Different IC's and their usage.


Now that we know how fabulous ICs are, let’s dive into their usage in robotics.

Motor Driver ICs
The microcontroller used in our robots can't control the motors directly because most of the microcontrollers operate on low voltages and require small amounts of current to operate while the motors require relatively higher voltages and current. Thus, the current cannot be supplied to the motors from the microcontroller. This is the primary need for motor driver IC. Motor drivers act as an interface between the motors and the Microcontroller.


There are different types of motor driver modules used:

L293D Motor Driver:

L293D is a typical Motor driver or Motor Driver IC which allows DC motors to drive in either direction. L293D is a 16-pin IC that can control a set of two DC motors simultaneously. The direction can be controlled too. It means that you can control two DC motors with a single L293D IC!



L293D IC Pinout Diagram
Power Supply:
The L293D motor driver IC actually has two power input pins ‘ Vcc1’ and ‘Vcc2’. Vcc1 is used for driving the internal logic circuitry of the motor driver IC, which should be 5V. ( It must not be greater than 5 V ) From Vcc2 pin the H-Bridge gets its power for driving the motors which can be 4.5V to 36V (for L293D IC). And they both sink to a common ground named GND.

Output Terminals:
The L293D motor driver’s output channels for the motor A and B are brought out to pins OUTPUT1, OUTPUT2 and OUTPUT3, OUTPUT4 respectively.
You can connect two DC motors having voltages between 4.5 to 36V to these terminals. It can supply a maximum current of 1.2A.
Direction Control Pins:
Using the direction control pins, we can control whether the motor spins forward or backward. These pins actually control the switches of the H-Bridge circuit inside L293D IC. It contains two H-bridge circuits controlling direction of one motor each.
How does the H-bridge control the direction of the motor? Try to recall. You already know this answer from the concepts shared in previous blogs.

If you can recall, Kudos! If not, refer to this link.

The spinning direction of a motor can be controlled by applying either a logic HIGH(5 Volts relative to ground) or logic LOW(Ground) to input pins.
The IC has two direction control pins for each channel. The INPUT1, INPUT2 pins control the spinning direction of the motor A while INPUT3, INPUT4 control motor B.



 INPUT1  INPUT2  OUTPUT1  OUTPUT2  Spin Direction
 LOW LOW LOW LOW Motor OFF
HIGH  LOW  HIGH  LOW  Clockwise(Forward)
LOW  HIGH  LOW   HIGH  Anticlockwise(Backward)
HIGH  HIGH  LOW   LOW  Motor OFF



Speed Control Pins:
ENABLE 1, 2 and ENABLE 3, 4 are used to turn ON, OFF and control speed of motor A and motor B respectively.

The ENABLE 1, 2 pin controls the H-bridge of left side (one with INPUT1 and INPUT2 pins). When ENABLE 1,2 pin is high i.e it has 5V supply then Ieft side input and output pins are enabled and H-bridge is turned ON. When ENABLE 1,2 is low then H-bridge is turned off, making motors stop in all conditions. However, when PWM power supply is provided to these pins we can actually control the speed of motors. We can also control speed by giving pwm power supply to INPUT pins. We will study about PWM (Pulse Width Modulation) in detail in further blogs.

L298N Motor driver module

L298N Motor Driver Module contains a 78M05 5V Regulator along with the L298 IC. It works the same as L293D but is more powerful. It can take power supply upto 46 volts. It can supply a maximum current of 2A.






Op-amp:

An Op-Amp, short for an Operational Amplifier, is the workhorse for all analog electronics. It’s a type of an amplifier, and an amplifier is defined as a circuit that produces output signal greater than its input signal. Generally, the ratio of value of output signal and input signal is called gain. More precisely it is the ratio of the output signal amplitude to the input signal amplitude, and is given the symbol "A".
Internally, it has a complex circuit (a bunch of resistors, some capacitors, etc), but for now, let’s just concentrate on its properties.

