Rover MEMS

mac · Post by **mac** » Mon Nov 13, 2006 12:46 pm

Hi,

Does anyone know if the rover mems runs the odometer function on the elise?

I've got a datalogging system in the caterham but it doesn't record mileages - I need the mileage recorded for insurance purposes but don't want to snub a 2k datalogging system.

So I was hoping that someone might know if the mems can do this - might even be a great wee project for Rich

Cheers

Mac

Rich H · Post by **Rich H** » Mon Nov 13, 2006 12:58 pm

No I don't think it does. Pretty sure it is in the Stack. I can't believe there isn't an odometer type thingy you can buy surely there must be loads of cars with the same problem? Do you have a pick off a road wheel?

Rich H · Post by **Rich H** » Mon Nov 13, 2006 1:09 pm

If you have a pulse input such as a hall probe on a road wheel pick off, a-la elise and a simple (Ish) counter circuit then you will have an odometer.

You will need to know how many revolutions of a wheel makes 1 mile, then how many pulses per revolution, this gives you the basic figure. I would then look at a ripple counter to count up to the number you need (Would probably be huge...) then trigger a digital counter with LED output each mile (Or part mile)

Simple curcuit but quite clumsy, I'm sure there would be a better way.

Checking now...

Rich H · Post by **Rich H** » Mon Nov 13, 2006 1:17 pm

Yes, a series of decade counters would give the raw counts, a set of and gates would give you a trigger at a specific number then another series of counteres would count the number of miles.

Does that make sense?

Pulses from wheel
Counted by chip in binary
And gates select number of pulses and pulse at 1 mile
counted by odometer and output to LED/LCD

Simple circuit but still clumsy. I'm also not 100% about the output of hall probes but that could be tested...

Rich

Rich H · Post by **Rich H** » Mon Nov 13, 2006 1:30 pm

IC 4026 will do the mile counting:
Will count up to 10 and drive a 7 segment LED display, stack them for more numbers

IC 4017 will do the pulse counting:
Will again count up to 10 stack for more numbers (Lots probably - the clumsy bit)

IC4081 will do the AND gate bits:
This will pick off outputs from the pulse counter that equal the pulses-per-mile value and pulse the mile counter once.

The rest is just wiring.....

I'm not very good at tidy electrics but they do tend to work, bit of a sledge hammer to crack a nut I suspect....

HTH

Rich

mac · Post by **mac** » Mon Nov 13, 2006 1:36 pm

I've got a wheel speed sensor.

The rest means nothing to me

Mac

r10crw · Post by **r10crw** » Mon Nov 13, 2006 1:49 pm

Since you have a wheel sensor with a digital output you could run wires to a single microchip which will then count each pulse and give a relevant output to a cheap digital or 8-seg led display. You wouldnt even need a fancy chip, something like a pic16f84a would do it, and they only cost around 2.50 each. Get someone to write the code, burn it and youll wire it up for under a tenner. Im at lunch just now but if I get a chance 2 night Ill look out some info. Also do you know if the speed measurment is inductive? or does it actually switch?

mac · Post by **mac** » Mon Nov 13, 2006 1:53 pm

I think it's inductive as it need to be a set distance from the wheel. I'm really not very good at this kind of thing - I'm more a nuts and bolts kinda guy.

Thanks for all the advice

Mac

robin · Post by **robin** » Mon Nov 13, 2006 2:49 pm

r10crw wrote: Also do you know if the speed measurment is inductive? or does it actually switch?

If it's like the ones we used on Lawrence's car then it's open collector so you would use a pull up to produce a square wave and you wouldn't need to buffer it into the uC, though it would make sense to do so anyway (cheaper to change a 10p transistor when you nuke it).

Mac - Do you need to have a dash readable one or just be able to access it on demand?

You also need to consider how to preserve the count - micro controller non-volatile memories typically have a maximum write cycle count after which they start to not work properly. If you updated the non-volatile memory for each 1/10th of a mile, it would wear out before you reached 100K miles. There are solutions, but it's all time consuming (though not expensive).

Cheers,
Robin

mac · Post by **mac** » Mon Nov 13, 2006 2:55 pm

robin wrote:
r10crw wrote: Also do you know if the speed measurment is inductive? or does it actually switch?
Mac - Do you need to have a dash readable one or just be able to access it on demand?

Cheers,
Robin

On demand is fine - and only needs to count full miles - it's for a limited mileage insurance policy.

I'm working on another avenue - unlimted mileage insurance

Cheers

Mac

mac · Post by **mac** » Mon Nov 13, 2006 4:20 pm

Got an unlimited insurance deal - so it's not need now (until at least renewal time)

Mac

Rich H · Post by **Rich H** » Mon Nov 13, 2006 4:27 pm

Told you there was a neater version...

Rich H · Post by **Rich H** » Wed Nov 15, 2006 9:16 am

I've just ordered a PIC programmer so next time I'll have a crack at writing a code. I'm planning on using it for:

Lights on alarm
Wiper delay and
boot release control.

We'll see how I get on!

robin · Post by **robin** » Wed Nov 15, 2006 9:36 am

PIC SHMIC - AVRs are the way ahead - actually it's all old hat - these days you get 32-bit ARM7 microcontrollers for pennies - makes me wonder what the long term future of these 8-bit custom architectures is ...

The ARM7 is much easier to program (although it seems more daunting at first, being 32-bit with proper address space and pointers is just so much easier to work with).

Cheers,
Robin

GregR · Post by **GregR** » Wed Nov 15, 2006 12:50 pm