k. My project is going fine thanks to resources like members on this site. I have an issue that I'm trying to solve.
My project reads the Car's Air flow meter voltage (0-5V). For some reason, when i connect my device it causes the sensor to read less volts that it actually is seeing. So my car leans out a bit (it is responsible for air/fuel ratio)
I'm wondering what could cause this? Here is a diagram.
I tapped into the sensor wire, in parallel. Not sure why it's causing a 0.3V drop..
Is it an analog signal or a PWM signal? The latter would be greatly affected by the capacitor
behind only 150 ohms of serial resistance. Try changing that resistor to 10k.
If the grounds of the ECU and arduino aren't identical it might be a problem - are you getting
the Arduino's ground reference from the same cable? That ought to be the best approach.
You don't say what the zener is, I would assume 4.7v or something like that. As Mark indicates, 150 ohms is pretty low for what you are doing there - the trick when measuring environment type things like you are is to not affect the existing circuit. In general, you want to use a high impedance input to minimize the effect on the existing circuit. If your measurement circuit requires a low impedance input then you need to buffer the signal, but you want to not affect the existing signal (that is why you see things like multimeters and scopes with specs of megohm input impedances).
True. Both good points. My Resistor 10k R0 was loading the sensor too much. I changed the pulldown to a 150K ohm and it is working fine so far.
I should prob check the ground of the sensor loom and see how diff it is from the chassis, and then if all is good i make a ground off it too and back to the big overall gnd of my circuit?
The 150Ω could be higher, but would that affect the observed voltage by the arduino?
