starting with a power jack. The power jack seems to clearly have a "+" terminal labelled, so I connected that to the positive input of my 5V step-down converter.

On the board layout, I should have noticed that what I thought was the positive terminal was labelled GND (but alas, I did not notice):

However, the board passed ERC.

Did I misinterpret the "+" symbol on the schematic view? I would appreciate any insight into my error.


texts: Is there any way to send serial data over physical ethernet layer with no encapsulation?

texts: I wonder if I can use the physical ethernet layer like a serial port. Is it possible? The case would be reading signals with an electronic device without dealing with networking headers.


texts: 12V zener diode has the same series as 6V2. It also has same wattage of 500 watt but VZ of 12V. Will it handle the same maximum current IZT as the 6V2? Any proof?


texts: PIR sensor detects motion only when a very near motion to the IR sensor and when the cover opened

texts:
I am tying to implement something using PIR sensor and Arduino UNO. I did the wiring like this
VCC - 5v
GND - GND
Dout - Pin 3

Here is my code
int calibrationTime = 30; //the time when the sensor outputs a low impulse
long unsigned int lowIn; //the amount of milliseconds the sensor has to be low //before we assume all motion has stopped
long unsigned int pause = 5000;
boolean lockLow = true;
boolean takeLowTime;
int pirPin = 3; //the digital pin connected to the PIR sensor's output
int ledPin = 13; /////////////////////////////
//SETUP
void setup() {
  Serial.begin(9600);
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  digitalWrite(pirPin, LOW); //give the sensor some time to calibrate
  Serial.print("calibrating sensor ");
  for (int i = 0; i < calibrationTime; i++)
  {
    Serial.print("."); delay(1000);
  }
  Serial.println(" done");
  Serial.println("SENSOR ACTIVE");
  delay(50);
} ////////////////////////////
//LOOP
void loop() {
  if (digitalRead(pirPin) == HIGH)
  {
    Serial.println("Detected motion");
    digitalWrite(ledPin, HIGH); //the led visualizes the sensors output pin state
    if (lockLow) { //makes sure we wait for a transition to LOW before any further output is made:
      lockLow = false;
      Serial.println("---");
      Serial.print("motion detected at ");
      Serial.print(millis() / 1000);
      Serial.println(" sec");
      delay(50);
    }
    takeLowTime = true;
  }
  if (digitalRead(pirPin) == LOW)
  { digitalWrite(ledPin, LOW); //the led visualizes the sensors output pin state
    if (takeLowTime)
    { lowIn = millis(); //save the time of the transition from high to LOW
      takeLowTime = false; //make sure this is only done at the start of a LOW phase
    } //if the sensor is low for more than the given pause, //we assume that no more motion is going to happen
    if (!lockLow && millis() - lowIn > pause)
    {
      //makes sure this block of code is only executed again after //a new motion sequence has been detected
      lockLow = true;
      Serial.print("motion ended at "); //output
      Serial.print((millis() - pause) / 1000);
      Serial.println(" sec");
      delay(50);
    }
  }
}

But after calibration its not at all showing its detects some motion when there are many. I tried more sensitivity by turning the right potentiometer all towards right (Clockwise). Still nothing detected.
Then I tried removing the White cover of sensor and it detected some motion only when I touched the sensor.
I tried with another sensor, it works the same. It detect some movement only when I touched it.
What should be wrong?? Both sensors are damaged??


texts: Testing an X2 capacitor with a capacimeter. Is it broken?

texts:
This came up as a comment in other question I posted, but I thought it could be of use for someone else if posted separately.

I have an X2 cap rated ".47K275V~X2". Is that 0.47uF = 470nF? When I set my capacimeter wheel to the "200n" position and test the cap, it reads "40.2nF".

If I set the wheel to both 2m and 200u the capacimeter reads zero. When I go down to 20u it reads 0.04uF, then with 2u it reads .040uF, and with 200n, it reads 40.2nF. If I step down one more time to 20n, it reads 1.

