nixie tube clock circuit

The nixie tube clock consists of a high voltage power supply, seven rings counters and an Atmel AVR processor. The power supply is shown in schematic Schematic 1. It takes 12 volts AC and converts it to DC which drives the Maxim 1771 switching power supply to generate 160 volts. The Maxim 1771 operates by effectively shorting the 12 volts DC to
 nixie tube clock circuit - schematic

ground through the coil L1 using the MOSFET Q1. When it turns off Q1, this releases the coil from ground and a large positive spike is generated which is then stored in an electrolytic capacitor C3. The diode D1 keeps the capacitor from discharging back though the circuit. Resistors R2, R4 and the potentiometer R3 make a voltage divider which feeds a small voltage back to the Maxim IC so that it can adjust the pulses frequency and duty cycle to regulate the voltage. Resistor R5 and zener diode Z1 are used to regulate down this down to 120 volts do drive the ring counters. The AC input is also used to provide a 60hz signal to the first ring as well as an interrupt to the processor. Three of the ring counters divide by 6, 3 others divide by 10 and the last ring divides by 12. The divide by 6 rings and the divide by 10 rings are paired to count the 60hz down to 1hz, the 1hz to 1cpm and the 1cpm to an hourly pulse. Each of the rings are similar. The difference being the trigger circuit is different for the first two rings than the subsequent rings. The first two rings use a single transistor to drive them, while a 3 transistor circuit is used to provide clean consistent pulses to drive the remaining rings. In addition to the different triggering circuits, the minutes and 10s of minutes rings have half of the diodes replaced with the base emitter junction of a transistor. Those transistors as well as others are used to drive...

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