Making a starting E-Gun

This is a much-improved version of an older post.
An electronic starting gun/pistol/device is a useful tool since it is entirely risk-free and lets you control how loud the sound should be. It can also be connected directly to SprintTimer, which makes it insensitive to external noise. But while an e-gun is not very expensive, it still costs from around $200. So if you are on a budget, or like DIY projects, you can build one yourself at a tenth of the cost. That might sound hard, but there is no programming involved, and you only have to connect two wires. It will also be more flexible than commercial guns since you can decide what type of sound you want and how to trigger the start.

I will go through the necessary steps and components. There is also a video that shows how it is done. The heart in our e-gun project is a small soundboard from SparkFun called Little Soundie. It costs $15 and can contain up to 64 sound clips.

Adding the sound
The first step is to add sounds to the Soundie-board. Connect a USB-cable between the board and your Mac/PC and press the Power/Play button to the board. The board will mount on your desktop and you can drag or copy the sound files as you would to a memory stick.

The board uses a sound format called ogg/vorbis. You can download a couple of start sounds here. You can also convert your own sounds here or with the free Audacity app. You can also use .waw files on the board, but in my experience, the ogg files are more reliable.

Adding the wires
First you must add a battery, the board runs on 3.3 V, so something between 3-3.7 V should be fine. I have used both two AA/AAA batteries and a rechargeable 3.7 V. Connect the + side of the battery to the VIN (Voltage In) pin on the board and the – pole to the GND (Ground/Common) pin. Secondly connect a pushbutton between the +/VIN side and the 00 pin.

That’s it, you now have a working e-gun! However, like with all commercial e-guns, you also need a powered speaker to hear what is played. You can connect a standard sound cable with a 3.5 mm plug between the outlet on the board and the AUX-port on the speaker/amplifier. Press the Power/Play to reset and press your push button to play the sound. Keep it pressed to repeat.

Connecting SprintTimer
To connect an iPhone/iPad you need to add a sound cable splitter and an adapter to convert the signal. This has been covered more in detail here. The final set up will then look like this:

Click to expand

Useful extensions

1. Multiple sounds
You can load a number of sounds to the board, theoretically up to 64 if they are short enough. You then play them with the 00-04 pins. To play a second sound you can add a second push button between VIN and 01. Or you can keep one button and add a switch to set which sound to play:

Two things to note here: Which sound is played by which pin is determined by the order in which the sounds are loaded on the board (not their names). Secondly, a combination of the 00-04 pins is used to pick a sound. Setting pin 02 high plays the fourth sound. So if you want a switch with three sounds the easiest solution is to add the last one twice. More about sounds here.

2. A SprintTimer plug
You can add a dedicated SprintTimer cable that can be plugged directly into the iPhone. If you use the audio out pins on the right side of the board you can skip the split on the speaker cable. By adding two resistors you can also skip the iPhone adaptor. Place the resistors after the pins, and use a 4-pole (TRRS) 3.5 mm plug and connect the two inner rings. The resistor R1 is there to lower the signal, 300 – 500 kOhm is usually suitable. The purpose of R2 is to tell the iPhone that there is a microphone connected and it should be about 2 kOhm (I have successfully tested both 2.2k and 1.5k). 

You probably also want to add some kind of connector or screw terminals if you don’t want the cable to be hanging out of the e-gun all the time.

3. Built-in speaker
Commercial e-guns usually rely entirely on external amplifiers since you want a strong sound during a noisy event in a large stadium. Still, a small built-in speaker makes a nice all-in-one package that can be used for practice sessions. There are a number of fairly cheap 2-3 W ($5-$10) amplifiers available. And when I tested it was enough to be clearly heard at 10 m.

4. Enclosure
Walking around with all the component hanging loose is of course not an option, so some kind of box is needed. There are litterally millions of electronics boxes available so you should be able to find one that fits. You have to drill holes for the buttons and the audio plug. You might also want to add a switch for turning the board on and off. But it will draw very little current (3.4 mA) when not playing a sound, so you can leave it on the whole day. I went for the bare minimum, but with a large button:

Links

A video of building the e-gun

Little Soundie
SparkFun
Resellers
Tutorial (recommended)

Sounds
Shot, whistle and beep in ogg format
Online ogg converter
Audacity (very good free sound app for Mac and PC)

Loudspeaker to iPhone/iPad mic converters
Røde SC4 (Amazon)
Headset Buddy ECM (Amazon)

Previous posts
An E-gun with a very low-cost board
An Arduino based starting device