Interesting.... Tricks to make boards. THe most common for one off is a cleaned piece of board and a Sharpie marker. The ink in the marker is resistant to most etching solutions. Fast and cheap. For y

#Electronics #IpsoFacto #Serial

Hi Tom: just a thought, is it worth scanning those 2x tape-on-mylar/vellum designs and uploading somewhere? -- Stuart.

#Electronics #IpsoFacto #Serial

A short while back I recall seeing some discussion of Prototyping PCB availability, which prompted me to go look in my old PCBs drawer, not expecting much. However, there were a few things I wasn't ex

#Electronics #IpsoFacto #Serial

Timothy Stoddard wrote: The hardware is still pretty simple. The 1802 BASYS/1 boards scanned an 80-key keyboard using DMA-IN, all in hardware, with no special chips. The keys appeared as 10 bytes of m

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Lee: Yes I'm aware... I use the LOAD mode in my SBC1802 posted here. I was answering the suggestion of using the 1802 to scan the key matrix rather than a dedicated scanning chip like the 922/23 ... t

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David Madole wrote: Certainly! 1802 cassette tape storage programs did exactly that. :-)

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Timothy Stoddard wrote: If you mean DMA keyboard input, the Netronics and Quest Elves (and others) used DMA for their hex keypad input, with LOAD mode.

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Hi All, Earlier I wrote "and I've added a 4-way DIP switch. The left-most switch holds the active-low MW pin of the battery-backed RAM chip high for switching off and on, that way the RAM contents don

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John wrote: Try just putting a speaker on Q and doing the tones in software. David

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John wrote: The original PE Elf wasn't a commercial product; it was hand-wired on perfboard. As you look through the series of articles, it keeps changing as Weisbecker added features. So there is no

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I've also done that in other projects, but that requires software overhead to use and would not be a good solution for a DMA input into the COSMAC.

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Hello Paul, The wiper of the switch does go to the active low write enable pin(s) on the RAM in both the original PE diagram and Paul's diagram. The poles are connected to +5v (write protect) and pin

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Paul Schmidt wrote: That's correct. Paul's schematic is the same as the original PE Elf article. Both leave the RAM's /WE pin "floating" during the time the switch transitions between WriteEnable and

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The 22K shouldn't go to the wiper, if it's wired like Paul's diagram. It should go to the terminal that connects to the RAM. Maybe your circuit is a little different though. The MAX232 is not "period

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Thanks again for all the help. I can confirm; There is no difference between the original circuit diagram and the one I called "Paul's design" The DIP switch I added does exactly the same as leaving t

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Ah ok, I was just replying to what John called it. I took a quick look at the schematic but I really didn’t read the history or other documentation with it to understand that. It’s been 40 years since

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For what it is worth (and I am gratified that folks are using the ELF documentation I prepared), there is no "Paul's Design" in regard to the ELF schematic. What I show is just the same as the magazin

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John, Another thought that came to me… why do you need a DIP switch to hold /WE high when that is exactly what the MP switch appears to do? It seems like you could have just flipped MP to power off? T

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Paul’s design looks like it lets the /WE input on the RAM float during the short time that the MP switch is between breaking one side of the throw and making the other. I suppose this is fine if the /

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John, when I built the first of my two identical 'original configuration' ELFs (I have the original and my duplicate is (I think) still on display at Bletchley Park, both I (with mine) and the Bletchl

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