Keyboard Adaptor Design & Construction Notes --------------------------------------------- 01. The indicated circuits, and some variants, have been built and tested, and work for us. As I'm sure you can understand, the use of these resources is at your own risk. Amongst other things, the construction ability and circumstances of each person vary. If you wire things up incorrectly, apply incorrect voltages, short something out, or zap something with static, you may damage your EBM, keyboard, or some of the adaptor components. And of course, we're human too, and the diagrams, software or written details might contain errors. We don't think so, and have taken all care, but can't take responsibility. 02. This adaptor is a work in progress. Whilst the design shown works (and well), there are some enhancements and other things that are on the drawing board, as well as more detailed instructions, suggestions, and pictures rounding out the design. For example, for the initial release, there are no details on how to make a "palm connector" to plug into the keyboard. Whit's made one - from a paintbrush handle, I believe - and I've jury-rigged a monstrosity that looks like it escaped from a 50's sci-fi movie, and is totally useless for anything other than the test bench. You're either going to have to use your own ingenuity, or wait until we can work out something with commonly obtainable parts (If someone knows how to procure these connector components, please tell! Unfortunately, I expect Palm Computing treats them like gold-plated hen's teeth, though). 03. This circuit is for the fold-up keyboards available for the Palm PDA range. Both the versions for the older Palm range and the Palm V work - though the connectors are slightly diffferent, the pin assignments are the same - and it doesn't matter if they are Palm branded or not (they are all made by a company called Think Outside, and licenced to Palm, Targus, or whoever). In fact, the versions for Pocket PCs will probably also work, although the pin assignments are quite different (further details at a later date, if anyone's interested). The Handspring versions won't work without adaptions to the circuit and software. 04. Don't forget, you've got to either plug the keyboard adaptor into the EBM2EBM adaptor or incorporate the crossover, 5V and pull-up resistors into your keyboard adaptor itself. 05. Resistor values (10K ohm) are somewhat flexible. 4K7 resistors will probably work, as should 47K resistors. 100K resistors may work, but probably depends on the particular properties of the other components - it would be the upper limit, I think. Experiment, if you wish - the circuit may not work, but the resistors aren't in a position to do much damage if it doesn't. In the next few days after I write this, I will be testing the circuit using 47K resistors. If it works, this will reduce the current through the pull-up and pull-down resistors, making a (theoretical, anyway) difference to battery life - perhaps a few percent increase in runtime. 06. The capacitor values are also somewhat flexible, but the 0.1 microfarad ceramic caps specified are physically small and dirt cheap, so you may as well use them. 07. If you use battery power (rather than an AC adaptor) you can leave out the capacitor shown on the EBM2EBM cable across the power inputs, unless you've got a long lead to the batteries and use it near strong magnetic fields (big speakers, coiled three times around your monitor, etc.). It's there to smooth out AC ripple from the plugpack. The cap across the inverter IC is there to nullify any RF noise picked up in the cables. 08. On the EBM2EBM adaptor, you can leave out the diode if you're 100% sure (as in 100%, bet your EBM, sure) you or anyone else is not going to connect in the batteries or AC adaptor backwards. This will increase the effective battery life somewhat, as there is a voltage drop across the diode. Actually, I have the sneaking feeling the EBM might survive reverse voltage, but I'm not game to test it, and I don't expect anyone else will be volunteering in the near future. 09. I strongly suggest socketing the inverter IC (integrated circuit). This means you can solder the socket in, build the rest of the circuit and then at the very end insert the IC, safe from static discharge during construction. Also good if your soldering is a bit heavy (IC's don't like too much heat), or if you tend to solder pins together, and makes replacement easier if the IC ever goes to the Great Junkbox in the Sky. Once the IC is in a completed circuit it's pretty well protected from static, by the way. 10. To identify the pins on an IC, look at it from the top (legs pointing down). One end will have a notch (typically semi-circular, but circular depressions and painted dots have been known to take it's place). With the notch away from you, pin 1 is on the right hand side of the notch, at the end. The pins are numbered anti-clockwise. If you look at the circuit diagram, I've made the IC symbol a bit non-standard, but it shows you the IC looking down from above, with the notch shown and the pins numbered. 11. The circuit's been tested with input voltages ranging from 4.5V (3 alkaline cells) to 6V (4 alkaline cells). Given that is with the diode in, this means that 3 NiMH cells (3.6V) will possibly work with the diode out (Haven't gotten around to testing it though), but 4 NiMH cells (4.8V) will definitely work, even with the diode in place (desptite not having been tested). Note that unregulated plugpacks will often supply higher voltages than indicated, if they are not under full load. This might cause unpleasant side effects; I strongly suggest a regulated plugpack if you wish to use AC power (or car power, for that matter). 12. I suggest connecting the power to the adaptor before plugging in the EBM, and disconnecting power after unplugging in the EBM. If, perchance, you have added a power switch to your EBM2EBM adaptor, you can disregard (except, turn it on after the EBM is plugged in, off before you unplug). This just minimises the chances of spikes and messy power. 13. Keyboard Adaptor Component List: 2 x 10KOhm 1/4 watt resistors; 1 x 0.1 microfarad ceramic (disc) capacitor; 1 x momentary normally-open pushbutton switch (single pole, single throw, if anyone asks); 1 x 7404 hex inverter IC (you'll probably find it as the "74HC04" variant. This is the one you want); 1 x 14 pin IC socket (strongly suggested); Connector to match your EBM2EBM crossover adaptor (typically either a male or female USB A connector); Connector to match the folding keyboard (which you'll probably have to construct). Paul Douglas - Yahoo ebookman group member.