What I am looking for is a way to maintain a stable and accurate 5V reference voltage for Arduino's analog inputs. Something around 0.01V stability and accuracy would be nice.
My experience with the USB supply has been: the voltage fluctuates and at times it spikes or dips. It also only is nominally 5V and often stays at 5.05V. Analog readings from sensors tend to fluctuate around 1-2% or more when there is a sudden voltage change. That's not good enough.
On the other hand, an AC adapter or a battery with LM7805 and two capacitors has given me less than 0.01V offset and little fluctuation. Sensor readings are far less fluctuating.
So, if I connect an arduino board to PC for data transfer but still want a good 5V reference, what IC can help provide it? I won't be connecting the arduino to an AC adapter, just the USB, so the IC's only power source is the nominal 5V.
Thank you!
A side note: on my custom board, I have a jumper to disconnect 5V from the USB TTL chip. But if I use something like a nano or the like, there is no way to disconnect the 5V from USB.
I would get a proper voltage reference chip, you can't get a good 5v ref from a 5v source because the chip will need some headroom, so either use a lower ref, say 2v5, or run the ref chip from VIN.
EDIT: Example chips, LM336, LM385, MC1403, REF1004, TS6001, TSM6025.
Graynomad:
I would get a proper voltage reference chip, you can't get a good 5v ref from a 5v source because the chip will need some headroom, so either use a lower ref, say 2v5, or run the ref chip from VIN.
EDIT: Example chips, LM336, LM385, MC1403, REF1004, TS6001, TSM6025.
Rob
Thanks Rob. I'll look into these chips, the first 3 seem to be references less than 5V. I guess I need some charge pump to take USB 5V and make it say 10V for one of these chips that does 5V?
LM7805 has a minimum load 5 mA, that may be a problem for charge pump. Why not use an internal reference? Resistors divider costs less than good reference chip
What about a combination of a voltage stabilizing chip (such as a 7805) to power the sensors and using the ADC to measure that supply voltage as well as the sensor outputs. That would allow you to make some software adjustments relative to the measured sensor supply voltage.
In this suggestion I don't mean that you use the 7805 output as the Arduino voltage reference - just use its normal reference. Fluctuations in the Arduino's natural 5v reference would be dealt with by software.
I haven't tried this.
Or just scale things down and use the Arduino's internal 1.1v voltage reference?
Robin2:
What about a combination of a voltage stabilizing chip (such as a 7805) to power the sensors and using the ADC to measure that supply voltage as well as the sensor outputs. That would allow you to make some software adjustments relative to the measured sensor supply voltage.
In this suggestion I don't mean that you use the 7805 output as the Arduino voltage reference - just use its normal reference. Fluctuations in the Arduino's natural 5v reference would be dealt with by software.
I haven't tried this.
Or just scale things down and use the Arduino's internal 1.1v voltage reference?
...R
@Robin2 thats not a bad idea, except that you would need to drop the voltage to the ADC because your normal reference will be the supply voltage anyways. So you adc will always measure 100%. So you could use a resistor divider infront of the ADC and compare that to the to 1.1v internal reference... better idea I think.
