What is H-bridge-motor-driver?

An H bridge is an electronic circuit that enables a voltage to be applied across a load in opposite direction. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards.

What is the purpose of it ?

A motor driver is a little current amplifier, the function of motor drivers is to take a low-current control signal and then turn it into a higher-current signal that can drive a motor.

Designing methods & COMPONENTS

•4 Resistors (2-100 ohms & 2-K ohms)

•6BJT – 2PNP (BC547) & 4NPN (BC557)

•1- 0.1nF capacitor

•1- 100uH inductor

•1 DC 9V motor

• 12V battery

Circuit diagram & Pspice simulation

Wiring Diagram Practical
Circuit Diagram
PsPice Simulation

  How does it works?

• Here, we have used very low inductor and capacitor in the circuit because a good amount of load required to start the motor, at that time circuit loses control of its load for a very few second and occur down to the voltage level. For getting rid of it, we have implemented that load idea. The capacitor at that time discharges and inductor recovers the load of the circuit, and that’s how the instant voltage drop can be minimized.

• For connection ‘A’ the motor will cycle as the clock wise position, and for ‘B’ part connection it will cycle as the anti-clock wise position.

• We have used power BJT in the circuit implementation as the power BJT is more sufficient for that purpose.

Cost & Benefits of it:

•We can use it to build Line-follower.

•We can also use it the switching circuit.

•It can be used to amplify current from high voltage.

•It can minimize the extra cost of buying Arduino or IC.

•It is a very cheap cost implementation circuit.

•The total cost of our circuit is only 100 taka (having 10tk for 6BJT, 30tk for wire, 2tk for resistor, 2tk for capacitor & inductor, 50tk for breadboard)


CPU Info Checker with Fan Speed Controlling

Category: Project Proposal

Topic: CPU Info Checker with Fan Speed Controlling

Subject: CSE323 – Operating System Concepts

In this Arduino based project, we are going to control DC fan speed according to the room temperature and show these parameter changes on a 16×2 LCD display. It is accomplished by the data communications between Arduino, LCD, DHT11 sensor Module and DC fan that is controlled by using PWM. PWM is a technique by using which we can control voltage.

Circuit Components

  1. Arduino UNO
  2. DHT11 sensor
  3. DC Fan
  4. 2n2222 transistor
  5. 9 volt battery
  6. 16×2 LCD
  7. 1K resistor
  8. Connecting wires
  9. LED Light


This project consists of three sections. One senses the temperature by using humidity and temperature sensor namely DHT11. Second section reads the dht11 sensor module’s output and extracts temperature value into a suitable number in Celsius scale and control the fan speed by using PWM. And last part of system shows humidity and temperature on LCD and Fan driver.

Fan speed and PWM values and duty cycles values that we are going to use is showing in given table:

TemperatureDuty CyclePWM ValueFan Speed
Less 260%0Off
2620 %5120%
Greater 29100%255100%
Fan Speed & PWM Values

Fan speed control technique:

 A low-frequency pulse-width modulation (PWM) signal, usually in the range of about 30Hz, whose duty cycle is varied to adjust the fan’s speed is used. An inexpensive, single, small pass transistor can be used here. It is efficient because the pass transistor is used as a switch.

One disadvantage of this approach, however, is that it can make the fan noisy because of the pulsed nature of the signal. The PWM waveform’s sharp edges cause the fan’s mechanical structure to move (like a badly-designed loudspeaker), which can easily be audible.

Circuit Diagram:

We will implement that circuit and add some extra features & sensors that will help to check proper info of CPU usage.

Fig. : Circuit diagram of the temperature-based fan speed control and monitoring CPU usage using Arduino