# OpenChrono

Chronograph for Airsoft use, released as Free Open Source hardware and software!

Uses a 3D printed housing to hold an Arduino, an OLED display, batteries and two photosensitive IR light barriers.

Fixed mounting on the front of the gun in the style of a silencer.

Can optionally also include UV LEDs to illuminate tracer BBs.

## Hardware

Use the included OpenSCAD design file in `hardware/openchrono.scad` to render your own custom STLs that fit your use-case.

### Required Parts

Besides some common stuff like soldering wire and hotglue you need the following parts to build this project.

| Description        | Type          | Count |
| ------------------ | ------------- | ----- |
| Arduino Nano       |               | 1x    |
| LCD 128x64 I2C     | SSD1306 0.96" | 1x    |
| Slide Switch       |               | 1x    |
| IR Phototransistor | SFH 309 FA-5  | 2x    |
| IR LED 3mm         |               | 2x    |
| Resistor           | 1k Ohm        | 2x    |
| Resistor           | 100 Ohm       | 1x    |
| Screw              | M2 10mm       | 4x    |
| Screw              | M2.5 10mm     | 2x    |
| Screw              | M3 16mm       | 8x    |
| Heatmelt Insert    | M3 <= 10mm    | 8x    |

For the UV tracer option you also need the following parts.

| Description | Type    | Count |
| ----------- | ------- | ----- |
| UV LED 3mm  |         | 2x    |
| Resistor    | 100 Ohm | 1x    |

You have different options for powering the project.
My first version for testing uses a pre-made AA battery holder.

| Description    | Type   | Count |
| -------------- | ------ | ----- |
| AA Battery     |        | 3x    |
| AA Bat. Holder |        | 1x    |
| Screw (sunk)   | M3 6mm | 2x    |

The originally intended variant is a AAA battery holder printed into the model.
I don't have the terminals for that yet so it is not finished.

| Description        | Type | Count |
| ------------------ | ---- | ----- |
| AAA Battery        |      | 3x    |
| Bat. Terminal Neg. |      | 3x    |
| Bat. Terminal Pos. |      | 3x    |

I'm also looking to design a LiPo version with charger included in the future.

## Software

This project uses the [U8g2 library by olikraus](https://github.com/olikraus/u8g2) to draw to the I2C OLED display.

You can compile and flash the software using either PlatformIO or the standard Arduino IDE.

With the Arduino IDE [install the U8g2 library using the Library Manager](https://github.com/olikraus/u8g2/wiki/u8g2install) and then flash as usual.

For PlatformIO run something like the following command.

    pio run -t upload --upload-port /dev/ttyUSB0

Replace `/dev/ttyUSB0` with the port you are using.

### Configuration

Take a look at `firmware/OpenChrono/config.h`.
This file contains all the settings you can change as a user.

The most important setting is `SENSOR_DISTANCE`, which is given from the 3D model of the case.
It is echoed when rendering the OpenSCAD design.

You can set `BB_WEIGHT` to the one you use most commonly, and `BB_WEIGHTS` to others interesting for you (`BB_WEIGHTS` should include `BB_WEIGHT`).
These values are used to calculate the energy in Joules.

Set `PREFERRED_UNITS` to what you would like to see in the 2D graph.

The range of speeds that can be measured is determined by `TIMER_PRESCALER`.
Take a look at the comment in `firmware/OpenChrono/ticks.cpp` for details.