Is the cap bad? Am I interpreting the rating on the cap case right?

Thanks!


texts: What tool do I need for measuring DC power consumption of device over a period of time?

texts:
I have a device that's being battery powered and I would like to measure the power consumption over a longer period of time (~24Hours). I want to read both the voltage of my battery and the current being drawn by my device. I would need something battery powered that could log the data into a raw .csv like format so I can later run analytics on it.

I know this should be really simple but I'm not exactly sure what to Google to find what I need for this application.

Edit: Hoping not more than ~$500. Looking at 12V-48VDC and current <10A. However I would like fairly high accuracy because my application is very sensitive to power consumption. Rate could be on the order of seconds...maybe even minutes but doesn't need to be miliseconds.


texts:
In the region where I live there's a state standard that says that mains voltage deviation can be within 5 percent continuously and within 10 percent for short periods of time, so if the mains voltage is within those ranges - it's just okay. The nominal voltage is 220 volts, so it can be in 209..231 volts range continuously and in 198..242 volts range for short periods of time.

Now I understand that sometimes there're undersized wires and huge losses and bad wire joints and this can cause undervoltage at the consumer site.

What would cause overvoltage? I mean there're carefully designed generators somewhere that rotate at carefully monitored "right" speeds and produce carefully precomputed voltage. Then there're transformers that again have the right number of winds in each windings and so convert the right voltage into the other right voltage. So I don't see how voltage would suddenly get higher than designed. Yet there's even a state standard that allows for rather huge deviations.

What exactly causes overvoltages in power grid?


texts: Does increasing the amplitude of a signal also increase the data rate?

texts:
I face an ambiguity when considering the carrier frequency, signal frequency, bandwidth and data rate.

When I consider the Shannon formula, I wonder if increasing the transmission power also means that the Data Rate is increased without modifying the bandwidth of the signal.

Or is modifying the power of the signal going to implicitly affect the bandwidth of that signal as well?

If you can give a thorough description through these terms and the relation between them, it would be very helpful


texts: Utility of two pins requiring same voltage

texts:
I have a LED backlight driver, which has input pin assignment as:

Pin        Function

1,2        12V Input

3          Brightness control
           PWM : 100Hz~20KHz DC : 0.5V~2.5V

4,6        GND

5   ON/OFF Control    5V ON , 0V OFF

Why do pin 1 and 2 both require 12V input, what is the utility of that? Can somebody give insights on why didn't they use just one pin and give input internally using the same pin?

Link to the datasheet.


texts:
The output voltage of my DC/DC converter and my power supply both slowly descend. I believe this is due to capacitors being close to the output of each device.

I want to get an instantaneous, or as close as possible, off signal from the power supply so that I can connect my backup supply at that moment.

I currently signal the base of a p-channel mosfet with the output of the power supply. Because the voltage slowly descends the mosfet is not signaled until much after the supply is disconnected which leads to a break in power.

It looks something like this,

Where the 5V supply is the main off of the DC/DC converter or Power Supply, the 4.7V is the backup supply, and the 100k resistor is the load. (The load draws much more than a 100k resistor.)

I have tried adding a voltage divider at the base of the mosfet to lower the voltage and a cap at the output to smooth out the main signal. The problem with this is depending on the load the output capacitor has to be very large.

I have also tried using two NPN transformers to pull the mosfet directly to GND. They are signaled sooner than the mosfet but not fast enough.

Is there any way to quickly drain the power supply output caps without adding a constant power drain on the system or signal the mosfet as soon as the power supply starts to decrease its power?


texts:
While I was reading a physics textbook, I've seen something unclear, which is about ΔV. What does this book actually mean by ΔV? It seems like it is potential difference, right? However, the thing I'm trying to get is why it is potential difference, assume that there are two batteries connected in series or parallel, How should we analyze the circuit? Honestly, I didn't see anything related to parallel/series batteries, Why? On other hand, it should've explained what to do when there are batteries connected in series or parallel. What am I missing?

Wishing My Kindest Regards!

