# Tachometer wiring to control DC motor?



## Woodsmith (Jun 5, 2008)

I am wondering the same thing with my MR2 conversion.

I'm not at all sure how the tach gets it signal at the moment as the car is riddled with 'processor boxes' with a million and one wires connected to them.

I guess if it was just a pulse then maybe something like this Hall effect sensor might do the trick. It could be mounted to pick up on a small bolt head or something on the motor shaft or flywheel rim or coupler body.
This one will give an active digital output if you needed it.

I have used eight of the smaller of these in the past to build a quadraphonic bass guitar pick up. Very toppy, twangy edge to the sound. Made stage work fun with different bass notes bouncing around the auditorium.


----------



## Stunt Driver (May 14, 2009)

for the start I'll fit whole distributor with pickup coil and ignition module to rear shaft, and put small bulb in place of ignition coil. Seems rather complex, but straight forward


----------



## bblocher (Jul 30, 2008)

Here is what worked for my vehicle (12v pulsed signal using hall effect sensor).
http://s2kev.blogspot.com/2008/08/motor-rpm-sensor.html


----------



## azdeltawye (Dec 30, 2008)

This was covered in another thread awhile back. One of the ideas that jumped out from that discussion was using a wheel mounted ABS sensor. You can find these on ebay for about $20 or so and they are already sealed and hardened for automotive use/abuse. Seems like the perfect sensor for this application to me...


----------



## Stunt Driver (May 14, 2009)

Would this ABS sensor provide sufficient impulses for the solid state tachometer to read?

I'll sure do some experimenting soon, but I wish someone could tell from looking at wiring what to expect


----------



## DIYguy (Sep 18, 2008)

There is a quite a good discussion on my build thread where some folks helped me with the wiring. I used an industrial proximity sensor. This is similar as an ABS sensor, also and inductive prox I believe.

Check out page 19 on here......... 
http://www.diyelectriccar.com/forums/showthread.php/good-ohmn-here-we-go-23492p19.html


----------



## Stunt Driver (May 14, 2009)

Excuse my ignorance - what is used to trigger proximity sensor? Magnet or just metal?
My tach uses 2 imp per rev - if using proximity sensor - i'll make two "triggering" points on shaft, so it would generate 2 imp per rev.


----------



## azdeltawye (Dec 30, 2008)

Stunt Driver said:


> Would this ABS sensor provide sufficient impulses for the solid state tachometer to read?
> 
> ...


It depends on the tachometer. Some tachs require an open collector sensor output while others may need an emitter coupled output. In any case you could use a something like the Dakota Digital universal tachometer signal interface to tailor the ABS sensor output to something which would be compatible with your tach.


----------



## Woodsmith (Jun 5, 2008)

Stunt Driver said:


> Excuse my ignorance - what is used to trigger proximity sensor? Magnet or just metal?
> My tach uses 2 imp per rev - if using proximity sensor - i'll make two "triggering" points on shaft, so it would generate 2 imp per rev.


Metal would do it. The sensor is a magnet in a coil and moving a bit of metal near it changes the magnetic field and that induced a current to flow in the coil, in the same way an electric guitar pick up senses the movement of the steel string as it vibrates.

For the tacho, having a protruding bolt head on a spinning part would give one pulse per revolution. Two bolt heads 180 deg apart would give better balance and gives 2 pulses per revolution, equivalent to the distributor output on a 4 cylinder car. 3 pulses, 6cyl. 4 pulses, 8 cyl.


----------



## Stunt Driver (May 14, 2009)

azdeltawye - can you tell from wiring above (looking at filter and ign module) what type of tachometer used there?


----------



## azdeltawye (Dec 30, 2008)

Stunt Driver said:


> azdeltawye - can you tell from wiring above (looking at filter and ign module) what type of tachometer used there?


I'd say by looking at the schematic your electronic ignition module appears to have an open collector style driver. This goes to the coil and then through a low pass filter to the tach. I would suggest keeping the tach filter in the circuit and hooking up one wire of the proximity or ABS sensor to the filter input and the other wire of the sensor to ground. The pulse train created from the sensor may have enough juice to trigger the tach. You'll have to see... 

It also may be a good idea to put a zener diode across the sensor to prevent the output voltage from going over 12V.


