Monday, May 30, 2016

Limit switches and spark ignition

Got the limit switches and the spark ignition working together.  This was a bit trickier than it sounds.  The limit switches are springs held onto the rail using a high temp epoxy.  (Photo below was from when I was testing them, before I soldered the leads on.)

When the shuttle contacts it, it closes the circuit to ground.  Running a 15 foot line causes a lot of line noise, especially from the line running next to the motor, so I added in a simple low pass filter similar to the one described here.

The spark gap igniter uses the same unit I used for the backpack poofer, which unfortunately is no longer manufactured; not sure yet what I'll replace this with (looks like you can get similar things on EBay by looking for "high voltage pulse ignition coil".  I thought I was being clever by using the chassis body as the ground for the igniter, meaning I only needed a single electrode.  And it worked!  But, as I discovered, this has other unfortunate effects:
Luckily, I have some spares lying around, and Arduinos are cheap.  So, I rebuilt this with two electrodes, held apart by high temp epoxy (I'm using this stuff a lot now, hoping it will hold up!)

And it all works together nicely.  Here's the limit switches and igniter being driven by an Arduino, with no crosstalk or interference:

Next step: add in the gas solenoid, and run the whole thing back and forth.  Also need to add some small cross strips in place on the top opening to keep the hose carrier from riding up.

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