Electronics > Beginners
Using ADS 10115 and Micro Current Gold.
andymouse:
Hi,
I have an ADS1015 ADC connected to an Arduino Uno and it is powered from the Arduino 5v supply, I am using the Arduino 3.3v and a potential divide to give me a 55 mV and have the sample sketch set to gain sixteen and I have an accurate value on the serial monitor that varies by 1 count every now and then. I also have a 3v battery with a 50M ohm resistor connected to a Microcurrent Gold which gives me 58.8 millivolts (58.8 milliamps) on my fluke 79 series 2 multimeter that is rock steady. However if I connect the microcurrent to the ADC the readout is unstable varying by 10 to fifteen millivolts, the only thing that I am unable to change is the samples per second, so not sure if this needs adjusting, and I can't understand because both sources are fine on my fluke but only one is ok with the ADC. Any thoughts please ?
Andy
iMo:
--- Quote from: andymouse on January 27, 2020, 11:08:00 am ---I also have a 3v battery with a 50M ohm resistor connected to a Microcurrent Gold which gives me 58.8 millivolts (58.8 milliamps) on my fluke 79 series 2 multimeter that is rock steady.
--- End quote ---
Do you mean 58.8nA?
Try to run Arduino+ADC+notebook on batteries (not USB or wall adapter powered) - the same setup as with the Fluke..
andymouse:
Hi,
Firstly, sorry yes nA.
I thought this would be it, sadly not.
I set up the ADC to measure a differential input and ran the uno of a battery and displayed the output on an LCD display and really expected this to work, however the result was also jumping around by a few counts, but again is steady on my Fluke, so I am at a loss, however my ADC itself does not appear to work fully, as A0 is showing full scale all the time but the other 3 inputs are fine so I guess the first thing to do is get a new ADC but I don't feel that's the problem as the "noise" only seems to appear on the microcurrent and not anything else connected to the ADC. I don't have access to a scope at the moment so its difficult to move on. Do you have any thoughts ? and what would you check with a scope? what part (if any!) of the microcurrent should I even suspect, if I hadn't tried to make a seperate display I would not have noticed this...cheers.
andymouse:
Hi,
I just had a thought.
I was asking myself what was the difference between the Fluke and the ADC ? because the Fluke worked ok and the ADC didn't, there is a difference between impedance, could this be the problem that the Fluke is high impedance input and the ADC isn't, or am I barking up the wrong tree ?
Kleinstein:
The Fluke DMM like most DMMs reads the signal over a multiple of the power line cycle. This gives very good suppression of 50/100 Hz residual present in the signal. For the external ADC is depends on the settings which integration time is used. If set to the US 60 Hz this could give poor mains hum suppression and one could see a beat frequency.
It could also be a problem with the reference. If the divided 3.3 V signal is very stable this makes me suspect that for some reason the ADC could use the 3.3 V supply as reference. This would be good for the divider, but bad for any external voltage if the 3.3 V are not stable.
The µCurrent, especially some versions don't like a capacitive load
Another possible trouble could be supply to the µCurrent. Is this separate from the ADS1015.
If the main task is reading small current, like in the pA to µA range, I would not use the µCurrent, but build a separate trans-impedance amplifier for the suitable range. This can use relatively normal OP, nothing really fancy is needed. Even just a MCP6001/2 or TLC271 is good for a start.
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