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Boselli Icon 30 modification

I was asked by a customer if I could provide him with a “power supply” for his circa 1970’s Italian ‘Boselli Icon 30’ (see picture) flip digital clock.


On examination of the clock, (which is entirely mechanically/ electromagnetically operated) needed a +24v pulse for first “flip”, followed a minute later by a -24v pulse, followed for the next cycle by a +24v pulse, and so on...


I said “yes I can do that for you”!


Originally I planned to use a NE 555 timer in astable mode set for 1 minute alternate “states”, but this would not have been anywhere accurate enough.


I explored many possibilities using crystal and logic division etc, but time was at a premium, as I’m really busy with my repair work, and this would have made things a bit too expensive for the project in hand.


I quoted the customer an acceptable price and set to work.


I decided to use a mechanical “trigger” from a cheap quartz clock movement. I firstly removed the fingers and replaced them with a revolving lightweight disc of plastic mounted on the SECOND HAND central spindle, with a 3mm hole drilled in the edge, and positioned a photo interrupter arrangement either side of the hole in the disc, so the disc revolves once per minute.


I now had a quartz controlled trigger, exactly one pulse per minute!


The electronic schematic comprises a two stage system plus the power supply.


The first stage includes the photo interrupter, which once per minute provides a positive pulse to switch the (normally hard on) PNP relay driver TR1 off briefly.


This de-energises the relay RLA2 breifly, the contacts are arranged to trigger the NE555 timer, which is in bistable mode, to “flip” to its “other” state, whether the output is a positve, or off output denotes the on or off state of the relay RLA1.


When the relay RLA1 is in one state the “Flip clock contacts” are reversed, compared to the “other state” where the contacts are non reversed.


Resulting output is + 1min - 1min + 1min – 1min and so on!!


I’m fairly sure there’s a few of these clocks around, I wonder how many are redundant due to a missing trigger unit, and what did the original trigger unit comprise of? I think maybe it was a mechanical unit, but does anyone know?


I’d love to know!


Here's my schematic diagram



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