Live from Gnomedex

The Moose is in Seattle now, recruiting sources for the Public Insight Network.

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Arriving in Seattle

Just getting into Seattle for the Gnomedex conference.  Should have just enough time to check in and head over the registration party. More later.

Just noticed I’m wearing my Nerdery Overnight Website Challenge t-shirt. Really, I didn’t plan it that way.

Old RC toy made into a garage alarm

My wife wants some sort of indicator to show when the garage door is open. The garage is visible through the back window, but sight lines make it difficult to determine. Also, when the shades are drawn, there is no visiblity. I considered X10 modules at first, but that just seemed like overkill when all I really wanted was a small led to illuminate.

Then, I remembered an old RC toy car my son had. The controller unit was simple, with just one button. Pushing the button made the car go forward. Releasing it made it go backwards while turning. On the receiver (car) side, the controller signal caused a voltage to toggle between -1.5 volts and +1.5 volts. With a little testing, I found a point that toggled between 0 and +3 Volts. This was just enough to provide drive an LED. A magnetic reed switch from Axman Surplus worked perfectly for the door sensor. This switch is in the off mode when the magnet and reed unit are near each other (door closed). When the door opens, the magnet will be pulled away and complete the circuit. The transmitter and switch are hooked up to a PIC16F684 chip. The reed switch is connected to pin 4, which is configured as a digital input. When the reed switch is open (door closed), the signal on pin 2 goes high. This turns on an NPN2222 transistor, which in turn causes the transmitter to send a signal. The receiving unit goes to +3 volts on the output when there is no signal, and drops to 0 volts when there is a signal. In other words, when the door is down, the LED indicator is off. This may seem overly complicated, but it has one advantage. If the garage-side (transmitting) unit fails, the light will come on. Although this may be a false positive for the door being up, it indicates that something is wrong on the transmitting side (power failure, loose wire?).

Circuitry from RC car repurposed as a garage door alarm

Side glow cable with LEDs

Many projects require illumination.  An LED is often a good choice because it can be bright while using a minimum of current.  An ultra bright LED can even drive enough light through short lengths of side glow fiber optic cable.  This cable is flexible plastic cable with a reflective core to direct light to the side, as opposed to simply transmitting the light to the end of the cable.  While it is designed to be used with bright halogen bulbs that push light through hundreds of feet of cable, I was interested to see how well an LED could work with just a few feet of cable.

My wife and I are interested in making safety clothing for night bicycle riding and thought this might be useful. We ordered a five foot section of 3mm wide cable from here. Once I had the cable in hand, I attached a bright red LED to each end with shrink tubing.

End connections

A quick test shows that two LEDs provides a fairly even glow along the entire length of the tube. Each LED was rated to deliver 18,000 millicandelas of light.

Two LEDs powered up

This looks like it could be used on a bicycle helmet to provide a flashing illumination. More to come as we experiment.