I have a question regarding analog reference. I have used the search function but cannot seem to find what I'm looking for.
Can analog reference be used to reference voltages over 5 volts?
I am trying to use the arduino to display gear position on a 7 segment display. A resistance sensor is located on the shift barrel of the engine. I am using a voltage divider to bring the voltage down from ~14v to a range from 4 to 9 volts. I want the arduino to read the voltage and based on the value update the display.
I currently am using deumilanove but would like to use a pro mini when on the car.
Any help on how to implement this would be greatly appreciated.
Yes, you could use an attenuator or voltage divider circuit. This sort of thing is commonly used to monitor battery voltages when you're using, say, a 12V battery.
Yes, the whole plan was to base analog voltage into the arduino on a voltage divider consisting of a known value resistor in series with the gear position sensor (Which is basically a "puck" with six different pads of varying resistance that connect to ground through the engine).I used the voltage divider in an attempt to lower the voltage to a range between 0 and 5 volts, but must not have used the correct value resistor because the values I get range from 3.5 to 9 volts. :-[
This is being used on a Formula SAE car (www.auracing.org) and I have already routed my "high" analog voltage into the main harness. Rather than hacking up the harness to add another value resistor in the divider I was trying to reference analog voltage to the cars electrical system which varies from 12 volts at idle to 14.4 volts when running.
From what it looks like I will have to use a 5 volt regulator and then base a divider off of that. Correct?
If you put a single resistor in series with the 12V signal, that's not a voltage divider. You must have two resistors, one in series and the other from the input pin to Ground, as shown in the circuit diagram on that Wikipedia page.
What value resistor(s) did you use?
But if you have multiple resistors that you need to sense from an Arduino analog input, then you may be better off with a 5V regulator. What are the values of the resistors in the "puck"?
The voltage divider I used is working, it is just not bringing the voltage down enough though. This is probably due to the fact that I calculated the fixed resistance incorrectly. I believe it was a 100k resistor that was used, which I thought would bring the value down from the electrical systems 12v to the 0-5v range (paired with the resistances in the sensor). This has proved to be flawed because I didn't take into account the changing voltage of the electrical system due to the alternator which generates around 14.4v during driving. That is why I was trying to reference the cars voltage so the analogRead values wouldn't change so much with varying engine rpms/electrical loads.
@Anachrocomputer : I agree with your suggestion to use a 5v regulated source. That way I know I can use analogRead and get a stable voltage source. As for resistance values of the gear position sensor, I do not have them with me right now but I have them written down somewhere.