----------



## Forklift Guy (Apr 20, 2009)

I used a simple solution. When i started, i wanted a aftermarket tach with a shift light, so i could use the shift light to limit my RPM, through a relay. I found a magnetic pickup tach adapter kit from Dakota Solutions on Ebay. It allows the use of any aftermarket tach to be used on diesel engines.
It uses a magetic pickup on the flywheel, and converts it to a tach output for any aftermarket tach, all in one tiny little box.
I simply set it for a 6 cyl output, and set my aftermarket tach to 6 cyl, and it worked great. Then i had a simple idea !
I used the 6 cyl tach output from the " Dakota" box to drive both the aftermarket tach and the original factory tach.
Problem solved.


----------



## Stunt Driver (May 14, 2009)

Tested my tach with 9v battery - works, just need proper switch to send signal.

Now, i'm not familiar with specs of inductive sensors, so if anyone can recommend the correct sensor - i'd appreciate it!

this one for example - http://www.am.pepperl-fuchs.com/pdf/documents/sc08_116_f79_inductive.pdf

says switching frequency - 1.2 kHz, which is not enough since RPMs can do up to 5k, which meand 10kHz signal for my tach (4 cyl). Just not sure this spec is the one that means something for tach sensor


----------



## Dave Koller (Nov 15, 2008)

Stunt Driver said:


> Tested my tach with 9v battery - works, just need proper switch to send signal.
> 
> Now, i'm not familiar with specs of inductive sensors, so if anyone can recommend the correct sensor - i'd appreciate it!
> 
> ...



I use a 6 (yes 6) lobe cam on my shaft - bypass the PCM and run direct to tach as I showed to someone else here ...

http://www.saturn.offical.net/node/326


click around to find the final sensor used works great in noise environment !

edit note a Saturn takes 6 pulses PER REV for a 4 cylinder - I will explain if you care......


----------



## Stunt Driver (May 14, 2009)

Found it at $30 with shipping. 

Wonder if ABS sensor would be a good fit?


----------



## BradQuick (May 10, 2008)

I hooked up the tachometer on my Del Sol a few weeks ago. After looking at the wiring diagrams, I tried to feed a signal in where the engine speed sensor normally goes. This sensor has three pulse outputs, all at different frequencies. They go into the computer which feeds pulses to the distributer and the tachometer.

Eventually, I figured out that I could simply feed a signal straight to the tachometer and bypass the other stuff (probably why my cruise control doesn't work).

I used a proximity sensor from automationdirect.com. I think it was $18. I took a piece of 1/2 x 1-1/2 (I think) steel bar and drilled a hole in it for the motor shaft. I tapped a setscrew hole in the edge and rounded the ends. I mounted the proximity sensor so that it sensed both ends as it went around. I fed the output of the prox directly into the tach input and it works great.

- Brad


----------



## Stunt Driver (May 14, 2009)

Thanks, interesting. Looked up your sensor - it also states top frequency less than RPMx2, but if it works - great!

I have ordered this one
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360192243436&ssPageName=STRK:MEWNX:IT


----------



## O'Zeeke (Mar 9, 2008)

Stunt Driver said:


> Tested my tach with 9v battery - works, just need proper switch to send signal.
> 
> 
> says switching frequency - 1.2 kHz, which is not enough since RPMs can do up to 5k, which meand 10kHz signal for my tach (4 cyl). Just not sure this spec is the one that means something for tach sensor


 
I think Hz is measured in seconds and your rpm is in minutes so it should work


----------



## SimonRafferty (Apr 13, 2009)

I started down this route - fortunately, my controller has an RPM output which with a bit of conditioning would feed the tacho directly.

However, driving it, I'm not sure that I get any value out of what the tacho is telling me - I have an AC drive, so it may be more useful for DC?

More useful I think is knowing the current being drawn and the pack voltage.

For my next little project, I'm using a microcontroller to measure the pack current and voltage and feed a conditioned voltage using PWM into the fuel gauge (so it reads full at 100% and empty at 50% DOD) and a variable frequency pulse train to the tacho that is proportional to current.

It's not 'properly' built yet - just on breadboard, but seems to work nicely.
If I get really board, I might fit an LCD in the dash to show what the tacho is reading and make it switchable between voltage, temperature, current, rpm, DOD and estimated range. Possibly, by dividing the current by the rpm - you get a reading proportional to torque.

Si


----------

