Booked in by shop as a 'Bingo calling unit'. It has a large 5 digit 7 seg display made from discrete LEDs. Has two 5 digit BCD encoded switch units to set start and end number. Has jack input to which is connected a hand-held push button unit. Chip date codes indicate that this thing is from 1981. It looks 'professionally' hand built, if you see what I mean. It has stickers on with a company name, but that could be largely meaningless. Two problems reported. First that it had a problem with the LEDs, and secondly that it had "lost its memory".
LED problem was straightforward enough. One segment of one digit was not lighting due to one LED in the series chain of five which made up the segment, being open circuit. A replacement LED restored that.
Now, the second problem. For playing bingo, the start number would be set to "1", and the end number to "90". All ok so far, and if this is done, it does indeed generate random numbers in the range 1 to 90, one per button push.
The next requirement is that the unit is going to need to know for any game in progress, which of the numbers between 1 and 90 that it has already produced so that they are not duplicated, and this is where it all goes t*ts up.
After a while, numbers *do* start to duplicate. If you set the start and end numbers to say "1" and "10", it might take 15 button pushes to get all ten numbers out, the other five being one or more times dups.
So I have a good look at what's in it. 2 x 4027 dual J-K, 3 x 4011 quad NAND, 2 x 4081 quad AND, 1 x 4040 12 stage counter, 1 x 4020 14 stage counter, 1 x 555 timer and last but not least, 1 x MK50395 decoder / driver. Now I don't know if I'm just being dumb-arsed here, or having a senior moment, but I'm buggered if I can see any chips in that line up that could form a memory and comparator for potentially 99999 numbers. Or even for 90 numbers come to that ... If this is what it was meant to do, even back in '81, I would have expected to see a couple of CMOS memory chips, and a Z80 or 8080 processor, maybe.
What am I missing here ? Could it be that they are mistaken in thinking that it can be used to properly call a game of bingo ? Is it in fact a raffle ticket drawing machine, where you would set the serial numbers of the first and last tickets sold out of a batch of perhaps 1000 and then draw maybe 10 prize ticket numbers with the chances of it duplicating any when it's only generating ten random numbers out of a pool of 1000, being at worst, slim ?
Haven't managed to get hold of the owners again yet to check if they feel that it has ever worked as a bingo calling machine, but at the moment, my feeling is that it is a 'new acquisition' to some little club, and that it has been given to them after sitting long forgotten in an attic somewhere for 20 years.
Any thoughts anyone ?