Boombox

A little project to make a wifi-enabled remote firecracker igniter using a linksys router and some nichrome wire.

Schematics:

Source Code

Vid Clips

Here is a clip of the interface being used from a laptop to heat the nichrome. The nichrome is not attached to anything, so all you see is the nichrome get red-hot.

Here is clip of the fuses being ignited by the nichrome. The lighting was such that it was very difficult to get the interface in the same shot.

Basic Overview

This is a pretty generic linksys router with LED outputs wired to switching circuitry to control current from a 9v battery passed through nichrome wire to ignite fuses. A 6v rechargeable battery pack from a hobby store is used as the power source for the router to make this portable - the 9v battery is used only for heating the nichrome. A power switch is located on the outside of the housing. An additional switch for arming (i.e. engaging the 9v batter) is also located on the outside of the housing for safety purposes.

firmware and interface

The router was flashed with openwrt firmware in order to allow us control over the LED ports and ease of writing a custom web interface. It's mostly perl code and a little bourne shell. Because it is wifi-enabled and uses simple http for control, it can easily be controlled from any laptop or wifi-enabled phone.

output stages

Each LED output is wired to an npn transistor, which steps up the current used to switch a power MOSfet. This is necessary to allow the MOSfet to flow 1.2 A in order to heat the nichrome in under 1 second. The full schematic is shown below. Note: at this time, using more than one output at a time is ineffective. Future design improvements should fix this.

Some history and experimentation

Initial tests using a 9v battery and some nichrome wire scavenged from an old hair dryer revealed that it was possible to burn paper after around 9 seconds of applied voltage, but this was quite a strain on the battery. Due to the size of the wire, significant current was required to reach this temperature. We were able to significantly reduce this time and current by acquiring much higher guage nichrome; note: this stuff is pretty cheap.