As mentioned earlier, in this chapter, you will develop a remote-controlled robot with some add-on features, so the first thing that you need to make a robot movable are wheels. Now, once you got the wheels, you need some mechanism that can control the speed of the wheels. Motors are used for this purpose; they convert electrical energy into mechanical energy. A world without electric motors is difficult to imagine. From the tiniest motor found in a quartz watch to a million-plus horsepower motor powering a ship, motors are used in many diverse applications. The following screenshot is an example of a motor:

There are basically two types of conventional electrical motor available: AC type motors and DC type motors. AC motors are generally used in high power single or multi-phase industrial applications, where a constant rotational torque and speed is required to control large loads such as fans or pumps. DC motors are used in many electronics, positional control, microprocessor, PIC, and robotic circuits. Another DC motors that is commonly used in robotics is the stepper motor. This is particularly well suited to applications that require accurate positioning and a fast response to starting, stopping, reversing, and speed control. Another key feature of the stepper motor is its ability to hold the load steady once the required position is achieved. For example, in a normal DC motor, once you stopped the power to motor, it will still go to some distance because of the continuous motion, while in a stepper motor, once you stop the power, it will stop instantaneously.

A multimeter is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter can include features such as the ability to measure voltage, current, and resistance. It is also known as a volt-ohm meter (VOM). It can be of two types: analog multimeter and digital multimeter based on the circuit used in the construction. An analog multimeter usually shows results using a pointer that moves over a scale calibrated for all the different measurements that can be made, while on the digital multimeter digits are displayed on the screen. A typical digital multimeter is shown in the following image:

A typical analog multimeter is shown in the following image:

Most of the time, you will be using digital multimeter, so you need to understand the capabilities and usage of digital multimeter. On the bottom-right corner of the multimeter, you will see three holes where you can connect a measuring cable. If your circuit operates on higher currents, connect the anode (typically a red probe) to the first hole and connect the cathode (typically, a black probe) to the last hole. The second hole is for circuits operating at low current. Most of the time, you will be using the second hole, where you will connect the anode (typically, a red probe) and the third hole, where you will connect the cathode (typically, a black probe). Here are some features that you will be using while developing a robot in this chapter:

Once you have the motors for the movement, you need some kind of base that can hold all the motors at a certain distance for the proper movement of the robot. Apart from holding the motor, you need some firm base on which you can place all the electronics components. In this chapter, you will build a 4-wheel robot, so you will require a 4-wheel robotic base. You will be able to get it from a nearby electronics shop. Have a look at the following image to get a clear idea of how it will look in the real world:

Because most of the electronics power supply provide 5V and most modern sensors displays are 3.3V only, you need to perform level shifting/conversion to protect the 3.3V device from 5V. Although you can use resistors to make a simple divider, for high-speed transfers, the resistors cause a havoc that is tough to debug. For this reason, you have to use a level converter. Those converters can be of two types: unidirectional and bi-directional. As the name suggests, a unidirectional converter can only convert in one direction, that is, either from 5V to 3.3V or 3.3V to 5V. While on the other end, a bi-directional converter can convert 5V to 3.3V as well as 3.3V to 5V.

Depending on the DC motor used, it requires voltage varying from 5V to 36V. Raspberry Pi GPIO can't provide such high range of voltage, so you need some kind of level converter. Moreover, you need to drive the motor in both directions, so some special circuitry is required for this purpose. That special circuit is embedded in a typically used motor driver L293D IC. It works on the concept of H-bridge. Before you understand the functionality of L293D, you need to understand what is H-bridge and the basic functionality of the H-bridge circuit.

H-Bridge

H-Bridge is an electronic circuit that enables the voltage to be applied across a motor (in general, any load) in both directions. It can be built using four switches. The following diagram shows the basic structure of an H-bridge:

Generally, it is used to change the direction of the motor, but it can also be used for other two purposes:

• "Brake" the motor: When the motor terminals are shortened, it will come to a sudden stop
• "Free run" the motor: When the motor terminals are disconnected from a circuit, it will free run to a point

S1	S2	S3	S4	Result
Close	Open	Open	Close	The motor moves right
Open	Close	Close	Open	The motor moves left
Open	Open	Open	Open	The motor free runs
Open	Close	Open	Close	The motor brakes
Close	Open	Close	Open	The motor brakes
Close	Close	Open	Open	Shoot-through
Open	Open	Close	Close	Shoot-through
Close	Close	Close	Close	Shoot-through

In the preceding table, you can see there is one more condition "Shoot-through". When the power supply gets directly shorted, it is called "Shoot-through". You should never use these conditions in your circuits.

