Devices not used to their full potential
It seems to me some very cheap devices are not used to their full potential in robotics. Currently I am focused on optical mice. There are tutorials on the web and even an easy to use PS2 library for Arduino but I never see a robot on LMR using them.
I am currently experimenting with a cheap PS2 optical mouse as a high resolution quadrature encoder. With a resolution of 800 DPI, I can get an accuracy of 3600 counts per revolution (1/10th of a degree) by having the sensor mounted near the outer edge of a disc about 40mm in diameter.
40mm diameter x Pi = 126mm circumference = 4.9 inches * 800 gives me about 3900. Well over the 3600 I need for 1/10th of a degree resolution and a 40mm disc is quite small.
This is a cheap PS2 mouse that I cut in half to make it smaller. I used the PS2 mouse library to test it. Some mouse sensors can actually give you a grayscale picture of what they see but my sensor only has the basic mouse capabilities according to the datasheet.
Keyboards also offer a very cheap and simple means to get over 100 digital inputs using just 2x I/O pins.There is a PS2 keyboard library here: http://www.pjrc.com/teensy/arduino_libraries/PS2Keyboard.zip.
Read how to use it here: http://www.pjrc.com/teensy/td_libs_PS2Keyboard.html
Can you think of any other cheap devices that are not living up to their full potential?