What does it do?
| The counter subsystem counts the number of signal pulses connected to its clock input. |
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How does it operate?
A range of counter ICs is available. All of them count up (and sometimes down) every time there is a pulse on their ‘clock’ input pin.
The clock pulse needs to be a clean sharp pulse. If it is being produced by any type of mechanical switch it is important to use a debounced switch unit. Otherwise switch bounce can cause multiple counts.
Electrical noise on an analogue signals can trigger counters. This can be removed by using a Schmitt inverter.
Some counters are decade counters, meaning that they count up in the sequence 0, 1, 2, … 8, 9 and then restart at 0. Binary counters use the binary number code and count up in binary: 0000, 0001, 0010, … 1110, 1111 and then restart at 0000.
Some have an input signal that can control whether they count up or down.
Counters are often used with a 7-segment display to show the count value. In most cases this means that a decoder-driver IC needs to be included.
This data sheet provides details of two useful counter ICs; the 4026B and the 4029B.
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4026 Counter
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
The big advantage of the 4026B counter IC is that it can drive a 7-segment display without needing a decoder driver IC.
The value of the count increases by one every time the Clock input signal (pin 1) changes from low to high.
If the Reset input signal (pin 15) is high the count value is reset to zero. For counting to occur this input signal needs to be low.
The output signals labeled a, b … g are connected (via current limiting resistors) to the corresponding pins of a 7-segment display. Most CMOS ICs can give output current of up to 0.12mA. The 4026B (with a power supply voltage of 5V) can typically provide 3.2mA which is enough for most 7-segment displays. |
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The Output signal to a second counter (pin 5) can be used to produce the ‘tens’ digits by connecting it to the clock pin of a second 4026B.
A big advantage of the 4026 is that it can be used with PICs to control one or more 7-segment displays and it only needs two of the PIC’s output signals. |
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4029 Decade Counter circuit
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit. |
The 4029B is a versatile counter IC. Depending on how it is connected it can:
- Act as a decade or a binary counter
- Count up or down
The value of the count changes by one every time the Clock input signal (pin 15) changes from low to high.
If the U/D (Up / Down) input signal (pin 10) is high the counter counts up. If it is low the counter counts down. |
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The output signals labeled Q1 (pin 6), Q2 (pin 11), Q3 (pin 14) and Q4 (pin 2) represent the count as a binary number. They can be fed to a decoder driver and 7-segment display. The Output signal to a second counter (pin 7) can be fed to the clock pin of a second 4026B.
In the example circuit diagram the B/D (Binary/Decade) input signal (pin 9) is connected to 0V which makes the counter work as a decade counter. If this pin is connected to +Vs it works as a binary counter. |
Possible applications
- Counting objects as they move along a conveyor belt
- Displaying an analogue value, such as a temperature, with a PIC
Making
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Pins of 4026B
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How part of the 4026 PCB might look
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Pins of 4029B
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How part of the 4029 PCB might look
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Build and test the unit that will provide the input signals before building the counter.
Use a Dual In Line (DIL) socket for the IC. Before inserting the IC, connect the power supply and use a voltmeter to check that:
- the voltage on pin 8 is low (0V);
- the voltage on pin 16 is high (the supply voltage);
- the voltage on input signal pins (the blue PCB tracks) go high and low in response to the units that provides the input signals.
Insert the IC the right way round.
Testing
Make sure that the signals going out (on the green PCB tracks) change from high to low.
Fault finding
If there is a fault, check that:
- The voltage on pin 8 is low (0V)
- The voltage on pin 16 is high (the supply voltage)
If there is a fault, check the tracks and solder joints.
Alternatives
- There are a variety of counter ICs: 4017B – decade counter, 4020 – 14-bit binary counter, 4024 – 7-bit binary counter, 4060 – 12-bit binary counter, 4510 – decade up/down counter, 4516 – binary up/down counter, 4518 – dual decade counter, 4520 – dual binary counter.
- PICs – more flexible but more expensive.
Web links
Return to list of datasheets
