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The LM2917 will convert your RPM frequency to a voltage too. You can then use something like a comparator to turn things on and off at a certain voltage.
I took a look at the LM2917 (
https://www.ti.com/product/lm2917-n) and have a couple questions. Looks like more than I would need for the circuit, but then again, I am now seeing some advantages to this.
"The LM2907, LM2917 series are monolithic frequency to voltage converters with a high gain op amp/comparator designed to operate a relay, lamp, or other load when the input frequency reaches or exceeds a selected rate. "
I am going to assume that the extra terminals are so I can design and incorporate circuits to determine the frequency and other variables at which to operate a switch. Is this a fair assumption?
Anyway, added to a board and enclosed in a case, the module would still only need four wires to operate. Tach signal (2 wires) and the bleed off (for lack of proper term). The high ohm resistor to drop voltage slightly. After I do another comprehensive dyno run and get more accurate O2 readings accross all RPMS, I can then narrow down the specifics.
I do not wish to produce voltage, or add voltage to the lambda output at this time. I have a lean condition, which the computer will identify as a higher voltage from the O2 sensor, so dropping the voltage using a resister in parallel will do the job.
So my next question is, what electronic gadgets, microwaves, vcr tv or other might I find the LM2917 in? Also as long as I am looking, are there any chips anybody else might be interested in while I am scrapping?
Dave