Since now I have working prototypes of the Gyro’clock, my next step is to make it more practical and usable. The prototypes are bulky and fragile, not something I can carry around with me in my pocket. So I have been working to make it smaller and more reliable.
I decided to find replacements for all the through hole components on the prototype board with their surface mount counterparts. For resistors and capacitor I decided to go with the 0603 package. I could have gone for a smaller size still, but looking ahead since I would have to place them on the board by hand, 0603 is a safer choice.
Next I had to find replacements for the two breakout boards I used in my prototype. The breakout boards got to go because they are expensive and take up too much space. The easiest of the two breakout boards to deal with is the ADXL345 breakout from Sparkfun. The only components on this breakout board are the ADXL345 accelerometer, two 0.1uF capacitors and one 10uF capacitor. All of them could be bought at a much cheaper price individually.
The other breakout board is the USB charger for the Li-Po battery from Adafruit. This breakout board includes a JST connector for the Li-Po battery, a micro USB connector, two status indicator LEDs, MCP7383 Li-Po charge management controller IC from Microchip and several resistors and capacitors. I decided to include the MCP7383 on my board with a single bicolor status indicator LED, a micro USB connector along with three resistors and a capacitor. Instead of using a JST connector for the Li-Po I am going to solder the Li-Po wires directly to the board.
The last thing was to choose the right LED for the job. I liked the water clear 3 mm red LEDs I used in my prototype. But to increase the viewing angle I had to sand the LED caps. I was searching for LEDs with a large viewing angle and ran into square shaped LEDs from SunLED. This LED has a viewing angle of 110° and are already diffused.
The figures below show the schematic for the new and improved Gyro’clock circuit
In addition to all the components I also added test points to certain locations to help with troubleshooting the board later on. One other very important consideration is how to program the ATmega328p microcontroller while it is attached to the board. In the prototypes I removed the microcontroller from the dip socket and transferred it to a breadboard setup for uploading the program. But now with the SMD version this is no longer possible. So I added a program header to the schematic and also added jump points in the traces so I could disconnect the necessary pins from the rest of the circuit when programming.
And here is a list of all the parts in the new Gyro’clock circuit:
The next step is laying out the components and traces, which I will cover in my next post. Stay tuned!