A very simple gadget was updated in this issue. I did an ADC collection in the school electricity competition before, but did not make any highlights. Later, under the reminder of my classmates, I realized that I could do an additional function of negative voltage measurement.
Of course, this problem can be done with an off-the-shelf bipolar ADC acquisition chip. I know that it can be done with AD976. If it is more luxurious, you can use a multimeter IC, but this issue introduces a lower cost and lower-level method.
The general idea is: use an op amp adder to raise the voltage as a whole, that is, raise the negative voltage to a positive voltage, originally the positive voltage can be raised to a higher level, if the voltage is too large, you can also adjust the ratio, but it will reduce the accuracy .
Not much to say, attach the schematic diagram:
Here we set R1=R2=RF=1K for convenience, if we want to adjust the ratio, we can adjust it through RK. Let's set RK=1K for now.
At this time, we set U1 to 5V and U2 to the input voltage, then the formula of U0 is U0=5+U2
So theoretically at this time our circuit can measure a voltage of about -5V, but because some single-chip microcomputer pins can accept negative voltages with a small amplitude, the real value here is generally less than -5V, we attach Simulation circuit diagram:
when the input is 2V, the output is 6.997v
When the input is -4V, the output is almost 1V, and the result is fairly accurate.
This simulation is an ideal situation. When the absolute value of the measured voltage is relatively large, we can adjust the value of RK or RF to adjust the ratio . Of course, it is not recommended to adjust R1 or R2 here for the sake of calculation simplicity.
It is worth noting that if you want to make a real object, you must carefully select high-precision operational amplifiers and resistors!
Thanks for watching!