from my testing its seems to me that the MJLJ output will drive your tach if it has the air core type mechanism that turns the rpm needle, this is the way most modern tachs are driven, older tachs tend to have a D'Arsonval movement, these require a bit more juice (volts) to make them work.
there are also tachs that use current sensing as a way to get the RPM these also use the D'Arsonval movement but require a different way to drive them from either a 5 or 12v source, these tachs are usually very old(1960's) apparantly according to lotus68racer "run the 12V common lead to the coils from the tach" and these tachs will work, ( i cant verify that as i havnt got a tach like it)
lastly there are fancy stepper motor tachs, these also seem to require more volts than the MJLJ rpm out can give. With the small tach adapter circuit i uploaded to the files section i successfully managed to get Smiths and VDO D'Arsonval movement tachs working, i also got a Stack stepper motor driven tach working with this circuit. So there you go
A bit about tachs
Moderators: JeffC, rdoherty, stieg, brentp
V3 Board Consideration
Brent, One more thing you may want to consider for the V3 board... You might want to look into having a spots where someone could tie into the TTL signal in addition to the RS232 output in order to make a communication port for a pocket pc. I soldered wires to the chip socket pins before the TTL signal is converted by the MAX232 chip. I then ran these wires to a 3.5mm stereo jack that I glued to the board to the right of the molex connector. I then made a cable to connect to my Axim x50v and can communicate via the program that another user wrote for pocket pc's. It works pretty slick. Still it would be nice to have holes on the circuit board that I could have connected to. (Forgive the terminology, it's probably obvious that I'm not up on the electronics scene.) Just a suggestion, for what it's worth.
Jax2A
Jax2A
Jax2A