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#105
by
YoSono
on 04 Apr, 2006 03:16
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thanks to Herr Cheesemeister, i now have a set of fully working tacho clocks
Just one thing though, both me n reg noticed that the 500 RPM line on the euro tacho face was a little high, as 0 rpm is actually 250RPM. I have adjusted this on the tacho face, and will gladly supply anyone with this update.
I've also taken a small video of the tacho working too... which you can see
HERE! you'll notice that i haven't put my dash back together yet also... as those clocks have been in and out more time than i can actually remember these past few weeks, lol.
one thing i have noticed, is that on startup, the needle dips for about 3 seconds, as the alternator charges up after the ignition... then it rises to its idle position - is this ok? like is this the characteristics of it taking its signal from the W TERMINAL?[/url]
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#106
by
fatmobile
on 04 Apr, 2006 03:24
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#107
by
fatmobile
on 04 Apr, 2006 04:05
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should whats labled as RV2 on the westmoreland schematics be a 47 nf cap, not a 220 nf cap.
That looks about right.
On the diesel tach there is a 47nf cap between pins 3 and 4 ... that's right where RV2 sits.
On the gasser it's 220nf.
It'll be ineresting to see what changing that cap does.
What are you guys using for R1?
Yo sono, you are doing a motometer tach? From what year of car? That high 0rpm reading is when the car is shut off or with the ignition turned on but car not running ... or both? Not something that can realy be changed by circuitry?
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#108
by
regcheeseman
on 04 Apr, 2006 04:43
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Karmann Sport,
You have some problems there, when the needle goes full scale and then drops back it, you have overloaded the chip past it's operational point and it's now dividing the signal by two and displaying that figure instead. You have adjusted the trimpot too far in the wrong direction.
However the 4K idle is an error in the circuit and will not be adjusted out by RV1. Johnny has a westmoreland working so I'm guessing it could be down to your build or a variation by westmoreland? EDIT - sorry Johnny's is a motometer so it is probably the circuit.....
Could you post a high quality component side photo for me?
Most of the caps are pretty unimportant value wise in the circuit however one controls the sampling time period as part of an RC network (RV1) and it's value is critical.
(edit. D'oh! :oops: )
Yo Sono's clocks are VDO and built by yours truely, the time lag for the W term to 'come up' is quite normal and you may find it coincides with the charge light going out. It's a 'feature' of the altenator - not my circuit!
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#109
by
regcheeseman
on 04 Apr, 2006 04:58
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Oh bugger :oops:
The clue was in your question and fatmobile's answer, I just didn't spot it.
The single critical cap in this circuit is the one across pins 3 and 4 and it should be a 47nF.
The initial post was done in haste and has now been changed, all the other values seem fine.
Sorry!
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#110
by
KarmannSport
on 04 Apr, 2006 10:32
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WESTMORELAND WORKS WORKS WORKS!!!!!
That 220 cap at RV2 on the westy schematic was the problem. Swapped it out for 47 and it brought the idle down from 4K rpm to 1K rpm. SO now we know the differance.
So...for all that want to know...the westy schematic definetly works.
If anyone has a large email account and wants the .PDF Of the gauge face I made let me know. It has the redline set up for a diesel.
Thanks again to all that made this possible. A diesel tach is a westy tach and a W terminal away for all of us in the USA!!
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#111
by
regcheeseman
on 04 Apr, 2006 10:58
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Thats motometer, VDO and westmoreland sorted.
I dunno if this should be some form of sticky or something? But I could repost all the schematics together without all the guff in between....
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#112
by
fatmobile
on 05 Apr, 2006 04:39
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..so I started the "tach in the '91 Golf" project today.
The dash is all torn up and this is the circuit board I pulled out:
I'm going to try to get a better picture somehow. The tach is just part of the circuit ... the part I circled.
The first time I drew up the diesel schematics, I was just passing time and didn't do a very good job. I took some time to redraw the diesel tach with the chip flipped the proper way:
regcheeseman, you asked me if the resistor was supposed to be in parallel with RV1... what do ya know, it is. In this drawing I gave the resistor value and the measured value (because being in parallel changes the value) across RV1.
The measured value was surprisingly close ... 8.2K diesel and 8.28k for the gasser.
Then I drew up the gasser schematic again:
R1 on this gasser tach is 6.8k, compared to 100 in the diesel. I got that wrong last time but I did some measuring this time.
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#113
by
fatmobile
on 05 Apr, 2006 04:53
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oh, and you also asked for a picture of the back of the diesel tach.