Like other amplifiers, it also has some “gain”. That means if we put an X signal here, then I will get a signal AX, where, A is the gain factor.
(input) x --> [A] --> Ax (output)

The gain A is generally high, i.e, in the range of 105 to 106.
The op-amp is represented by the symbol shown here.

The two input pins, V+ and V-, are called non-inverting and inverting pins respectively. And Vs+ and Vs- are supply pins.

Now the output voltage, Vout is proportional to the voltage between the two input pins, i.e,
V0 = A * ( V+ - V-- )


Vout or V0 can go both positive or negative w.r.t. the ground.
So this output is proportional to the difference of input voltages. The results are plotted on the graph given left. Notice the graph after Vsat? This Vsat ,the saturation voltage, is less than the highest possible gain voltage of an op-amp and is the maximum possible voltage, reason being, the gain voltage is very high and it is impractical for op-amp to produce such voltage. Thus the limit is capped to the supply voltage and Vout = Vsat.
The slope in this graph is the gain A.

Coming back to the question of the meaning of inverting and non-inverting voltages, let’s take a look at the equations given above the diagram.

As the Vin varies, let’s say V+ increases, the difference Vin also increases, thus increasing the gain.
As the V- increases, the difference Vin decreases, thereby decreasing the overall gain.
Thus, V- is inversely proportional to the overall gain. Therefore it is called an inverting voltage. On the other hand, on increasing the V+, the gain also increases. Hence, it is called the non-inverting voltage. If this explanation is bit clumsy for you, look it another way.

Let’s set the V- voltage to ground (zero) and then calculate the Vout using the same equation, Vout = A*(V1) .Here the voltage Vout is directly proportional to the Voltage V1. Hence the voltage V1 is called the non-inverting voltage.
For the V- , the equation for Vout would be:
Vout = A*(0-V2)

Vout = -A*(V2)
The Vout and V- are in opposite phase, i.e, if V- increases, the Vout decreases. Hence it is called the inverting phase.
Now beware, when schematics of the op-amp are drawn on paper, the plus and minus could be reversed, and accordingly, you have to make sure you are proceeding with the correct signs!




Op-amp as a comparator:

So what do you understand by comparator? A tool to compare things, right? Here we compare two voltages. The next question that will pop-up in your mind is HOW? Well, when you have learned how an op-amp works as an amplifier then the answer to this question is not so difficult.
Let’s assume we have two voltages V1 and V2 to compare. Let’s give V1 as input to V+ and V2 as input to V--. There are two types of comparators, depending on the reference point we choose to compare i.e. whether we take V1 as a reference and compare V2 with respect to it or vice-versa.

Inverting Comparator: If the input voltage is applied to the inverting terminal and the reference voltage to the non-inverting terminal.

[Here V+= Vref and V-- = Vi and Vp equal supply voltage]

The operation of inverting comparators is quite simple. The output which is equal to (A* ( Vref - Vin )) equals to either +Vsat or -Vsat depending on the values of input voltage Vi and reference voltage Vref.





Vin > Vref : Vout = A(Vref - Vin) = -Vsat
Vin < Vref : Vout=A(Vref - Vin)= +Vsat



Why Vout = +Vsat when input voltage is greater than reference voltage.
Answer to this question lies above in the explanation of the graph of op-amp.

The amplifying factor is so large( 105 to 106) that even if there is very little difference between input and reference voltages the output voltage equals saturation voltage. For output voltage to be 10V, difference of voltages should be maximum 0.0001V.


Non-Inverting Comparator: If the reference voltage is applied to the inverting terminal and the input voltage to the non-inverting terminal. Rest is very much similar to an inverting comparator, try to figure it out with the help of the given diagram.
You all must have observed that analog signals are converted into digital form when we learnt comparators. Acting as analog to digital signal converter is another important application of op-amp.

Still wondering what you can do with a comparator? See this cool project! A LM358 Op-Amp IC is used as a comparator for making this project.

To understand better have a look here.


