doc/PinetimeStubWithNrf52DK.md


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# Build a stub for PineTime using NRF52-DK
[NRF52-DK](https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF52-DK) is the official developpment kit for the NRF52832 SoC from Nordic Semiconductor used in the PineTime.

This development kit can be very useful for PineTime development:
 * You can use its embedded JLink SWD programmer/debugger to program and debug your code on the PineTime
 * As it's based on the same SoC than the PineTime, you can program it to actually run the same code as the PineTime. 
 
This page is about the 2nd point : we will build a stub that will allow us to run the same code you can run on the PineTime. This will allow you to work more easily if you don't have a PineTime dev kit around, if you don't want to modify your dev kit for SWD programming, or if you want to use some feature from the NRF52-DK (like power measurement).

This stub only implements the display, the button and the BLE radio. The other features from the pintime are missing: 
 * heart rate sensor
 * SPI flash
 * touchpad
 * accelerometer

These devices could be added on this stub, but I do not have the parts to try them out for now.

![Pinetime stub](../images/pinetimestub1.jpg "PinetimeStub")


Here are the parts you need to build this simulator:
 * [NRF52-DK](https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF52-DK)
 * An ST7889 display (I bought [this one](https://www.aliexpress.com/item/32859772356.html?spm=a2g0s.9042311.0.0.1b774c4dSoc4Xz))
 * A push-button (the one I use comes from a previous project build around ESP8266 board Wemos D1 Mini).
 * Dupont wires
 
You just need to make the following connections:

| NRF52-DK | ST7889 display |
| ---------|--------------- |
| VDD      | VCC            |
| GND      | GND            |
| P0.03    | SDA            |
| P0.26    | RES            |
| P0.02    | SCL            |
| P0.18    | DC             |


| NRF52-DK | Push Button            |
| ---------|----------------------- |
| P0.13 | Button IN (D3 in my case) |
| GND | GND                         |

You also need to enable the I/O expander to disconnect pins from the buttons and LED on the NRF52-DK and leave them available on the pin headers:

| NRF52 -DK | NRF52- DK |
| --------- | --------- |
| DETECT    | GND       |

Now, you should be able to program the SoC on the NRF52-DK board, and use it as if it was running on the PineTime.