1.6TD jetta. tach question

[DUBFELLA]

Hi all. Im new to diesels, just got an 84 jetta TD with a clock where the tach should be. i want to put a vdo mini tach in the gauge pod..

where would i get the signal? i want to get the unit if it will work.

thanks. these forums are fantastic.  :shock:

Anthony A.

[flapjack]

if its a diesel tach, you can run it off the W terminal on the alternator
if your alternator doesn't have a W terminal, theres a faq on how to put one in, i can't find it at the moment, but it is pretty easy

[VWCaddy]

A whole bunch of options listed on the web page below:
http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml#OEMInstall

[DUBFELLA]

thanks gentlemen.

cheers, Anthony.

[saurkraut]

Lets all bug Vincent.

He maybe could build a circuit to read a piezio dingus on an injector line.

Paging Dr. Walden, to the tach drive emergency room please. :wink:

[rabbit GTI/GTD]

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ATM%2D3788&N=700+115&autoview=sku

I just bought one of these, installed it in my caddy, works awesome, looks good to, inductive probe get strapped to the alternator. i bought mine off autopartsway.ca tho.

[Vincent Waldon]

Lets all bug Vincent.

Yeah.

Building a frequency multiplier that's stable and only uses parts from your local Radio Shack is proving to be a little bit of a challenge... it's solvable, but  is gonna take a little bit of time.

In the meantime, an inductive pickup off the alternator is a great universal solution for an aftermarket pod-mounted tach.

VDO sells a universal pod-mounted tach that might be a bit cheaper, for those with an existing W terminal.

[saurkraut]

Would 4 piezio sensors and four diodes make life easier?

I need an accurate tach.

[TedV]

I found ISSPRO has a magnetic pickup sender for their tachs, but don't know what form the signal is, will try to find out next week.  I need a 12 volt square wave for gas tach, shift light, data acquisition, etc. common to racing.  I've made the 4crawler opto sensor setup and it works good to 3K rpm, above that it gets a little unstable.  Could be the trigger wheel or sensor orientation tho.

forget Radio shack for electronic components, try Digikey.com or Newark.com.   pardon the echo :lol:

[somepunk22]

Would 4 piezio sensors and four diodes make life easier?

I need an accurate tach.

X2

Does the alternator spin at the same RPM between the AC and non AC versions? Different alternator pulley size?

[Vincent Waldon]

I need a 12 volt square wave for gas tach, shift light, data acquisition, etc. common to racing.

Cheapest option:  add a W terminal to your alternator, borrow an optical tach from someone to calibrate, and you're done.

If you need a 12V square wave that looks like an standard ignition system add the W terminal followed by the Dakota Digital signal converter.... 80 bucks or so.

Lots of different ways to peel this onion...  the appeal of doing the piezo sensor method to me is only there if it's significantly cheaper and uses locally -available parts that anyone can assemble.

And.... lets you leverage your investment in the sensor into a timing light adapter... but that's another thread and another section on my breadboard.

[Sc0rian]

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ATM%2D3788&N=700+115&autoview=sku

I just bought one of these, installed it in my caddy, works awesome, looks good to, inductive probe get strapped to the alternator. i bought mine off autopartsway.ca tho.

have you got any pics of it installed?

i was thinkin of getting a little RPM gauge.. were is a good place to mount it though?

Mines got a clock instead of RPM...

[saurkraut]

The appeal of piezio to me is a direct measurement of rpm = accurate.

I'm working with the early dash, no diesel OEM tachs exist.

Anything off the alternator is not accurate.  Belts get loose, pullies wear, and it has to get calibrated.  An alternative measurement system has to be purchased just to do the calibration.

I guess I'll have to pull my transmission, bore a hole in the bell housing, and use the Dakota digital gear tooth sensor.

Alternatively, if someone could come up with a piezio design, I'll get some one else to build it.

[TedV]

the ISSPRO sensor uses 2 magnets glued to a pulley or flywheel.  It makes a sine wave signal.  I'll have to check if the schmidt trigger (555 chip circuit) I have for the opto-sensor would work with it.

I like a direct signal off crank, flywheel, etc because I need the accuracy.  FSP class rules I don't think will allow me to drill a hole in the trans to mount the Dakota Dig toothed wheel sensor for the flywheel ring gear.  The Dakota sensor will work on a wheel down to 32 teeth.

Vincent, do you have a circuit that will work with the piezo that is made from not so easy to find parts?  I have no problem soldering :wink:

[Torchd]

The original Tach on the MKII GTD, how does that work???  off the W terminal? or sum other way?