FAQ's on the Membership Board ----------------------------- Oct 11, 2005 Many thanks for all the comments and encouragement, both on the list and off. A few questions came up, which are helping me to clean up some details. 1. Where's the power supply? I'm powering it off the PC's parallel port. This port has no +5v pins, but there are pullup resistors to +5v on every data pin. Any pins left high provide the power, via the CMOS IC's input protection diodes. This is adequate since the membership board only draws a few ma. But, I think I will add an "official" power connector. What would you prefer? I could just leave a couple pads to solder on wires; or expand 2-pin header J2 into 3 pins (power, ground, LED enable); or something else. Keep in mind I only have 0.35" of height above the board. 2. Can you bring out the other flag lines and other pins? The membership board is pretty small. I used a 25-pin single-row connector because it fits, and I have a bunch of them (so they are basically free :-) I don't have room to bring out a full expansion bus, and it's unlikely anyone would ever design anything for it anyway. But, I'll look for a way to get a few more pins out (EF1, EF2, EF3, and INT). Any others that aren't already there that you feel would be a "high priority"? 3. How do you use the membership board without the front panel board? That's a good question! I hadn't thought through this very well. Right now, you can use the membership card standalone with an EPROM. The EPROM ignores the floating /WE line, and there is a simple power-on reset circuit (100k pullup to VCC and 0.1uF to ground on the 1802 /CLR pin). But running with no RAM is pretty restrictive. You can install a jumper to short /MWR to /WE in the 25-pin connector to write-enable RAM. That part's easy. The hard part is, "How do you get a program into RAM with no front panel?" I need to add a mechanism to: a. Keep the RAM powered when you unplug the front panel. I can do this by changing the 22uf capacitor to a 0.047f (47,000uf) supercapacitor. Electronic Goldmine has these for $0.80 each), and they are small enough to fit. b. Protect the data in RAM while the front panel is being removed. Do this by adding a resistor to pull /WE high when the front panel board is unplugged. c. Stop the 1802 while the front panel is being removed. Replace the pullup on /CLR with a pulldown resistor. That also means an external switch will be needed to pull /CLR high when you want the board to run again. I think this would work as follows: - plug membership board onto front panel - load your program with the switches or a PC - set the RUN/CLEAR switch to 'clear' (stops the 1802) - unplug the membership board (it's now powered by the capacitor) - plug it into your project ( - flip the RUN/CLEAR switch in your project from 'clear' to 'run'. - the program stays in RAM as long as your project keeps the membership card powered I'd like the membership board to be a poor man's BASIC Stamp. Compared to the real (Parallax) BASIC Stamp, it could be cheaper, faster, more memory, lower power, no PC needed, and you can build it yourself! :-) Oct 12, 2005 Bill Rowe wrote: > Lee: I'm so excited! Thank You! You're welcome. > I'm gathering parts and planning to put mine together on an old > protoboard for starters. I'll probably start without the parallel > port and a simple dip switch led setup. That will work, as long as you have pullup resistors for the DIP switches (as I assume they are SPST). > Could I get away with something like a 3 volt watch battery? Yes; the power consumption depends on the LEDs and RAM used (the 1802 and other chips are negligible in comparison). I have some nice white LEDs that are incredibly efficient; they are clearly visible at 100 microamps! For the RAM, you'll need to do some hunting to find a true CMOS part that has a low power consumption even when active (chip select low). Most draw 5ma to 100ma when chip selected. Oct 13 2005 Bill Rowe wrote: > Will the chips work on 3V? Yes. All the chips I've tried work at 3v, and even less. Basically, the lower the supply voltage, the slower you need to run the clock. Somewhere around 2.5v is the lower limit. Below that, the chips still work but don't have enough drive for even the 100k pullup resistors. -- Jan 21 2006 >[Q: lifetime for the toggle switches?] if you don't plan to use the switches a lot (just long enough to try things out initially, before moving on to some better input device), then just get some cheap surplus toggle switches. Almost any will work. But if you expect to use the switches a lot, then "human factor" issues come to play. You'll rapidly come to hate cheap switches! In this case, get some good ones that have really nice, easy-to-use actuators. I like the "piano key" style actuators. See the C&K 7000-series toggle switches with J5 actuator. This is a flat tab about 1" long and 3/4" wide. -- Feb 9, 2006 >[Q: where can I get 1802's?] Last year, Electronic Goldmine http://www.goldmine-elec.com had a bunch of MSI88 barcode readers (a gadget about the size of a paperback book) that had an 1802, as well as a lot of other good parts. They were selling them for $2 each! I don't know if they have any left. --