This document is also translated in Polish(by Sebastian), Korean language.

Most IT companies participate in the race to grab people’s wrist. A smart watch becomes the most significant item in a wearable device category. You can easily find this mood in this link, there are tons of smart watches.

But here is a simple way to evaluate smart watch’s future on your own. Make it! With Arduino micro-processor and Android, I made a simple smart watch and named it “Retro Watch“. You can do this too!

Retro Watch is an open source project to let you make a smart watch based on Arduino and Android. This document explains about modules, blueprints, how to install and use the Arduino and the Android source codes step by step.

Release note

Updated (2015.01.12) : RetroWatch supports u8glib. Now you can use various kind of OLED(or else) as you want and it consumes less memory. Instead it’s liitle slow at screen refresh. You can find updated sources at GitHub.

1. Overall Structure

RetroWatch is a simple system that is used a hardware platform called Arduino, which is intended for artists, designers, and hobbyst, and an Android app. The overall structure is below here.

Structure overview

Imagine a very small computer that you can wear on your wrist. Arduino board is a micro-processor and a storage, and there’s only one input method : a button. Bluetooth is to communicate with other devices, and the battery would be necessary for power. I’ll install an Android app for collecting or editing various RSS and system information and for notification on the Android device. This app will also process the data because the Arduino board has very limited resources.

2. Preparing for RetroWatch

You need to prepare modules as small as possible to wear the watch on your wrist. There may be tons of variations, but I chose parts that are commonly used and inexpensive. You can replace modules to the others if you want, and you can even use source codes as they are in case you use Arduino-compatible boards. But do not forget you have to change pin numbers that are connected with the parts.

2-1. Hardware for smart watch

before assembly

2-1-1. Arduino micro-controller

There are tons of Arduino boards, but I chose the smallest one, Pro mini. Arduino Pro mini is a light version of UNO R3. It doesn’t have a USB interface chip in order to reduce the price and the size. There are two version depending on the operating voltage(3.3v/5v). And I used a 3.3v version, because the bluetooth and display that are connected with the board support 3.3v and the board goes well with the 3.7v LiPo battery. It runs at 8MHz and a 5v version at 16MHz, but 8MHz is enough. Overall, all you need to prepare are Arduino Pro Mini 3.3v and USB to UART module.

  • The main chip of the board, ATmega328, has only 2KBytes RAM, but ATmega128 has just 1KBytes, which is very limited to run my system. Most boards have ATmega328, but you have to make sure.

2-1-2. Bluetooth

Most common bluetooth modules that you can get are HC-06 main module and the one with interface base board. The latter one has a reset button, the status LED, and it supports both operation voltage(3,3v/5v), so this one is more convenient but the size is rather big, the LED, which is not quite necessary drains the battery and a little more expensive. So I used a HC-06 without the interface board. size: 28mm x 15 mm x 2.35mm (35.7mm x 15.2mm with base board)

2-1-3. Display

The core part would be a display. To make a SMART WATCH, it would be necessary to find a small, low-power display. I’d given lots of thoughts, then I chose -.96’’ OLED Display. size: 26.7mm x 19.26mm x ??

There are various sizes of the displays(0.96’’, 1.3’’, etc), it works on low-power, English font and the image out available, and it supports I2C, SPI, which makes easy to connect with Arduino. The pros and cons is the graphic library. The library for drawing shapes, fonts, and images is supported, but it requires many RAM(I guess the graphic buffer is the problem). So I need to be very stingy in terms of memory usage when I make a program.

Be careful at selecting a display!! I used an 128×64 OLED which is using I2C and SSD1306 driver chip. If you are using different one, you may need to use different graphic libraries and modify arduino source code.

Updated (2015.01.12) : RetroWatch supports u8glib. Now you can use various kind of OLED(or else). Check supported devices at this link.

