Occasionally, Woot has extravaganzas where they post item after item in what is known as a woot-off. Little .gif lights spin round and round to alert visitors to this spectacle. Playing on this, Woot occasionally sells physical woot-off lights. They run off of USB power, with a switch in each light/motor piece. Since it’s a standard 5V connection, this opens the doors for all sorts of hackery.

The ultimate goal of this project is to have these lights come on whenever there is a woot-off.

If you aren’t already familiar with the Arduino, become familiar now. I’ll wait.

Ok, so the Arduino is a microcontroller system with a USB-serial input communication, a microprocessor with a bootloader to run “sketches”, and the ability to control over a dozen digital logic pins (including a few with PWM or Analog-In).

The setup will use a PC application for monitoring a “Woot Tracker” (many of these are available online to reduce load on Woot’s own servers). The application will check for the presence of the woot-off lights logo, indicating a woot-off – in the future, the lights will be activated by each changing of an item. The application will then send a byte over serial to indicate the woot-off status to the Arduino. Based on the input from the computer, the Arduino will turn the lights on or off.

Great – so in order to turn on the lights all we have to do is turn on one of the Arduino’s pins (they are 5V at digital high). Unfortunately each pin is only capable of supplying at most 50mA, and these lights run on over 100mA. Luckily, the 5V power regulator on the Arduino is capable of supplying much more current – up to 500mA or so if a good DC power supply is used. So if we hook up the positive lead of these unit to the 5V, we now need to control the ground connection to control the circuit – connect the ground and the lights go on because the circuit completes.

The ULN2803 chip provides this exact function. The chip is connected to 5V and ground. The ground from the device to be controlled is connected to a pin (remember that the positive of the device is already connected to 5V), and the control signal from the Arduino is connected to the corresponding control pin. When the control pin sees 5V (from the Arduino control signal), the ground lead from the device is connected to the ground of the chip, completing the circuit and sending current to the device. In this case, the lights spin up.

Early Woot-Off Light Software/Arduino Control

So far I have the hardware running, and have used the Arduino PC software to send input down the serial connection, turning the lights on and off. The next step will be to write an application to send serial information, and then to expand that application to search the textfile of the woot tracker for the lights.gif. The final stage will be to integrate all the hardware into a small package so the device can be used permanently.