Tacho tech

[sideshow]

i have had some autometer tachos needing signal boosters
so i go afew especially for these

most toyota ecus dont have tacho signal outputs unless they are diesels

most toyotas have ig- on ignitor

i have never had any tacho probs with mr2s
except for a microtech with m and w ignitor i had to use an autronic tacho booster
these arernt cheap thou i do have a dmamaged one in my car so ill pull it apart and see how they made it

[Cuzzo]

Who wants to make me one of those signal converters for me? Ill give ya $20 plus parts and postage.

[sideshow]

20 bucks

i dont get out of bed for less than 100 bucks ehehehe

[Mos]

I would like to add that when I was playing with the tacho on the 1JZ, it had a +12V square wave output, not +5V...

It is 12V indeed, as is the 2JZ one (and probably a bunch of others). Each pulse is also approximately 1mS in duration.

Not sure what the IS200 has, but it's a signal generated by the engine ECU as it has individual coils with integrated ignitors.

Who wants to make me one of those signal converters for me? Ill give ya $20 plus parts and postage.

You can make the example given by Hen yourself More sophisticated units (better signal conditioning and output pulse shaping) are time consuming to assemble (I wouldn't make one for less than $100 either ).

Something I cant understand about the "add ur own potentiometer" article (although i didn't have a good read) is how putting one across the incoming square wave signal can adjust the reading? A pot does sweet FA to the frequency of a signal... only affecting the voltage and maybe the speed of the edges.

So the tach doesn't actually count the frequency, instead it converts it to a DC equivalent. So the added pot just scales this DC equivalent.

Sounds weird... i thought he said it connects between the two inputs on the tach. would seem odd to have an analog signal into the tach in these digital days

The older tachos (like the ones in the images, IE AE86, AE82, G/MA70, etc) have one winding on the coil of the needle which the article suggests putting the pot across - not the input to the circuit. This coil responds to the effective or resultant average voltage applied to it. Applying a short spike of a certain voltage will result in a low average voltage. A longer spike will give a higher average voltage. The driver circuit takes the frequency of the incoming signal and applies it to the coil of the needle, while also varying the width of the pulses. So two things are being changed - the frequency of the pulses, and the width of each pulse - to affect the needle position.
If you add a pot or other resistance in parallel with the coil, the resulting voltage will be lower as the resistor will draw some of the power available from the driving circuit (in theory - not measured or tried).

Newer tachos (and I think all electronic speedos) use a 4 winding coil with 4 inputs - sine +, sine -, cosine +, cosine -. The benefit of these is a high degree of linearity along a wide arc - full 360 degree rotation is possible. The pot mod will not work with any degree of accuracy on one of these.
While the driver chip for such a meter might be operating digitally, the required signals on the 4 inputs are analogue. (If you want more info on how these work search for "differential air core meter driver" in google and read the background theory of the application notes for the various chips).

Mos.

[sideshow]

i sell boosters startin from 40 bucks to 150 for autronic ones

[User Name]

well done. very interesting read

[Vios-GT_07]

i sell boosters startin from 40 bucks to 150 for autronic ones

you have PM

[TheStitt]

Just a quick opne here

I just bought a speco tacho and it will read upto about 700rpm however will not rev past.

with the inbuilt shift light set low the shift light goes off but the needle won't go above the 700rpm mark

do I need a booster

running the signal from the diagnositcs box,

engine is 7MGTE

[sideshow]

maybe its trial and error

[TheStitt]

nah a calibrated tap solved the problem

[LiTTLe_DRaGoN_HuNTeR]

Excellent guide Hen!

So has anyone tried modifying their AE86 cluster following the guide?

Where abouts is the tacho drive located? Behind the cluster?

[sideshow]

i use my tacho boosters when fititng 20v or gze into an ae86 they work all the time n ae86 tachos

[aw11man]

very good, this info should sort out my cousins aw11 with /beams, the tacho jumps around eratically, so it looks like the beams ecu is putting out a square wave form and the old tacho is expecting voltge spikes from the old 4age dizzy.

Love learning stuff like this that i didnt know before! plus rep+

In addition to this my tacho works better with more electrical load such as lights, heater, wipers and while using electric windows the tacho reads perfectly right up to 7400 rpm's.

[willwal98]

I've got a gen3 1g-gte with a VDO tacho and it seems to read fine up until 4000rpm or so then won't go any higher. I have tried running it off both the signal wires on the coil (I believe there is something strange in there on a 1g, 2 ranges or something). One of them goes a little higher but then goes backwards. I have also made a signal booster which did SFA. Don't spose anyone could shed some light on this for me because I would really like a working tacho and don't really have the spare funds at the mo to pay someone to fix it.

[brett_celicacoupe]

there is a thin black wire coming from the engine thats in one of the plugs that dont connect to the ECU. get a multimeter and put it in resistance mode (beep mode) and put one probe in the "IG-" port in the diag box.....then just test everypin corresponding to a thin black wire on the loom (in the cabin).