2-1-4. Battery

I use LiPo(Lithum-Polymer) battery in this project. 1-cell LiPo battery flows out current in 3.7v, which works perfectly with Arduino Pro mini, and there are many kind of batteries in terms of the size and the capacity. You might need to try with batteries with different capacity. I used 501430 – 170mAh, 302030 – 140mAh, 552036 – 350mAh when I made RetroWatch prototype(The first two digits refer to the depth, next two are the width, the last two are the height). The uptime for 501430 – 170mAh and 302030 – 140mAh with periodical sync and no user interaction is :501430 – 170mAh – 7h 30min, 302030 – 140mAh – less than 7h. The most ideal battery depends on what size of watch you want to make. The choice is yours. Under 100mAh one is small, but it doesn’t guarantee stable power, and if it’s too low, you can’t even boot the system. I recommend the battery with protection circuit(overcharging, over-discharging safe), and it’s better if it has a removable socket. It might helpful for you if you get a female socket and USB or 220v DC adaptor recharger.

2-1-5. Etc.

You need wires, soldering iron, a switch and 10K ohm resistance(for a button), and a batter jack. It would be helpful for you to prepare the assembly manual.

In my case, I stacked modules like below picture.


2-2. Preparing for Android

Android v.4.3 supports the service that is used to get notification information from an app. So RetroWatch app is based on Android v.4.3 to enable notification service. For users who don’t use Android v.4.3 yet, the app without this function is released also. You can download the sources at GitHub, or download the app from Google Play Store.(Search with “RetroWatch” or “RetroWatch LE“)

3. Assembling the watch

Folks who are accustomed to handling Arduino or physical computing would proceed this procedure, but I recommend the others not to assemble Arduino Pro mini board first, but try to make the watch with the board that is easy to connect and use like UNO board. The assembly structure for RetroWatch is below here.

Compare your stuff with mine in the picture below. Beware not to fuse, and make sure each layer keep isolated with each other by using tape.

3-1. Connecting Arduino – bluetooth

You may refer to the website for the common way of Arduino – bluetooth connection and test.(but in Korean) You can use the device name and password as is or after resetting them. In the link, you can see the bluetooth module that is connected with the interface board, but the connecting is very similar.

BT -> Arduino :
VCC -> 3.3V,
TX -> D2,
RX -> D3,


There’s a report that says the bluetooth modules can malfunction if they contact with other conducting materials or antennas.

3-2. Connecting Arduino – OLED

The OLED that is used on RetroWatch communicate with the Arduino board by I2C. The common connection of I2C interface is below, and you just follow the instruction.

OLED -> Arduino Pro mini :
SDA -> A4(the analog 4th pin),
SCL -> A5(the analog 5th pin),

If your display has SPI interface, refer to the link. In case of 7pin SPI OLED, connect like below.

  • D1 : MOSI – Arduino D11 (MOSI)
  • D2 : MISO – Arduino D12 (MISO) : this pin is optional.
  • D0 : CLK – Arduino D13 (SCK)
  • DC : DC (Data Command) – Arduino D8 (or else)
  • CS : CS (Chip select) – Arduino D10 (SS)
  • RES : RESET – Arduino D9 (or else)

3-3. Connecting Arduino – button

You may connect with a button which is small enough for the smart watch and a 10k-ohm resistance as below. Connect a digital pin and modify the pin number which is defined as “buttonPin” on the source code. I used a digital 5 pin. In order to refer to button control, you can find the examples about switch control by googling.


3-4. Connecting Arduino – battery

You can simply connect battery by connecting (+) -> RAW, GND -> GND. I chose a LiPo recharging battery, so I left 2 wires and connected them to a female socket. You need to put (+) line to RAW pin in case you use any sort of external power supply, such as an external battery, on Arduino Pro mini board. Otherwise, it can damage the board.

3-5. Connecting Arduino – UART module

You should connect USB to UART to the board in order to upload the source code by USB serial connection. You can read the details here. It depends on the modules how they connect to the board, but normally, you should cross-connect RX-TX.

