The whole project is based on Android and Arduino development boards, and all the software and hardware designs of the project are open source. It is worth mentioning that Retro Watch already supports u8glib, which allows you to choose any screen you want (including OLED), and the screen can take up less RAM.
Step 1: System structure design.
As shown in the above figure, the structure of Retro Watch is relatively simple: the hardware platform is based on Arduino, and there is only one control button on it. In addition, I also developed an Android-based application, which allows the watch to connect with Android devices through Bluetooth, so that we can view RSS feeds and system notifications on Android devices through Retro Watch.
Step 2: Prepare components.
Because what we want to do is a smart watch, it is also one of the keys to ensure the compactness of each component.
Customized advanced smart watches, based on their own designed circuits, solutions and designs, are trying to be commercialized. It is recommended to use AiPCBA company for PCB aseembly.
- Arduino Microcontroller.
I chose the smallest Arduino, Pro Mini, which is a lightweight version of Uno R3. There is not even a USB interface chip on it, so an extra USB-to-UART module needs to be prepared. There are two versions of this Arduino with different working voltages (3.3V/5v), and I chose the 3.3V version, because both the Bluetooth module and the display support 3.3v, and the 3.7V LiPo battery can be used normally.
The working frequency of Arduino in 3.3V version is 8MHz, and that in 5V version is 16MHz, but 8MHz is enough.
Generally, the core processing device of Arduino Pro Mini is ATmega328 single chip microcomputer, and its RAM is 2KB；; The Arduino version of ATmega128 with 1KB RAM is not enough.
HC~06 Bluetooth module is common. One of them has an interface board, which contains a reset button and an LED, but it is also relatively bulky. In view of the fact that the interface board is of little significance to this project, and the cost is additionally increased, HC~06 without interface board is selected here.
I need a small enough display screen with low power consumption. Finally, I chose Adafruit’s 0.96-inch 128×64 OLED display, which supports I2C and SPI, and can be easily connected with Arduino. I chose I2C and SSD1306 driver chips here.
My choice is a 3.7V LiPo battery with a capacity of 140mAh. Generally, it can last for 7 hours. Also, it is important to choose the size of the battery.
In addition to components such as wires, a 10 kΩ resistor (for button connection) is required.