Introduction: With the criteria of ease of assembly, the first problem is the FTDI USB chip which even for the experienced assembler is not an easy mounting task, but the availability of small FTDI breakout boards solves the problem. I am using the BUB II by Modern Devices since they leave the connector for you to assemble which I add underneath the board.. Adafruit has the Friend, but it is pre-assembled with the connector on the top.
The standard 7805 type regulator is real-estate hungry and two will be needed, so surface mount LDO regulators are used. These are three pin devices and mounting is not difficult. Low drop out, LDO, devices are used to limit heat dissipation. In fact, we use a 6V wall power supply which at low current has a 8.5VDC output where a 9V wart is at 12VDC.
The commercial Arduino uses a circuit for switching between external power, wart, and USB which can take up surface space unless smd parts are used. Further, it would be nice if RS232 serial communiction could also be used which means the clone would need to supply power to that breakout. So we opted for jumpers for both power selection and board voltage. In addition a power switch was added for convenience during development and if not wanted can be jumpered out.
Finally, a vertical reset switch is placed at the front of the board as well as the LED's. This means that with a shield mounted on the Arduino the reset button is still accessible and the LED's can be seen.
- Use of thru hole parts except for regulators
- Dual regulators for 5V and 3.3V
- Use a breakout board for serial communiction
- Place LED's and reset switch at front of board
- Add power switch
- Use jumpers for selecting power source.
|GMduino with BUB II. Note the mounting position of BUB II connector.|