EDIT:


texts: For part of my project for college I have co control a 12V DC pump which requires 12A. I was wondering what is the best solution for allowing the PIC to complete this as the output from the PIC is only 5V. Would a relay be best or a FET?


texts: Generating square wave using NXP LPC1768?

texts:
I am reading a book that teaches about programming the LPC1768.

I have the following exercise here:
Using any digital output pin, write a program which outputs a square wave, by switching the output repeatedly between Logic 1 and 0. Use wait( ) functions to give a frequency of 100 Hz (i.e., a period of 10 ms). View the output on an oscilloscope. Measure the voltage values for Logic 0 and 1. How do they relate to Fig. 3.1? Does the square wave frequency agree with your programmed value?

My problem is that I don't have an oscilloscope. Without it, this exercise is sort of impossible for me but I am guessing that indeed my frequency will be higher than expected.

I am thinking that it will be higher due to the output timing being dependant on the internal clock.

Am I right in thinking this? If not, what sort of frequency would I get and why?


texts:
I am dissecting a design and I'm trying to wrap my head around the design pictured below. It is based on the TL064C amplifier and takes in single ended audio and outputs single ended audio as well.

What kind of amplifier is this?

Here's the schematic:

I believe R15/C1 & R16/C2 are RC filters, for what it's worth.


texts: Convert a sawtooth with an offset to to an average voltage of 0

texts:
I have a sawtooth waveform generator whose frequency varies from 20Hz to 4000Hz and has an amplitude of 5V (0 to -5V), I want it to have an average voltage of zero. There seems to be many examples on the web of using an RC HPF. however not many of the actual calculations used to require the RC values. I am using values currently of 10uF and 10kohms, which nearly gives me what I desire, but how were these values this derived?

Also the sawtooth is not perfectly around 0V, is this a fault in the values or the method?


texts:
My VHDL-testbench loads a text file. I want to be able to set the filename from the outside. As I'm using ModelSim (Altera starter edition) to simulate my design, it should be possible to set the string containing the filename over a force command or similar.

How can I "force" a VHDL-string to a certain value? What is the correct syntax?

library ieee;
    use ieee.std_logic_1164.all;

    use std.textio.all;
    use work.txt_util.all;

entity dpu_tb is
end dpu_tb;

architecture Behavioral of dpu_tb is
    signal clk: std_logic;
    signal simulation_finished: std_logic;
    signal simulation_input_file: string(1 to 100); --<-- Set value during simulation
    signal rst: std_logic;

    signal sample: std_logic_vector(12 downto 0);
    signal valid: std_logic;

begin
    ....

What I tried and did not work (and different combinations):

force -deposit simulation_input_file "/tmp/test"

Or is there an different approach to choose the file?


texts: Unable to identify the symbol in schematic

texts:
In my job I came across reading a customer schematic. I am facing trouble in identifying the marked part of the schematic, which is connected at the pins of uUSB Interface Controller.

It seems like a fuse but not very sure of the symbol, as its confidential, unfortunately the engineer did not give a part name also. Any way, it doesn't effect the design but I am eager to know about it out of interest.

The design is of a mobile phone.


texts: Differential voltage measurement at high voltages

texts:
I'm trying to measure a differential voltage. There are two ranges of measurement, one from 0-5V and the other from 0-50V (the reason for different ranges is to get a higher ADC resolution in the lower range.) The output needs to be around 0-2.5V on both ranges. The differential voltage will always be positive and the negative will only be a few tens or hundreds of millivolts above ground. (I'm measuring a voltage at power supply terminals, which isn't necessary at the same potential as the differential amplifier, but the grounds are common.)

I thought of using an op-amp as a differential amplifier, but I'd need an op-amp with supplies of at least 25V, for the noninverting input, unless I had a gain <1, but many op-amps are unstable with gains <1.

Accuracy is reasonably important, although there is the provision to perform an internal calibration, so only a ±2% or so initial accuracy is necessary.

