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> Upgrading the tachometer, to remove that bounce
timothy_nd28
post Aug 11 2013, 05:42 PM
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First I would like to give thanks to Terry, my uncle, for his time on this and my other RGB backlighting project. He has spent more time working on this than he cares to admit. He's more of a Corvette guy, but his vast knowledge and willingness to help, transcends which benefits our community.

Okay, so I have been told that our tachometer has a problem with bouncing. I personally have never seen this problem and I have to admit that I've never really paid much attention to the tach while driving, so I decided to put the signal generator on the tach and see how it performs. This signal generator bypasses the ignition system and provides a clean signal. This also serves as a control because a bad condenser on the dizzy can cause problems as well.

This video shows the untouched tach in its original state running on a function generator. As you will see, it does bounce and over shoot during the sweeps.

https://www.youtube.com/watch?v=rbC37l1z_oA


This next video shows our tach but with a cheap modern 30 dollar tach stuffed inside. The bounce seems to have disappeared, and there is no more overshoot during the sweeps.

https://www.youtube.com/watch?v=cmk1lSop_iE



The VDO tach was designed for mass production and had a very simple but effective design. This modern tach uses an air core massless motor which is controlled by sine/cosine inputs which tends to be a bit more responsive and accurate. The original vdo design is a motor/spring contraption which will always have some bounce. Over time, capacitors and dampening fluid may leak or fatigue which will aggravate the problem.

In this write up, I will show how to incorporate a off the shelf 30 dollar tachometer commonly found at the auto parts store, and make it work with our VDO gauge can.
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CptTripps
post Nov 1 2013, 04:13 AM
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Hmmm. Now this has me thinking about gutting the rest of them and making custom faces too.

Great thread, and super helpful for those of us with other computers/engines installed.
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timothy_nd28   Upgrading the tachometer   Aug 11 2013, 05:42 PM
timothy_nd28   First we need to purchase this cheap 30 dollar tac...   Aug 11 2013, 05:42 PM
timothy_nd28   After the jumper has been soldered, we need to cha...   Aug 11 2013, 05:42 PM
timothy_nd28   Now the machining part. Go ahead and remove the g...   Aug 11 2013, 05:43 PM
timothy_nd28   Now the fun stuff. You will need one of these. ...   Aug 11 2013, 05:43 PM
timothy_nd28   Now we need to apply power to this. The red an...   Aug 11 2013, 08:26 PM
Dave_Darling   Very cool! Have you verified this with the po...   Aug 11 2013, 10:04 PM
timothy_nd28   Very cool! Have you verified this with the p...   Aug 11 2013, 10:42 PM
mikelsr   Looks really nice and thanks for the work. Do you ...   Aug 11 2013, 11:09 PM
monkeyboy   Wow. Thank you for the amazing work. Will the new...   Aug 11 2013, 11:06 PM
timothy_nd28   Here's the manual for this unit tach manual ...   Aug 11 2013, 11:32 PM
Chris H.   How much for you to do it Tim? Not sure how bounc...   Aug 12 2013, 08:30 AM
timothy_nd28   How much for you to do it Tim? Not sure how boun...   Aug 12 2013, 11:26 AM
ThePaintedMan   Tim, You are unstoppable. Nice work man. I like...   Aug 12 2013, 11:45 AM
timothy_nd28   The video below shows the tachometer running on 5v...   Aug 12 2013, 03:52 PM
monkeyboy   Now I need a motor that will run through the gears...   Aug 12 2013, 11:05 PM
McMark   Just ordered my Sunpro CP7911 off Amazon. This is...   Aug 13 2013, 12:59 AM
timothy_nd28   Just ordered my Sunpro CP7911 off Amazon. This i...   Sep 9 2013, 07:41 PM
McMark   Got it modded and installed. Had to order the 49...   Oct 15 2013, 08:58 PM
timothy_nd28   Nice. One minor flaw has been found with this ret...   Oct 15 2013, 09:40 PM
McMark   Yeah, I installed mine with the factory connector ...   Oct 15 2013, 09:48 PM
Vacca Rabite   I'll be ordering one of these tachs today. Aw...   Oct 16 2013, 06:01 AM
McMark   Not particularly interesting, but here's mine ...   Oct 25 2013, 10:26 PM
timothy_nd28   Not bad at all :beer2: Is this running off a 5v...   Oct 26 2013, 09:21 AM
McMark   Not sure. I'll have to look at how I have the...   Oct 26 2013, 09:32 AM
CptTripps   Hmmm. Now this has me thinking about gutting the r...   Nov 1 2013, 04:13 AM
timothy_nd28   For the price, it's a great project to do. I...   Nov 1 2013, 08:06 AM
timothy_nd28   I just finished a tach conversion for a V-8. R9 n...   Nov 13 2013, 08:51 PM
McMark   Does this mean that the switch on the back is alwa...   Nov 13 2013, 09:04 PM
timothy_nd28   Does this mean that the switch on the back is alw...   Nov 13 2013, 09:05 PM
McMark   Can you edit you original thread at the R9 step an...   Nov 13 2013, 09:11 PM
timothy_nd28   Edited the values   Nov 13 2013, 09:27 PM
Dr Evil   Reviving from the dead due to awesomeness! Thi...   Sep 20 2014, 10:57 AM
timothy_nd28   Thanks :) Yes, R9 can be configured from a 2 cy...   Sep 20 2014, 12:05 PM
tomrev   Hi Tim, Reading thru this post, did you decide to...   Jan 22 2016, 03:23 PM
914Bryan   This is awesome! Glad to see you are offering ...   Jan 22 2016, 04:37 PM
rnellums   Tim's service is great. I had him do high inte...   Jan 22 2016, 05:14 PM
tomrev   Tim's service is great. I had him do high int...   Jan 22 2016, 06:09 PM
timothy_nd28   As a HVAC tech, I've been busy with this recen...   Jan 23 2016, 11:29 AM
tomrev   As a HVAC tech, I've been busy with this rece...   Jan 23 2016, 01:47 PM
ThePaintedMan   Might as well take the chance to give another bump...   Jan 23 2016, 04:15 PM
timothy_nd28   I have some bad news as it seems that AutoZone has...   May 30 2016, 02:22 PM
craig downs   I got mine thru Summit a few months back and it wa...   May 31 2016, 09:07 AM
Optimusglen   Good news for anyone wanting to do this. I recentl...   Mar 14 2018, 11:48 AM
Optimusglen   Packaging and face .   Mar 14 2018, 12:00 PM
Optimusglen   Taking another approach. Thought I would share. ...   Mar 15 2018, 01:01 PM
Bartlett 914   This is a good approach. This would also work with...   Mar 16 2018, 05:17 PM
mepstein   I'm giving it a shot. Still have a lot to lear...   Mar 16 2018, 10:11 AM
timothy_nd28   Wow, i thought the sunpro's were long gone. T...   Mar 16 2018, 02:03 PM
Bartlett 914   I purchased the Bosch 7904 and it does look like t...   Apr 7 2018, 08:15 AM
Montreal914   Added small detail to this excellent thread :trop...   Mar 6 2022, 03:52 PM
Dominic   @timothy_nd28 Tim, Are you still in the...   Oct 29 2023, 09:54 AM
FlacaProductions   It appears that Tim hasn't logged on here sinc...   Oct 29 2023, 10:00 AM
fiacra   It appears that Tim hasn't logged on here sin...   Oct 29 2023, 01:06 PM


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