Randomness and a Beatable Opponent

At the end of October I described some secret cheat switches on the bottom of the Computox and linked them with a mechanism found in the Haufe design that switched the machine strategy between unbeatable and beatable.

 

Looking at the circuit, this confirms the purpose of these switches, and also highlights some cool intricacies of the design.  In the article on move selection we noted in the circuit below that whether the machine was beatable was controlled by the X relay.  If this was activated via the X-INP input, it would be latched by X-T1 and would disable the fork-blocking strategy by flipping X-T1 and X-B1.

Computox fork blocking circuit

What we did not do was explain how X-INP was generated, and it turns out it's quite clever.  As expected, the two secret switches will activate the X relay, as shown on the left of the diagram below.  However, the coil of X is also fed from the common terminal of the second uniselector SAL.  This provides an alternative method of activating the beatable mode.

Beatable mode activation circuit

The SAL uniselector is active whenever the RESET button is pressed and it rotates freely.  This connects one of SAL's 16 inputs to the common output when the reset button is released.

SAL - the secondary uniselector

Mode switches

The majority of these contacts are not connected and the Computox reverts to unbeatable mode.  However, if SAL comes to rest on contacts 04, 08, 13 or 17 these may be connected to the positive supply, resulting in X being activated and the beatable mode being selected.

Whether the SAL connections to 04, 08, 13 or 17 is connected to the positive supply is a function of 3 of a bank of 5 MODE switches.  These switches are hidden under the fuse panel on the right of the machine.  

The bank of MODE switches act like radio buttons, so only one mode can be selected at a time.  It seems that modes 1 and 2 will generate a beatable game with a 1 in 16 chance.  Mode 3 doubles this to 1 in 8. 

The difference between modes 1 and 2 isn't clear at this point.  However it might be to do with modes 4 and 5 which have to do with whether the Computox's bell is silenced. 

Overall, this means of randomly selecting whether the Computox will be beatable when playing a particular game is quite cute.  Generating randomness in deterministic systems can be quite tricky.