Microsquirt & Rev Counter

[Nick Jones]

Maplins are (regrettably) pretty useless for actual electronics these days.  Too busy selling Chinese gadget tat.  Some stores do hold a few components in stock.  You can check stock levels online but take with a pinch of salt and as you've observed the spotty oik customer service person probably can't tell a resistor from a transistor.  The Yeovil Store does have a couple of good people but not always on shift.

 

I occasionally use them via mail order mail order, but more often Rapid Electronics, Farnell or RS Components.

 

Variable resistor/potentiometer are not strictly the same thing.  A variable resistor has two connections only and the resistance between them will vary between 0 and the rating as the adjusting screw/shaft is turned.  You can use a potentiometer as a variable resistor as it has three connections.  Two of these will be either end of the resistance track (resistance between them should equal it's rating and will not vary as adjusted) and the third is the wiper.  Measuring between the wiper and one end of the track will see a resistance variation in one direction as the shaft is turned and using the other end of the track would reverse the direction of variation.  Connecting between one end of the track and the wiper will cause it to function as a variable resistor.

 

I'll have a rummage through my collection of random electronics bits and see what I have - I quite often buy two sets in case I let the smoke out the first time.....

 

VR settings were established on a twiddle-it-and-see-basis...... not very scientific but it's been working 10 years.

 

Nick

[Darren Groves]

Hi Nick,

 

You won't be surprised to hear that neither of the fixes that suggested adding resistors actually worked.

 

I've identified the bits I need for you fix except the Variable Resistors, so if you have them great, if not maybe you could identify them online for me. Still could only find potentiometers even on the suppliers you recommended.

 

Thanks for the help

 

Darren

[Nick Jones]

You can use potentiometers - just connect one end of the track and the wiper.

 

Nick

[Darren Groves]

I tried your set-up Nick, but it didn't work for me. Done it twice just in case, but nothing at all. So I have taken the easy (read expensive) option and sent the rev counter off to Speedy Cables for them to convert. I was sending them my Speedo to be re-calibrated anyway, so just bit the bullet. At least combining the 2 gauges saved some postage....

[Nick Jones]

Sorry to hear that it didn't work.  Little surprised also as it did for me when nothing else had!

 

One other thing for the record is that you can use an RVI type Lucas tacho quite easily.  If the car you are converting had one as standard, just use the original coil +ve wire as the coil pack supply and it will work as before.  If adding one, just connect the tacho in series with the coilpack supply and it just works.  Made getting the tacho to work in my PI very easy!

 

For a 4 pot Triumph the problem is finding a suitable tacho as I don't think any 4 pot Triumph had an RVI tacho from the factory.  You'd probably have to use an MG one 

 

Nick

[Darren Groves]

Thanks for all the help, I'm sure it's more to do my skills with electronics why it didn't work, but decided I'd spent enough time on it. I've been meaning to send off my Speedo for calibration for ages so seemed the simplest option, it's only money after all!