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Posted by: jim_hoyland Nov 15 2012, 04:32 PM

I'm looking for an MSD module ( or pill), or set of modules, that are pre-set for 4400 rpm + or -
I have a 5000 to sell or trade, its a little high for my needs.

They look like this:

Posted by: jim_hoyland Nov 17 2012, 12:49 PM

Would also consider a trade. I have a new and unused MSD Module selector with a range of 4600-6800 rpm; would like to trade for selector with 3000-5000 rpm range, or for individual modules in that range.

Posted by: ArtechnikA Nov 17 2012, 04:25 PM

There is no magic - the 'pills' are just resistors like you can buy at any well-stocked supplier like DigiKey or Mouser.

Pick the resistance you need from the chart...

Posted by: Jeffs9146 Nov 17 2012, 04:36 PM

I have a 3000 pill!


Attached thumbnail(s)

Posted by: campbellcj Nov 17 2012, 04:54 PM

LOL, what are you guys driving, 8L diesels? (Actually I think the 3,000 RPM pill is the one they include for testing, right?)

Posted by: jim_hoyland Nov 18 2012, 09:21 AM

The 3000 pill comes with the MSD RPM Activated Switch. Given the resistance/rpm chart above, can an rpm activated switch be made from Radio-Shack parts ? How might that be done ? Curious minds want to know...

Posted by: ArtechnikA Nov 18 2012, 09:41 AM

Those two thoughts aren't related...
The resistance is what the MSD-6AL rev-limit circuit uses in its comparator circuit. Each comparator circuit design will be different.
For instance, I believe the Crane HyFire is actually digital.

I'd guess the MSD circuit is probably charging a capacitor of a known value through the resistance. Or possibly discharging at a known rate through the resistance, since no pill == no limit...

But either way, you have something that's reset by each trigger, and a resistance-proportional charge/discharge rate, and an analog comparator (just a transistor?) that turns on the rev-limit circuit when the charge level is at the threshold.

I bet a real EE could sketch up such a circuit on a napkin in 10 minutes. I'd have to re-learn a bunch of stuff to figure out appropriate values for the resistors and capacitors, as well as the relay drive part to do whatever it is you want done when the rev limit is achieved.

You could also complexify it with microprocesor control and digital counters and such, but it's really not that complicated and the application tolerances don't require it. (E.g. - if you had a couple of rpm drift from cold to hot, it'd be fine...)

I gave up on finding any useful parts at Radio Shack a long time ago. Now they just sell cell phones and such...

Mouser and DigiKey get my business now...

Posted by: ConeDodger Nov 18 2012, 03:51 PM

No. The 3000 RPM pill is the one I put in when my kids turn 15.5.

Posted by: ConeDodger Nov 18 2012, 03:55 PM

Jim, I have bunches of the resistor pills. The are at my storage garage right now though...
Two 6AL boxes for sale and an 8910 tach adapter. I just have to take pictures and come up with pricing...