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

P Todd Decker via groups.io wrote:

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

On Sep 26, 2020, at 1:24 PM, Lee Hart <leeahart@earthlink.net> wrote:

ca1naj610 wrote:

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?

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.

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 worked.

The problem comes because the N2/LOAD signal can't drive a 74LS input (much less 3 of them, as would happen if the PE Elf's IC10 was a 74LS10 instead of a 4023).

That makes me wonder: How does the RC1802 drive the TIL311 hex displays? The PE Elf used eight 4050 buffers to drive its display, because these are TTL parts. They would overload the bus without the buffers.

Lee

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com

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

ca1naj610 wrote:

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?

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

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com

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.

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

Back in the late 70's....

After my Elf II,  I had a homebrew 1806 system which used the TMS9929A (PAL version of the 9918) for it's video output, it worked fine, and is relatively easy to interface as I remember. You can use either a couple of I/O ports, or just one and the Q line.

My current homebrew system, which some of you may have seen on the Cosmac Elf 1802 Facebook group doesn't have video out yet, but the plans are to add a video board using that very same chip (assuming it still works).

Mark.

Tor-Eirik Lunde wrote:

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 have to
revisit the design once I get a semblance of a hobby workshop up and
running again 😀

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 74C10. It's CMOS, and is a plug-in replacement for the 74LS10 (same pinouts). But it's an old chip and a bit hard to find.

Lee Hart

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com

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

Can you Gentlemen confirm that this old Harris CMOS RAM chip circa' 1979 will work correctly as a substitute for the '2101 chips in the original PE ELF circuit, please?

TIA.  Cheerful regards, Mike, K8LH

On 09/26/2020 7:44 AM Alan Jones <oalanjones@...> wrote:

Folks,

I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?

https://hackaday.com/2020/09/11/tv-output-from-arduino-1980s-style/#more-431395

Al, N8WQ

On 09/26/2020 7:44 AM Alan Jones <oalanjones@...> wrote:

Folks,

I was reading this hackaday article this morning and was wondering if we could use this chip to provide video on a 1802 system? What do you think?

https://hackaday.com/2020/09/11/tv-output-from-arduino-1980s-style/#more-431395

Al, N8WQ

_._,_._,_

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 will be building it. And, I know of a sixth who is also interested. You may have also seen from other posts that I have created a more detailed BOM.  Could you take a moment to review it?  Especially the specs for the 7-segment LEDs.  

John,

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