Shoe Polish Clock
1973 Designed and Constructed by Jerry
The clear, round lid came from a shoe pollishing kit. This clock demonstrates how the complexity of integrated circuits has advanced. The MM5314 CMOS integrated circuit contains the circuits for dividing 60 Hz down to hours, minutes, and seconds, the time setting circuits, and the driver circuits for the 7 segments of the four digits of the LED readout. Not so easy to see are the four driver transistors, one for each digit. The clock gets its 60 Hz reference from the line plugged into the wall, but during a power outage a simple R-C oscillator keeps the clock running reasonably accurate until commercial power is re-established. The 120-volt line voltage is stepped down to 15 volts directly by using a capacitor coupled current pump. No transformer is used. A 9-volt battery, that is trickled charged, keeps the clock running during power outages.