Programmable Airsoft Trigger - designed to replace traditional electromechanical switch present in airsoft replica to control gearbox opeartion.
In development
- Implement fire selector switch ,,on fly" programming, to let user decide burst cycles, semi only etc.
- An OLED I2C display to show the player how many shots were shot
- Minor hardware update
As the usual circuitry closes and lets the current flow, just a moment before contacts meet each other a spark is present between these contacts. After a longer usage it leads to oxydation of metal and creating a layer of carbon, which leads to higher resistance, therefore heat is generated and switch gets damaged. Here's some quick maths:
For an 11,1V LiPo battery with 20C/40C at burst and at t=0 a DC motor acts as a short circuit, thus resulting in a full current burst from the battery,
which is roughly 30A at t=0. Following this thinking, let's say the resistance of a damaged trigger switch is 1 Ohm - that's not really that much, huh?
Power dissipated on contacts may be calulated with a simple equation: R * I^2 . As the current is squared, it's easily seen how dramatically power raises to 900W ! If it would work for a couple of seconds, the airsoft replica would be like a portable microwave :)
A transistor has been used as a switch ever since it has been developed. If we consider large currents like in this application, a field transistor suits our needs. A P-channel MOSFET transistor STL42P6LLF6 has it's drain-source resistance at typically 0,023 Ohm, so for a moment maximal power dissipated on a junction is less then 21W.
For this project following technologies, programs and hardware were used:
- C (embedded C11)
- Altium Designer 18.1.7
- Eclipse IDE with GCC compiler
- ST-Link V2.1 programmer/debugger
- STM32F030C8T6 ARM architecture based microcontroller
- Custom hardware
This project was designed to be out-ouf-package ready to work with, no software setup is needed.
Use SWD connector presented onboard to flash the board with an external ST-Link programmer. Pinouts are available in this repository. Next, connect your hardware programmer and flash the .elf file (how to do that depends on IDE or software flashing software used - please refer to tutarials specific to your setup)
As an airsoft player I found it frustrating to fight with my own setup in a longer game as my battery would eventually die after a couple of magazines shot. Also, trigger response wasn't acceptable. Inspired by airsoft forums I decided to use an N-MOSFET as a switch. Results were fascinating, as my battery life doubled, and trigger felt gentle as a feather. Later I found out that there were commercial programable triggers that had fancy funcionality like 3-shot bursts, low battery warnings etc. I bought one eventually, but I couldn't see why these cost about 100 euros (there are even 180 euros price tag ones). Then I got an idea - why can't I make one by myself? After a couple of years I learned more and more about hardware design, started studying at technical university and got into C coding. It was about that time I decided to give that project a try. Books I always find usefull:
- Tomasz Francuz ,,C language for AVR microcontrollers"
- Robert C. Martin ,,Clean Code"
- James Grenning ,,Test-Driven Development for Embedded C"
Created by Paweł Klisz @ pawelochojec@gmail.com- feel free to contact me!