COSMAC Elf switch panel using PCBs

Mike Stein mhs.stein at
Sat Apr 23 12:45:09 CDT 2016

>From p.11:

"RUN and LOAD switches S1 and S2 in Fig. 5 control the operation of the computer. With both switches set to OFF, ~LOAD is +5V and RUN is at ground potential. This resets the 1802."

Note the tilde, suggesting ~LOAD is active low.


----- Original Message ----- 
From: "dwight" <dkelvey at>
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at>
Sent: Saturday, April 23, 2016 1:28 PM
Subject: Re: COSMAC Elf switch panel using PCBs

I looked at the schematic pdf and it looks right.
The ground lead is the NC.
Can you tell us what page reference you think is wrong
or confusing?

From: cctalk <cctalk-bounces at> on behalf of Eric Smith <spacewar at>
Sent: Friday, April 22, 2016 5:06 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: COSMAC Elf switch panel using PCBs

I built a new Elf switch panel, but this time I used two printed
circuit boards for the switches and the bezel.

The bezel PCB has white soldermask with black silkscreen.  The next
revision will have black soldermask with white silkscreen, and the
legend font, weight, and positioning changed to more closely match the
original Elf photo in Popular Electronics.

The 20-pin header has the same pinout as Bob Armstrong used for the
Spare Time Gizmos Elf 2000, but I don't presently have an Elf 2000 to
test it with. For now the main intent is to use the panel for a new
version of my FPGA Elf.

I'm not sure whether I got the wiring of the LOAD switch correct; the
Elf 2000 documentation refers to normally closed and normally open
contacts of that switch, but for a toggle switch that doesn't make any
sense to me.  If anyone can tell me which pins of the Elf 2000
connector are grounded when the load switch is active vs inactive,
that would be appreciated.

The 20-pin header should have been right angle; since I only had a
vertical header on-hand, the ribbon cable had to be plugged in before
the switches were soldered in place, and the switches are not flush
with the switch PCB.

The toggle switches and push-button switch are C&K 7101SDV3BE and
8125SDV3BE, respectively, which have 0.42 inch actuator, 0.28 inch
threaded bushing with keyway, vertical PCB mount with V-bracket, gold
contacts, chrome actuator finish, and nickel bushing finish. These
particular C&K switch variants are not very common, so I'll probably
use different ones in the future, without the V-bracket.

I don't yet have enough of the red and white toggle caps, which are
C&K 896803000 and 896801000, respectively.  The red button for the
push-button switch is C&K 801803000.

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