Thread: Harbor freight pressure pad and air cannon

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I just picked up one of the harbor freight pressure pads and wired it up to my homemade air cannon. Super easy and works like a charm. I have about $80 invested in this project. I was going to use a motion senor, but there was too much delay time for the cannon.

Very cool! you should post a tutorial.

Does it drain the tank when it fires or is the pressure mat a momentary switch so it just fires quickly? I have a cannon built but didn't use it last year because it would empty my tank every time it fired.

those are not momentary switches. I had to use the fog timer contraption I made up last year to use these pressure pads with my pneumatic toe pincer's

Originally Posted by tekcor1

Does it drain the tank when it fires or is the pressure mat a momentary switch so it just fires quickly? I have a cannon built but didn't use it last year because it would empty my tank every time it fired.

It fires as long as you are standing on the mat. So yes, a momentary switch.

Hello, this is Bozz’s son; I’ve been tinkering with electrical engineering for a few years now, and have been assigned the problem of hacking the various pressure mats.

After testing both the Harbor Freight and Spirit pressure mats, I have concluded that they are different types of mats. By checking the resistance of the mats, we can see that the Harbor Freight mat is acting like a simple momentary switch; lowering in resistance when pressure is applied. However, the Spirit mat shows no change in resistance, but produces an impulse of voltage when pressure is applied. This implies that the Spirit mat is a piezoelectric transducer (http://en.wikipedia.org/wiki/Piezoelectricity, http://en.wikipedia.org/wiki/Piezoelectric_sensor); and should not function with props that require a closed circuit. It may be possible to build a simple trigger circuit for the Spirit mat using an amplifier and FET transistors.

My friends and I are fixing a car to race low-budget style. Found a used engine today and looked at it, everything looked great but the new leak down tester I bought from Harbor Freight gave strange results. We used 100psi input, but the regulator starts at zero. At about 20psi the right gauge that shows the pressure in the cylinder was at "zero" which on that gauge means "max" and is as far as it goes, but the instructions said to use 100psi. Anyway, heard air coming from various places. Later read a post somewhere where guys were complaining about this tool and indicated that the right gauge instead of being 100psi is only 15psi. Anyway, wondering if our engine is OK internally, the rest of it checked out ok. May have to get a better tester I guess and do like at 100psi like they say and see what the drop is. Any hints? Realize I need to have the crank secured at 100psi.


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You may want to check over in the "Low Budget Halloween Racing" subforum. This is the "Props" subforum, so unless you're fixing that race car up to scare the TOT's, you may be in the wrong place...