OP-amp help

[HomerDodd]

Agree. Not enough info yet.

Your comparator idea might work in any case if it is basically the frequency that matters, which seems likely.

Bob

The signal from the sensor is AC, and must be at least 5 VAC strong to the PCM, or the code will be set and the light comes on.

 

[HomerDodd]

Again, my goal is fairly simple. I want to "fool" the computer into thinking the sensor is healthy and sending a 5VAC signal or more. What ever can accomplish this for just a few hours to get the car to pass smog (the visual test includes the "Check engine" light off). An inline amplifier or comparator is fine, whatever works simplest.

 

[kellys_eye]

I think you misunderstand the true meaning of 'AC' - the signal is actually DC with an AC component. Irrespective of this either the op-amp or comparator circuits will do as you require.

Personally I'd go for the comparator solution. Can you measure the voltage at points 'V' and 'S' with respect to ground?

As I suggested above, the 'V' signal is kilely to be a fixed DC voltage (12V or 5V) and 'S' will be the variable frequency squarewave output. In theory it will switch between the supply and zero but if your problem stems from it not switching 'far enough' then the comparator circuit will resolve that issue.

 

[HomerDodd]

I think you misunderstand the true meaning of 'AC' - the signal is actually DC with an AC component. Irrespective of this either the op-amp or comparator circuits will do as you require.

Personally I'd go for the comparator solution. Can you measure the voltage at points 'V' and 'S' with respect to ground?

As I suggested above, the 'V' signal is kilely to be a fixed DC voltage (12V or 5V) and 'S' will be the variable frequency squarewave output. In theory it will switch between the supply and zero but if your problem stems from it not switching 'far enough' then the comparator circuit will resolve that issue.

As long as I can send 1 or 2 VAC into the comparator, and get 5 or more VAC out. You think I can simply snip the signal wire and insert the circuit inline? Since the power is coming from the car then, would the circuits ground be on the vehicles ground? I really appreciate all of your help on this. I really like my car and need the light off to clear smog and be on my way. Thanks !!

 

[kellys_eye]

Providing you identify the SIGNAL wire then yes, you cut that wire and send the signal into your comparator circuit and take the output from the comparator back to the free end of the cut wire.

Ground is 'common' to all the circuits and is the chassis of the vehicle too.

 

[HomerDodd]

Providing you identify the SIGNAL wire then yes, you cut that wire and send the signal into your comparator circuit and take the output from the comparator back to the free end of the cut wire.

Ground is 'common' to all the circuits and is the chassis of the vehicle too.

Your help and guidance has been immense. Thank you very much for everything. There are several Radio Shacks and a larger electronic store close by. I will buy everything I need in the next few days. Much appreciated.