Dave Prochnow

4Caster with Hacked Firmware

If you’ve ever wanted to learn how to hack a circuit’s firmware, a great beginning point would be SparkFun Electronics. Many of the development, prototyping, and sensor products sold by SparkFun come equipped with a special programming interface. Even better, most of these products feature downloadable firmware. Therefore, with just a modest amount of effort, you can modify one of these products’ firmware, reprogram the circuit, and create your own customized product.

You can add your name to a splash screen, develop a new product feature, or — living life on the edge — rewrite the whole shebang and make an entirely new product: the sky’s the limit when hacking firmware. There is one very important caveat, though: if you don’t know what you’re doing when tinkering with firmware, you could destroy the product.

In this introduction to firmware hacking, let’s try a simple modification. We’ll reformat the output from the USB Weather Board v1 so that it can be meaningfully displayed on a serial-enabled 20×4 LCD.

In its stock configuration, the output from the USB Weather Board is a continuous string of numbers, like



Not very friendly, is it? We’ll modify the firmware so that the output is easier to comprehend. Something like:

1.Humidity=47.25% 2.Temp=81.23F 3.Press=101723Pa


But wait; there’s more. We’ll also add an LCD for displaying this new output and a battery power supply, and wrap everything up in a handheld enclosure. The result is a portable, handheld personalized weather forecasting system. Or, as I’ve dubbed it: the 4Caster 1000.

TIME: 3 hours
COST: $160.73


USB weather board v1 (SparkFun Electronics #SEN-08765; $99.95)
Serial-enabled 20×4 LCD (SparkFun Electronics #LCD-00462; $32.95)
5V DC-to-DC step-up (SparkFun Electronics #PRT-08248; $10.95)
6x headers (SparkFun Electronics #PRT-00116; $2.50)
SPST push on/off switch (RadioShack #275-011; $1.99)
Project box (All Electronics #1593-YBK; $4.95)
Hookup wire (RadioShack #278-1224; $5.99)
AA battery (locally available; $.50)

Optional (might already be attached to some USB weather boards):
2×5 AVR ICSP male header (SparkFun Electronics #PRT-00778; $0.95)

4Caster USB Weather Board


  1. Make the firmware accessible by soldering the 2×5 AVR ISCP male header to the USB Weather Board. NOTE: some boards might already have this header attached.
  2. Solder the 6×1 header to the BlueSMiRF connector on the USB Weather Board.
  3. Download, install, and start the FREE AVR Studio 4 Integrated Development Environment (IDE). The target AVR on the USB Weather Board is an ATmega8.
  4. Download the USB Weather Board firmware and create a new AVR Studio 4 project for your hacked firmware. For example, call your project 4Caster and paste the SparkFun Electronics firmware into the main 4Caster program window.
  5. Modify the firmware. The lines that I added for creating my 4Caster 1000 can be found here.

4Caster Close-Up

Take your portable, handheld personalized weather forecasting system with you wherever you go. Just press the pushbutton on the outside of the project box for a quick snapshot of your current weather conditions. By monitoring these weather stats from your hacked firmware, you might be able to make a quick “guess” about upcoming weather changes.

Please note: spurious characters might sometimes appear on the LCD. For example, all “Ps” will suddenly change to “@.” Or, a “0” (zero) will drop out. This distasteful effect usually disappears within 1-2 seconds.

4Caster Display