Again another Johnson counter IC for digital display. CD4033 is the 5 stage Johnson Decade counter with Decoder. The output decoder converts the Johnson code to a Seven segment decoded output which can drive LED or 7 segment display in numerical values. This IC is widely used in 7 Segment decimal display circuits, Frequency division 7 segment displays, Clocks, Timers etc. Let us see it’s is working and the circuits.
The IC is high voltage type and can handle up to 20 volts. Like CD 4017, CD4093 ICs, the clock input of CD 4033 is highly sensitive and can detect the e.m.f from atmosphere or the static charge from the finger tip. It has 7 decoded outputs. A High pulse in the Reset pin clears the counter to its Zero count. The Counter advances one by one with each positive Clock signal in its input when the clock inhibit pin is held low. When the Clock inhibit pin gets a high pulse, the Counter advancement will be inhibited. To ensure proper counting sequence, an Anticlock gating is provided in the Johnson counter. The Carry out pin signal completes one cycle for every 10 clock input cycles and this pin is used for cascading more ICs. The 7 decoded outputs a to g illuminates the proper segments of the 7 segment display to represents the digits 0 to 9.
In normal operation, the Reset and Clock enable pins are held at ground and the Ripple blanking input is connected to ground or a more significant count stage. The counter then advances one count on each negative to positive transition of the clock pulse. The counter resets when the reset pin is high and this results all 7 outputs low. The reset pin must be returned to ground to restart the count again.
Maximum clock frequency of CD 4033 is 5 MHz at 10 volts and 2.5MHz at 5 volts. Total current at 1MHz clock rate with unloaded output is 0.4 mA at 5 volts and 0.8 mA at 10 volts.
Pin1 – Clock In – Receives clock signals from Oscillator
Pin 2- Clock Inhibit – Inhibits clocking
Pin 3 RB In – Ripple blanking Input. Receives Ripple blanking signal from preceding Chip
Pin 4 RB Out – Ripple blanking output. Sends Ripple blanking signal to succeeding Chip
Pin 5 – Carry out – Used in Cascading more ICs
Pin 6- F output
Pin7 – G Output
Pin 8 – Ground
Pin 9 – D Output
Pin 10 – A Output
Pin 11 – E Output
Pin 12 – B Output
Pin 13 – C Output
Pin 14 – Lamp test input ( Strobe)
Pin 15- Reset pin
Pin 18 – Vcc – 5-15 volt DC
Ripple blanking input and output
Ripple blanking makes only one Zero to be displayed while all other Zeros remains blanked in multi segment displays. For this, the IC has a Ripple blank input (RB In ) pin 3 and Ripple blank Output ( RB Out) pin 4.
For example in a Calculator, there are normally 8 displays. But it shows only one 0 and not 00000000.If the Ripple blank input is activated, the first chip will send a blanking signal to the RB In of the second chip to blank the display. The second chip will send the signal to the third chip and so on. For example to show the number 4012 in an 8 segment display, the chips will attempt to display 00004012. If Ripple blanking is activated, the first four chips will blank the four zeros and the 4th chip will not send a blanking signal to the blanking input of 5th chip. So the digit 4012 will be displayed. This is called Ripple blanking and it improves the readability of the display and is the most common feature of calculators.
Lamp test ( Strobe) pin 14
It is used to test whether all the segments of the display are working or not. This pin is active low at logic level 1.To enable the lamp test feature; momentarily bring the pin14 to ground. This will illuminate all the segments of the 7 segment display.It should be connected to ground in normal operation.
Carry out pin 5
The Carry out pin signal completes one cycle for every 10 clock input cycles and this pin is used for cascading more ICs.
Clock Inhibit pin 2
The counter advances one by one with each positive clock signal in its input when the clock inhibit pin is held low. When the clock inhibit pin gets a high pulse, the counter advancement will be inhibited.
This display driver circuit shows how a Seven Segment Display is driving with the help of the 5 stage Johnson decade counter IC CD4033.Clock pulses can be given from a 555 oscillator as in the case of CD4017 chaser circuit.
The IC counts continuously up to 9 if the Clock Enable, Strobe and Reset pins are grounded. The cycle repeats till the Reset pin gets a High pulse. The input of CD 4033 is a sensitive Schmitt trigger and readily accepts positive to negative transition pulses to starts the counting.
The counter advances and the signals are available at the outputs as decoded signals which can drive the numerical display. CD 4033 can be Cascaded to connect many displays to count 100, 1000 etc. If the Carry Out pin 5 of one IC is connected to the Clock Input pin 1 of the second IC, counter continues and the second IC starts counting when the first IC completes 9 counts. In such a way many ICs can be cascaded.
Cascading CD 4033 ICs. Any number of ICs can be cascaded like this
The input of CD 4033 is a sensitive Schmitt trigger and readily accepts pulsed electromagnetic radiation around the CRT monitors of TV and Computer. This circuit detects the radiation from a distance of 2 feet. It also detects the lightning strikes, presence of AC in wires etc.