Tach Adaptor Using Relay (Speeduino to 70's Tachometer)
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- Опубліковано 16 жов 2024
- Old tachs that hook up to the negative of the ignition coil typically rely on a flyback voltage spike from the coil's inductive load being interrupted to trigger a tach pulse. By using the coil from a relay and some schematics found on the google, I was able to simulate this effect and hook my Speeduino ECM up to the stock tach.
Thank you work perfect on my megasquirt with oem tach.
People like you realy rely we need in this world. Muchas gracias mi amigo saludos desde guatemala.
Te funcionó?
@@juniormendoza2879 claro que funciona.
@@juancarlosamadomorales196 no sé cómo hacer ese relay así 😭 ya voy a investigar entonces después de tener ese reley, le conectas una masa, el 12v del arranque y la salida de RPM de la ECU. Y la salida del relay va al tacómetro. Es así? Disculpa la molestia 😬
@@juniormendoza2879 si claro sigue el diagrama que pusieron en el video la bobina del relay hace la funcion de la bobina de ignicion te recomiendo que quites el mecanismo de contacto del relay asi no esta sonando el relay cuando abre y cuando cierra .
@@juancarlosamadomorales196 si ya entendí esa parte que es eso de color rojo? Mi única duda gracias por responder
This worked for my Chinese Quad bike, tach gauge wasn’t able to work direct from coil power. This circuit works like a charm.
Thanks alot!!
ARDARSH SINGH Awesome! Glad it helped someone else. I thought it was a really simple, self-contained, and cheap solution so had to share.
I know I’m a bit late for the party, but thanks for posting this! I was trying to figure out what I wanted to drive the tach with on my ‘76 2002. I converted to EFI, and just recently upgraded to a Haltech and crank-trigger ignition. (Almost done with the mechanical/electrical setup)
Once again, a random YT video saves the day! Thanks Ryan!
@Ryan Layne Did you also wire the relay to ground and constant power to the other pins as well? Most writeups online only show 86 and 85 populated.
Thanks for the tip. I have a ULN2803 chip onboard my Speeduino already. I'll now try using an o/p to drive a relay coil. My tachometer is a mid-80s VW Scirocco, so it may also need the flyback signal.
Did it work?
Hi. Unfortunately it didn't for me.
@@061garage
That worked like a charm! Thank you!
used as is for a engine swap from F6A to K6A in my autozam AZ1, works perfectly
That's nice to know about.
I have a tacho that was originally connected to a points ignition, with the negative connected to the coil. I have recently upgraded to HEI and the manufacturer recommended to connect the tacho to coil negative, as before, but my tacho needle is erratic. Will this module possible fix my issue, tia
Unlikely since the purpose of this is to emulate being connected to a coil, but you already have it connected to a coil.
The new HEI module has a tachometer output wire also that can be utilised, would I need to connect the module to this instead? Tia
@@johnnypellegrino4581 Did you switch to a different coil from stock when you installed the hei?
Yes, the new HEI comes with module , coil and distributor. Currently I am using a aftermarket tachometer which is connected to the module tacho output wire and works fine. Same wire connected to my original tacho, the needle is erratic .
@@johnnypellegrino4581 Try using the original coil if you can. If that works then the inductive pulse of the new coil is too different from original and old tach doesn’t like. If that’s the case then my hack might work. Costs very little to try.
I copied this in the exact same way inside a Hella relay housing. I'm getting ignition +, I verified my ground, I can measure 5v coming from the ECU but I'm not getting a 12v signal out of this. I noticed by looking at (google) images some transistors have the collector and emitter reversed, but swapping the tach out and ground on the relay pins didn't change anything either. Does anyone have a suggestion? Could this be because I used an NO relay and I should've used an NC?
If you look up the part num on your transistor you can see the pinout, voltage ratings, etc. Sounds like you may not have used the correct type of transistor. Note that this circuit can be tested without the relay just by checking to see if 5v is turning on and off 12v via the transistor. The coil in the relay is only there to generate a flyback voltage spike.
@@ryan_layne Thanks for your suggestion. Actually, I now started over and grabbed a 5 prong relay that I had lying around and first tested the whole schematic with components connected with alligator clips. It worked! So I soldered it within the relay case and it's all good and working 👌🏻
Hi, where did you weld the left part of the transistor?? The "Red One" for let you undrestand..thanks
Just follow the wiring diagram. Each input/output connects to one of the pins on the outside/bottom of the relay.
did you make any changes to the relay? I mean did you change something internally in the relay did you remove some of the pins? Or did you just install the 1K resistor and 2N5551 inside the relay?
I just took off the little flap that the electromagnet switches and added the resistor and transistor inside the relay. Then snapped the relay cover back on. It's been working great! No issues so far.
@@ryan_layne Thanks!!! : )
Where did you ground the 0v side?
To the nearest available ground wire in the harness.
How can it be tested before installing... I fear of destroying my tach
If your current tach hooks up to the negative terminal on the coil, then you will not destroy your tach. If it does not hook up to the negative terminal on the coil, you probably do not need this circuit at all for your tach to work and simply a pulsed 12v signal is probably enough.
How come you needed to do this? Did you change to multiple coils?
Ashley Sirr Yes, I have multiple coils. Eventually it will be COP.
Very nice! Can you use 2N3904 instead?
I don’t know but I would suspect the lower voltage rating might be cutting it close. The flyback voltage is supposed to spike up to close what that is rated for. They are so cheap, why not try it and see if it blows out?
@@ryan_layne Yes, I think it's a good test. Wouldn't I risk the processor though?
Hmmm... i donn’t think thats very likely. You could add a protection diode between the processor and the transistor to be sure?
@@ryan_layne Yes, perfect, will do that then! Thank you very much for the tips and congratulations for the nice work and video!
@@marioturbo1 did it work?