I have some spare relays; other parts of the board use relays (also range selection) so it would make sense to use those for the range selection of the diff-amp too.

What other solutions are there?


texts: What is the purpose of "MOSFET driver" IC's

texts:
There are dedicated "MOSFET driver" IC's available (ICL7667, Max622/626, TD340, IXD*404).
Some also control IGBTs. What is the practical purpose of these? Is it all about maximizing the switching speed (driving gate capacitance) or are there other motives?


texts: How to design a simple linear DC circuit in Ngspice?

texts:
I'm trying to implement a simple linear DC circuit in ngspice, but the program and manual are overwhelming. The circuit I'm trying to get started with is a voltage source (e.g. cell) connected to itself through a resistance.

Looking at the list of independent voltage sources (which I assume is what I need), I can't find a simple potential difference:

Pulse
Sinusoidal
Exponential
Piece-Wise Linear
Single-Frequency FM
Amplitude modulated source (AM)
Transient noise source
Random voltage source
Arbitrary Phase Sources

Am I misunderstanding something? How to design the circuit?


texts: While loop instructions in pic disassemby not clear

texts:
In an efford to save space I try to reduce the generated C code with inline asm("");
Looking at the original disassembly and good working code I do not understand line 0x17E4.

void MENU_BUTTON(uchar Parm){

    // This loop ends when the enter key is pressed
    while EnterOpen(){                 // SW3 = RE2

       if ArrowUpClosed(){             //    RE0
           while ArrowUpClosed(){};
            asm("call MBD");
            if ArrowUpOpen()
                  LCDGotoPos(ArrowUp[index]);
        };
        if ArrowDownClosed(){          // SW3 RE1
            while ArrowDownClosed(){};
            asm("call MBD");
            if ArrowDownOpen()
                 LCDGotoPos(ArrowDown[index]);
        };
        if ArrowRightClosed(){          // SW4 RC1
            while ArrowRightClosed(){};
            asm("call MBD");
            if ArrowRightOpen()
                   LCDGotoPos(ArrowRight[index]);
        };
        if ArrowLeftClosed(){           // SW5 RC0
            while ArrowLeftClosed(){};
            asm("call MBD");
            if ArrowLeftOpen()
                   LCDGotoPos(ArrowLeft[index]);
        };
    };
    Pause(300);
    return;
    // a little trick to save space
    asm("MBD:");
    delay();
}; // End of MenuButtons.

    // This loop ends when the enter key is pressed
    while EnterOpen(){                 // RE2
    0x178E: BCF STATUS, 0x5
    0x178F: BCF STATUS, 0x6
    0x1790: BTFSS PORTE, 0x2
    // jumping out of the loop as expected
    0x1791: GOTO 0x7E5
    // returns to the beginning? but during execution goes to 0x1792.
    // The way I expect
    0x17E4: GOTO 0x78E
    // during execution
    //if ArrowUpClosed()             //   RE0
    0x1792: BTFSC PORTE, 0x0

    //other code
    } // end of while EnterOpen

    //    Pause(300);
    0x17E5: MOVLW 0x8


texts: Unexpected results measuring AC from secondary of toroid transformer

texts:
I am trying to measure AC voltage from the secondary of a toroid power transformer, and I am baffled by what I am seeing.  The AC measurement (less than 4 volts) is too low; the transformer is rated at 50vct, and the DC output is 71 volts, measured after rectification/filtering.

I built a test rig for transformers that is fused, includes a rectifier/filter board for DC, and terminal strips to create a dummy load from power resistors, but for this test, no load was used.

The transformer is an Avel Lindberg AV-67530 toroid, 50VCT 2A.  It has two primaries, allowing it to work with 120vac or 240vac; I have tested using only one primary, and again with both primaries wired in parallel according to the polarity from the specs, with similar results.

The rectifier/filter board (see schematic) has a 600v 6A full-wave bridge rectifier and four 680uF @ 70v filter capacitors in series/parallel.  It can test both single-pole and bipolar supplies, depending on whether the transformer has a center tap in the secondary; COM is only used for bipolar testing.

