I am looking for a way to create a variable resistance signal to mimic the signal that would typically be provided by a thermistor, but by using a digital signal that switches to ground.
I currently have an older car that for the coolant temperature on the cluster gauge is usually run with a thermistor on the engine. I have upgraded the engine management (ECU) and am trying to duplicate that signal but the ECU only has digital outputs that switch to ground (DPO). I can change the duty cycle OR frequency of this DPO.
Other important details: -the gauge cluster puts out a constant voltage (still need to verify how much but it's either 5v or 12v), the single wire would typically be grounded by the now removed thermistor sensor -the DPO can only change the frequency or the duty cycle but the other needs to be fixed. In the ECU I can create a table of frequency/duty cycle vs temperature (reading from a new/different type of sensor) -the frequency range available for the DPO is from 0-1200Hz -the resistance range for the thermistor being replaced is roughly 10 Ohms-350 Ohms
I've had someone mention a capacitor being used somehow for this but my circuits knowledge stops shortly after Ohms law and vehicle wiring diagrams lol
Any help that could be provided would be great, even better if it's easily digestible!
If further info is needed let me know too