DIY Tacho

[Gilesy998]

Just cruising the net to feed my imagination for a DIY tachometer (the sub-£10 Velleman kit Digital tacho is a pain to get hold of in the UK), and I tripped over THIS.
When I had a good look over it, it seems the natural tach to run with MJLJ - experimental, open source, compact and cheap (well, given the $/£ exchange rate being in my favour ).
I know the display board shown is a little large, maybe too much so, but it'd be easy to knock together a small board that just carrys the display and push buttons, and that'd be really easy to hide/incorporate into your existing dash. It'd even be inobtrusive on a classic's dash. I'm seriously thinking about this for the Mini, but what do you guys think about it?

Perhaps a MJLJ version would be possible? Maybe even something more simple like this one - http://www.quasarelectronics.co.uk/1143.htm or this one - http://www.quasarelectronics.co.uk/1120.htm

[brentp]

A cool idea- I'm working on offering something similar, but based on reading the runtime data from the serial port. Consequently it will be able to show more than just RPM, but other values.

The trick is deciding how elaborate to make it- just display, or offer editing/updating features. I'm still working that out.

Thanks,

[david jenkins]

Personal experience suggests that a digital tacho isn't very useful - when in a hurry, my visual signal is "the needle is about there" and "the shift light just came on" rather than looking for a specific value on a display. A needle or a line of LEDs is far more useable, IMHO.

It's a different matter for a speedo, where digits are perfectly acceptable.

In the world of real cars, my Toyota Yaris has a bar-graph display for the tacho, and digits for the speedo, so my opinion can't be far wrong!

David

[Gilesy998]

I get exactly what you mean about the digital ones, so the last link on my post might hold sway? A circular arrangement of LEDs, with yellow/amber as you approach the rev limit, then red at the very top? The user could even decide at what points to fit the different colours.

[david jenkins]

That would be fine - as long as you can see the LEDs in bright sunshine. It probably wouldn't work in my sort of car as it's open, but it could be OK in a saloon, or if the tacho was in a recess. Alternatively, you could fit extra-bright LEDs - but you may find them too much at night!

David

[capri_turbo]

I designed and built my own digi tacho a while back.

http://www.ford-capri.fsnet.co.uk/white ... ounter.htm

http://www.ford-capri.fsnet.co.uk/white ... xt_gen.htm

it works quite well with the V3 MJLJ tach output.

Prototype digi circuit:



Circuit boards:





Finished unit:

[aarc240]

Very tidy work!

Re the display brightness (and this ONLY applies to the above design by capri-turbo) you can use ultra-bright LED's easily.

See that 1k2 resistor between pins 6/7 and ground?
You need to replace that with a resistor of higher value chosen by fit and try to get the dislplay at the required brilliance at night. I would start with a 3k9 and then adjust up or down.
Then put a small reed type relay with NC contacts from pins 6/7 to a 1k2 resistor and the other end of the resistor to ground.
Connect one side of the relay coil to parking light circuit and the other side to ground.

What happens then is that with lights off the NC contacts cause the brilliance to be set by the 1k2 resistor and when the lights are on the brilliance is set by the higher value resistor.

Naturally, if you drive the car mostly at night you can set the relay up with NO contacts and wire the coil between the ignition and the parking lights. That way the relay will actually be off when the lights are on and will not heat up.

[fragged8]

looks good , i got a half built lamda sensor reader here and dont know what to do to complete it
anyone want to offer to help out as im an electronics moron..

thx