USB to UART module -> Arduino (Pro mini): ,
3.3V -> VCC,

3-6. Checking connection

The result is as below.

Now, it’s time for checking the connection. If you connect FTDI module(USB to UART, upper-left in the picture) to PC and the light is on, the boot process is successfully done. The following pictures are the assembly procedure and RetroWatch that is completely assembled.


4. Compile Arduino source for watch and upload.

You can download RetroWatch Arduino source on the source tab on the GitHub.

GitHub – RetroWatch project page

Click ‘Download ZIP‘ to download and unzip it. The source which would be uploaded on the Arduino board is in RetroWatchArduino folder. You need to do something before you complie the source code.

4-1. Install graphics driver

You need a graphic library to draw images, shapes, fonts on the OLED. In order to use it, you must install Adafruit_SSD1306Adafruit-GFX-Library. Click ‘download ZIP‘ button on the down-right in the link to download and copy the library folder to /Arduino install folder/libraries. If you find the details, go here.

(According to your development environment, Adafruit library conflicts with Robot_xxx library. In this case, backup and delete Robot_xxx libraries from arduino library folder.)

WARNING: If you are using an OLED with SH1106 driver, use Adafruit_SH1106 driver at below link. Korean user Wonho made this based on Adafruit_SSD1306 driver.

In this case you must modify codes like below.

#include <Adafruit_SH1106.h>
SoftwareSerial BTSerial(9, 8); // Bluetooth TX, RX connection
int buttonPin = 5;  // Button pin
display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // OLED I2C address. Use your own settings

Updated (2015.01.12) : RetroWatch supports u8glib. If you wish to use various display, use u8glib instead. U8glib is more easy to use, consumes less memory(RAM) and supports various display. In this case download and install u8glib at official homepage.

4-2. Copying the bitmap image header

You must copy the header file that contains bitmap images to load and use them. You should copy bitmap.h in RetroWatchArduino folder to /Arduino install folder/Arduino/hardware/libraries/RetroWatch. If there’s no such folder, simply make it.

4-3. Modifying the source

Open Arduino IDE and load RetroWtchArduino.ino. Next, set pin numbers that you used when you connect the watch. It’s not necessary to modify if you use Arduino pins that are used in this instruction. But if you didn’t, you need to modify the source codes below.

SoftwareSerialBTSerial(2,3); // Input your TX, RX pin numbers
int buttonPin = 5;       // Input your button pin number
display.begin(SSD1306_SWITCHCAPVCC, 0x3D); // Replace Ox3D with your I2C address

You better not to change the other source codes before compling and uploading are done. If there is a problem on the hardware or the software, it can be hard to find what causes the problem.

Updated (2015.01.12) : If you are using u8glib, load RetroWatchArduino_u8glib.ino file. And check below codes.

U8GLIB_SSD1306_128X64 u8g(U8G_I2C_OPT_NONE|U8G_I2C_OPT_DEV_0);	// change this line according to your display
SoftwareSerialBTSerial(2,3); // Input your TX, RX pin numbers
int buttonPin = 5;       // Input your button pin number

Updated (2015.01.22) : RetroWatch supports SPI OLED. I’ve updated at GitHub.

4-4. Compile / Upload

If you follow the instruction well, you need to compile the source code. If this procedure fails, you have to check the error message and what went wrong so far. You can even google the error message to find the web page that tells you about the modules. Once the compile is succeeded, you need to upload it to the Arduino board. If you look at the Arduino IDE closely during the upload procedure, you can see that compiling messages keep showing and suddenly, the progress bar stops for the short period of time, and the messages change to uploading messages. You have to push the reset button on the Arduino board to get the uploading complete message correctly. If the error occurs, you may get this message.

avrdude: stk500_getsync() : not in syc: resp=0x00

In case this message keeps showing and upload doesn’t succeed, go to the link and solve the problem.

