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Topic: Car engine sensors ? (Read 490 times) previous topic - next topic

flak88

Hi I have a project going im currently using an atmega 644 to monitor a fuel injector and the vehicle speed sensor to calculate mpg by using mpguino which is open source.Im planning on modifying the source code and circuit so that I can monitor and log data from various engine sensors by reading their dc signal voltage by adc. My current circuit  design is to connect each sensor output to the input of its own opamp which is set up as a buffer and is powered by a 5v dc single rail supply.The output of each opamp then goes to its respective adc pin on the atmega where it is then read at intervals.The goal is to isolate as much as possible the link between the engine sensor outputs and anything to do with the atmega circuit.

What ways could I protect against the potential of the opamp failing and there being a short between the input of the opamp and its power supply terminals 5v dc and ov ?

The following sensors are below:

Engine coolant sensor (thermistor)
Powered by 5v dc supply
12kohm @ 20 degrees c to 0.4kohm @ 80 degrees c

Throttle position sensor
Powered by 5v dc supply
0.5v dc throttle fully closed
4.5v dc throttle fully open

Map(manifold absolute pressure)
Powered by 5v dc supply
0.5v dc @ 625mmHg to 3.0v dc @ 0 mmHg

O2 sensor on exhaust(1 wire)
0.1v dc high oxygen (lean)
to
0.9v dc low oxygen (rich)


Will my planned  approach work ? if not what do you suggest ?

Thanks



MarkT

Because vehicles can be very electrically noisy it might be worth using
analog differential signally - opamp generates signal and its complement,
twisted pair to a 120 ohm load (and low-pass filter?) at the microcontroller,
read differentially (either two ADC pins or an opamp differential amplifier to
return to single-ended version of the signal).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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