July
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TECHNO TE(A)CH INTRODUCTION: As promised last issue this time I give you with a basic project involving integrated circuits (ICs). Before getting into the details about this months project I would like to give an overview on the basics of digital ICs called logic gates. They are the smallest inventions, which can be broken down into simpler transistors giving rise to a complete set of logic functions. You can refer to any basic electronic manual to get a hint on their basic operations and truth tables. Combinations of these logic gates gave the breed of logic circuits that can control multiple outputs using some control logic. They are nothing but predefined conditions which when satisfied drives the output. The output may either be logic low or high. The logic low output gives zero volt (0V) and the logic high provides (VDD or +5V). Thus indicators such as LEDs or buzzers can be used. I skip the details on these gates because they are very easy to learn and not time consuming. MOS\ CMOS ICS: The IC technology contains two popular varieties. They are called CMOS (Complementary Metal Oxide Semiconductors) and TTL (Transistor Transistor Logic). The other popular variety is the LS technology. The MOS technology (Metal Oxide Semiconductors) can perform more functions per chip than that of the TTL\LS technologies and are very easy to use. They consume very little power and operate over a wide range of +3V to +15V. The power supply can be a standard battery powered or mains powered. If it is mains power supply, the usage of voltage regulators is a must. This is what we saw in the last two issues. The CMOS chip is made from PMOS and NMOS transistors. P and N refer to positive and negative MOS transistors. Though the CMOS ICs are very pretty in their operating speeds and power considerations there are some operating requirements that need to be satisfied for efficient operation. They are as follows: ?
The input voltage should not exceed VDD that is the power supply voltage that is used to power the entire chip. The input means the logic 1 input that is fed into the gate.
?
Avoid if possible slowly rising and falling input signals since they can cause excessive power consumption.
?
All unused pins must be connected to VDD (+) or VSS (GND). Otherwise erratic behavior of the chip and excessive power consumptions are observed.
?
Never connect an input signal to the chip with power turned off.
STATIC DISCHARGE: The design of the MOS IC is such that the silicon substrate used is very thin. This is how they consume very little power. The construction if observed proves that a capacitor is formed in the layers of the chip design. So if the user puts his/ her fingers on the pins the holes or electrons (in case of P type and N type respectively) can be absorbed by the human body leaving the IC without any initial charges to conduct with and the IC thus becomes useless and ready to dispose immediately. But often this is avoided as the time taken to such a discharge is very high. So observe the points given below to prevent static discharge: ?
Never store MOS ICs in non- conductive plastic “snow” trays, bags or foam.
?
Place MOS ICs pin down on an aluminum foil sheet or tray when they are not in a circuit.
?
The soldering should be made with battery powered iron. If AC powered iron is used then use IC sockets.
?
Better use thermo-coal to place ICs in a safe and secure manner.
IC CD4017BE DECADE COUNTER: This is a counter IC that counts the external clock pulse. It also sequentially makes the 1 of 10 outputs high (others stay low) in response to clock pulses. The pin configuration can be studied from the data sheets provided for this months issue. The clock source can be from any oscillator. A simple 1 second interval oscillator is discussed using ICNE555 at the end of this issue. More details about ICNE555 on later issues. The decade counter comprises of these logic gates arranged in particular fashion such that once it receives a pulse (a clock input) it increments its output pins. There are totally 10 outputs hence this is called as the ‘decade’counter. The circuit diagram given below illustrates the simple usage of this decade counter. The decade counter is mainly used in counting purposes such as clocks, frequency counter, timers, switching operations etc. The main purpose of this is to increment the count of the counter by one when a clock input is received. The rate of clock pulse determines the speed of change in output. The recycle option is provided to regenerate the counting process without any supply interruption or any reset action, more on this later. Study the pin details and try to figure out the connection methodologies. There are totally three configurations discussed and also a challenge is provided at the end to increase your understanding of the circuit.
CIRCUIT DESCRIPTION: The circuit uses the decade counter as the heart. The control logic is that once the clock pulse has the upper edge the output switches to Q0 that is output 1. On the next positive transition the output switches from Q0 to Q1. It should be noted that the output Q0 was high during the previous case and now the output Q1 is high and Q0 is low. This can be observed in the LEDs provided. For the clock pulse use a push to on switch. One push will increment the output stage thus giving a display of LED chaser. Many such applications can be derived from this simple circuit. The circuit once reaching its output level of Q10 stops and the power is switched off and on to continue this procedure or the other method is to connect the pin 15 to positive supply (VDD) and again connecting with ground can act as a “reset” action and pushing the button now will start the procedure again. Note that the former method is a brutal method and should never be followed only the latter is advised. This circuit as shown is very primitive and in order to make the outputs to recycle that is once the cycle is over the cycle repeats itself, the pin 15 is connected to the last output (Q10) to count up to 10 outputs. If only counting of 5 outputs is necessary the pin 15 is connected to output Q5. Thus the cycle recycles and the operation continues.