If upload is completed, the RetroWatch Arduino logo and the Adafruit logo(the OLED manufacturer) have to be display on the OLED. If you don’t see them, push the reset button once. If it doesn’t work, you should check the connection between the OLED and the board. (sometimes lack of battery charging causes boot problem). After the logo phase passes and time shows up “00:00”, the initialization perfectly succeeds.

boot test

Now, it’s time to check the bluetooth. Turn on the bluetooth on your phone(Setting > Bluetooth). Your phone starts to search bluetooth devices nearby, and the bluetooth module should show. If the phone fails to search it, there’s something wrong in the connection between VCC, GND. If there’s no problem in power supply, the bluetooth module works fine itself even if there’s a problem in TX, RX pin connection. Once the bluetooth module shows, you may proceed the pairing phase, and the two devices connect after putting 4-digit password(in my case, default 1234).

5. Android app install & source download

It’s too big to demostrate how to compile and modify the android source. FYI, check /RetroWatch_Android/RetroWatch folder in the source downloaded from GitHub. I registered this app to Play Store, so go download it(search ‘RetroWatch’).

RetroWatch app pageRetroWatch LE app page

Follow the instruction as below and check the operation of RetroWatch.

If you install the app, turn on the bluetooth first(Setting > Bluetooth) and pair with the module. Next, start RetroWatch app. Choose the second menu(Notification access) on the top and grant RetroWatch the authorization for Notification. Choose the first menu(Choose the device) in the action bar and select the Arduino board that is already paired. If you can’t find it, check the power and the bluetooth module. Or choose ‘device scan’ menu to scan manually.

If the connection is succeeded, you may see “Connected” in connectivity display area at the bottom. Touch the action bar menu(…) and choose ‘Data transfer to Watch’. This menu transfer the data to display time and messages by bluetooth. If the bluetooth module works fine with the Arduino board, time information changes to current time. The bluetooth connection is OK, but time doesn’t display, check the connection between TX, RX. Now, it’s time to have fun with MY OWN SMART WATCH!!! Pictures below show the progress so far.


6. RetroWatch Android

The performance of RetroWatch itself is limited, but I prepared some features to show various of data. The biggest feature is filtering messages sent to the watch. And I put an RSS feed feature to use data from different kind of areas. Try each feature by switching 4 tabs.


Message list tab : Messages are the information collected from the app. Every message is inactivated except for emergency messages. Inactivated messages are not sent. You can change the status by filtering. Messages are the information collected from the app. Every message is inactivated except for emergency messages. Inactivated messages are not sent. By touching each message, you can enable each message or messages from same package.

Filter setting tab: The RetroWatch app controls every single information by filtering. You can add, fix, and delete filters in this tab. You can change strings of messages(ex. change language Korean -> English since it supports English only), delete messages not to show, or just activate them without a string modification.

RSS tab: You can register and monitor RSS feeds. The watch can show lots of information by RSS feeds. For instance, if you add a weather RSS and modify strings to filter, you can receive the weather alarm from the watch!!! You can easily search RSS feeds from the web site which I made and add them to the app.

Watch control tab: You are able to alter styles of the app and watch. If you put your Gmail account here, unread messages are registered in a message list. You can change the clock style and time display indicator to show(Display interval is already set because of power saving, the change applies at interval).


The RetroWatch app collects three kinds of data.

Notification: A notification that is registered in the Andriod indicator bar. App uses the Notification service to collect notifications, only over Android 4.3 supports this feature. Please download RetroWatch LE app for other android version. LE app doesn’t have the notification collection feature.

System info: The system info of the phone such as battery status, RF(LTE, 3G) connection status, WiFi status, recharging progress is collected in the watch. In addition, if you register a Gmail account, it counts unread e-mails.

RSS feed: If you set RSS title and URL, it periodically read RSS data.

Here are the other minor features.

