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Measuring +50v to -50v with ADC

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STU_KNTU

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Hi friends...:thumbsup:
I want to build a digital oscilloscope with 8 bit ADC but I've some question...
1.how can i display voltage between +-50v with adc?!
after some searching I've realized that i can scale this rang to adc range with Op Amp, but i think it will decrease accuracy to 100/256 = 0.39'v
2.can you give me some idea about circuit protection??
for example what can in my circuit for protecting input channels from 220v voltage and ....

thanks...
 

if you want to build a scope with an 8bit adc,
then the step size is the one you have to accept.
 

Hi

an 8 bit ADC has a resolution of 256LSBs or 256 steps or 1/256.

Accuracy is something different. It says how close the measured value is to the real value. Maybe you measure 2.5V but the real value is 2.3V, then the accuracy error is 0.2V
It has nothing to do with resolution.

For +/-50V usually you don´t need an OPAMP but a resistive voltage divider. (Maybe with capacitive compensation)
Two resistors: 500k + 10k gives a about +/-1V with a +/- 50V input.

Circuit protection: Two diodes. Maybe to +/-3V3. A simple search in this forum or in the internet give a lot of information. (It is nothing new. And it is very frequently used)


Klaus
 
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