A description of RUN operation after separating the M/S card set.

Lee Hart, March 29 2011.

A Membership Card owner wrote:

> My oscillator IC 4093 pin 11 won't stop if I remove RUN from VDD.
> With my logic probe I notice that the wire attached to pin 2 remains
> high.  When I put ground to pin 2 then the oscillator stops.
> Is it OK to to keep this grounded to get the oscillator to stop?

(Refer to the Membership Card schematic for circuit details.)

Yes, it is OK to ground RUN to get it to stop. But if the front panel is plugged in, it is easier to just set the CLEAR/RUN switch S9 low. The circuit is a little bit tricky. There are two ways to stop the oscillator:

1. If you leave the two cards plugged together, the oscillator stops if:

a. You open the RUN connection (disconnect P4 pins 1-2).
b. *AND* set S9 (the CLEAR/RUN switch) off (down).

2. If you unplug the two cards, the process of unplugging automatically opens the RUN connection, so R7 pulls pin 12 of the 4093 low. Also, R4 pulls the 1802's /CLEAR pin low.

Here's the details. R7 and C3 provides a "long" time constant (0.1 seconds). R4 and C2 provides a "short" time constant (0.05 seconds). This was done so when you unplug the boards, C2 discharges first so 1802 /CLEAR goes low (to reset it and stop any program that was running). Then C3 discharges, and the oscillator stops (minimizing power consumption).

The supercapacitor C4 will maintain the program in memory for many minutes with RUN low. That's long enough to

a. Load a program with the front panel.
b. Unplug the front panel.
c. Plug the membership card into some project with its own power.

When you want to run the Membership card without its front panel, just connect RUN to VCC (with your "on/off" switch). The time constants are now arranged so the oscillator starts almost instantly (C3 charges very fast through D10). The 1802's /CLEAR pin is initially held low by C2, and is pulled high by R6, so the 1802 gets a proper reset. And your program is now running!

When you turn your "on/off" switch off, it opens the connection between RUN and VCC. 1802 /CLEAR goes low first, cleanly stopping the running program. Then the oscillator stops, to minimize power consumption. In this mode, a set of AA cells will last over a year.

- Lee Hart