trip computers ?

[grainger]

thanks for the ideas, cam and justin, you gave me something to mull over on a wet windy welsh sunday ...

would a reed switch mounted on the petrol pump (with say 5 volts going through it), make a frequency, caused by the electromagnet in the pump, that something like this LM2917N from maplin could turn into a voltage ?

http://www.maplin.co.uk/Module.aspx?Mod ... &doy=21m11

what does anyone reckon a pretty accurate way of getting another voltage related to the speed might be ? ..... a magnet on the propshaft with another chassis mounted reed/proximity switch and another F>V convertor ?

then i could add in a few components (the LM2917N voltage out is easily tuned, with capacitors i think) to give a linear 1 volt = say 10 mpg readout ?

as you say cam, the pump might not be a very accurate way of measuring the consumption but its got to be easier and cheaper than a good flow meter, could it possibly be more accurate than a vacuum gauge ?

yawn, let me put another log on the fire, heartbeats just finished

cheers
grainger

[lowedb]

I like the idea of the fuel pump. It would need a bit of careful checking though to see if tghings like back pressure reduced the flow per stroke. I know you can't compress the petrol, but maybe the diaphragm would deform differently?

For a speed pickup you could put a pickup on the diff that sees the teeth of the crownwheel. Adding magnets and things on the prop would work but could cause out of balance problems unless you add two. You can get modified speedo cables with an electronic pickup added (as used for taxi's) but I've no idea on cost or a supplier.

I'm not sure with either, though, whether the range of frequencies would be big enough to get a fair range of voltages for your analog computer. To avoid interference and such nasties, it's easier to do things digitally, although you do need a basic development kit. Microchip were doing a very basic USB version for around £20, available from farnell amongst others. As for a flow sensor, RS do them starting from £30.

[Cam]

Grainger, no need for the reed switch, just connect a wire to the points inside the pump that will create a pulse when it pumps. But you are still left with the non-linear problem. Might be OK though generally. Hot days would mean it's totally innacurate but heigh ho!

It might be easier to attach a magnet to the brake drum at the rear? or 2 to avoid imbalance......

To be honest. I think a trip to a modern car breakers would be better and rip things out of there to do the job.

Or simply buy a vac gauge!

[grainger]

right cheers cam, i remembered my multi meter reads frequencies im going to have a play round see if i can get any kind of reading off it. the frequency should go up and down as the consumption varies ... i'll let you know

ps a vacuum gauge wunt give an indication that the mixture is wrong will it ? im not sure if the reading from the petrol pump will be any more accurate ?

gr

[lowedb]

Here's a speed transducer.
http://www.sailesmarketing.com/hunter/index.html

Of course it's always a good challenge to DIY. How about another idea? You could magnetise an area of the steel cords in the tyre and detect that. No, I am serious, apparently some add on kits for navigation computers do this

[Kevin]

You could magnetise an area of the steel cords in the tyre and detect that. No, I am serious, apparently some add on kits for navigation computers do this

When driving my Moggie I will stick with the correct period navigational aid, a Map

[Cam]

ps a vacuum gauge wunt give an indication that the mixture is wrong will it ? im not sure if the reading from the petrol pump will be any more accurate ?

No, it just gives an indication as to how much vac there is in the inlet manifold. The more vac, the better the economy. It's just to let you see how much you are hoofing the throttle really! Nothing to do with the fuel.