The Texting Trapper

Posted by on May 16, 2012 in Blog, Etc | No Comments

Oliver Tanner and I are exhibiting the Texting Trapper at Maker Faire Bay Area this upcoming weekend. The Texting Trapper is a large scale exhibit which detects the strength of your cell phone.
Oliver designed and fabricated the 8 foot tall VU meter. It’s made from 8′ tall aluminum, which he welded into custom extrusions to hold eight 8″ x 24″ pieces of white acrylic.
Here it is in the light:

And here it is in the dark (yes, that’s Oliver):

I made the LED panels from reels of LEDs. It was a lot of work, but The Buessli helped me!

I spent days troubleshooting a really annoying issue. When the whole thing was set up, the 10th panel (at 8 feet up) was noticeably less bright than the others. In fact, it drew only 0.44 Amps, while the 1st panel (2 feet up) drew a full 1.08 Amps. The 3rd, 4th,…8th, 9th panels also got increasingly less bright and drew less Amps as they got further away. The first troubleshooting direction I went in was line losses. This brought me to charts and wire gauge inspection – I’m using 18 AWG – and to a number of sites about 12V lighting schemes which said beware of the line loss problem.
I was almost convinced except that 18 AWG loses 1.27 Volts over 100 feet. Even with the extra back and forth of making the panels, I had at most 30 feet of wire. It just didn’t make sense. I then took the whole thing out of its nice acrylic frame and laid it all out on the floor. I measured a 4 Volt drop at the 10th panel! Well, this didn’t make sense at all. After a couple of people insisted that I need to use heavier gauge wire, I swapped out the 10th panel’s 18 AWG for 12 AWG. No joy.
I texted my friend Jon and he suggested that my power supply was bad. After going through THREE power supplies that did not meet specification (they did not have the Amp draw advertised on the label), this was determined to be the problem as they stopped producing power at 3 to 5 Amps.
So I traveled to California with an RC heli battery charger in my carry-on and have a 30 Amp power supply shipping here. Let’s hope it all works on Saturday!

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