Phone bluetooth notifier

Oled 20x2 text screen with bluetooth BLE.

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This is a 5" oled screen controlled by a Cortex-M0 and with a RN4020 bluetooth module. Also has a USB connector to charge the battery and to make a serial terminal to debug and interact.
The purpose is to show the notifications received at the phone, like incoming calls, sms messages, email, calendar, etc...
It try to be like a wearable watch but you could use it in a shop, kitchen, living room.. So you could see it form distance and know what's the notification before reach the phone. And you could do any task without having to wear a wearable watch.
Also could store past notifications and act like an answer machine navigating with the buttons.

I've made the schematics with the low power in mind. The battery is charged by the micro-usb connector and also supplies the circuit when plugged. When in battery mode, the battery voltage is routed to the power switch that then powers-up the microcontroller. At the start of the microcontroller, it will enable a power switch ic that will keep the power supply connected to the battery. This way you could have a battery without discharging when not used. The microcontroller also has a supercap connected to the Vbat pin, so you could maintain the clock for a long time. When the phone app will be done, there will be a time sincronization also so you don't have never to put in time the screen.

The usb connector also is used to have a serial terminal communication with the microcontroller. There are commands to send text to the scree, there is feedback from the switches status. It's intended to be used as a debug and for an easy using of the screen for a pc application. Also there is a command in this serial terminal that uses the micrcocontroller as a bridge to the bluetooth module, so you could interact directly with it.

The LCD is an OLED from Winstar, with a very good color and contrast. It has a paralel communication but it needs a 5v logic level, so there is level translators for data and control signals, due the microcontroller is 3v3.

The microcontroller is a STM32F051R8T6 Cortex-M0 from ST. I used this due I had a STM32F0DISCOVERY board for development. Also the MDK-ARM-STM32 complier from Keil its free for the Cortex-M0.

The bluetooth module is a RN4020 from microchip. I've selected it due it has a serial terminal and was easy to develop, but there are somo others cheapers than this module. It's a BLE 4.1 module, so the power consumption will be low. Right now the microcontroller starts the bluetooth discovery mode let the phone application find it.

The navigation switches are in a separate board, due I was not sure how to make the box and which switches to use: I've finally used some illuminated switches from Würth Elektronik, but the were very expensive and with very low quality, not recommended. I will redesign this circuit with another switches maybe without illumination and use a notification RGB led.


Schematics for the switches board

Adobe Portable Document Format - 209.88 kB - 12/21/2017 at 14:44



Schematics for the main board

Adobe Portable Document Format - 1.85 MB - 12/21/2017 at 14:27



Block diagram of the project

Adobe Portable Document Format - 88.54 kB - 12/21/2017 at 14:24


  • 1 × XR21B1411IL16TR-F ENHANCED 1-CH FULL-SPEED USB 2.0 UART 12mbps SMD
  • 1 × SN74LVC8T245DBR 8-Bit Transceiver Voltage Translation 3state 5,5V SSOP 24p SMD
  • 1 × WEH002002BLPP5N00000 Alphanumeric Oled LCD 20x2 characters, 5,8" 5V 180x40mm 16p TH
  • 1 × ABS07-32.768KHZ-T Quartz Crystal 32,768 kHz12,5pF SMD
  • 1 × CSTCE8M00G55-R0 Ceramic Resonator 8.00MHZ 40ohm SMD

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Simon Merrett wrote 03/21/2018 at 18:16 point

Nice project - as you're not happy with the buttons, perhaps you could 3D print some, with cutouts for the symbols and backlight with SMT LEDS, next to some momentary push / tactile switches below.

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Abel Rodriguez wrote 03/22/2018 at 08:38 point

I'm not happy because they are expensive, the leds connections breaks, and you could only see them illuminated from above. My intention is to rid off these switches and use a RGB led to show the kind of notification, and use normal tact switches for the navigation..

  Are you sure? yes | no

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