Tacho Booster !

[camrygt?]

If the tacho needs and inductive type signal just hook it up to the coil wire after the igniter, does the same thing as the relay circuit above.
Also works for multi coils and aftermarket setups like microtechs just join the signal wire to each coil together through a ordinary recifier diode (about 20 cents for 4 or something) then join to tacho signal wire.
The diodes will allow the signal from each wire to pass throught to the tacho but won't allow the signals to coils to interfere with each other.
The stripe on the diode goes to the coil wire.
also works for all you 1J into MX83 people don't need a tacho booster just 6 diodes from the coil outputs of ignitor to tacho

[ViPeR_NiPPleX]

Maybe i haven't looked long enough, but is there a reason why ur using the coil out of a relay? I'm assuming it is more to do with the internal resistance giving a nice current limit with 12 volts across it as opposed to any advantage(?) of it's inductance.

Without testing it i would've guessed at a circuit with the input running through a 2k(ish) ohm resistor into the base of a common NPN BJT (BC337,546 etc) and a small (2k-ish ohm) resistor from 12v down to the collector and the emitter to ground. Take the output from the collector.

why use the coil instead of a resistor???

i was wondering the same thing...

[camrygt?]

Maybe i haven't looked long enough, but is there a reason why ur using the coil out of a relay? I'm assuming it is more to do with the internal resistance giving a nice current limit with 12 volts across it as opposed to any advantage(?) of it's inductance.

Without testing it i would've guessed at a circuit with the input running through a 2k(ish) ohm resistor into the base of a common NPN BJT (BC337,546 etc) and a small (2k-ish ohm) resistor from 12v down to the collector and the emitter to ground. Take the output from the collector.

why use the coil instead of a resistor???

the coil creates large voltage spikes when switched on and off in the same way as an ignition coil does. Some tachos need these large spikes to register a signal as they were designed to be connected directly to a coil

[timbosaurus]

Gotcha, makes perfect sense. Thought this was just a 5-12v level translator, but aparently it needs the flyback as well!

cheers
Tim.

[timbosaurus]

The stripe on the diode goes to the coil wire.

ummm... just thinking maybe it should be the other way around? you dont want current flowing back to any of the coils.

[camrygt?]

ummm... just thinking maybe it should be the other way around? you dont want current flowing back to any of the coils.

yeah but the pulses to the coils from the ignitor are negative (ground pulses) so having the stripe facing the wire from the coil will let a negative signal go to the tacho but not to a different coil. It works done it many times

[timbosaurus]

good point... i obviously didn't think about it

[itchybum1]

Thanks for the input guys . Problem solved !

[Ribfeast]

I made that circuit off the diagram on the first page for a mate, works fine in his 1JZ cressy.
I think I used a different transistor, have to check when I get home but I think it was a BD681. You can't use a regular super compact inductor instead of the coil, you need something with a decent amount of size, so that gutted relay coil works like a treat.

[Hen]

Only reason I suggested a gutted relay is that it is an easy solution to get a reasonable sized inductor. Basically anything within reason should do though.

A diagram for the other circuit being discussed is:


I've lnstalled it and seen it work perfectly in an AE86 running 4AGZE with twin coils. Of course for a 7M you'll need 3 diodes for the 3 coils. I think it works slightly better than the other circuit. Less sluggish.

Hen

PS, thanks for the acknowledgement wilbo

[mumblezzz]

Sorry to drag this thread up but I've tried making a cuircuit diagram like on the first page to get my MX83 tacho working with the 1jz conversion. All i've succeded in doing is making the "O/D off" turn on. I beleive I connected the signal to the black wire on this plug.



Is this right or am I barking up the wrong tree?

[kuchie]

I Fitted a 7M-GTE to a MS112 (82) crown and to make the tacho work i uplled out the tacho and reduced the value of the resistor connected to the tacho signal input. has worked 100% for the past 5 months


Cant find a pic of it though !! thought it was on my website.

[Grant]

I haven't read all the preceeding posts so this may of already been mentioned but the diagram above will only work for a 12 volt tacho not a Cressida tacho or any other that requires a voltage spike to operate.

[Hen]

... the diagram above will only work for a 12 volt tacho not a Cressida tacho or any other that requires a voltage spike to operate.

No, the whole point of the first circuit is to manufacture a voltage spike from a 5V or 12V square wave (hence the inductor).

The second one just adapts twin coils to a single coil dash.

Hen

[rokusan]

my turn to drag up this old thread now!

How do i get my factory tacho (SA63) to work off a signal wire from my aftermarket ECU?
is it the same senario as the first problem requiring diodes and the like??????????
PS i am eletrically iliterate...speek sloli...