Thanks a lot. You’re right but they need special instrumentation amplifiers. I have to do with what I can get.
I’ve got a few OPA340, I’ll try again as I failed a few times. Having and Arduino shield for measuring current and voltage with considerable accuracy and more digits is not a wonder. If someone improvises it, we will find it on the next day available in the market to replace those 3 digits displays.
You can build your own from some (4?) ordinary opamps.
according to your circuit, are Arduino analog inputs sensitive to 10 millivolts which should correspond to a load of 1 ampere?
Only these LM324 and TL074.
That is do to the opamp offset voltage which can be as high as 7mV.
Again as I said before the output is only guaranteed to be valid up to 3.5V. You need to supply the 358 with at least 5.5V to get an output up to 4V, that is at least 1.5V more than the expected output voltage
For 1A current, voltage across shunt = 0.01x1 = 10 mV.
Operate ADC with Vref = 1.1 V which gives resolution: 1.1/1023 = 1.07 mV.
You can very well measure 10 mV by UNO R3's ADC to get ~= 00 0000 1001
Do the actual measuremet and check if the accuracy meets your requirements; else, go with ADS1115 (16-bit Serial ADC).
You can use then in my circuit. They will provide a 4V output swing and less voltage offset.
I’ll try it.
Yes I’ll also try those.
I would abandon the whole opamp idea and buy an INA226 breakout board.
It will give you current, voltage and power from it's 16-bit A/D.
Or the cheaper INA219 (12-bit).
Temu has both.
Leo..
Thanks a lot. I have the ACS712T. I wasn’t satisfied with its performance. But as for the INA219, I have to consider them if they’re not based on hall sensors. Frankly, I had the conception(misconception?) that it’s similar to the ACS712. Well, no, I’ve already looked in the datasheet. They are necessary and they’re cheap. Time to order them with the ADS1115.
Hello Jim-P,
I soldered the parts using two OPA340, 3 X 30mOhms in parallel, and powered the module from 5 volts. I get 14 millivolts at the standby. When connecting loads from 10 Volts, I get the following readings:
100 Ohms resistor 1% 1W 145mV
47 Ohms 5% 194mV
10 Ohms 5% 5W 450mV
4 Ohms 5% 5W 944mV
5 Ohms 2 x 10 in parallel 779mV
Is that OK? I expected to get 1 Volt when supplying 10 volts to a 10 ohms resistor or something near.
I can imagine that. you get less than 9-bit resolution with that one.
The INA breakout boards have a 0.1 Ohm high-side shunt fitted.
They measure 3.2Amp withour modification.
High-side, so supply voltage can be measured at the same time and ground is not interrupted.
Why did you mention the ADS1115, which is not needed. The INA does it all.
Use the 226 if you want a higher resolution, but the 219 is surely already more capable than your current setup.
Leo..
No.
The circuit has a voltage gain of 125.
So for a current of 1A (10mv across the shunt) the output should be 1.25V
Sorry my fault! I forgot to solder R4. Now it’s OK.
Glad I could help
Have a nice day!
25volt with five decimal places is wishful thinking.
Not possible with common off-the-shelf parts.
Be happy with three real decimal places with an INA226.
Leo..
Yes you did. Have a nice day!