Hi guys,
I had a quick question on floating pins. I know it needs a pull up resistor to prevent the floating, but I'm not sure what value I need. I will be measuring >5V on A0 from a solar panel (approx 3.5V). Because the panel will be at 0 volts at night, or may be disconnected, the pin may float. What value would be appropriate, and will that resistor interfere with a true reading? i.e. it needs to be adjusted for in the calculation.
Thanks!
Being at 0V and being disconnected are very different things. Do you expect both to happen at some time ?
I hope that you don't mean that more than 5V will be applied to pin A0. How are you intending to measure the higher voltage ?
Yes, it is possible for it to be disconnected with the chip running, so it must report 0 instead of float, and sorry yes less than 5V (3.5v Max). I'd be using a voltage divider otherwise.
Most common a resistor of 10K will do, but choosing a 22K or 47K is also possible.
Disclaimer:
I know nothing about solar panels and my electronics knowledge is rusty.
The theory is that the output resistance of your solar panel is part of voltage divider; the other part is the input resistance of your Arduino.
For voltage sources like power supplies (and I assume your solar panel), the output resitance is low (can't give you a practical value). If it isn't, drawing current will result in a significant drop in output voltage on it's output.
For the analog input, the input impedance is (relatively) high, else it would affect what your measurement.
From your perspective, the pull-up (or pull-down) resistor will be part of the input resistance and you can calculate based on that. If the output resistance is 1 Ohm (no idea of actual values), a 100 Ohm resistor will result in approx. 1% error, a 10k will result in a 0.01% error in measurement.
What is it ?
>5V (greater than)
Or
≈ 3.5V
10k on an analog input to GND is about the best value to use.
≈ 3.5V MAX
Typical voltage will read from 0-3.5V
I have put a 10K on ground and get a straight zero reading when nothing is connected (desired). When I connect a battery for testing, I get a 5V reading? (Even though battery is 1.5V).
My code:
float measurePnl() {
float vin = (analogRead(pnlPin) * 5.0 / 1023); //Not using a divider here so it's straight math
return vin;
}
There is a 10K resistor between the input and ground, with the input going straight to the pin (picture attached).
So I am unsure what I am doing wrong.
Are you using the 1.1V internal analog reference perhaps?
Yes. Thank you for mentioning that.
Once I removed that line it is reading correctly.
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