Three Digit Counter Kit (RoHS)

This kit is a low cost basic 3 digit counter kit which can provide the basis for many applications where a counter is required. Connections are provided to connect together two or more counters to make a six or nine digit unit. The display is a single unit LED multiplexed display. The kit is constructed on a single-sided printed circuit board.

In general three or four digit counters can be made a number of ways. You can use a single 74C92x 4 digit counter chip or a number of 4029 cmos single digit counters. Problems with the former are cost, while the latter require too many ICs and thus take up too much PCB space. The circuit used here is a compromise between these two approaches. The circuit described in this kit uses two ICs. The 14553 is a 3-digit BCD (binary coded decimal) counter. Inside the chip, each counter drives a 4-bit latch which quad 3-input multiplexer. The chip has Carry, Reset, an input clock and Latch Enable. The 1nF mylar capacitor on pins 3 and 4 sets the multiplex scan rate to about 1 kHz.

The four outputs (Q0 to Q3) are fed into the 14511 cmos 7-segment decoder driver. The outputs of this driver then go to the 3-digit multiplexed display unit. Each digit is turned on at the correct time via the display control outputs at pins 2, 1 and 25 of the 14553. They are active low outputs. Each drives a BC557 pnp transistor via a 4k7 resistor. The transistors in turn switch the common cathode of the digits in the display.

9vDC powersupply.