Hi, I'm currently constructing an operational amplifier for a power output meter for a project.
I've done the analogRead() tutorial with the potentiometer, however I don't know how to read the analog signal of my operational amplifier with my arduino. Literally don't know how to connect the completely separate amplifying circuit to my arduino.
Refer to the schematic I added. The voltmeter at the end basically represents my arduino reading the voltage.
Thank you
Connect negative Bat1 to arduino ground, output of the OPA to resistive voltage divider(coef. around 4, to bring 18V down to less than 5V. let say 30 k and 10 k), than output of divider goes to analog input of the arduino. The problem, bad PSRR, as battery drains, readings would be affected.
If your arduino support "differential" mode of the ADC (not AtMega328 chip), than take readings from points where voltmeter conected now ( with resistor divider).
Other option with non-supporting diff mode ADC, introduce offset to output stage of amplifier.
Thank you for your quick reply. So am I right in saying that the for the arduino to read the voltage correctly, it needs to be connected to the circuit ground too?
I will need the the offset amplification since I am using the AtMega328.
I don't completely understand the connection of the Arduino as you explained it though. With the ground being between the separate batteries, the voltage supply from bat1 is theoretically -9V. With this set-up, the Voltage output range I expect is between -2 and 2 volts.
Assuming that I connect the amp output to the arduino analog input, could you please explain to me how connecting bat1 to arduino ground would result in such a significantly higher output voltage to be read by arduino.
So am I right in saying that the for the arduino to read the voltage correctly, it needs to be connected to the circuit ground too?
Yes that is true for any voltage. A voltage is a potential difference between two points. Ground is one of those points.
the Voltage output range I expect is between -2 and 2 volts.
Yes and that is the trouble. You feed a negative voltage into the arduino and you will fry it.
What is being suggested is that you shift the ground by referencing the ground to the most negative supply. That way you will always get positive voltages. However, that voltage is then too high as you can only put a maximum of 5V into an arduino (well the same as the chip supply actually), so this will give a maximum of 18V again enough to fry the arduino. So you cut it down with a potential divider so the maximum voltage is 5V. You can measure that safely.
Alright, I see. Thank you for your help! I'll see what I can put together
what about a ltc1043?
it could be connected to OpAmp ground and OpAmp out (with extra safety protection diode)...
and then to 2.5V and an arduino analog pin...
supply for the ltc1043 should be not higher than 14V (=9V+2V+2*1.5V)...
and all (ltc1043, op amps, arduino) should be connected to bat1neg with their negative supply pin)...
EDIT: the arduino analog pin should b protected with a 2V5-zener (pointing from ground to the pin) or a schottky (pointing from the pin to +5V) diode 2...
