Hardware Documents
Some interesting PDF documents at http://www.oselectronics.com/downloads.htm
QRP Transmitter Design 300 kb
Winding and Using Toroids 306 kb
US Amateur Radio Bands courtesy of ARRL 39 kb
Direct Conversion Receivers 66 kb
All About Broadband Transformers 57 kb
Tutorial on building PC Boards 349 kb
All About Capacitors 293 kb
A One Tube QRP Transmitter 514 kb
All About Coils, Transformers and Relays 465 kb
All About Diodes 77 kb
Design Tips For Simple Superhet Receivers 341 kb
Designing And Using VFOs 334 kb
Introduction To Resistors 134 kb
Introduction To Transistors 178 kb
One Tube Transmitter For 40M Or 80M courtesy of the ARRL 429 kb
Schematic Symbols 65 kb
Simple Crystal Radio Set 100 kb
Understanding Scientific Notation 154 kb
AM Receiver using the ZN414Z IC 19kb
Economy Shortwave Receiver
One Watt CW Transmitter
A Homemade Isolation Transformer to Cure H-K Shorts
Tutorial on OP Amps
Simple Electronics Project
If you have a PDA (especially one with Windows CE) you know what a problem battery life is. I have a Casio E-100 and an AudioVox Maestro (just a Toshiba E570 with half of the memory taken out). These both have the same plug as an iPaq. Radio Shack sells these connectors (274-1532) in packs of 2. They also make a really neat enclosed AA battery holder that has a switch built into it (270-409). I also used a 1N4001 and a bit of heat shrink tubing.
The PDA's center pin is + and the ring is ground. Here are the basic steps (you can probably guess):
- Remove the plug sleeve and thread the battery pack wires through it so that the back of the sleeve faces the pack.
- Solder the banded end of the 1N4001 (or any similar diode) to the center pin of the plug. Hook the wire so that it passes from the "inside" of the plug to the outside. Get the body of the diode as close as possible to the plug body. Keep in mind that the sleeve has to fit over this, so you want the center line of the diode to pretty much be on the center line of the plug. Trim the excess wire as close as possible. You might want to test fit the sleeve when you are done.
- Thread a bit of heatshrink over the red wire. It should be enough to cover the uninsulated part of the wire plus the uninsulated part of the diode you will leave behind (see next step). Double check that you have the sleeve the right way and the battery wires passing through it.
- Loop a bit of the red wire over the diode's non-banded end. Get it close to the diode body and solder. Cut the wire close. Try to keep the diode wire straight and just make a small loop out of the battery wire. The heat shink will have to fit over this joint, so neatness counts.
- Solder the black battery wire to the "ring" part of the jack.
- Slide the heat shrink over the connection where the red wire meets the diode. Shrink it with your soldering iron (don't use the tip, use the heat from further back) or a hair dryer.
- Crimp the strain relief gently so it grips the diode assembly. Reassemble the plug.
- Install 4 AA alkaline batteries. Use a wire or paper clip to touch the inside of the plug and measure the voltage with a voltmeter.
- Curse and panic when the meter reads 0V. Then remember that the box has an on/off switch and turn it on.
- If your voltmeter reads about 5.5V or so with the red lead on the center pin, you are done. Go try it on your PDA. Under load, the voltage will drop a bit and both of my PDAs don't seem to mind a bit of extra voltage.
I was afraid that without the diode the 6+ volts from fresh batteries might be too much, but I'm not sure. It also would prevent the pack from draining a battery with higher voltage although that doesn't seem to be a problem on these PDAs. If you wanted to use rechargeable cells (usually about 1.2V each) you could, but the voltage would be less. You might try omitting the diode or using a Schottky diode (which drops about .3V instead of .6 or .7 with the silicon diode I used).
Have fun, and remember: if you blow up your PDA, I AM NOT RESPONSIBLE! DO THIS AT YOUR OWN RISK.
I HEREBY DISCLAIM ALL WARRANTIES WITH REGARD TO THIS CIRCUIT, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL I BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE CONSTRUCTION, USE, OR PERFORMANCE OF THIS HARDWARE.
Oh yeah, and void where prohibited by law.
