Now for something completely different

[Edweird]

An idea my Dad came up with that I thought sounded pretty bad-ass. One for those with an old school dizzy and no rev counter.

I was speaking to my Dad a little while ago and apparently didn't know my truck lacked a rev counter. He then suggested that I could make one. Taking a high resistance 'sensor' wire from the low tension of the dizzy to a device which creates a digital signal at half the frequency caused by the points, at you get two lows and two highs for every one revolution of the engine.
You send that digital signal through a decoder of some form so that for every, lets say, 500 rpm you get an extra LED come on, on a strip of LEDs ranging from green at low rpm through yellow to red at high rpm. Looking like a graphic equalizer I'm thinking.

I'm thinking this could cover the year 2 A-level Electronics project, be a handy gadget and look like it's straight out of knight rider all at the same time. Obviously it's just at the flow chart and block diagram level now, but I know that with a bit of though and a little help from my tutor and my Dad I can get this designed, prototyped and eventually make something I'd be happy to put in my car. I'm thinking nothing absolutely permanent, so it just slaves off of other systems and can be easily removed, but can be left in place forever just as easily. Probably use sticky-pads or something to attach the gauge to the dash.

If anyone is interested, once the first one is completed and I know it works, I'd happily make a kit or something where the circuit board and gauge were pre-built and it just needed splicing in or whatever.

This is only made in paint, but gives a rough enough idea of what I'm talking about and the kind of places I think it could go. The gauge would probably be a little bigger than that too.

dash with reveq.jpg (241.17 KiB) Viewed 7708 times

[dan_2k_uk]

good idea. for my A-level electronics project I made a circuit to make a solar panel track the sun on a gimble.

Probably should have made something more usefull like this.

I would try use as many smaller LEDs as possible to give a smoother and more accurate movement through the rev range.

maybe one for every 250 rpm.

Dan

[ScottieJ]

I've thought of this myself before, if you want some led bars I will pop them in the post for you, think they are all just one colour though? But I have 1 green and one red, they have been in a box for about 10 years

IMAG0073.jpg (742.69 KiB) Viewed 7701 times

these are from my GCSEs one circuit board is as thermometer and other a light level sensor

[Edweird]

I would try use as many smaller LEDs as possible to give a smoother and more accurate movement through the rev range.

maybe one for every 250 rpm.

Dan

I guess I could do that using 3mm LEDs instead of 5mm.

What sort of speed will an SJ rev up to? I'm guessing 6500 ish.

I've thought of this myself before, if you want some led bars I will pop them in the post for you, think they are all just one colour though?

Cheers Scott, but they've only got ten leds in a bar, they're single colour ones and I don't think they'll fit the prototyping boards at college.

[Edweird]

Okay, it's gotten around to coursework time and I'm starting to design this tacho. I still need to know how high an SJ will rev if anyone knows.

[dan_2k_uk]

The standard dial in the 1.3 goes red at 6500 and maxes at 8000

Dont know about the 1.0 though

Dan

[ScottieJ]

the 970cc will rev higher, but I'd stick with a 7000 redline well 6000/6500 to be safe

they make peak power around 5200 I think

[Edweird]

Thanks guys, I was thinking of having 7000 as the end of the gauge anyway. Although, as I've had to rethink my input, the output's going to be different now anyway.

I'm going to multiplex 4 7-segment displays instead of having the Knight Rider voice module looking display, so it'll show a 4 digit number instead. I liked the bar idea, but this'll be a lot easier to build and more accurate.

Another problem now, to do with the input. What kind of voltages and current would the low tension side of the distributor deal with. I'd like to think no more than maybe 14 volts, but there's the back emf from the coil to worry about and I've no idea about the current. The problem is I want to connect a picoscope from college to it and get some graphs, but I'm not sure if it would blow up the picoscope, as it can only handle 20 Volts and small currents.

Does anyone know what the voltage/time graph for the low tension would look like? I had something like this in mind, but now I'm not so sure.

Low tension graph.png (19.05 KiB) Viewed 7585 times

Also, how is the low tension side wired in an SJ? Is it the same as this interactive thing?
http://www.magnet.fsu.edu/education/tut ... index.html" onclick="window.open(this.href);return false;

[dan_2k_uk]

Wouldnt have a clue!

Luckily its not your picoscope

[Edweird]

Yeah, but if I blow it up I have to pay for it, that's why I'm bothered.