An error in the previous post was brought to mi attention by another user. -Thanks again! This is the memory circuit in my system. It is added onto a Super Elf. View the drawing in MS Paint or Photo V

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David Schultz wrote: Ah! No CMOS loading problems there. Lee

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If changed to HC, then the 47K will work just fine.

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MC14495 latch and hex to seven segment decoder

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It doesn’t use TILs, it uses a common cathode 7-segment LED display.

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P Todd Decker via groups.io wrote: I haven't looked at the RC1802 schematic closely. But the diode OR gates in the original PE Elf used 47k pull-down resistors. Since they all drove CMOS inputs, it wo

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Should all the LS chips be replaced with HC? And, if so, can the originally specified 47K resistor values be maintained? --- P. Todd Decker 913-284-8814

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ca1naj610 wrote: Sure; a 74HC10 would work as well as the 74C10. I was just thinking of a vintage chip that would have been Elf-period correct, without having to rewire it for a 4023. Lee

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In my case the wrong chip was stopping the strobe signal from being pulled low, so the display was not useful. Gates on the same chip also drove the TX/RX pins and so those didn’t work properly either

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Thanks, Lee for the suggestion to substitute a 74C10 for a 74LS10. Since many of us have 74HC chips, what would be the consequence of substituting a 74HC10 for the 74LS10? Denny Ruigenstein

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Tor-Eirik Lunde wrote: No worries, mate. Hobbies are all about fun and new experiences. We learn more from our mistakes than from our successes. :-) On the 74LS10: One way to avoid fix it is to use a

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Tor-Eirik - thanks for sharing your design! I had a lot of fun and learnt a lot by building it!

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Hi Tor-Eirik, I guess it's your design. There's no better way of testing a project than by having a group build! When you finish the corrections on the design, would you consider doing a board run for

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Tor-Eirik—Thank you for contributing your design! I am glad we now know which member did these designs. It wasn’t obvious to me from your GitHub site. There are five of us now who have your boards and

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Yeah... I'm a bit of an amateur when it comes to electronics, so when it comes to faults I can just about figure out the logic of things. Nice going on finding a fix for the errors in my ways. Will ha

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John, Great trouble shooting! You really spotted the problem there when the 74LS10 input was lifting the logic. You have nothing to apologize for, it was not a well thought out design. It should never

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John, Nothing for you to apologize for, looking at the published BOM for the RC1802, it called for LS chips so perhaps this is a design flaw and we should be using HC instead. If we use LS chips, shou

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And I’m sorry for my CMOS / TTL sins.. :-(

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YES! Thanks all! I swapped out the 47K for a 3K3, and look what happened.. Not only did the strobe start working but the serial port burst into life! (If 300 baud can burst anything).

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I am thinking R3 at 47K is too high of a value for an 74LS10, cmos would be fine. Try dropping the value a bunch (maybe 3.3K) or swap the 74LS10 to something like a 74HCT10. The 74LS10 circuit is show

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