One more methodology is that the decade counter may also be designed to count and halt. If you want the circuit to count up to 7 then, connect pin 13 to the led 7 (anode side). Similarly any count can be designed. CONTROL TERMINOLOGIES: It should be clearly noted that the pin functionalities is used in a wise method to provide three different operations without modifying the circuit at all! This is why it was told in the previous issue that data sheets are very necessary for each and every component used. This circuit can be constructed in the bread board and tested. The 1K resistor is very important as the supply voltage of 9V is very high for a LED to handle. It acts as current limiter. Study all the pin details and experiment your own style of making different LED fashions. Trust me its very pleasing to see at nights so you can use this circuit in your bicycle and turn it on during the nights to give a flashy effect. CLOCK SOURCE: The clock source mentioned in this issue (using push button) is not a standard one. This type is only used for testing purposes. So I suggest you build this square wave oscillator in a corner of your bread board and keep it permanent as that of your power supply. The power supply and the clock source are very important to observe the operational characteristics of the digital logic circuits. Vary the knob adjustments of the preset with a small screw driver to change the output frequency. The rate of the frequency determines the speed of counter increments. Make sure the frequency is close to 1 sec to have a predictable output. Connect the output of pin3 of NE555 to pin 14 of decade counter omitting the switch. Thus a constant clock is supplied and no manual increment in necessary.
µ
CIRCUIT DESCRIPTION: This clock source is very versatile can provide clock pulses to CMOS and TTL\LS ICs. The circuit has a NE555 from National Semiconductors often referred as the ‘wonder baby’ in the world of electronics. Though small its operations are limitless. It is wired in astable miltivibrator mode where a constant pulse is continuously obtained. Once the circuit is given, connect a LED in its output and vary the 1Meg preset to check the delay interval. It will hardly cost you RS.20. Keep this permanent circuit on your bread board to supply clock for all the logic circuits that will be published in the future issues. THE CHALLENGE: In order to make your learning more fun I thought of presenting you with this challenge. It goes like this: if I want you to use the decade counter and multiplex or extend another decade counter such that the first one is the unit digit and the second one is the tens digit. The output is like this; once the cycle in the first counter is over the second counter should increment by one. That is if all the 10 LEDs finished glowing in the first counter, the next cycle should make the 1st LED of the second counter turned on. This is nothing but a 0-99 counter. Such that the process should continue till all the 20 LEDs are serviced. Please propose the models in our comments section. Any doubts regarding the circuits or this article may be posted to [email protected]. Please include your name while posting your queries. If any circuit diagrams or projects are proposed they are most welcome. Thank you and all the best for this task.
The input voltage should not exceed VDD that is the power supply voltage that is used to power the entire chip. The input means the logic 1 input that is fed into the gate.
?
Avoid if possible slowly rising and falling input signals since they can cause excessive power consumption.
?
All unused pins must be connected to VDD (+) or VSS (GND). Otherwise erratic behavior of the chip and excessive power consumptions are observed.
?
Never connect an input signal to the chip with power turned off.
STATIC DISCHARGE: The design of the MOS IC is such that the silicon substrate used is very thin. This is how they consume very little power. The construction if observed proves that a capacitor is formed in the layers of the chip design. So if the user puts his/ her fingers on the pins the holes or electrons (in case of P type and N type respectively) can be absorbed by the human body leaving the IC without any initial charges to conduct with and the IC thus becomes useless and ready to dispose immediately. But often this is avoided as the time taken to such a discharge is very high. So observe the points given below to prevent static discharge: ?
Never store MOS ICs in non- conductive plastic “snow” trays, bags or foam.
?
Place MOS ICs pin down on an aluminum foil sheet or tray when they are not in a circuit.
?
The soldering should be made with battery powered iron. If AC powered iron is used then use IC sockets.
?
Better use thermo-coal to place ICs in a safe and secure manner.
