Type 3 Clock-Tachometer Conversion

This covers the calibration only. It has been too long since (and too many late nights during) the conversion to try to
chronicle it now.

This is for those without access to a quality function generator, but enough technical know-how to understand what I'm
saying here. To put it another way, if you are having trouble following along, get somebody else to do it for you! ;-)


	Totally re-worked. Can't tell, huh? ...except there's no hour hand. I was going to use it as a redline needle, but just getting it in there was turning into a huge pain! One of these days I'll take the rings back off and restore them to their original condition. But not today.		Not too bad. MANY hours. I used the cap to the conformal coating spray can as a housing and PCB mount. It says 'NO CFC's.' Also, there is a tiny drain hole on the underside just in case. If I recall, the clock housing had one. Oh, I didn't build the PCB. It and the movement are the guts from a $50 FLAPS tach. I did, however, remove and hardwire the cyl switch to 4cyl, remove the backlighting components, RTV the capacitors to the board, shape it to fit and apply about ten coats of conformal coating. Hopefully that will be enough!

The files:
cal-tach-6-3.wav (3446 KB)    This is the original wav file for calibration
cal-tach-6-3.mp3 (626 KB)      Smallest size file that gives 'good enough' results (For the bandwidth-challenged)
cal-tach.divx.avi (846 KB)      My neato clock-tach conversion in action, and a good reference for your calibration.
                                                       You'll need the Divx 5.0.2 codec, available here.  The original capture was 41 MB!

The Instructions:
First of all, use these At Your Own Risk. This worked for me, but I cannot be responsible if it doesn't
work for you or if you short out your power supply or blow up your tach.

What's Needed:
- Powered speakers with a headphone jack. (Most sound cards just don't have enough ass.)
- 1/8" stereo patch cable
- Grounded 12V power source. I use an available connector in my computer. +12V is the yellow one.
          > A twelve volt wall adapter will work, but I don't like the way you have to set it up.
- A whole bunch of wire and connectors, and most importantly, patience. This is worth it, remember?

Best practices:
- Plug the patch cable into the speaker and connect the Tach
     Signal Lead to the Tip of the Patch Cable.
- Connect the Black and Red tach wires to the Black and Yellow
     power connector leads in your computer.
      > Okay, so you're not going to open it up, right? Go ahead
         and use the wall adapter, but now, the Adapter Neg(-)
         lead must also be connected to the Patch Cable Shield.
         (There has to be an audio return path to the amp.)
- Do your best to shut down any program that makes noise. My
     tach especially hates the system default ding.
- Turn the volume on your speakers and the audio control
     panel up until your tach responds smoothly. Keep in mind
     that the first ramp starts at 1 Hz and ends at 33 Hz, so even
     the best sound cards will have trouble producing this range.
     We are not concerned with rpm below about 800 (26 Hz)
     anyway, right?
- Play the cal-tach-6-3 file which I have painstakingly created. ;-p
     Your tach should go from 0 to 6000 rpm, 1000 at a time,
     with 3 second transition and hold times and then a ~5 sec
     return to 0. If your player has an EQ, minimize frequencies
     above ~300 Hz to reduce distortion.

Adjustments:
- Generally there is a potentiometer on the control board that affects accuracy. For linearity, most coil spring meter
movements are adjustable by twisting and are usually sealed at the factory. You can get around this,
but chances are you don't need to.