IC 4017 – Pin Configuration & Application

An Introduction to IC4017

Most of us are more comfortable with 1, 2, 3, 4… rather than 001, 010, 011, 100. We mean to say that we will need a decimal coded output in many cases rather than a raw binary output. We have many counter ICs available but most of them produce binary data as an output. We will again need to process that output by using decoders or any other circuitry to make it usable for our application in most of the cases.

Let us now introduce you a new IC named IC 4017. It is a CMOS decade counter cum decoder circuit which can work out of the box for most of our low range counting applications. It can count from zero to ten and its outputs are decoded. This saves a lot of board space and time required to build our circuits when our application demands using a counter followed by a decoder IC. This IC also simplifies the design and makes debugging easy.

IC 4017 Pin Diagram

It has 16 pins and the functionality of each pin is explained as follows:

• Pin-1: It is the output 5. It goes high when the counter reads 5 counts.
• Pin-2: It is the output 1. It goes high when the counter reads 0 counts.
• Pin-3: It is the output 0. It goes high when the counter reads 0 counts.
• Pin-4: It is the output 2. It goes high when the counter reads 2 counts.
• Pin-5: It is the output 6. It goes high when the counter reads 6 counts.
• Pin-6: It is the output 7. It goes high when the counter reads 7 counts.
• Pin-7: It is the output 3. It goes high when the counter reads 3 counts.
• Pin-8: It is the Ground pin which should be connected to a LOW voltage (0V).
• Pin-9: It is the output 8. It goes high when the counter reads 8 counts.
• Pin-10: It is the output 4. It goes high when the counter reads 4 counts.
• Pin-11: It is the output 9. It goes high when the counter reads 9 counts.
• Pin-12: This is divided by 10 output which is used to cascade the IC with another counter so as to enable counting greater than the range supported by a single IC 4017. By cascading with another 4017 IC, we can count up to 20 numbers. We can increase and increase the range of counting by cascading it with more and more IC 4017s. Each additional cascaded IC will increase the counting range by 10. However, it is not advisable to cascade more than 3 ICs as it may reduce the reliability of the count due to the occurrence glitches. If you need a counting range more than twenty or thirty, I advise you to go with conventional procedure of using a binary counter followed by a corresponding decoder.
• Pin-13: This pin is the disable pin. In normal mode of operation, this is connected to ground or logic LOW voltage. If this pin is connected to logic HIGH voltage, then the circuit will stop receiving pulses and so it will not advance the count irrespective of number of pulses received from the clock.
• Pin-14: This pin is the clock input. This is the pin from where we need to give the input clock pulses to the IC in order to advance the count. The count advances on the rising edge of the clock.
• Pin-15: This is the reset pin which should be kept LOW for normal operation. If you need to reset the IC, then you can connect this pin to HIGH voltage.
• Pin-16: This is the power supply (Vcc) pin. This should be given a HIGH voltage of 3V to 15V for the IC to function.

This IC is very useful and also user friendly. To use the IC, just connect it according the specifications described above in the pin configuration and give the pulses you need to count to the pin-14 of the IC. Then you can collect the outputs at the output pins. When the count is zero, Pin-3 is HIGH. When the count is 1, Pin-2 is HIGH and so on as described above.

Application of CD4017

LED Sequencer using 4017

The LED sequencer circuit by using CD4017 and IC 555 is shown below. This circuit is also called as “LED chaser circuit”.

Components

• CD4017 decade counter
• 555 timer IC
• Ten-segment bar graph LED
• switch and One 6 volt battery
• 1 MΩ resistor
• 0.1 µF capacitor
• Coupling capacitor, 0.047 to 0.001 µF
• 470 Ω resistors-10

Primarily it is important to remember that, as the CD4017 is a CMOS device, it is very sensitive to the static electricity.

The LED sequencer circuit uses the 555 timer to produce the clock pulses required for CD4017, which is operated in Astable mode. Output of this Astable timer circuit is connected to the clock signal input of CD4017.

It produces stream of pulses continuously, in which the each pulse increases the counter by 1. So thus each LED will light up and then off before turning on its next LED in the sequence.

LED sequencer working

• Led sequencer works on the principle of CD4017.
• Let us understand the working by starting with 555 timer.
• 555 timer is operated in astable mode.It produces clock pulses continuously to the decoder IC.The duration of this clock pulse can be calculated by using R and C value in the circuit.
• For each pulse the CD4017 increases the counter value.Thus  each pin of the counter goes high in a sequence.
• LEds  connected to the output pins of CD4017 ,thus glows in a sequence.

Note 

In order to make the counter to count upto certain number ,the last sequence pin should be connected to reset.

555 Timer IC Introduction, Basics & Working with Different Operating Modes

Introduction:

IC 555 TIMER is a well-known component in the electronic circles but what is not known to most of the people is the internal circuitry of the IC and the function of various pins present there in the IC. Let me tell you afact about why 555 timer is called so, the timer got its name from the three 5 kilo-ohm resistor in series employed in the internal circuit of the IC.