IC CD4017BE DECADE COUNTER: This is a counter IC that counts the external clock pulse. It also sequentially makes the 1 of 10 outputs high (others stay low) in response to clock pulses. The pin configuration can be studied from the data sheets provided for this months issue. The clock source can be from any oscillator. A simple 1 second interval oscillator is discussed using ICNE555 at the end of this issue. More details about ICNE555 on later issues. The decade counter comprises of these logic gates arranged in particular fashion such that once it receives a pulse (a clock input) it increments its output pins. There are totally 10 outputs hence this is called as the ‘decade’counter. The circuit diagram given below illustrates the simple usage of this decade counter. The decade counter is mainly used in counting purposes such as clocks, frequency counter, timers, switching operations etc. The main purpose of this is to increment the count of the counter by one when a clock input is received. The rate of clock pulse determines the speed of change in output. The recycle option is provided to regenerate the counting process without any supply interruption or any reset action, more on this later. Study the pin details and try to figure out the connection methodologies. There are totally three configurations discussed and also a challenge is provided at the end to increase your understanding of the circuit.
CIRCUIT DESCRIPTION: The circuit uses the decade counter as the heart. The control logic is that once the clock pulse has the upper edge the output switches to Q0 that is output 1. On the next positive transition the output switches from Q0 to Q1. It should be noted that the output Q0 was high during the previous case and now the output Q1 is high and Q0 is low. This can be observed in the LEDs provided. For the clock pulse use a push to on switch. One push will increment the output stage thus giving a display of LED chaser. Many such applications can be derived from this simple circuit. The circuit once reaching its output level of Q10 stops and the power is switched off and on to continue this procedure or the other method is to connect the pin 15 to positive supply (VDD) and again connecting with ground can act as a “reset” action and pushing the button now will start the procedure again. Note that the former method is a brutal method and should never be followed only the latter is advised. This circuit as shown is very primitive and in order to make the outputs to recycle that is once the cycle is over the cycle repeats itself, the pin 15 is connected to the last output (Q10) to count up to 10 outputs. If only counting of 5 outputs is necessary the pin 15 is connected to output Q5. Thus the cycle recycles and the operation continues.
One more methodology is that the decade counter may also be designed to count and halt. If you want the circuit to count up to 7 then, connect pin 13 to the led 7 (anode side). Similarly any count can be designed. CONTROL TERMINOLOGIES: It should be clearly noted that the pin functionalities is used in a wise method to provide three different operations without modifying the circuit at all! This is why it was told in the previous issue that data sheets are very necessary for each and every component used. This circuit can be constructed in the bread board and tested. The 1K resistor is very important as the supply voltage of 9V is very high for a LED to handle. It acts as current limiter. Study all the pin details and experiment your own style of making different LED fashions. Trust me its very pleasing to see at nights so you can use this circuit in your bicycle and turn it on during the nights to give a flashy effect. CLOCK SOURCE: The clock source mentioned in this issue (using push button) is not a standard one. This type is only used for testing purposes. So I suggest you build this square wave oscillator in a corner of your bread board and keep it permanent as that of your power supply. The power supply and the clock source are very important to observe the operational characteristics of the digital logic circuits. Vary the knob adjustments of the preset with a small screw driver to change the output frequency. The rate of the frequency determines the speed of counter increments. Make sure the frequency is close to 1 sec to have a predictable output. Connect the output of pin3 of NE555 to pin 14 of decade counter omitting the switch. Thus a constant clock is supplied and no manual increment in necessary.
µ
CIRCUIT DESCRIPTION: This clock source is very versatile can provide clock pulses to CMOS and TTL\LS ICs. The circuit has a NE555 from National Semiconductors often referred as the ‘wonder baby’ in the world of electronics. Though small its operations are limitless. It is wired in astable miltivibrator mode where a constant pulse is continuously obtained. Once the circuit is given, connect a LED in its output and vary the 1Meg preset to check the delay interval. It will hardly cost you RS.20. Keep this permanent circuit on your bread board to supply clock for all the logic circuits that will be published in the future issues. THE CHALLENGE: In order to make your learning more fun I thought of presenting you with this challenge. It goes like this: if I want you to use the decade counter and multiplex or extend another decade counter such that the first one is the unit digit and the second one is the tens digit. The output is like this; once the cycle in the first counter is over the second counter should increment by one. That is if all the 10 LEDs finished glowing in the first counter, the next cycle should make the 1st LED of the second counter turned on. This is nothing but a 0-99 counter. Such that the process should continue till all the 20 LEDs are serviced. Please propose the models in our comments section. Any doubts regarding the circuits or this article may be posted to [email protected]. Please include your name while posting your queries. If any circuit diagrams or projects are proposed they are most welcome. Thank you and all the best for this task.
