I am using the Arduino Nano with a MAX187 external ADC.
Using a sine wave generator (0-5V range) as reference input i get the following output:
The problem is that voltages close to 5V are trimmed. I think this is because the Arduino Nano only uses close to 4.7V when powered over USB. This limits the input range of the ADC. So my question is: how can I get a 5V reference voltage for the ADC? All components have to be through-hole which limits the possibilites. I couldn't find an ADC which has an internal reference of 5V, meets my specifications and can be easily soldered.
I also can't connect an external power supply because my project requires that only a single cable is used for both the power supply and data transfer.
I guess i have to use a combination of an amplifier and a precision voltage reference (like a LM4040?).
I'm new to electronics and just need some pointers in the right direction, all help is greatly appreciated.
Use a 4.096V precision reference for the ADC, and a resistor-divider on the input of 2k2 + 10k, which maps 5.0V down to 4.098V ?? (Assuming the ADC has high resistance inputs).
If you power a Nano through it's USB connector, then it's 5volt rail is only ~4.6volt because of a backflow protection diode.
That might or might not be enough for this chip (VDD = +5V ±5%), but it certainly will clip a 5volt input signal.
The Nano runs on 5volt if you power it with 7-9volt on the V-in pin, but because of a design error it might blow the 5volt regulator if you also connect it to a laptop/PC.
You could connect a 5volt cellphone charger to the 5volt pin, or use an 5volt Arduino with proper USB switching capabilities (Uno/Mega).
Leo..
