Modding Arduino USB Board to Auto Reset

The project illustrates an old Arduino USB board being hacked by finding the right pins and stringing a capacitor between the serial connector and the reset line.

One side of the capacitor connects to the DTR line of the USB-serial chip and the fourth pin from the left on the upper edge. The other side connects to the reset line which appears to be available only on the microprocessor, the ISP header, and the reset button. The reset button on the underside of the board was chosen. A wire-wrap wire is used instead of a capacitor with long leads, sleeving them, and connecting them directly to the pins at both ends. The insulated wire-wrap wire was laced through open bias in the board to keep things tidy and the capacitor snagged down.

The hacked Arduino board is old that it has the ATmega8 instead of the ATmega168 and the ATmega bootloader image has not been updated for the auto-reset. Interestingly, the ATmega168 bootloader code includes conditional compilation for many different ATmega chips including ATmega8.

The capacitor-reset hack was easily adapted to the Arduino USB with a little soldering and an upgrade.

Read more