Motor driver IC L293D has two H-bridge circuits, so you can control a set of two DC motors simultaneously in any direction. This is a 16-pin dual H-bridge motor driver integrated circuit. Due to its small size, it is widely used in robotics applications to control the DC motors. The pin diagram of the L293D IC is shown in the following diagram:

• Enable Pins: Pin 1 and Pin 9 enable pins. Both pins need to be HIGH if you want to use both H-bridge of the IC. For driving the motor with left H-bridge, you need to enable Pin 1 to HIGH. Similarly, to drive the motor with right H-bridge, you need to enable Pin 9 to HIGH. If one of the Pin 1 or Pin 9 goes low, then the motor in the corresponding section will suspend working.
• Power Supply: Pin 16 is an internal power supply pin where you need to connect 5V power supply. Pin 8 is for motor supply. Depending on the motor used, you can connect corresponding power supply required for that motor to Pin 8. ADD MORE DETAILS
• Output Pins: As mentioned before, L293D can drive two DC motors simultaneously. One motor should be connected to Pin 3 and Pin 6. Similarly, another motor can be connected to Pin 11 and Pin 14.
• Ground Pins: Pin 4, Pin 5, Pin 12, and Pin 13 are ground pins. These pins should be connected to GROUND/LOW.
• Input Pins: There are four input pins on the IC. Pin 2 and Pin 7 are for regulating the motor connected to the left side of the IC, and similarly, Pin 10 and Pin 15 are for regulating the motor connected to the right side of the IC. The motors are rotated based on the input provided across these inputs.

The following table shows the inputs provided and the corresponding result:

Pin 2 / Pin 15	Pin 7 / Pin 10	Result
HIGH	LOW	The motor moves in clockwise direction
LOW	HIGH	The motor moves in anticlockwise direction
LOW	LOW	No rotation
HIGH	HIGH	No rotation

Since the launch of Raspberry Pi board A, people all around the world are exploring it in numerous ways. Computer scientists and researchers have explored the USB camera with Raspberry Pi. However, not all the USB cameras are supported with Raspberry Pi, so Raspberry Pi foundation decided to build a camera module that can directly connect with the Raspberry Pi CSI connector. The 5MP camera module is capable of capturing 1080p video and still images. The module is around 25mm*20mm*9mm and weighs just over 3 gm, which makes it perfect for mobile or other applications where size and weight play an important role.

import picamera
camera = picamera.PiCamera()
camera.capture('image.jpg')

raspistill -o cam.jpg

import picamera
from time import sleep
camera = picamera.PiCamera()
camera.start_recording('video.h264')
sleep(5)
camera.stop_recording()

raspivid -o video.h264 -t 10000

Ultrasonic sensors work on a principle similar to radar or sonar, which calculates properties of a target by interpreting the echoes from radio or sound waves respectively. This sensor will generate the high frequency sound waves and evaluate the echo, which is received back by the sensor by measuring the time interval between sending the signal and receiving the echo to calculate the distance to an object. In this chapter, you will be using an HC-SR04 ultrasonic sensor Arduino module. It uses sonar to determine the distance to an object. It gives distance with the nearest object with high accuracy and stable reading in an easy-to-use package for distance ranging from 2 cm to 400 cm. Unlike a sharp sensor, which can also be used for measuring the distance, its operation is not affected by sunlight. The following image is an example of ultrasonic sensors:

As you can see in the preceding image, there are four pins on HC-SR04:

Vcc: +5VDC

Trig: Trigger input for sensor

Echo: Echo output of the sensor

GND: Ground

First, you need to send the trigger pulse of 10 µs (micro Second) to the Trig Pin, which will enable the ultrasonic sensor. The ultrasonic sensor module will send the output to the Echo pin.

There are many applications where you might want to use Raspberry Pi as a standalone device. The Internet connection and power supply are the only two things that will hinder the use of Raspberry Pi as a standalone device. The Internet connectivity issue can be resolved using the Raspberry Pi WiFi module. To resolve the power supply issue, a rechargeable battery can be used.

As mentioned in the previous section, to make your Raspberry Pi a standalone device, you need to get rid of the Ethernet cable. For this reason, you will be using the Raspberry Pi WiFi module to use the WiFi network. As you know Raspberry Pi doesn't have the capability to connect to the WiFi network, you will be using $5 WiFi module. To make it work, you need to update the current Internet configuration. Here are a few steps that you need to follow to make the WiFi module work properly:

In this section, you were introduced to a few more electronics components that will be used in the next section for building the remote-controlled robot.