IC 555 timer is a one of the most widely used IC in electronics and is used in various electronic circuits for its robust and stable properties. It works as square-wave form generator with duty cycle varying from 50% to 100%, Oscillator and can also provide time delay in circuits. The 555 timer got its name from the three 5k ohm resistor connected in a voltage-divider pattern which is shown in the figure below. A simplified diagram of the internal circuit is given below for better understanding as the full internal circuit consists of over more than 16 resistors, 20 transistors, 2 diodes, a flip-flop and many other circuit components.

The 555 timer comes as 8 pin DIP (Dual In-line Package) device. There is also a 556 dual version of 555 timer which consists of two complete 555 timers in 14 DIP and a 558 quadruple timer which is consisting of four 555 timer in one IC and is available as a 16 pin DIP in the market.

CIRCUIT DIAGRAM

Basics Concepts:

·         Comparator: The Comparator are the basic electronic component which compares the two input voltages i.e. between the inverting (-) and the non-inverting (+) input and if the non-inverting input is more than the inverting input then the output of the comparator is high. Also the input resistance of an ideal comparator is infinite.

·        Voltage Divider: As we know that the input resistance of the comparators is infinite hence the input voltage is divided equally between the three resistors. The value being V_in/3 across each resistor.

·         Flip/Flop: Flip/Flop is a memory element of Digital-electronics. The output (Q) of the flip/flop is ‘high’ if the input at ‘S’ terminal is ‘high’ and ‘R’ is at ‘Low’ and the output (Q) is ‘low’ when the input at ‘S’ is ‘low’ and at ‘R’ is high.

Function of different Pins:-

1.      Ground: This pin is used to provide a zero voltage rail to the Integrated circuit to divide the supply potential between the three resistors shown in the diagram.

2.      Trigger: As we can see that the voltage at the non-inverting end of the comparator is V_in/3, so if the trigger input is used to set the output of the F/F to ‘high’ state by applying a voltage equal to or less than V_in/3 or any negative pulse, as the voltage at the non-inverting end of the comparator is V_in/3.

 3.      Output: It is the output pin of the IC, connected to the Q’ (Q-bar) of the F/F with an inverter in between as show in the figure.

 4.      Reset: This pin is used to reset the output of the F/F regardless of the initial condition of the F/F and also it is an active low Pin so it connected to ‘high’ state to avoid any noise interference, unless a reset operation is required. So most of the time it is connected to the Supply voltage as shown in the figure.

5.      Control Voltage: As we can see that the pin 5 is connected to the inverting input having a voltage level of (2/3) V_in. It is used to override the inverting voltage to change the width of the output signal irrespective of the RC timing network.

6.      Threshold: The pin is connected to the non-inverting input of the first comparator. The output of the comparator will be high when the threshold voltage will be more than (2/3) V_in thus resetting the output (Q) of the F/F from ‘high’ to ‘low’.

7.      Discharge: This pin is used to discharge the timing capacitors (capacitors involved in the external circuit to make the IC behave as a square wave generator) to ground when the output of Pin 3 is switched to ‘low’.

8.      Supply: This pin is used to provide the IC with the supply voltage for the functioning and carrying of the different operations to be fulfilled with the 555 timer.

Uses:-

The IC 55 timer is used in many circuits, for example One-shot pulse generator in Monostable mode as an Oscillator in Astable Mode or in Bistable mode to produce a flip/flop type action. It is also used in many types of other circuit for achievement of various purposes for instance Pulse Amplitude Modulatin (PAM), Pulse Width Modulation (PWM) etc

Modes

The IC 555 has three operating modes:

1. BISTABLE mode or SCHMITT TRIGGER – the 555 can operate as a Flip flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce-free latched switches.
2. MONOSTABLE mode – in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers, missing pulse detection, bounce-free switches, touch switches, frequency divider, capacitance measurement,  (PWM) and so on.
3. ASTABLE (free-running) mode – the 555 can operate as an electronic oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, PWM  and so on. The 555 can be used as a simple ADC, converting an analog value to a pulse length (e.g., selecting a THERMISTOR as timing resistor allows the use of the 555 in a temperature sensor and the period of the output pulse is determined by the temperature). The use of a microprocessor-based circuit can then convert the pulse period to temperature, linearize it and even provide calibration means.

Bistable

Schematic of a 555 in bistable mode

In bistable (also called schmitt trigger) mode, the 555 timer acts as a basic flip-flop. The trigger and reset inputs (pins 2 and 4 respectively on a 555) are held high via pull up resistor while the threshold input (pin 6) is simply floating. Thus configured, pulling the trigger momentarily to ground acts as a 'set' and transitions the output pin (pin 3) to Vcc (high state). Pulling the reset input to ground acts as a 'reset' and transitions the output pin to ground (low state). No timing capacitors are required in a bistable configuration. Pin 5 (control voltage) is connected to ground via a small-value capacitor (usually 0.01 to 0.1 μF). (discharge) is left floating.