Here's one that turned out Ok:
...and a repost of the populated side of the '85 Jetta Td circuit board:
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#114
by
regcheeseman
on 05 Apr, 2006 04:55
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A better picture like this? :wink:
A bought a set of GTD clocks just to have a look... I followed the circuit until I got bored and cross-eyed. It is the same as the MK 1 conversion circuit pretty much.
Anyone want a set of GTD clocks in good condition?
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#115
by
fatmobile
on 05 Apr, 2006 15:52
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Yeah, like that. You mentioned that you had been messing with one of these circuits. Good I don't have to try to capure a good picture of it now.
ooops I remeasured the resistance measurement across the variable resistor and it's 81.6 for the gasser and 8.2k for the diesel.
Resistance from pin 4 to pin 7 was 21.3k for the diesel and 15.6k for the gasser. Funny, the resistors used in this portion of the diesel tach were smaller but the end result was measured as higher than the gasser tach. I don't think any of the caps in this RC circuit need to be changed because it's adjustable through the range with what it has. Meaning R6 can stay the same and measuring for 21.3k should get you close to the desired result. ...as long as C5 (cap between pins 3 and 4) is 47nf.
This post is getting long, it would be nice to put all the relevant data in one thread, keep comments over here and link the 2 posts ... or stick all the good stuff on the first page or something.
Another cap question ... in the lower left of my new gasser tach drawing I posted the numbers of the cap that's stuck to pin 4. Is there any way to tell this cap's value from whats printed on it?
regcheeseman, I am wondering why you have a cap from pin 1 to the positive stuff (C3). From the circuits I was just messing with, it looks like pin 1 has a better relationship to ground.
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#116
by
fatmobile
on 05 Apr, 2006 20:17
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Ok, I google searched for cap values and got this page:
http://xtronics.com/kits/ccode.htm Looks like I am looking for a cap with a 103 on it if I want a 10nf cap... and 473 if I want a 47nf cap.
Did I get that right?
If so, it already has a 10nf cap that I can use. Just have to swap it in place of that 1k resistor that sits between pins 1 and 2.
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#117
by
regcheeseman
on 06 Apr, 2006 04:47
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Spot on with the cap values - the 3 is a muliplier i.e. 'x10 to the power of - x'
C3 feature in all the tach circuits, I'm not going to argue with them - it'll be some form of noise elim/filter / decoupler , I'd guess.... :?
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#118
by
fatmobile
on 07 Apr, 2006 01:10
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I sure messed up the last drawing/schematic of the gasser tach. I missed a resistor.
You asked me about R6 in some of the early PMs we traded.
I thought it was in series with RV1 ... added to it. I was wrong.
Like shown in my last diesel tach drawing, R6 is in parallel with RV1.
I didn't understand why at first but now it makes perfect sense.
Trying to make fine adjustments to a tiny 22K potentiometer is impossible. Putting a fixed resistor in parallel with it makes fine adjustments possible.
For those that don't speak fluent electronics:
If you put two 8K resistors in parallel (side-by-side with both ends connected to the same points, like R6 and RV1 in my diesel tach drawing) they will equal 4K. Now changing one of the resistors by 1000 ohms won't change the total output by 1000 ohms. I can't remember the formula but it would only change the total by about 500. So big changes in the 22k variable resistor (small movements of this tiny pot will make big changes in the value) are tamed by R6.
I did another measurement of the resistance from pin 7 to pin 4 and got 21.3k. Thats the total resistance of the RV1, R6 (in parallel) and the 13k resistor added to it.
When I went to adjust this resistance on my '91 Golf tach so it matched the diesel tach's, the adjustment was very fine. I was able to get it right on 21.2k, 21.4k or the 21.3k that it's supposed to be.
I'll fix the gasser tach schematic/drawing and probably start a thread dedicated to the '91 gasser tach conversion and link to it here ... break this thread up a little so people can go to their application without having to read this whole post.
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#119
by
regcheeseman
on 07 Apr, 2006 04:27
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Parallel resistor network of two resistors
(R1 x R2) / (R1 + R2) = Rtotal
for three or more...
1/R1 + 1/R2 +1/R3 +....... = 1/Rtotal
On a different note, I think most of my pictures are on imageshack and they will disappear soon.. any of the powers at be on here wanna help me out with some hosting.
I can redo a single thread with all the diesel conversion variations of A1 tach and the conversion instructions and the A2 variant with it's instructions.