Where are the N2O electronics experts? Need help.

[TT5.9mag]

TT,
The cct in post #15 I used with a HEI module to power the factory tach in my GTO. To contain the components: I used a small plastic medicine [ pill ] bottle. Drilled two holes in the side about 1/2" apart. Passed a tie wrap through the holes, to tie the bottle around the wiring harness [ or similar ] under the dash. Four wires to connect. I tied a knot in each wire close to where the connected in the cct; they act as anchors. After soldering the connections, I pushed the parts inside the bottle, making sure wires were not touching. Knots weere also inside the bottle. I pumped the bottle full of neutral cure silicon & left for a few days to cure.

Thanks. Do you know what kind of signal you were after to make the tach work?

 

[tjpatte]

Nothing is loomed. Not even zip tied. It’s all loose. This is not an interference problem. This is a signal problem from what I understand. The hei produces an odd tach signal some digital tachs can’t interpret it. The filter I built has worked for a bunch of guys for analog style original tachs in older chevys. I thought maybe it would work on the window switch. I actually think with a few different value resistors I could come up with something but I’m running out time. The link below has info on the type of signal generated by the hei.

Info I've found about the HEI Tach signal

Interesting how the tach signal jumps around unfiltered on the O’scope.

 

[Bewy]

TT.
Answer is no. The cct came from a fellow called Peter Serio about 20 yrs ago, in the US. He specialised dash/instrument refurbishing. Do not know if he is still around.

 

[MadScientistMat]

Looks like the filter is a little too aggressive. Try dropping the value of the 0.15 mF capacitor to somewhere between 0.02 and 0.03 for a cut-off about 5 times higher or a little more.

 

[Newbomb Turk]

Interesting thread. Is the general assumption this is some kind of electrical noise issue?

 

[Big.J.007]

Sounds like the problem lies in the HEI system..

 

[TT5.9mag]

Looks like the filter is a little too aggressive. Try dropping the value of the 0.15 mF capacitor to somewhere between 0.02 and 0.03 for a cut-off about 5 times higher or a little more.

I’m going to try a few things but after this weekend. I’m out of time to order stuff and have it in time. For Saturday I’m just going to use the window switch as a WOT switch and send it. Thank you for the suggestions.

 

[TT5.9mag]

Interesting thread. Is the general assumption this is some kind of electrical noise issue?

It’s not noise. It’s a signal problem. The window switch wants a common 12v square wave and the hei produces some weird random ac digital partially square wave or something.

 

[Newbomb Turk]

It’s not noise. It’s a signal problem. The window switch wants a common 12v square wave and the hei produces some weird random ac digital partially square wave or something.

Yeah, now that you mention that Tuner and I have talked about that a bit. Let me ask him about this. He may have a simple fix. After this weekend so you can get some hits in.

 

[TT5.9mag]

Yeah, now that you mention that Tuner and I have talked about that a bit. Let me ask him about this. He may have a simple fix. After this weekend so you can get some hits in.

Please do ask him. And if necessary, reference the link I posted above in #25. The first post in that thread describes the type of signal we’re dealing with.

 

[TT5.9mag]

Currently I’m researching other ways of generating a 12v square wave tach signal. The two options below have peaked my interest.

MSD 8913 Distributorless Tach Driver
MSD 8918 MSD Tach Signal GMR Pickup

 

[MadScientistMat]

The AXM-110 also does a square wave tach signal.

Another way to get a square wave is to use a 7 pin HEI. Don't connect the "B" or "E" pins and get the tach signal from the "R" pin. This is a clean square wave.

 

[TT5.9mag]

The AXM-110 also does a square wave tach signal.

Another way to get a square wave is to use a 7 pin HEI. Don't connect the "B" or "E" pins and get the tach signal from the "R" pin. This is a clean square wave.

How is the AMX-110 powered? There is no published instruction sheet. Does it generate a 12v square wave tach signal from current sensing on the positive side of the coil?

 

[TT5.9mag]

Another way to get a square wave is to use a 7 pin HEI. Don't connect the "B" or "E" pins and get the tach signal from the "R" pin. This is a clean square wave.

That’s interesting I’ll look at them. Thanks.

 

[TT5.9mag]

Pin R on a 7 pin module is a clean 5 volt square wave. I am not sure that would work.

 

[MadScientistMat]

It's going to depend on the window switch's trigger circuit. There are a few simple ways to step it up to 12v if needed.