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Silver PP9 capacity

 
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Re: Silver PP9 capacity

Post by Michael Watterson » Thu Jan 09, 2014 11:02 am

The clock chips used an R/C oscillator to multiplex display. No crystals even in many new ones that are mains. I don't know offhand if the PP3 backup battery uses R/C 50Hz osc or internal divider from the multiplex R/C, but they can gain minutes in an hour, only use for a very short power cut!

 
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Re: Silver PP9 capacity

Post by Refugee » Thu Jan 09, 2014 11:22 am

I have had the clock from new and it has never been opened.
I can never be absolutely sure if the exact internals but I can never remember the strobe effect while passing by over the years.

 
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Re: Silver PP9 capacity

Post by davegsm82 » Sat Jan 11, 2014 12:35 am

Re: Clocks,

Generally, there are 2 sets of segments each with a common anode (or cathode), to reduce the number of connections between the chip and the display. The transformer is center tapped, one side goes to one set of anodes, the other goes to the other anodes. There is a phase detection pin on the chip, it knows to output one part of the display on the fist half of the cycle, then when the mains goes to the next part of the cycle, it displays the next part.

For example,
Diode segments A,B,C,D, common anodes are on 1st half of the cycle,
Diode segments E,F,G common anodes are on the 2nd half of the cycle.
Segment A cathode is connected to segment E Cathode, similarly B and F, and C and G.

The clock chip counts the mains cycles, and knows which part of the display to show at each point.

My clock draws about 60mA continuously on bright, about 40-50 on dim. The original transformer was about 5v, I'd be using a single cap and resistor on each output as a voltage doubler on a 3v transformer to provide a current limited output, this would give about 5.3v taking the diode drop into account.

Dave.

 
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Re: Silver PP9 capacity

Post by Refugee » Sat Jan 11, 2014 1:37 am

I have plugged in the clock I have and and moved it past my eyes in a darkened room.
It does appear to be multiplexed in some way. I have never opened it and will not be able to do it right now as the bench is all full up with bits of TV cameras that I am building up.

 
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Re: Silver PP9 capacity

Post by Mark Hennessy » Sat Jan 11, 2014 12:40 pm

Quite a few clocks from that era weren't multiplexed - I had several to take apart as a kid, and still have one upstairs. Non-multiplexed LED modules were much easier for me to "re-purpose", of course...

Perhaps surprising, but labour and electricity was cheap, and ICs were still infants, relatively speaking.

Then again, any digital volt meter based on an ICL7107 also isn't multiplexed. About 7mA per segment, IIRC. Of course, this IC was derived from the LCD version - ICL7106 - which was originally designed by with Fluke for the 8020 DVM. Intersil releasing it generally (with just one small difference) is what prompted Fluke to set up their own fab for future custom ICs.

I'm quite sensitive to display flicker, so I prefer non-multiplexed displays. The new Sony alarm clocks we have are terrible - far too low a refresh rate. Even Thurlby-Thandar messed this up when they updated their PL320 PSUs - the original ADD3701 IC that provided the 3,999 count displays went obsolete, so they redesigned it using another ADC and a PIC to drive the displays, but these were done at a lower refresh rate than the ADD3701, and quite flicker noticeably (I'm looking at both generations on the bench now).

 
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Re: Silver PP9 capacity

Post by Refugee » Sat Jan 11, 2014 1:36 pm

I do have a non multiplexed nixie tube counter that uses all 74 series TTL.
It has a very useful preset switching system that allows it to switch an output at a set count so it is now in the kit for construction of a coil winder.
The LED drivers that were sold in the 1970s through magazines used not to be multiplexed.

 
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Re: Silver PP9 capacity

Post by davegsm82 » Sat Jan 11, 2014 3:34 pm

Have a look at this datasheet - http://www.paulanders.com/G5-LED/ver1/datablad.pdf

Not the exact chip I was thinking of but you get the point.

Dave.

 
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Re: Silver PP9 capacity

Post by Refugee » Sat Jan 11, 2014 4:00 pm

Those were sold in kits in the 1970s and early 1980s.
I have not looked inside the clock I have as it has never broken down.

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