A USB Connector For The SparkFun AVR Stick
Lately I’ve been playing with the AVR Stick sold by SparkFun Electronics. Although it’s described as a “simple data logging device”, it can also be used as a minimalist AVR USB development board. It contains an ATtiny85 and the circuitry necessary to implement a USB client using the V-USB library. Though the default firmware implements a HID keyboard the programming pins are brought out to pads, which makes it simple to replace the default firmware with your own. In the words of the product description, “This thing is meant to be hacked!”
However, the USB connection on the AVR Stick printed-circuit board (PCB) can be a problem. You may notice in the picture above that instead of a connector, the USB connection is made via traces coming to the edge of the board. This can result in poor connectivity for many USB ports or hubs. To fix this, it’s been suggested that a male USB A connector be attached to the PCB. That’s the fix I’ll describe here.
To make this modification you’ll need the AVR Stick, a USB A male through-hole connector, a rotary tool with a grinding or cutting attachment, and a soldering iron with solder. To start, take the USB connector, straighten the four USB signal pins, and bend them slightly downward. Using a pair of clippers, remove the two plastic posts that are used to hold the connector in position when mounted on a printed-circuit board but don’t touch the two metal tabs on the side of the connector.
Use the rotary tool to grind two notches (one on each side) on the AVR Stick PCB about 1/16″ from the end with the USB connector traces. The notches do not need to be very deep. The idea is to make them only deep enough so the metal tabs on the USB connector fit into them with the AVR Stick PCB butting up against the connector edge. See the pictures below for an example of the completed notches on one of my boards and how the connector should fit into them.
Put the USB connector on the AVR Stick board so the metal tabs fit into the notches and the connector’s USB signal pins overlap the USB signal traces on the PCB. Fold the USB connector’s metal tabs over to hold the connector to the board, then turn the board over and solder the connector’s USB signal pins to the AVR Stick USB signal traces. This completes the modification. The pictures below show top and bottom views of one of my modified boards.
The modification can be tested using the procedure described on AVR Stick product description page. Just be careful when plugging and unplugging the board so the connector doesn’t break free. It’s probably easy to replace but if it takes one of the traces with it you’ll be out of luck.