944 Tachometer Test and Calibration

[Tom]

I had an offline question the other day about whether the 944 tachometer can be calibrated. The short answer is yes! There are two pots on the side of the tach and the upper one allows you to adjust the reading. I discovered in the process that my spare tachometer wasn't working, so also came up with a super simple way to tell if the tachometer is dead or alive, using just a 9v battery and a small screwdriver (or paperclip or whatever) -- as shown in the first part of this video. For anyone who wants to calibrate their tach on the bench using my set-up, I'll also post the code for the Arduino in the download section below. Happy to answer any questions. Hope this helps!

[spacecad3t]

Thanks Tom! Never mind, my audio was muted, you explain it...

[PSU_Crash]

Hopefully my cluster is back in for a while, but I'll definitely do this the next time it's out!
What's the relation between Hz and RPM?
Thanks for the how to

Edit: Nevermind, I read the code. Another reason to pick up another Arduino

[Tom]

Hopefully my cluster is back in for a while, but I'll definitely do this the next time it's out!
What's the relation between Hz and RPM?
Thanks for the how to

Edit: Nevermind, I read the code. Another reason to pick up another Arduino

Fun fact: I've done quite a bit of Arduino coding for various projects. I started doing a program to step through the rpms and was finding it tedious -- so I went to ChatGPT and asked it to write the sketch and... it got it perfect on the first try. It had programming techniques I'd never seen, so I asked it to dumb it down so that humans could understand it, and it did that too. All I did was edit the comments a bit -- didn't touch the actual code at all. It's a brave new world!

If you are picking up a new Arduino to do this, consider the Mega2560 over the Uno. The Mega2560 has a crystal oscillator that creates a reasonably accurate clock. (And, the pulse timing relies on the clock obviously.) The Uno has a ceramic resonator, which is significantly less accurate. The scope says the Mega2560 generated a pulse that was about 5998 rpm, when programmed for 6k, so plenty accurate for this purpose. An Uno might not be as close.

[spacecad3t]

Hopefully my cluster is back in for a while, but I'll definitely do this the next time it's out!
What's the relation between Hz and RPM?
Thanks for the how to

Edit: Nevermind, I read the code. Another reason to pick up another Arduino

Fun fact: I've done quite a bit of Arduino coding for various projects. I started doing a program to step through the rpms and was finding it tedious -- so I went to ChatGPT and asked it to write the sketch and... it got it perfect on the first try. It had programming techniques I'd never seen, so I asked it to dumb it down so that humans could understand it, and it did that too. All I did was edit the comments a bit -- didn't touch the actual code at all. It's a brave new world!

If you are picking up a new Arduino to do this, consider the Mega2560 over the Uno. The Mega2560 has a crystal oscillator that creates a reasonably accurate clock. (And, the pulse timing relies on the clock obviously.) The Uno has a ceramic resonator, which is significantly less accurate. The scope says the Mega2560 generated a pulse that was about 5998 rpm, when programmed for 6k, so plenty accurate for this purpose. An Uno might not be as close.

I have also used ChatGPT to write or improve Arduino sketches, its works VERY well.

[Evan]

I had an offline question the other day about whether the 944 tachometer can be calibrated. The short answer is yes! There are two pots on the side of the tach and the upper one allows you to adjust the reading. I discovered in the process that my spare tachometer wasn't working, so also came up with a super simple way to tell if the tachometer is dead or alive, using just a 9v battery and a small screwdriver (or paperclip or whatever) -- as shown in the first part of this video. For anyone who wants to calibrate their tach on the bench using my set-up, I'll also post the code for the Arduino in the download section below. Happy to answer any questions. Hope this helps!

That's a great find. The 9v battery trick is a really clever way to test it. Thanks for sharing the info on the calibration pot and the Arduino code.

[spacecad3t]

Tom, my Arduino is in use and Im curios if you had a sense of how much of an adjustment made 100rpm difference. I don't need mine to be dead on, just looking to get closer while Im in there installing your lovely gauge clusters

[Tom]

Tom, my Arduino is in use and Im curios if you had a sense of how much of an adjustment made 100rpm difference. I don't need mine to be dead on, just looking to get closer while Im in there installing your lovely gauge clusters

Very little! I'd guess like the width of the screwdriver slot. Although... you can get an Arduino these days for less than a can of Coke...

Image 11-2-25 at 7.54 PM.jpeg (572.61 KiB) Viewed 1069 times

[spacecad3t]

Tom, my Arduino is in use and Im curios if you had a sense of how much of an adjustment made 100rpm difference. I don't need mine to be dead on, just looking to get closer while Im in there installing your lovely gauge clusters

Very little! I'd guess like the width of the screwdriver slot. Although... you can get an Arduino these days for less than a can of Coke...



Image 11-2-25 at 7.54 PM.jpeg

Oh holy cow... havent looked in a few years.

[Carmagic]

Is that 9v battery trick only applicable for the 944 tach, or can that also be used for any other tach ? I have a few tach sitting around and would be good to know if these are still OK.

Thanks for posting this
Engelbert