Author Topic: Inexpensive (aftermarket) Tach Read Out/output (BETA)  (Read 7618 times)

December 06, 2008, 08:05:50 pm

Smokey Eddy

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Inexpensive (aftermarket) Tach Read Out/output (BETA)
« on: December 06, 2008, 08:05:50 pm »
EDIT: please skim over this whole thread. It's gone through a couple stages of failures so the first posts are almost always useless.



This is still a work in progress so please bare with me!
Tachometers read a frequency emitted by means of an electric field (signal or what ever) from a spark plug firing or from a magnet passing a detector on a spinning gear (as i believe jimbote? is doing).
I always wanted a tach but i didn't have a VDO cluster with a tach on it so i couldn't follow the guide on converting one. I figured, there must be a way! I also didn't like the idea of reading a digital number for RPM...I knew there must be a better, inexpensive DIY VW way!


I am currently, with the help of my electronics wizz friend, making a "flip flop" out of d-latches to divide the frequency signal from the stock alternator W terminal by a factor of 8. You can buy these components at any electronics store but a method of testing your boards is a must. Check your solders with a multimeter and have a suction gun to de-solder if need be.


Courtesy of Vince,

Quote from: "Vincent Waldon"
Square wave:



8 volts AC:



Since it's a square wave we can easily divide the signal and get a rough idea as to what the RPM is. This is not a concrete measure of what you're reading and without a micro controller it will not be perfect but for those wanting to keep expenses down this will cost you less than 10$.
Vince reckoned that you would need to divide it by a value of 7.456. Slightly less than a value of 8, therefore, the reading will not be perfect by any means let alone the chance of the belt slipping and so on. But, in theory, it should be spinning at exactly the same rate as the crank.

the D-latches can take up to 15 volts so we don't need to protect them with resistors or any of that stuff. It's a very straight forward three d-latch in a series divide by 8 circuit.
I can post pictures of the parts and the idea at a later time.

I may add a micro controller later if this works out.
Essentially if i do that i am making a dakota diesel digital tach (http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=128/category_id=-1/home_id=-1/mode=prod/prd128.htm) read out that would out put to any tach you want. It wouldn't have to be a digital screen. And would likely cost way less than $65.00 if you made it your self.
But that's another thread for another day :P

We'll have to see how it goes.

Note: I'm keeping this separate from the other tach thread because this may not turn out to be quite as successful as i hope. it's an experiment and i thought it would be nice to get some feed back from you all.
I plan to use this idea in addition to a micro controller to make the equivalent of a tach read out, with no engine mods, that you can use an aftermarket tach on.

Vince if you read this can you post about how many hertz you were reading at 900rpm (idle) or 1000 or what ever. I don't have a running engine right now to test it.  I have a working circuit on a proto-board right now  :D I'll post pics maybe tonight.


Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #1December 07, 2008, 07:48:47 am

jimbote

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Inexpensive (aftermarket) Tach Read Out/output (BETA)
« Reply #1 on: December 07, 2008, 07:48:47 am »
another use for a "latch" may be the inductive pickup already installed on TDI's....they read from a wheel that has four slots cut in which would give double the pulses needed....would the "latch" divide this by two and only give two pulses?

Reply #2December 07, 2008, 03:44:05 pm

Smokey Eddy

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« Reply #2 on: December 07, 2008, 03:44:05 pm »
A single D-latch would yes. Smart thinking! and give an exact reading.
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #3December 07, 2008, 05:41:10 pm

Smokey Eddy

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« Reply #3 on: December 07, 2008, 05:41:10 pm »
I am using a MM74C74
Dual D-Type Flip-Flop

mm74c74n being the part no. of the latch.

http://www.alldatasheet.co.kr/datasheet-pdf/pdf_kor/53721/FAIRCHILD/MM74C74N.html

Using the connection circuit and truth table we can make a flip flop!

Here is what the chip looks like on the inside...

The top numbers being the right hand side and the bottom numbers being the left.

They are two separate latches as i am using DUAL D-type chips.
You can read how they work on wiki if you wish  - http://en.wikipedia.org/wiki/Flip-flop_(electronics)   - That link wont work because of the parenthesis. I assure you i am not talking about thongs for your feet. You have to copy and paste the link. (sorry)
There are hundreds of different chips (as well as uses for each chip) so the one i'm using may not necessarily be on that page.

Now then, the first latch! (remember, 14 is power 7 is ground. The chip needs to be powered in order to do anything. BE SURE YOU POWER IT BEFORE YOU CONNECT ANYTHING - as it could burn the chip out and you would be struggling not understanding why your circuit wont work and it turns out from step 1 you fried the chip.)

Your input (from the w terminal) you want to go into "clock" which is pin number 3.

next you want Data(2) to go to Qnot (6).

And now Qnot (6) is your new output. This signal will be 1/2 of what you put in.

SO let's keep going.

from Qnot (6) you want it to feed the new Clock of the Right Hand Side which is pin number 11

Now Data (12) goes to Qnot ( 8 )


Then with your second Dual chip, or third single latch, add the third latch and there you go!
Make sure both chips are getting power and off you go!


