Electronic Wizards Help? (non-MJLJ)

JamesC · Post by **JamesC** » Tue Jul 18, 2006 11:37 pm

I am fairly up with my electronics - done my own PCBs and bits and bobs. Studied it a bit at school etc

What I want to make is a rally tripmeter - it pains me to pay Â£100+ for something that really just counts and divides.

So then I remember back to looking through electronics catalogues - and I remember counter gauges! Aha - this could be useful.

For those that don't know how rally tripmeters work - you set the "master" unit to "1" and drive a set distance (a mile or kilometer) - so the display now counts every time your wheel turns - lets say it ends up at 256. You now then set the master unit to 256 - and the display will now count your miles.

I think something like this well work...? Seems to be an all in one unit...

http://www.mew-europe.com/home/www/eu/d ... 4hs_en.pdf

The counter units on their own are far cheaper - but they need some sort of settable "divide" circuit for the input - so that it counts to 256 then makes the thing count up to 1.

James

4600cc · Post by **4600cc** » Wed Jul 19, 2006 2:43 am

Find out about Ford VSS, Vehicle Speed Sensor, and how to interface it with processor Brent is using for MJ. Basically, you'd want to use much of what is Megajolt is already using, only now you'll be reading the VSS sensor. That way you could make a computer program that will do that and much more. A bit complicated, but a combination of a simple unit and laptop or PDA could make a best implement of what you want. (i.e. reuse Megajolt hardware)

MartinM · Post by **MartinM** » Wed Jul 19, 2006 7:56 am

Well, you've just picked on an area that I've investigated pretty thoroughly!

I, too, was unhappy that it cost nearly Â£200 for a twin (total/trip) display tripmeter, so I designed and built two prototypes last year/early this year. The component cost is around Â£30 or less. I used the first prototype on a real event - it was good, but the second version is even better!! It is more functional than the equivalent Brantz/Terratrip and there's plenty of processing power to make it as good, if not better than the Coralba stuff

My idea was to market them in a similar style to MJLJ - ie a reference circuit board, open source software, component kits, ready made units etc.

What I desperately need is a PCB design - I tried to learn Eagle to design my own but I found it very hard and frustrating. Also, it needs a suitable case with quite a few cutouts for displays and switches, plus legends, and I don't know how/where to get cost-effective low'ish volume production runs

So if you're good at taking hand-drawn circuit diagrams, turning them into schematics and making high quality board layouts (will need to be double-sided), then we could have a partnership! Or anyone else for that matter! I would estimate that the board is 2-3 times more complex than the MJLJ board

I also have another in-rally car unit, built and prototyped with great succes, that needs the same process and it's a completely unique offering that I'm sure would be very popular if marketed in a similar style. I've other ideas on the back of envelopes as well...

BTW, the preprocessing of the incoming distance signal is a bit more complex than dividing by 256 (an unfortunate choice since it's a power of 2 and might seem easy to implement - try the maths with 483!) - you actually have to divide by 2.56 (or 4.83), since the display must be accurate to 0.01 miles, and that can be tricky, but I've designed and coded all the algorithms and they work perfectly in the real world. You also need to maintain two independent counters, one for each display - perhaps even running them in different directions (one of my USPs!)

You need a fairly high speed processor to do all this, and when you've got one of those you might as well do the display handling yourself and then you're into the realms of Â£2 4 digit 7-segment LED displays to keep it all cheap.

I don't think the counters you've found are ideal - two problems are that they dont have decimal points and I think the digits are too small to be useable in a rally car

Send me an email (m il l e n ers (at) h otm a il (dot) c o m) and we can continue off line....I really would be keen to pursue both these ideas!

JamesC · Post by **JamesC** » Wed Jul 19, 2006 6:34 pm

Martin - email sent.

Alex - the last thing you want when doing a rally is a laptop or PDA... it's got to be super simple and clear.

This is what one looks like...

Simple... <img src="http://www.donbarrow.co.uk/bint1.gif">

Complex... <img src="http://www.donbarrow.co.uk/br2sa.gif">

4600cc · Post by **4600cc** » Thu Jul 20, 2006 5:47 pm

I know I know. Simple is simple, complex make you curse.

I might be able to help with PCB design. Is there good PCB design software?

bhwm · Post by **bhwm** » Thu Jul 20, 2006 8:42 pm

I think this could work as a basic tripmeter. Looking at your data sheet (page 8 / 89) it appears to include a decimal point and prescaler / divider for calibration. Assuming it will connect to your sensor ok, then you would have an all in one unit.

bhwm · Post by **bhwm** » Thu Jul 20, 2006 8:44 pm

I am interested - will send you an email.

MartinM · Post by **MartinM** » Fri Jul 21, 2006 8:07 am

How much are they?

JamesC · Post by **JamesC** » Fri Jul 21, 2006 8:29 pm

I'm not sure on that model - the one with no scaling function is Â£30 or so from Rapid Electronics.

You could make one using the non-scaling one quite easily... as it has an output when a set value is reached. You could use this connected to a counter display. Would probably work quite well like that. For decimal places - you could just divide your pulse per mile number by 10?

Martin - did you get my reply email?

Gilesy998 · Post by **Gilesy998** » Sat Jul 22, 2006 5:06 pm

I use EasyPC at work, seems a good package.
You input the circuit, then draw the board and it tells you when you have a wrong/non-connection. Good stuff for a free trial -
http://www.numberone.com/downloadrequest.asp?P=Easy-PC

Autosport Labs