rpm sensing circuit?

I am looking more for an adjustable rev limiter that can be activated by a switch. Because on some tracks it is necessary to fully use up to 7500rpm while teaching novices it would be better to limit the rpm.

Search for adjustable rev limiters.

I posted one up on the last page but their around $350 or so with the only feature being it has a gain knob that can adjust how fast it cuts the ignition purely to make big flames shoot out. I found someone online that used a tachometer with an adjustable shift light and the shift light instead triggers a relay to shut off the ignition coil. I don't need the tachometer part just the rpm sensing circuit and I think the jaycar electronics circuit http://www.jaycar.com.au/productView.asp?ID=KC5378 will do the job, just have to wait until its available.

What you want is a full circuit, and that would probably be done with a PIC. EG - frequency in, set/dial trigger points(s), gradually drop out spark. It is not done as a total cut out - especially for racing/performance engines.

hi,

maybe add an ignition control box (msd, mallory) that has a rev limiter function built in?  that should drop the cylinders randomly, give you adjustable set point.

m

I'd second that - get CDI at the same time - the "best & only" ignition (F1 excepted). Unless of course its distributorless....

check summit racing...rev limiters. they show products that don't require an aftermarket ignition box.

m

I recently found some old 1985 mags. One had a LED tacho with a 20-LED bargraph. Of interest was its over-rev indication - it flashed the display. It was simple wrt merely being leads clipped to the appropriate LED. It could switch between 2 limits. The circuit is standard for its type - the ignition pulses (coil) feed an LM2917 frequency to voltage converter which then fed 2 cascaded LM3914 LED dot/bargraph divers (voltage controlled). It highlighted the simple building-block type circuits to achieve aims. Not much knowledge required - the main skill being soldering. But as I originally suggested, just the front end of it could be used - the LM2917 triggering different (pre-set) sensors (op-amps or comparators). These could be set to whatever RPM. Else maybe the original tacho circuit above if the "LED spacing" is acceptable - ie, 20 LEDs over 8kRPM means 400RPM increments. Double the number of LED drivers for 200RPM etc. And there is no need to include the LEDs - in fact you could reduce it to ONE only LED driver by having a offset (eg, so the LED driver only reacts to 6,000-8,000 RPM etc (hence 200RPM resolution for one LED driver). The outputs of either circuit could be combined with a gear sensor or other inputs (like nitrous or temp - whatever it is you want to vary the over-rev alarm) through diodes (else logic gates). The alarm could the trigger whatever - the ignition inhibitor, lamps, buzzers, etc. I posted this because I often find those older "discrete" circuits simpler and cheaper to realise than uPC or PIC designs, though all are cheaper than most commercial "single use & dedicated" offerings! PACAXEs require programmers etc which - even though cheap - get somewhat technical. Otherwise there are modules like the FB. Though I'd consider uPC modules instead..... I opted for the Arduino (Duemilanove) for its $40 price tag, USB connectivity, and plethora of free web programs & projects etc. And with its 20Mhz ATMega328 it is more than powerful enough. (I think that'll blow away at least the old IMB-AT 286 machines.)