I'm looking to replace a fuel sending unit in a old Jeep that has a range of 20ohms (full) to 220ohms (empty) because I've converted it to electric. I have a battery management system that gets me % battery SoC (state of charge). With the Arduino, I've successfully read that % via a CANBUS board and now want to send it to a digital potentiometer. It's not as simple as sending it 20ohms-220ohms as most digital pots are 10k ohms and don't have that level of resolution.
Anyone have any ideas on how I can get to that range of resistance? Thanks!
Vary the current, as appropriate, instead.
If the gauge is an electro-mechanical meter movement it's current operated and you should be able to use PWM (analogWrite() ) through a transistor or MOSFET driver.
There may be a parallel resistor or other simple resistor network, and it that's external and accessible I'd start by removing that. Then apply a variable voltage to see what the meter requires.
You can get a 220 pot from Mouser, get a 20 ohm resistor as well and place that in series, you will wind with 20 to 240 ohms.
Thanks for the pointer, I will check this out. So the Arduino is 5V and the Jeep's system is 12v, I think I need to do more reading as I'm not too familiar with PWM.
Great idea, and get some LEDs and play with it, it will make sense in a short time.
What year/model Jeep is it? Do you know if the gauge is the bimetallic strip type or the magnetic type?