My third latch is wired slightly differently just as a test. Ignore it or follow it exactly. My directions are for the first chip.

Funny Note: the operating speed of the chip has a limit of 10Mhz so as long as you don't have an RPM of like 10,000,000 RPS (rev/second) you should be good.
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #4December 08, 2008, 04:44:32 am

Smokey Eddy

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« Reply #4 on: December 08, 2008, 04:44:32 am »
I just finished soldering the actual circuit board. My friend is testing it with his frequency generator and oscilloscope right now and i'll take a new pic of THAT tomorrow.

I hope this is informative enough. I really want feedback in case anyone doesn't understand how to do it or if my instructions are unclear of if anyone wants ... anything! clarified.

I cleaned up the board so it's easier to follow. Just waiting to get it back now.


Apparently my first latch doesn't work so it's troubleshooting time  :roll:


(getting slightly delayed sorry!)
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #5January 03, 2009, 01:34:30 am

jtanguay

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« Reply #5 on: January 03, 2009, 01:34:30 am »
i'd be interested in finding a way to make use of the crank sensor on my TDI  :lol:


This is how we deal with porn spammers! You've been warned.

Reply #6January 03, 2009, 03:32:04 am

Smokey Eddy

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« Reply #6 on: January 03, 2009, 03:32:04 am »
Augh i fried my latches so i have to start over but i've been really busy lately.
I will post in detail when i get around to wiring up a new circuit.
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #7January 28, 2009, 06:38:55 am

Smokey Eddy

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« Reply #7 on: January 28, 2009, 06:38:55 am »
*useless post*
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #8January 30, 2009, 02:45:00 pm

79rabbit4dr

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« Reply #8 on: January 30, 2009, 02:45:00 pm »
i have to squint to see those pix... from 10 miles away  :lol:
Paul
LOCATION = Idaho 83440
----------
1979 Rabbit 4dr Gasser - For Parts
1981 Rabbit 4dr Diesel - For Parts
1981 Rabbit Pickup 1.6 NA - For Parts
1983 Jetta Coupe 1.6 TD - Feeler Part out
1997 Jetta VR6 - Part Out

Reply #9January 30, 2009, 03:31:53 pm

Smokey Eddy

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« Reply #9 on: January 30, 2009, 03:31:53 pm »
sorry it's sort of useless at that size... i don't know why they're like that...
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #10February 14, 2009, 04:59:31 am

Smokey Eddy

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« Reply #10 on: February 14, 2009, 04:59:31 am »
Sorry for the slowness of this thread.


The d-latched proved to be absolutely useless in testing. They were wayyyyyyyyyyyy too touchy with interference and all sorts of crap.

I've come to the conclusion that for what it's worth, its probably a lot more worth your time to just buy a Dakota Diesel digital read out and figure out where it's output is, tap into that, and send THAT to a gauge. Why they don't already do this i dunno? I don't have one. Maybe it has an output for a gauge.

If you wanted to make your own you would need to be someone pretty savvy with electronics and have a USB programing hub which is a device you plug into your computer and it will plug into any circuit board that you make your self and you can program micro controllers (mini calculators sort of speak) to divide and input frequency by 8.18 and send that out the output pin of the chip. And from that pin you just add a wire that goes directly into the input of the gauge.
Here is a few examples of said device to give an idea

It literally just plugs into the pins of the micro controller which is just a chip


The micro controller method I'm pretty sure is just way out of the field of reasonable options for someone looking for a cheap tach conversion for their IDI diesel. If you were to go through that much work the counter on something that spins  (ie. the crank sprocket) method would make much much more sense.


As an outlook for an easier method i bought a couple "divider" chips that do already what i tried to get the d-latches to do. Those are simply plug and play division . (EXACTLY what i was trying to do. I'm a little frustrated i only just came across these last week)

They literally just sit in the bread board like in my above pictures and do what im trying to do without the interference garbage. If i can get a divider that will give a reasonable RPM read out on my tach i will definitely post a list of part numbers and cheap vendors. OR i could just make some and ship em out to your guys if you're interested. OF COURSE depending on the outcome  :P

I know this thread is pretty wish wash and i needent have posted at all. In fact, this whole thread could just be deleted at this point but i was hoping to get some of the real electronics nerds interested (if there are any more on here other than me and vince  :lol: )
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.

Reply #11February 14, 2009, 05:07:16 am

Smokey Eddy

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« Reply #11 on: February 14, 2009, 05:07:16 am »
I've decided the point of this thread is to hopefully end up making something moderately useful, prove on my thread that it works and possibly make/ship them out to you guys wanting a rough idea what your rpm is without having to hunt down a gauge cluster with a tach or spend the coin on a digital tach read out (and if you just wanted an analog tach not a digital display)

A rough guess of the product cost would be less than 10$ CAD - if it works
and you would just have to connect it to the W terminal and your tach's input wire and secure it somewhere in the car. I could make them enclosed in allum. project boxes.

Anyways, i find this stuff interesting so we'll see how it goes!
Ed
Blacked out mk2 AAZ Jetta RIP. You will be are missed.
White 1999.5 ALH Golf 2dr. 2" wider. 2.5" lower.