555 Timer IC


It is used in a variety of one-shot or delay timers, pulse generation, LED and lamp flashers, alarms and tone generation, logic clocks, frequency division, power supplies, and converters, etc, in fact, any circuit that requires some form of time control as the list is endless. The internal block diagram and working of 555 Timer IC are given below.




As you might have learned through your secondary school, these three resistors are used to create reference voltages, creating 1/3 Vcc and 2/3 Vcc of supply voltage Vcc.

Next-up is a comparator, it is used to “compare voltage”, for example, for its two input terminals, inverting and non-inverting, if the input voltage is higher for the positive terminal, the comparator will output 1, otherwise, it will output 0. The first comparator negative input terminal is connected to the 2/3 reference voltage at the voltage divider and the external “control” pin, while the positive input terminal to the external “Threshold” pin.

On the other hand, the second comparator negative input terminal is connected to the “Trigger” pin, while the positive input terminal to the 1/3 reference voltage at the voltage divider.

So using the three pins, Trigger, Threshold, and Control, we can control the output of the two comparators which are then fed to the R and S inputs of the flip-flop. The flip flop can also be reset anytime using the reset pin, additionally resetting the whole 555 Timer IC.

The Q-bar output of the flip-flip goes to the output stage or the output drivers which can either source or sink a current of 200mA to the load. The output of the flip-flip is also connected to a transistor that connects the “Discharge” pin to the ground.

There are primarily three modes of operations named Astable, Monostable, and Bistable. Each mode represents a different type of circuit that has a particular output. Learn more about it here.

Voltage Regulator

For a start, different electronics require different voltages. A microcontroller may require 5V, your motors perhaps 12V Batteries are never at a constant voltage. A 6V battery will be at around 7V when fully charged, and can drop to 3-4V when drained. The image shows how a typical battery voltage changes over time.

See the drained battery zone, what if the sensor you are using is sensitive to 5V and then the battery drops!! Thus we need a Voltage Regulator to rectify this issue.

While using some electronic components, we might need to increase or decrease the voltage to fulfil our purpose. As the name suggests, the Voltage Regulator also adjusts the incoming voltage to the desired and acceptable limits.

There are two types of VRs: linear and switching.

Linear Regulators: It works by automatically adjusting the resistance via a feedback loop(“Feedback” is the process by which a fraction of the output signal, either a voltage or a current, is used as an input, in this circuit, negative feedback is used), accounting for changes in both output current and input, all while keeping the output voltage constant.
The 78xx series voltage regulators are the most popular linear voltage regulators which produce positive fixed DC voltages. For negative voltages we have 79xx series. “xx” corresponds to a two-digit number and represents the amount (magnitude) of voltage that voltage regulator IC produces.
Eg: LM7805 produces +5V and LM7812 produces +12V.


1. Input voltage : (5V-18V)
2. Ground : (0V)
3. Regulated output : 5V (4.8V-5.2V)

All other IC’s of this series have similar structure.

Four 7800 series linear voltage regulators, each with a different voltage output: 5V, 9V, 12V, 15V


78xx series ICs have built-in protection against a circuit drawing too much power. They have protection against overheating and short-circuits, making them quite robust in most applications.

Switching Regulators: These regulators such as buck (step-down), Boost (step-up), and buck-boost (step-up/step-down), require a few more components as well as increased complexity of how various components will affect the output. Switching regulators are far more efficient in terms of power conversion where efficiency plays a big role, but linear regulators work very well as voltage regulators in low-voltage applications.

There are three types of switching VRs:

Buck(step-down): A Buck Regulator is used to step down the voltage at the output, we can even use the voltage divider circuit to reduce the output voltage but the efficiency of the voltage divider circuit is low because resistors dissipate energy as heat.


Boost (step-up): Increases the voltage, while decreasing the current. Buck-Boost (step-up/down): Lowers or boosts the input voltage according to the requirement.


Buck-Boost (step-up/down): Lowers or boosts the input voltage according to the requirement.