How to build your own tacho adaptor

[ed]

never mind, enjoy the rep - about time this was spelt out simply and easily as you have done.

saves some sucker, what, $140....

[ViPeR_NiPPleX]

indeed, thanks to everyone for the rep, much appreciated

after hearing the noise those MSD things make, I thought it was time.

[Negative Boost]

Make, thats terrific! Top stuff even if the pictures are blurry . Adding to my Parts number and watsicallit thread.

[brett_celicacoupe]

could this be used in reverse? Such as old motor new tacho?

this works in theory. would need a 5-6V voltage regulator and a 741 op amp. wouldnt be too expensive to make

[kanazai2001]

my car ECU produce square wave tacho signal but im having an old ST183 meter cluster...
its tacho has 3 connection points...
anyone can tell me which points is Vcc, GND and tacho signal?
how to adapt this gadget to work with my old meter cluster?
i wouldnt like to cut my ecu connector's wires...

[kanazai2001]

thanks mate

[ZZT231]

Great write up James... Glad to see you making it smaller!

[brett_celicacoupe]

Most of you wont have an oscilloscope at home so testing your new adaptor will have to be on the car. I've tested the design on an MA61 with a 7mgte and another MA61 with a 1jz-gte, both work as if you were looking at a normal tacho.

what does the voltage spike to?

[wilbo666]

what does the voltage spike to?

In car I measured over 200V...(edit: stock coil system i.e. 5M-E)...

Cheers
Wilbo

[brett_celicacoupe]

it might be sensible to put a flyback diode and resistor then.....

my cheap electronic sim program is reading a >500V spike



now, with a diode in there;

like so



dodgey circuit program 101 response;
more like a 50V spike - so maybe more like 20 in real life.




maybe someone could experiment, someone with their dash already pulled apart. my tacho is rather limp sometimes.

[wilbo666]

Brett, you are missing the point, the back emf spike is what drives the old style tacho systems...

If it ain't broke (and it isn't ) why add more compoents to it?

Cheers
Wilbo

[The Witzl]

Brett, you are missing the point, the back emf spike is what drives the old style tacho systems...

If it ain't broke (and it isn't ) why add more compoents to it?

Cheers
Wilbo

+ rep for being gun.... and a nerd.

[brett_celicacoupe]

If it ain't broke (and it isn't ) why add more compoents to it?

because mine is broke.... its limp

[Mos]

The factory high voltage spike is around 40V peak (at least in an MX83).

I use a zener on my units to clamp the spike to something more sensible. You can also use a capacitor to reduce the height and increase the width of the spike.

Mos.

[Supra6]

Most of you wont have an oscilloscope at home so testing your new adaptor will have to be on the car. I've tested the design on an MA61 with a 7mgte and another MA61 with a 1jz-gte, both work as if you were looking at a normal tacho. I've got a diagram which is handy for those of you who had a 5m-e and have now swapped something else in... other toyotas might have this plug too.



Well that's enough from me. Hopefully this guide will be useful to someone out there. Any questions or problems feel free to ask.

Cheers,
James

Hey
I've made one of those adaptors cos my 7ma61 tacho doesnt light up. But when i went to install it last night i wasnt sure where to plug/solder it in! Where do i find the said wires/plug? Photos or a description would be sweet
CHEERS