[RLe]

Hello!

How can i get aftermarket analog tacho working from speeduino tacho output? Or can i get it to work some other way?

My board is 0.4.3d and coil is VAG wastedspark coil 032 905 106.

I’m not electrical engineer and this is going to my race car, so keep it simple

[Jason Green]

Yes just about all aftermarket tacho's have a switch to select your pattern select which ever matches your setup and you can either using a transistor or uln chip to send 12v pulses.

Had quick look for a write up on this forum but didnt find it see below link.
https://speedyefi.com/ulns-and-pullups- ... nch-oh-my/

[Jason Green]

Sorry just noticed you have a 0.4.3d you will already have the ULN built onto the board so this is very straight forward. simple connect and setup in TS.

[RLe]

Ok thanks for your reply. Perhaps my problem is that my tacho is some relic from Kleopatras tomb I might need a bit more modern tacho..

[PSIG]

@RLe - there are several different triggering systems for tachometers, and Speeduino can drive most of them one way or another. The most common is the older "flyback" type, that connects to the coil(-) terminal for signal. If that is your type, the ULN is not a good source as it has internal flyback diodes that kill the flyback spike used to trigger those tachs. If it is a newer 5V or 12V logic signal tach, then the ULN will work. There are other types.

Please verify what signal type your tachometer needs, or how it was previously wired, for specific instructions.

[Jason Green]

@RLe - there are several different triggering systems for tachometers, and Speeduino can drive most of them one way or another. The most common is the older "flyback" type, that connects to the coil(-) terminal for signal. If that is your type, the ULN is not a good source as it has internal flyback diodes that kill the flyback spike used to trigger those tachs. If it is a newer 5V or 12V logic signal tach, then the ULN will work. There are other types.

Please verify what signal type your tachometer needs, or how it was previously wired, for specific instructions.

Fair point I didn't even consider it could be the flyback style trigger.

[RLe]

It is old flyback tacho. I think i have to buy tacho that connects straight to speeduino connector, because it would be much more simple installation.

[PSIG]

Your "easy" options at this point could be:

• A small signal wire from the 106B coil (-) (between the driver module and coil in the bracket) to the tach.
• An adapter flyback circuit (similar to commercial tach adapters).
• A new tach that is logic-signal type.

I have done the first option to get a car on the track with a working tach, using a 22AWG wire soldered to the coil terminal. Note here that unless it was originally wasted-spark, you may need a couple diodes to join signals to get proper rpm reading. No big deal and its a hack, but you likely have what you need on-hand and a quick way to get it going for now, and functions like the original tach wiring.

The adapter circuit is a simple inductor (relay coil, old injector, whatever) triggered by a high-voltage transistor. Speeduino triggers the transistor, which drives the inductor just like an ignition coil, creating the flyback voltage pulse the tach needs. Search the forums for tach adapter threads. Easy and functions well.

Of course the new tach idea has it's own costs and merits for you to judge. Have fun, and let us know what you settle-on.

Example flyback generator circuit made from any handy inductor. I've used micro automotive relays to make several, with the transistor tucked inside:

Flyback_tachometer_signal_adapter_circuit.png (64.41 KiB) Viewed 6597 times

[RLe]

Hi! Tachometer is now connected with the adapter circuit. Works great. Thanks!

[crazybenn]

HI,,,i'm new here. I understand the relay coil "stabilize" the sig output from the ECU.... if i want a smaller device, what can i use instead of the relay coil?