Electronic tach issues still with dyna S SOLVED

The filer I made was a simple PNP transistor that was meant to transfer a square wave signal to your tach. Every time the ignition unit grounds the coil, a small pulse of 12V power would be sent to the tach.

At least that was the idea. I'm thinking that maybe the EMI from the coils proved a bit too much for the cheap transistor I chose. Something a bit more hardened (or otherwise protected from EMF) would do the trick.
 
Ok! I have a final solution for this. It's so simple I kicked myself in the ass for not seeing it sooner. Guaranteed to work, nice steady stable needle.

Set tach to p6, high input

Patch tach signal wire into one of the hot legs out of the stator (yellow wires going into rectifier)

Done.

How it works: there are 3 coils aranged in a 6 pointed star in the stator. Each coil gets passed once by each pole of the rotor and generates a pulse of AC current. 3 coils x 2 poles (North and South) = tach signal!

Hope this helps.
 
Any one you like. I disconnected the box junction going into the rectifier, bent the tab and pulled out one of the yellows from the connector and just soldered into where the other wire is crimped onto the spade, slip it back in and bend out the tab. Also make sure your gauge is grounded directly to the battery.
 
Enjoy! I originally joined this forum looking for the answer to this issue. Hope others can benefit from the year I've spent working on it.....well not the entire year every day but you know....
 
Sorry to bump this one guys, but this is a great conversation. I'm having this same issue with my Trail Tech Vapor to the point that the tachometer is completely useless. Working with their tech support I've tried wrapping the wire with different numbers of wraps, directly connecting to the negative of the coil signal, different inline resistor values, separate power supply for the Trail Tech...nothing works. It's actually to the point where I can completely disconnect the tach signal wire and the tach continues to bounce around (must be a lot of noise).

I decided to get back to working on building a simple tachometer using an Arduino, so I busted out the scope on the coil / Dyna S. But then I realized I might as well try and get this damn Trail Tech working first.

These aren't the best snaps of what is going on, but it helps...

IMAGE002_zpsgnyd4ajm.png


IMAGE005_zpsgyv1axb2.png


Basically, the negative connection on the primary coil sees about 1v while the coil are powered up (this is with 3 ohm coils, so I'm assuming closer to .6v with 5 ohm coils using a basic voltage divider calculator). When the Dyna S cuts off the ground path to fire the coil, the voltage spikes to 50v+. As the voltage sharply drops back down, there is a little curve around 10v where it looks like it will stabilize the voltage, spikes back up slightly, then it sharply drops again. This drop will sometimes go into a negative voltage, then it will rise back to 1v.

However, I did randomly pick up about a 3v spike that I assume occurs when the other coil fires. I only picked this up on the scope once, so I'm not sure of the magnitude, and I assume it entirely depends on the location of the scope probe.

So, what would be the best circuit to turn this signal into more of a square wave for the Trail Tech to pick up on? I'm basically an idiot when it comes to zener diodes, phototransistors, etc. I'm thinking if a voltage can be sent to the Trail Tech if coil voltage is above 5v, otherwise ground, that might work.
 
Get an LM7805 voltage regulator and hook up the input to 12V. Ground from the 7805 goes to a 1N4004 rectifier diode spliced into the ground side of the coil. Output from the 7805 should be a square wave 5V.
 
Sonreir said:
Get an LM7805 voltage regulator and hook up the input to 12V. Ground from the 7805 goes to a 1N4004 rectifier diode spliced into the ground side of the coil. Output from the 7805 should be a square wave 5V.
Click to expand...

Interesting, but I'm wondering how fast the 7805 is able to switch on and off.

I'm looking at a Schmitt trigger as an option, and it's really sad how I can't wrap my head around basic electrical circuits.
 
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