## 20100529

### Do it Yourself : Trip Visor

Thanks to a dumpster diving friend I had come into possesion of a pair of welding goggles, as well as some white translucent plexiglass. So, the old hallucination goggles project was adapted for this new, awesome, rugged, form factor.

Step 1 : electronics :
I chose to use an Arduino Pro-mini, two RGB LEDs for the goggles, and a 4 character multiplexed 7 segment display.

Step 2 : draw a circuit board. I like to use a generic drawing program so I can put graphics in the copper pattern. Some PCB drawing software will also allow this, although not all PCB fabrication services will do custom graphics. I skipped out on the current limiting resistors for the blue and green channels, since the supply voltage is actually lower than the LED driving voltage. I still needed them for the red though. This kind of design is very general, as you just need to get some LEDs to blink in a controlled manner. The circuit looks like this :

Next, transfer pattern, etch, drill, clean. It is easier to wire this up on a breadboard and then transfer it to a radioshack protoboard, to save on the hassle of making your own board. Here is a tutorial that I loosely followed, and here is a previous post where I practiced the technique, and below is the finished result. I made the traces from the Arduino to the LED display a too narrow, and unless you're careful this design requires clean up after etching.

I was wrong to try to drive this circuit from coin cell batteries. These batteries do not put out enough current to drive the LEDs. I worked around this by adding a 2xAAA battery pack to the interior of the goggles. If you copy my design, bear this in mind and adjust accordingly.

My friend laser cut white plexiglass to replace the tinted glass of the welding goggles. This is a square cut that could also be accomplished with a saw. These goggles have a slot for a piece of plexiglass on the inside, and another piece on the outside, with 7mm clearance in-between, so it is straightforward to sandwich the LEDs between two sheets of plexiglass to create diffused light. Position the LEDs approximately in the center of the visual field in each eye, so that when you look at them through a pane of the white plexiglass, they line up as if they were one diffuse source. I used standard connectors for indicator lights and power buttons in PC cases to connect the LEDs, and a rocker switch from an old Ikea lamp, to finish off the connections.

This is more durable than past designs, since it doesn't have a separate part for the driving hardware and the goggles, connected by a failure prone cable. Reminds me of this. I can actually toss this one around without breaking it.

1. Building a pair of my own may become my summer project, since I think I found a way of getting the parts for free or cheap

2. So, this pair was surprisingly cheap since I didn't have to pay for the actual goggles part, and then not having to try to construct a cable from the electronics to the goggles also saved some money. I think it cost maybe $30-$40 in actual new parts, which is about half of what if costs me to make some of the other ones.

You wouldn't be interested in sharing think knowledge of getting free cheap parts by any chance ? Does it involve theft ?

3. Evan2.6.10

I'm planning on using the resources of these fine individuals.

4. Update : one of the characters has dropped out on the display; maybe those traces were just too narrow. Any special tricks for running traces that don't crack under repeated strain ( besides not using RadioShack boards )?

5. @Evan

.... salivating over free parts; never saw anything like that at Caltech and here at CMU we just had a scrap heap you had to pull from, and now even that seems to have vanished or moved.

6. So, in retrospect, I think traces have been breaking on my boards for two reasons.

the main reason the traces are breaking is because I mount my boards in such a way that they can flex. The copper traces can't flex, so the thin ones crack. This happened with the AtTiny13 goggles near the connector, and happened on the welding goggles because the board was mounted sloppily on flexible plastic, and is under strain.