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RePhone Strap Kit for Pebble

The introduction of RePhone (Xadow) modules makes your smart watch even smarter. Based on the new smart accessory port on the back of Pebble Time, we integrate the slim and small Rephone modules – Xadow GPS v2 and Xadow NFC v2, into Pebble’s existing ecosystem, to help improve its capability from the perspective of built-in electronics. Xadow Pebble Time Adapter enables the RePhone(Xadow) modules to talk to the Pebble Time via the Smartstrap interface using One-wire serial protocol.


Base of Xadow Adapter for Pebble

The ‘GND’ and ‘PWR’on the back frame means you can charge your Pebble Time without taking the shell off.

Xadow GPS v2

Microcontroller Kinetis KL02
Core ARM® 32-bit Cortex® -M0+CPU
Power Supply 3.3 ~ 6 V (via breakout pins)
Flash 32 KB
Clock Speed 48 MHz
Power Consumption 18mA@Tracking, 21mA@Acquisition
Power Saving Typ. 3mA@AlwaysLocateTM, 7uA@Backup

Mode, 180uA@Standby Mode

Channel 22(Tracking) / 66 (Acquisition)
Update Rate 1Hz(Default), up to 10Hz
Horizontal Position Accuracy <2.5m CEP
Velocity Accuracy <0.1m/s
Maximum Velocity Max.515m/s
Cold/warm start with EASYTM 215s/5s
Acquisition Sensitivity -145dBm
Tracking Sensitivity -163dBm
Operating Temperature -40℃ to 85℃
Protocols NMEA 0183/PMTK
Antenna Type Chip antenna
Interface Interface with Xadow GSM+BLE through

I2C (7-bit address 0x05)

Dimensions 25.37mm X 20.30mm / 1” × 0.8”

Xadow NFC v2

Microcontroller Kinetis KL02
Core ARM® 32-bit Cortex® -M0+CPU
Power Supply 3.3 ~ 6V (via breakout pins)
Flash 32 KB
Working Current 5mA at standby; 55mA when read/write
Radio Frequency 13.56 MHz
Supported protocols ISO/IEC 14443 Type A and ISO/IEC 14443 Type B
Max Operating Distance ~28mm depending on the current antenna size
Dimensions 25.37mm × 20.30mm / 1” × 0.8”

Xadow Battery 100mAh

Voltage 3.3 V
Dimensions 25.37mm × 20.30mm / 1” × 0.8”

Assembling process

In daily use the modules are evenly placed at each side of the watch, and interconnected with FPC cables. The connections between the module and the adapter are specially designed to be an extendable form so that unexpected connection pull-off may be avoided. The charging ports of Pebble Time are still accessible on the back of adapter for daily charges of watch.

A schematic drawing of the assembling process of the RePhone Strap Kit for Pebble Time is given below

Download the Xadow APP for Pebble Time

You can follow the instructions to download the Xadow APP for Pebble Time, access the GPS information and Tag ID on your Pebble Time.

The Demo App can be downloaded from You can download it from your smart phone or send it from your PC to smart phone. Then select to open it with "Pebble Time" App in your phone. You will have an option to install the demo App into your Pebble Time.

Programming Guide

Talking to the Adapter

The firmware of the adapter implements the protocol described on pebble's official documentation:

So the resources which can be called from the watchapp side are as following:

Service Attribute R/W Data Type Data
0x0 Raw Data 0x0 Raw Data RW uint8 *buffer No handler in adapter side, leave the expandability for adapter firmware programmer
0x2003 Battery Service 0x1001 Get voltage of the battery R uint16 The voltage of the battery for strap in Volt with a precision of 1/100. For example, the voltage is 3.70V, which would be specified as 370.
0x2003 Battery Service 0x1002 Enable or disable charging pebble with the battery of strap RW uint8 0: Don't charge pebble. 1: Charge pebble.
0x2001 Location and Navigation Service 0x0001 Location R sint32[2] The current longitude and latitude in degrees with a precision of 1/10^7. The latitude comes before the longitude in the data. For example, Pebble HQ is at (37.4400662, -122.1583808), which would be specified as -1221583808.
0x2001 Location and Navigation Service 0x0003 Speed R uint16 The current speed in meters per second with a precision of 1/100. For example, 1.5 m/s would be specified as 150.
0x2001 Location and Navigation Service 0x1001 Altitude R uint16 The current altitude in meters with a precision of 1/100. For example, 100m would be specified as 10000.
0x2001 Location and Navigation Service 0x0101 GPS Satellites R uint8 The number of GPS satellites (typically reported via NMEA. Note that this number is for satellites in view.
0x2001 Location and Navigation Service 0x0102 GPS Fix Quality R uint8 The quality of the GPS fix (reported via NMEA). The possible values are listed in the [NMEA specification](
0x1E01 NFC Service 0x1001 Get UID of a NFC tag R uint8 * The UID will be returned with variable length which can be indicated in the SmartstrapReadHandler with parameter length. **This attribute can be notified in SmartstrapNotifyHandler.**
0x1E01 NFC Service 0x1002 Read NDEF Data R uint8 * The NDEF data will be returned with variable length which can be indicated in the SmartstrapReadHandler with parameter length.
0x1E01 NFC Service 0x1003 Write NDEF Data W uint8 * Write a uint8 buffer into NFC tag
0x1E01 NFC Service 0x1004 Erase NDEF Data W any type Write any content or empty to trigger the erasing.

The source code of the demo pebble app can be downloaded at github:

This app is only for demonstration of partial attribute call, please feel free to imagine your own fantastic pebble app based on the ability of GPS, NFC and more on.

Programming the Adapter

The adapter is built with LPC11U35 and running mbed software inside. The initial firmware is located at Please take a look at

The eagle schematic of the adapter can be downloaded here:

After building the firmware binary, you can follow the steps below to flash the binary into the adapter.

1) Hacking a USB Cable and solder the wires to the soldering pads accordingly

2) Make sure the battery disconnected and plug the USB into PC.

3) Short the "ISP" and "GND" pins.

4) Plug the battery on to power on the adapter

5) There will be a usb drive at your PC, open it and delete anything inside the disk, then copy the firmware binary into the disk.

6) Power off then on, the firmware is updated.

RePhone Community

We’ve been looking for a better place where our backers (RePhone Users) can sit together, warmly and comfortably, have conversations about RePhone, discuss technical problems, share ideas/projects, and give feedback on the modules’ development in the future. And then here we go, the RePhone Community.

Now join us in the RePhone Community! Together we seek answers, make interesting stuff, care about each other, and share our experiences.

Frequently Asked Questions

Some frequently asked questions in RePhone Community are collected and answered to the topic "Frequently Asked Questions of RePhone (FAQ)" , the topic will be kept updating whenever a new FAQ comes out.

Schematic Online Viewer


The schematic diagram of Xadow Pebble Time Adapter is provided in the following link:

Tech Support & Product Discussion

Thank you for choosing our products! We are here to provide you with different support to ensure that your experience with our products is as smooth as possible. We offer several communication channels to cater to different preferences and needs.

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