modulating switches with an RPM signal

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Thread Starter


Joined Apr 8, 2010
I am working on a car project, and I may need to build a little hack to make a transplant engine behave correctly. Unfortunately, I don't know much about circuits, yet! :confused:

The circuit will need to read the engine RPMs and based on that, operate a couple of switches. Problem is they don't just open at particular RPMs - they close at certain other RPMs too. So how could I build a circuit to operate them? The RPM signal is a variable voltage.

There are three states besides the 'rest' state. I wrote some peseudocode for how it should behave:

switch a = default state CLOSED
switch b = default state OPEN

idle - a closed, b open (no action required)
<3400 - a closed, b closed (b operates)
<4100 - a open, b closed (both operate)
>4100 - a open, b open (a operates)

if((rpm>1200) & (rpm<3400)){
switch b

else if((rpm>3400) & (rpm<4100)){
switch a
switch b
else if(rpm>4100){
switch a

Can anyone help me get on the right track with building this please? I don't need an exact diagram or anything, just an idea of which components can be used to do what. Thanks.


Joined Apr 20, 2004
With the plethora of state and federal regulations in existence, we are not able to assist with changes to car lighting or ECU modifications. Too many safety issues and regulations come up. We can't control the quality of the circuitry, or that it has the ability to fail safe.
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