USB-to-Serial Adapter to PICAXE Com Test

Pololu and SparkFun market inexpensive USB-to-Serial adapter board modules (P/N 391 and FT232R), that with the appropriate drivers appear to both the computer and the client as serial com ports. This really simplifies USB connectivity. I thought it would be fun to wire this to a PICAXE-18M2 microprocessor and see what could be done with it. The end program permits a terminal program on a PC (like Teraterm or Hyperlink) to send commands to the microprocessor to either retrieve telemetry or to turn an LED on or off. To feed the microprocessor's ADC input I connected a potentiometer form Vcc to ground and the wiper to the ADC. From the terminal, if I type "l" the LED lights up, "d" extinguishes it (l for light, d for dark); "r" reads the ADC and displays the byte value. Incidentally, the USB connection also powers the entire project.

Link to Video [Link]

Link to BASIC code [Link]

Link to Wiring Diagram [Link]

Link to USB Module Specs [Link]

Link to my other interests [Link]

Super Tech Lab Joule Thief

One of my pet peeves is throwing out AA batteries because most gadgets consider a 1.5V battery dead by the time it degrades to 1.3V or below. It seems like 86% of its energy is wasted. My digital camera is the worst offender; understandably, the flash requies a lot of current. Rather than sending these 'spent' batteries to a land fill, I have been saving them for some energy harvesting/joule thief circuit experiments. I did not design the joule thief circuit pictured above (there are dozens of variations across the net), but I redrew it in tinycad and built a demonstration circuit. It is simply an oscillator that will run on very low power, providing an inductive 'kick' to keep an LED illuminated well below a straight DC supply voltage. The induction comes from a toroid wound with a bifilar winding (opposing coils). The easiest way to make it is to get a twisted pair of wire (like black and white so you can tell them apart), wind about 10 turns around the toroid, and then connect the black wire from one end to the white of the other (this gives us opposing coils). The 2N3904 could be replaced with just about any NPN transistor (2N2222, etc.)

The circuit I built oscillated at 10KHz, and it illuminated a LED for 108 hours on a 'bead' battery (1.3V).
It made a nice night light. The toroid could have been much smaller, I just used the first one I could scrounge.
A good green project would be to retrofit some battery operated device to use a circuit like this to get more life out of a set of batteries.

Larger Circuit Diagram [Link]

My other interests [Link]

TinyCad free schematic capture [Link]