Digital automotive tach circuit?

Since you want 'digital', you will need a microcontroller (or a shitload of logic gates). So the hardware design is only about 10% of the project - the rest is software.

Parle vous PIC?

Luhan

PIC, no...

But programming is a snap to pick up... Did some Z80, 6809, etc...

I'd love to get into it, but aren't programmers, etc. expensive?

I did all those and more in assembler. Pic programmers start at about $50, or build your own for a few bucks.

You could always to it with a Z80, rom, ram, and I/O chips; but PICs start at under $1.

Luhan

============================================ try epanorama. This would also be a good project to learn c programming on a microcontroller. Use a text lcd as the bar graph. Or a graphics lcd. Look at the Olimex MT128 at olimex.com

You can buy an AVRISP programmer (for Atmel AVR series chips) for about 6 bucks on ebay (it looks like a clone of one of the official Atmel programmers)

Software's free.

thses programmers are neat as you wire them to the device you're building and program the chip in-situ. it's all controlled from the host PC, you don't even have to pull the cable after the program has been sent to the chip.

real handy for debugging.

I think the avr assembler is easier to pick up than pic assembler too,

Bye. Jasen

How about doing it the old-fashioned analog way ? An LM2907/2917 as F-V converter, and a 4 1/2-digit DVM module for readout. Another venerable IC, the LM3914 could provide the bar graph display, two of them for a 20-dot scale.

A Digital Tachometer For Your Car

Compact design features a 4-digit LED display and a bargraph. It can also provide gearchange indication and drive a rev limiter.

Build a frequency counter, and pick the right gate time. I think if you make the gate time 1/300 of a minute, the display will show RPM/100. Make it

Tam

That's too obvious.

I'd stuff a down counter with a preloaded number corresponding to some very high RPM then use the tach signal to gate a series of pulses from a crystal oscillator into the counter.

Sort of measuring period, but displaying RPM . . .

Requires some latching/gating to display the count while the next count is being acquired.

Main advantages: capable of very high resolution and fast response, with low pulses per revolution. The concept works; I had it bread boarded and up. An analog display was more intuitive and I could acquire the RPM in a millisecond glance, so used analog instead. Digital displays make more sense in slow flying aircraft IMHO.

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