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Electronics => Electronics => Topic started by: jsmoker on June 02, 2008, 02:09:49 PM

Title: autozero circuit for quarter bridge
Post by: jsmoker on June 02, 2008, 02:09:49 PM

I have 16 quarter-bridge circuits and presently I have to adjust each one with a potentiometer for calibration.  Does anyone know a circuit that I can set up where a single pushbutton can calibrate everything?  I know it exists but I can't find it anywhere online.  Note, I can't do this purely in software because I need the whole range of the ADC.

Thanks

Title: Re: autozero circuit for quarter bridge
Post by: Admin on June 07, 2008, 05:21:25 PM

So the varied voltage controls the quarter-bridges?

Why not make/buy a DAC (digital to analog converter)?

Title: Re: autozero circuit for quarter bridge
Post by: jsmoker on June 18, 2008, 08:45:43 AM

Not really, the ratio of resistances controls the output.  When all the resistances are balanced, you get a 0V output.  If there's negative strain, the resistance changes and the voltages goes one way, otherwise the voltage goes the other way.  If you mean placing a DAC to power the bridge, it would just change the reference voltage, but it won't zero the circuit.  Am I understanding you wrong?

Title: Re: autozero circuit for quarter bridge
Post by: Admin on June 19, 2008, 06:54:16 AM

Ok I'll better explain . . .

You want to digitally control a bunch of voltages. The DAC will give out whatever voltage you want. If you want it in a feedback loop, you'd use an ADC to measure each output, then modify it with a DAC using PID control.

You could do this with several microcontrollers using PWM, resistors, caps . . . I can't think of an easier way . . .

Or, just a thought . . . have 16 servos control the pots using an ADC PID feedback loop . . .

Title: Re: autozero circuit for quarter bridge
Post by: Asellith on June 19, 2008, 07:55:44 AM

What about something like this:
http://datasheets.maxim-ic.com/en/ds/MAX5400-MAX5401.pdf (http://datasheets.maxim-ic.com/en/ds/MAX5400-MAX5401.pdf)

A digital pot would let you press a button and have you controller cycle through each adc input and adjust till zero is reach. They run on 3 wire serial but there are lots of options out there this was just some really quick research on my part.

This would replace you be in series with your existing pots to let you programatically fine tune the system every time you wanted to calibrate it.

Actually I love this site for this reason. Your question help me find a possible solution to another problem I am working on :)

More on that later.