BCD counter

The 4510 chip is a BCD, or Binary Coded Decimal counter with four outputs capable of counting up or down, following the BCD pattern, according to the logic states of various inputs, when a source of pulses is connected to the CLOCK input.

BCD stands for Binary Coded Decimal. A BCD counter has four outputs usually labelled A, B, C, D. By convention A is the least significant bit, or LSB. The easiest way to understand what a BCD counter does is to follow the counting sequence in truth table form:

pulses output D output C output B output A
0 0 0 0 0
1 0 0 0 1
2 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 1 1 0
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
10 0 0 0 0
11 0 0 0 1

The sequence then continues.

When pulses are delivered to the CLOCK input (and all the other connections needed for basic operation are made), the outputs of the 4510 follow a sequence starting from 0 0 0 0 up to 1 0 0 1, the binary equivalent of the decimal number 9. The next pulse causes the 4510 to RESET and counting starts again from 0 0 0 0.

In other words, the counter outputs follow a binary sequence representing the decimal numbers 0-9…. this is why the 4510 is called a binary coded decimal counter.

To make the 4510 work, I need lots of connections. Every input of a CMOS integrated circuit has to  be connected to something. The CLOCK input, for example, will be connected to the output of source of pulses such as an astable.  I will also need to connect all the load inputs, the carry in/enable and the up/down input.

Again I have included a 47 uf capacitor across the power supply as it is a CMOS circuit.

The 4093 Schmitt trigger NAND gate provides one of the easiest ways of making an astable. When I have constructed this part of the circuit, the LED next to the 4093 should flash at approximately 1 Hz, possibly a little faster.

LOAD input
normally held LOW, 0 V
output D, Q8
output, bit 3
load input D, L8
connect LOW
load input D, L1
connect LOW
carry in/enable
normally held LOW, 0 V
output A, Q1
output, bit 0
carry out
no connection needed
power supply 0 V
RESET input
normally held LOW, 0 V
UP/DOWN input
output B, Q2
output, bit 1
load input B, L2
connect HIGH
load input B, L4
connect HIGH
output C, Q4
output, bit 2
CLOCK input
pulses in from astable
power supply +9 V (range 5-15 V)

The final part of the circuit allows you to see the logic states of the counter outputs. When I have built the circuit correctly the LEDs will illuminate following the truth table for BCD counting.  The BCD counter I constructed has been submitted with this work.

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