(Started: 20 November 2008, last update: 20 November 2008)
This project started out as an idea to build a remote controllable robot, that can connect to a PC, and that can charge itself by seeking out sources of light and generating electricity from solar power. Since I live in a third world country (with a dismal exchange rate at the moment), and have limited funds and access to components, I am taking great measures in finding the cheapest and simplest components available, so this will probably be one of the most cost effective robotics projects you will find online.
For wireless communications, I first looked at the Quasar 2.4GHz Transceiver Module, as this was the cheapest wireless communications unit available at around $9, and is low-power which is perfect for this application, however it would require an additional adapter for the PC. Existing wireless technologies used in PC’s include Bluetooth and Wifi WLAN.
The cheapest (and mostly superior) UART-to-Wifi module on the market today is the Mini Socket iWifi from ConnectOne.com at $59. This little module makes use of AT command-sets to make a standard MCU Wifi enabled, and includes advanced functionality such as encryption, http- and email clients, and an on board web server with customizable web pages. I made use of this module for my final year engineering project which I wrote about here: Automated Attendance Register System. I was really impressed by it and it’s well worth checking out for any projects requiring Wifi capabilities. The downside is that Wifi generally takes a lot of energy, and transmission takes in the order of 250mA, which is too much for this project’s goals.
So I looked at the alternative: Bluetooth. Serial to Bluetooth modules are also in the range of about $60, but that is a bit too expensive for a pet project for somebody who gets less than $50 a month. A really amazing solution is the Nintendo Wiimote, which I also wrote about here: Wiimote - The Ultimate Hacker’s Toy. You can pick up a used Wiimote for under $30, and it includes a lot of functionality that could come in useful in the robot’s design: A bluetooth module for connecting to the PC, an infrared camera for detecting sunlight, tilt sensors for determining orientation and an i2c port for connecting to an MCU.
I took the following energy consumption measurements for the wiimote which should give an indication of battery life and the solar power requirements:
Idle mode: 0.5mA
Connected but IR sensor not in use: 21mA
Connected with IR sensor in use: 63mA
Each LED: +2mA
Rumble: 30mA
The input voltage is in the range from 3.3V to 2V, so the Wiimote probably uses a step-up converter to get 3.3V for its electronics. Assuming I will be using IR, the power requirements for the wiimote is then: 63mA * 2.4V = 151mW, which is much less than the Connectone iWifi @ 250mA * 3.3V = 825mW.
This is a work in progress, I will add text here as I go along.
