I use a Linux box with a cheap (but extended-range) bluetooth dongle to monitor the invertor for my solar panels, and also my central heating monitor. This is fine, except that occasionally the bluetooth dongle seems to crash, and it needs to be physically unplugged to recover. Since there doesn't seem to be any comprehensive way to do this through software (you can reset the device, but it doesn't perform a power interruption so doesn't recover it sufficiently), I decided to make a little hardware dongle to do it for me.
The design is extremely simple - just use an ATTiny to periodically (perhaps once a day) interrupt the 5V USB line. All other USB lines (data +/-, GND) pass straight through. Rather than power the attached device directly from an ATTiny I/O pin (which can only source ~40mA) I drive the attached device's power line through a PNP transistor (in this case rated at ~ 200mA, which is enough for my purposes, but 500mA would be needed for general purpose USB loads).
Continue reading "Automatic USB disconnector"
