Hey guys, been a while but glad to be back! I wasn't able to find anything that really answered my question so I made a new thread. Is there any spot on the fuse panel or anywhere else that I could use as sort of a psuedo tach signal? Something like a flat-ish rate voltage drop as rpm increases? I am attempting to make a digital readout for most gauge info using an Arduino microcontroller and it can't properly read the raw signal from the distributor (HEI). If not, is anyone well versed on the microcontroller boards that are on the tach itself? Anyplace there I could find a solid signal? Thanks.

 

You will need to filter the raw tach signal, as it includes the inductive kickback of the coil. Easy to do this.

For a frequency to voltage conversion, see the Nat-Semi LM2917 chip.

RBob.

 

Thanks man, didn't even know that there is already a handy little thing that will basically do all the filtering for me

 

So I've ordered the LM2917N/NOPB chip from TI, which I believe bought out Nat-Semi. It looks like it does the same thing anyways. The one I ordered is the 14-pin version, and it has a TACH+ and TACH- terminal. For a standard HEI distributor like mine, should I just take the TACH- terminal to ground or have it set to some threshold below the max TACH+ terminal voltage? I have attached the product data sheet.

Also, when you mention filtering the raw signal, I made a low-pass filter for the signal within my microcontroller. Is that what you were getting at?

 

Yes, TI bought out Nat-Semi. As for how to hook up the chip to the coil, see figure 21 in the data sheet. Shows exactly what is required. The resistors, diode, & cap is the filter network.

RBob.