  • Messages are sent in two kinds – emergency message, normal message. But users cannot modify them.
  • You can set icon that shows on the watch when it filters messages. You can use 65 icons.
  • All information is updated to the watch every 30 minutes.
  • The RetroWatch service runs in background even if you shut the app.

Need more details about how to use app? See this link: Retro Watch app quick guide.

7. RetroWatch Arduino

RetroWatch changes mode in a circle as below.

Initial display: The phase which the logo shows up when the watch boots.

Clock display: The basic display which tells you time. You can change the style of the clock in the Android app. Analog, Digital, Mixed styles are supported so far. If you push the button, the display changes to the Emergency message display. It changes to the idle mode in case there’s no data update for 10 minutes.


Emergency message display: The display that shows when users push the button in the watch display or a new emergency message is updated. If users push the button again or 10 seconds passes, the next message is shown. The display changes to a the normal message display after every emergency message shows.

Normal message display: The display that shows after emergency message ends or users push the button. The next message shows up when users push the botton or after 5 seconds. The display changes to the clock when the last message shows.

Idle display: The display that is shown if there’s no data push during 10 minutes. It displays Indicator and time(hh:mm) the display update interval changes to run at minimum power consumption. If you push the button or get a new message, the display changes to the clock display.

RetroWatch module has these features.

  • Three emergency messages can be stored. The message that the watch is already received is deleted if the messages are over 3. It can’t store lots of data due to memory shortage(2KB RAM).
  • Normal message stores up to 7. Like emergency messages, the first messages are deleted when the received messages reach to the maximum.
  • You can change the clock style as you want. Or you can even make your own clock style by altering the source code.
  • There are 65 icons so the app can use them. You can also add your own icons.(need to compile Arduino code)
  • You can choose whether the indicator would be shown or not in the app.
  • The internal battery is 140mAh, so the battery time is about 7 hrs at a normal status. I guess the battery time would be longer if I fix the source code for battery save.

8. RetroWatch specification & working demo

  • Processor : ATmega328 – 3.3v(8MHz)
  • 32KB Flash (2KB is shared for Bootloader), 2KB RAM, 1KB EEPROM
  • Size : Width x Height x Depth = 34mm x 32mm x 12mm (Not packaged)
  • Battery : LiPo 140mAh(idle time 7hrs, 1-2hrs for recharging)
  • Connecting with Android app
  • Supports notification, system info, RSS feed
  • Message filtering
  • Open source

Working demo: YouTube link

9. Packaging

RetroWatch Android, Arduino module is done, and if there’s no problem to operate, you need to pack the watch. Make a package as you want.


Below picture shows 3D printed hard-case by Kyung-Rae Park. 

Download here. [wpdm_file id=29]


Awesome one at below picture is designed by Wonho. You can get the 3D modeling files here. And find more at his blog.


10. Epilogue

You can feel how fascinating and powerful the open source and the open hardware are through this project. The idea comes true even though you are not professional because hardware is getting inexpensive and numbers of people shares source codes and know-how. Let’s try!!!

You can see the working demo atYouTube link.

More specific how-to document at : RetroWatch project

Download sources at : GitHub RetroWatch page

RetroWatch case design for 3D printer:  [wpdm_file id=29]

RetroWatch Android Application (v4.3 or over) 

RetroWatch LE Android Application (v4.0 ~ v4.3, Notification service removed)

Retro Watch app quick guide

RetroWatch Android is based on Apache license, RetroWatch Arduino follows GPL v3.0.

Special thanks to Chang-Han Jeon and Kyung-Rae Park. Jeon translated this text in English and Park made a case for RetroWatch with his 3D printer. Wonho made an awesome example and share the library for SH1106 OLED user.

This document is also translated in Polish(by Sebastian), Korean language.

If you wish to translate this document into other language, feel free to do it! After translation, just notify to me with your result and your name. I’ll update this document. And if you made you own watch, please share with me. (