Calling all you electronics experts out there. I'm thinking about building either a simple shift light, or maybe a full scale led squential shift lift.

My basic thinking is that I need to convert a single from the coil to a voltage and use that to drive a row of LED's.

My electronic design skills are a little rusty and suggestions for typical circuits that can do this?

thanks

Andrew

i'm crap at electronics myself, but my solution would be to have a second tachometer hidden behind the dash, with say 5 contacts on the face and one on the needle, and use these to sequentially light up LEDs as the needle sweeps past each contact on the face. The contacts could also be moved to change when each LED comes on, and obviously you can pick any colour and position for the LEDs on the dash.

sounds easier than fiddling with chips and the likes...!

That solution sounds a bit "Heath Robinson".

I'd expect that it would take plenty off effort to get the contacts to work cleanly, then as soon as you bring vibration into the equation.....

I'b also be surprised if the needle was diriven with enough force for the friction of the contacts to not effect it's accuracy.

I've built something like that a while back. No programmable stuff, all just simple components. I used a 555 (for those in the know) to convert the rpm information to an analog signal and ran that through 4 comperators, and hey presto, sequential shiftlights!

It cost about 20 euro's in component cost and it had 4 LED's

I'll try to dig up the schematics some time this week (if i can, this was 2 years ago....)

Andrew,

there's a couple of people on this board that make these things. Have a "search" and some names will pop out at you. Might be worth an email to them?

Me? I can't wire a plug! (well almost that bad!)

I didn't know you could use a 555 to turn a pulse frequency into an analogue signal.. learn something every day.

I suppose depending on the characteristics of the signal you might be able to do it with just a resistor and a capacitor..

The 555 is wired as a monostable to give a fixed width pulse out for every ignition pulse in. After low pass filtering, this gives an average voltage that is proportional to frequency.

The pulse from the coil is not a simple waveform, it's characteristics change with RPM and throttle loading so I doubt that trying to perform some kind of slope detection directly with an RC network would work satisfactorily.

There are lots of ways you could implement this though. A Phase Locked Loop would work nicely, and are almost much as cheap as a 555 timer. A small micro such as a PIC would be able to perform this task very easily, and is also inexpensive.

I started to build a system like this however due to a number of circumstances I have not had the time to complete the system. However the input stage that I used from the coil to the PIC is featured in the circuit diagram below.

Thous of you who have looked in to this subject might recognise this from the http://www.bgsoflex.com/megasquirt.html ecu I tacho I mention this for completeness I was also in a small way responsible for the development of this input.

Personally I would use an LM3914, which is a device that displays voltages as a row of LEDs - either as a 'bar of light' or a moving spot. You can have 10 LEDs per chip, and you can couple the chips together for a greater number of LEDs.

For an example, click HERE
(Yes, I know it's for a scooter, but the principle's the same!)

Instead of the whole row of LED's you could have just a few. Alternatively, you could use all 10, but set it so that it doesn't start to display until you get to the 'now's a good time to prepare for changing gear' point.

These chips are old technology now, so places like Maplins sell them quite cheaply.

David

I must be Honest this thread is WAY above my head, all i want to know is:-

a - who's making 'em and

b - How much?

Cheers

Chris

Dear,

A litlle question regarding the input stage for the tacho signal, can it also be used in the shematic that I want to use ( see pitures archive for datasheet from CS8190).CS8190
I'm building my instruments from a Audi 100 dash (5 cil), but need to make a new PCB for the tacho.
All the other instruments can be used ( only need the proper sensors)
And the for the speedo I found the schematics, and it can be adjusted to match the speedo sensor.
Any help wood be apriciated

[Edited on 18/11/03 by AvonBelgium]