This is a breadboard recreation of Radio Shack's 1972 Digi-Count, Kit Number: 28-136.
The Digi-Count is a simple J-K flip-flop ripple counter. Each stage divides the output from the previous stage by 2, which results in a simple binary count.
In this instance the input is provided by a Cadmium Sulfide (CdS) light dependant resistor (LDR). The original user manual suggests a variety of uses, including binary counting, basic mathematical operations, attendance counting, and as RPM (revolutions per minute) meter. The units could also be cascaded to expand the range of the counter.
The Digi-Count was announced by Tandy / Radio Shack on page 113 of their 1972 catalogue, with a retail price of $7.95.
www.radioshack...
www.radioshack...
You can find a copy of the manual, including the circuit diagram, for the Digi-Count as part of Sparktron's P-Box pages.
www.sparktron....
www.sparktron....
A close-up of a damaged, but assembled, unit can be seen on the DIY Audio Forum. This allowed me to identify the original ICs as the Motorola MC853P.
www.diyaudio.c...
This breadboard version uses two original vintage Motorola MC853P J-K flip-flops, with date marks and package characteristics suggesting a manufacturing date of the 11th week, 1968.
While the original circuit is powered by four 1.5V batteries, split into two banks of 3V each, this version is being run from a single 5V breadboard power supply.
To accommodate the use of LEDs, rather than 3V incandescent lamps, the circuit has been modified slightly to tie the anodes of the LEDs (+ve) to the 5V power rail via individual 220 Ohm resistors.
For the serious enthusiast, at the time of writing, an unassembled kit is currently being listed on eBay for $299 (not by me, no affiliation).
www.ebay.com/i...
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