This circuit is used to test a usb IR "PC Remote" receiver available on eBay. The USB-Serial bridge is used to communicate with the ATxmega128A1 with the custom firmware provided below. Bytes received over serial are retransmitted over IR. Alternatively, commands may be selected by pressing SW0-SW6 and then sent by pressing the SW7.
The IR transmitter circuit is simply an IR LED with a 180 Ohm resistor in series. This is fine for testing purposes, but the range is not great. A transmitter circuit can be added to increase the range of the signal.
This circuit is used to tune a guitar using two strobing LEDs. The circuit is used like a pick and then held next to the string so the LEDs shine on the string. If the guitar is out of tune the two spots illuminated by the LEDs will move relative to each other. Adjust the tuning of the string until there is no movement. Pressing the button switches between strings (as indicated by the small LEDs). After cycling through all of the strings the device goes to sleep.
In order to program the ATTINY25 microcontroller, a temporary connection must be soldered to the programming pins.
The battery is charged using another temporary connection.
The end of the "pick" should be sanded down to remove any solder mask/copper and to smooth the edges.
The via under the battery should be covered with a small piece of tape to ensure that there is no unintentional shorts.
Shrink tubing should be placed on the strobe LEDs to direct the light to the guitar strings.
This circuit generates a constant current between 400 and 700 mA (controllable with a potentiometer). I originally designed this circuit to power a high-power LED, but it can easily be used for other application.