A red LED with a 2.4k 1/2W resistor is connected between + and COM, a green LED with resistor for - and COM, and a white from + to -, with two 2.4K 1/2W resistors in series; the LEDs are the only load in this test.

Measuring the AC of the transformer secondary, and the DC output of the rectifier/filter, with four DMMs I have, I get the following results:

Wavetek 5XL: AC 0.1v (stable), DC about 71v
BK 2707A: AC 2.2 to 3.1v (varies!), DC about 78v
Sinometer MS8268: AC about 2.4v (varies), DC about 71v
DMiotech Smart-V: AC 3.1v (varies), DC about 71v

The Wavetek is an old DMM that I have had for years.  The BK is a more recent purchase, as are the two Chinese DMMs.

The AC measurements (less than 4 volts) are much too low for the DC output (more than 70 volts) I see.  The AC is the same if I disconnect the transformer from the rectifier board.  The AC readings do not always settle down, and on the BK there is a variation as much as one volt, but the DC readings settle down quickly, aside from some fluctuation of the least significant digit.

The DC measurement is slightly higher than I would expect from multiplying (rated) 50v AC by 1.414 and subtracting for rectifier voltage drop, but it is in the ballpark.  I do not understand why the BK 2702A reads 10% higher for DC than the others.

When using other, conventional (E/I iron core) transformers, I get expected results for both AC and DC.

Why am I getting such low readings when measuring the AC output of the secondary of a toroid transformer?


texts: Most efficient way to handle addressing / termination in a daisy-chained CAN bus?

texts:
I'm working on some devices that will talk to each other over CAN.  The simple idea is to daisy chain essential signals between each device: power (+12V and ground), enable and CAN high / low.

Now, there main two problems I have with introducing this daisy-chaining set up are node addressing and bus termination.  My current solution to these two problems are:

Current Solutions

Node Addressing

I'd have some sort of switch (analog switch, MOSFETs, something) break the CAN bus between the input connector and output connector of every device.  They would be, at start up, configured to essentially only be "attached" to the input connector portion of the bus wiring.  Thus, when all devices power up, node #1 (connected directly to the master node) will be the only node connected, and will be able to pull an address.  Once a node pulls an address, it closes its bus wiring switches and lets the next node connect.  The master keeps assigning IDs until it determines no other nodes are out there waiting.

Bus Termination

I have worked up a way to use extra pins in the connectors as a "sense" signal... driving a voltage to the output connector and seeing it if comes back (each device shorts the pins on their input connectors) to tell us if we are the end of the bus or not.. and whether we should apply termination.

What I'm Not Sure On / Want To Make Better

Using Analog Switches

The analog switch thing works conceptually, but the electrical aspect confuses me.  For example, a lot of the bit rate charts you see for CAN are referenced by how long the network is... this makes total sense.  Harder to drive a signal farther without repeating, etc.  Now, my confusion is... would an analog switch, with it's inherently high (compared to raw wire) resistance be killing my maximum bit rate on the bus?

From calculating it out, if my bus was entirely 20AWG wire... adding in an analog switch with a really low Ron (lowest I've found is 0.3 ohms so far) to each node to provide the circuitry to do node addressing would be the equivalent of adding an extra ~30 feet of wiring for every node.  Am I overestimating the impact these switches would have?  The bus is already terminated at each end by 120 ohm termination resistors so it's not adding a ton in terms of the passive bus resistance... but calculating it in terms of how much extra wiring it appears as makes it seem bad.

Remote Node Sensing

Also, as far as sensing remote nodes.... I'd like to avoid an approach that relies on using dedicated pins in the connectors.  Long story short, being able to ditch the sense pins lets me save money on a lower pin count connector AND it lets me switch to thicker wiring which means I can carry more power and support more end nodes.  I'd also like to be able to slightly reduce the component count of the driving/receiving circuitry of the sense functionality which involves a lot of passives, zeners for clamping, discrete logic ICs, etc.

So... thoughts? :)