Monostable

Schematic of a 555 in monostable mode

The output pulse ends when the voltage on the capacitor equals 2/3 of the supply voltage. The output pulse width can be lengthened or shortened to the need of the specific application by adjusting the values of R and C.

The output pulse width of time t, which is the time it takes to charge C to 2/3 of the supply voltage, is given by

${\displaystyle t=\ln(3)\cdot RC\approx 1.1RC}$

where t is in seconds, R is in ohms (resistance) and C is in farads (capacitance).

While using the timer IC in monostable mode, the main disadvantage is that the time span between any two triggering pulses must be greater than the RC time constant.Conversely, ignoring closely spaced pulses is done by setting the RC time constant to be larger than the span between spurious triggers. (Example: ignoring switch contact bouncing.)

Astable

Schematic of a 555 in astable mode

In astable mode, the 555 timer puts out a continuous stream of rectangular pulses having a specified frequency. Resistor R₁ is connected between V_CC and the discharge pin (pin 7) and another resistor (R₂) is connected between the discharge pin (pin 7), and the trigger (pin 2) and threshold (pin 6) pins that share a common node. Hence the capacitor is charged through R₁ and R₂, and discharged only through R₂, since pin 7 has low impedance to ground during output low intervals of the cycle, therefore discharging the capacitor.

In the astable mode, the frequency of the pulse stream depends on the values of R₁, R₂ and C:

${\displaystyle f={\frac {1}{\ln(2)\cdot C\cdot (R_{1}+2R_{2})}}}$

The high time from each pulse is given by:

${\displaystyle \mathrm {high} =\ln(2)\cdot C\cdot (R_{1}+R_{2})}$

and the low time from each pulse is given by:

${\displaystyle \mathrm {low} =\ln(2)\cdot C\cdot R_{2}}$

where R₁ and R₂ are the values of the resistors in ohms and C is the value of the capacitor in farads.

The power capability of R₁ must be greater than ${\displaystyle {\frac {V_{cc}^{2}}{R_{1}}}}$.

Particularly with bipolar 555s, low values of ${\displaystyle R_{1}}$ must be avoided so that the output stays saturated near zero volts during discharge, as assumed by the above equation. Otherwise the output low time will be greater than calculated above. The first cycle will take appreciably longer than the calculated time, as the capacitor must charge from 0V to 2/3 of V_CC from power-up, but only from 1/3 of V_CC to 2/3 of V_CC on subsequent cycles.

To have an output high time shorter than the low time (i.e., a duty cycle less than 50%) a small diode (that is fast enough for the application) can be placed in parallel with R₂, with the cathode on the capacitor side. This bypasses R₂ during the high part of the cycle so that the high interval depends only on R₁ and C, with an adjustment based the voltage drop across the diode. The voltage drop across the diode slows charging on the capacitor so that the high time is a longer than the expected and often-cited ln(2)*R₁C = 0.693 R₁C. The low time will be the same as above, 0.693 R₂C. With the bypass diode, the high time is

${\displaystyle \mathrm {high} =R_{1}\cdot C\cdot \ln \left({\frac {2V_{\textrm {cc}}-3V_{\textrm {diode}}}{V_{\textrm {cc}}-3V_{\textrm {diode}}}}\right)}$

where V_diode is when the diode's "on" current is 1/2 of V_cc/R₁ which can be determined from its datasheet or by testing. As an extreme example, when V_cc= 5 and V_diode= 0.7, high time = 1.00 R₁C which is 45% longer than the "expected" 0.693 R₁C. At the other extreme, when V_cc= 15 and V_diode= 0.3, the high time = 0.725 R₁C which is closer to the expected 0.693 R₁C. The equation reduces to the expected 0.693 R₁C if V_diode= 0.

The operation of RESET in this mode is not well-defined. Some manufacturers' parts will hold the output state to what it was when RESET is taken low, others will send the output either high or low.

The astable configuration, with two resistors, cannot produce a 50% duty cycle. To produce a 50% duty cycle, eliminate R1, disconnect pin 7 and connect the supply end of R2 to pin 3, the output pin. This circuit is similar to using an inverter gate as an oscillator, but with fewer components than the astable configuration, and a much higher power output than a TTL or CMOS gate. The duty cycle for either the 555 or inverter-gate timer will not be precisely 50% and will change based off any load that the output is also driving while high (longer duty cycles for greater loads) due to the fact the timing network is supplied from the devices output pin, which has different internal resistances depending on whether it is in the high or low state (high side drivers tend to be more resistive)

Specifications

These specifications apply to the NE555. Other 555 timers can have different specifications depending on the grade (military, medical, etc.).

Supply voltage (VCC)	4.5 to 15 V
Supply current (VCC = +5 V)	3 to 6 mA
Supply current (VCC = +15 V)	10 to 15 mA
Output current (maximum)	200 mA
Maximum Power dissipation	600 mW
Power consumption (minimum operating)	30 mW@5V, 225 mW@15V
operating temperature	0 to 75 °C