Bench testing gauge cluster...mostly tachometer
03-13-2013, 03:53 PM
#46
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What is the difference between doing what you guys did, and
Attaching 12v signal to A and then gounding the other two, B and C, constant. The reason I ask is that I have a signal generator where I work, and some of the EE's would help me set it up.
Attaching 12v signal to A and then gounding the other two, B and C, constant. The reason I ask is that I have a signal generator where I work, and some of the EE's would help me set it up.
03-13-2013, 04:42 PM
#47
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You have those mixed up. You want to connect 12v voltage to C in the picture and a steady ground signal to B. On terminal A send a sharp square pulse to ground like in the o-scope screenshot I posted above. The positive voltage level on the pulse signal is not critical -- it worked fine for me at 5vdc. The grounded portion of the pulse needs to be able to sink a little current -- not sure how much but say 50mA to be safe. You can literally take a 12v wall wart power supply, connect the positive to C and connect the negative to B and to a screw like in the video -- the just scratch the screw over the A terminal to make a crude ground pulse for testing.
03-13-2013, 06:11 PM
#48
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I'm sorry! I did mix them up.
I guess I was just wondering, because I have access to a signal generator which produces a positive voltage signal and not a grounding signal, if I could use that. Then I could actually generate a known frequency and check the accuracy of the gauge itself. I think mine is broken anyway. I wish I had my soldering iron and multimeter. I want to tach up all my solder points and then check for discontinuity. I am sure the parts can be had from digikey for 4 cents each
I guess I was just wondering, because I have access to a signal generator which produces a positive voltage signal and not a grounding signal, if I could use that. Then I could actually generate a known frequency and check the accuracy of the gauge itself. I think mine is broken anyway. I wish I had my soldering iron and multimeter. I want to tach up all my solder points and then check for discontinuity. I am sure the parts can be had from digikey for 4 cents each
03-14-2013, 03:31 AM
#49
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It's actually the ground pulses that drive the tach, so a signal generator will only work if it produced a ground pulse that can sink voltage. I created a pulse using an $35 Arduino and it worked like a charm...(see first video above).
03-14-2013, 10:38 AM
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That's funny, I have an old Arduino somewhere, but I remember having trouble with the software on my MacBook (2008). If I can get that to work, the coding is simple. I need to hurry, it's turbo weather in Oklahoma right now 
Another thing is, how would you calibrate a tachometer? I feel like they would never veer off in accuracy since they are based strictly on a pulse signal and not a voltage signal.
I'm interested in your other gauge accuracy threads/posts. I might be selling my turbo for a 968, but they all have 180K miles. Either way, the cars have the same gauges (at least I think)
Another thing is, how would you calibrate a tachometer? I feel like they would never veer off in accuracy since they are based strictly on a pulse signal and not a voltage signal.
I'm interested in your other gauge accuracy threads/posts. I might be selling my turbo for a 968, but they all have 180K miles. Either way, the cars have the same gauges (at least I think)
