74142: 1-of-10 Counting System (BCD Counter, Latch, Decoder, Nixie Output) (60V, 7 mA)

This is a one-package-per-decade counting/storage/display system intended to drive a Nixie or other neon high-voltage 1-of-10 indicator.

The counter advances one state on the ground-to-high or positive edge of the input Count clock. The Clear input is normally left high; bringing it to ground briefly will reset the counter to zero, The counter counts to ten, The Carry output may be directly connected to the Count input of the next stage to cascade decades.

If the Latch input is low, the output follows the counter. If the Latch input is high, the output stores the state of the counter the instant before the Latch input went high. The circuit can thus display an old answer while working on a new one.

The outputs are similar to the 74141 and directly drive a Nixie indicator whose anode is connected to a 175-volt DC source through a current-limiting resistor of 15K. Consult readout data sheet for other operating possibilities. For other applications, the outputs can withstand 60 volts and can provide up to 7 milliamperes. The saturation voltage in the on state is very poor: +2.5 volts.

Note that the supply voltage remains at +5 volts. Be extremely careful when testing this device. A short from pins 1 to 2 or from pins 9 to 12, however brief, will destroy the IC.

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