VDO Tach Upgrade, replacement for internal electronics Options

[914GT]

I'd like your comments about a project I'm working on. I have made a single integrated circuit design that replaces the old-technology internal VDO tach circuit. This is a more modern frequency-to-voltage converter (actually it's freq.-to-current) and it has several advantages over the original. Here are the key improvements:

• Internal voltage regulation and noise transient/surge protection
• Jumper selectable for 4, 6, and 8 cylinder engines
• Stable with wide temperature and supply voltage variations
• Better performance over stock units that have been modified for 6 or 8 cylinder engines (improved response, etc.)
• Simple calibration adjustment
• Wide range of input voltages, from standard points ignition and *should* work on most electronic ignitions (only needs a couple volts input signal)
• High input impedance

I've made a prototype circuit board to finalize the design for bench-test, and I want to lay out the final board next. I planned to design it to replace the original circuit board. This does make it harder to get at the cylinder selection or calibration. It would be nice to keep the board inside the tach and not have something mounted on the back. Would most people be willing to remove the bezel to attempt doing this? That's the hardest part, using a small screwdriver to carefully pry the rim off. The rest is pretty easy, small screwdriver and soldering iron are needed.

So, any interest in this? I'll build one for myself, but if this is something that would be popular it's possible for me to build up more as a kit. This would be for others like me who don't want an aftermarket tach and to keep it original-looking. Thanks for any suggestions.

[lapuwali]

I've been batting around the idea of making an assembly that used a geared servo and a microcontroller instead of a freq-volt convertor and the stock meter guts. This *should* eliminate the bounce, and would allow easy adaptability to number of cylinders, range of sweep, peak RPM capability. You could also add a peak recall and even run the tach backwards if you like (would allow the guts to be adapted to some older British and Italian cars).

I've even considered adding a small 8x2 LCD display to the bottom third of the tach, which would have enough room for a number of other "gauges", like CHT, EGT, etc. This would all be substantially more complex than what's being proposed here, of course.

If no one wants to wait for me to get off my duff (and that's advisable), there's some outfit in the UK fitting "classic" gauges with new servo-driven guts. Good for speedos as well as tachs. I'm sure it's not cheap, esp. with such a weak dollar, but if you want stock looking gauges with new internals, look east.