[ravi547]

Hey all,
I am trying to build a custom ECU for a project in which speeduino is burned into the mega board and potentiometers are used as sensor inputs. I need to build a power unit to power the board and also the potentiometers. Any insights on how to do that would be helpful. Also this is my first speeduino project, so any tips would be really helpful.

[JHolland]

You can copy the Speeduino circuitry from the schematics here:

https://github.com/speeduino/Hardware

Ideally you should change the resistor and capacitor values on the ADC inputs to suit your code, one of the weaknesses of the Speeduino is that those values have never been correct and are they are prone to noise.

[jevgienij]

Ideally you should change the resistor and capacitor values on the ADC inputs to suit your code, one of the weaknesses of the Speeduino is that those values have never been correct and are they are prone to noise.

What are correct resistor and capacitor values?

[JHolland]

That depends on how fast you are sampling the signal, typically a time constant of (1/0.5 * sample rate) is chosen to stay within the Nyquist criteria. So if you are sampling a signal at 100Hz then your time constant would be 1(50) = 20ms. The maximum input resistance for a Mega is around 10k , T = CR so that gives a capacitance of 20ms/10k = 2uF. If you calculate the charge time for the ADC sampling capacitor then 2.2uF works quite well to give a decent resolution with a 20kHz conversion time.