Bored of making the same old circuits again and again? Want to try out something cool? Then just follow the article and find out how to build a USB HID keyboard device.
The keyboard is used to key in a password everytime it is plugged. The password keyed in is stored in the EEPROM. Tabbing CAPS LOCK a couple of times will cause a new password to be created.
The same power source that is used in an ATtiny85 USB is used in this case to power the device. The entire circuit would be better of being enclosed in a casing. Adding a 0.1uF capacitor between GND and VCC would be a good idea, but it is not mandatory.
In this case, the outer casing of an 512 MB flash drive is used to enclose the circuit. The entire circuit is accommodated on a tripad veroboard with 1×8 pads.
All the components including the zener diodes, resistors, jumpers and the ATtiny are soldered to the board. This marked the end of the circuit design. The circuit also worked without any problems, when tested. It is always recommended that the circuit be implemented initially using a breadboard. If the circuit works fine on the breadboard,then it can be soldered to the veroboard.
The computer recognizes the device as a USB HID keyboard. It is possible to communicate with the device by means of a boot-compliant keyboard, that gets status change updates from the PC.
One thing that has to be remembered when building the circuit is that restoring the password that has been reprogrammed is not possible. So to be on the safer side, the passwords generated should be stored in a proper place.
Click here to visit the project page.