These are the motors that are commonly found in the toys and the tape recorders. These motors change the direction of rotation by changing the polarity. Most chips can’t pass enough current or voltage to spin a motor. Also, motors tend to be electrically noisy (spikes) and can slam power back into the control lines when the motor direction or speed is changed.
Specialized circuits (motor drivers) have been developed to supply motors with power and to isolate the other ICs from electrical problems. These circuits can be designed such that they can be completely separate boards, reusable from project to project.
A very popular circuit for driving DC motors (ordinary or gearhead) is called an H-bridge. It’s called that because it looks like the capital letter ‘H’ on classic schematics. The great ability of an H-bridge circuit is that the motor can be driven forward or backward at any speed, optionally using a completely independent power source.
This circuit known as the H-bridge (named for its topological similarity to the letter “H”) is commonly used to drive motors. In this circuit two of four transistors are selectively enabled to control current flow through a motor.
opposite pair of transistors (Transistor One and Transistor Three) is enabled, allowing current to flow through the motor. The other pair is disabled, and can be thought of as out of the circuit.
By determining which pair of transistors is enabled, current can be made to flow in either of the two directions through the motor. Because permanent-magnet motors reverse their direction of turn when the current flow is reversed, this circuit allows bidirectional control of the motor.
It should be clear that one would never want to enable Transistors One and Two or Transistors Three and Four simultaneously. This would cause current to flow from Power + to Power – through the transistors, and not the motors, at the maximum current-handling capacity of either the power supply or the transistors. This usually results in failure of the H-Bridge. To prevent the possibility of this failure, enable circuitry as depicted in Figure is typically used.
In this circuit, the internal inverters ensure that the vertical pairs of transistors are never enabled simultaneously. The Enable input determines whether or not the whole circuit is operational. If this input is false, then none of the transistors are enabled, and the motor is free to coast to a stop.
By turning on the Enable input and controlling the two Direction inputs, the motor can be made to turn in either direction.
Note that if both direction inputs are the same state (either true or false) and the circuit is enabled, both terminals will be brought to the same voltage (Power + or Power – , respectively). This operation will actively brake the motor, due to a property of motors known as back emf, in which a motor that is turning generates a voltage counter to its rotation. When both terminals of the motor are brought to the same electrical potential, the back emf causes resistance to the motor’s rotation.
In this project we will make solar water heater . Its is our project in this semester. We will charge battery with power supply charging circuit. Then we will run heater from battery. Problem will be to run heating element from battery. in this we will connect a push to on switch with timer circuit which will provide time delay. PIN 2 is input pin of timer. A Transistor npn 548 transistor is connected with the output of Timer 555. Output of 548 npn transistor connected to Relay drive circuit. Water pump is connected to with Relay. Whole supply of pump will be received from Battery 12v 7Ah. We will connect solar pump output with Charging circuit for battery. Battery output will be converted to 12 v to 220 v Step up circuit.
A solar charger differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and or by means of diesel generators and flywheels for high power users. The on-battery runtime of most uninterruptible power sources is relatively short—5–15 minutes being typical for smaller units—but sufficient to allow time to bring an auxiliary power source on line, or to properly shut down the protected equipment.
While not limited to protecting any particular type of equipment, a UPS is typically used to protect computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption and/or data loss. UPS units range in size from units designed to protect a single computer without a video monitor (around 200 VA rating) to large units powering entire data centers, buildings, or even cities
The primary role of any UPS is to provide short-term power when the input power source fails. However, most UPS units are also capable in varying degrees of correcting common utility power problems:
Power failure: defined as a total loss of input voltage.
Surge: defined as a momentary or sustained increase in the mains voltage.
Sag: defined as a momentary or sustained reduction in input voltage.
Spikes, defined as a brief high voltage excursion.
Noise, defined as a high frequency transient or oscillation, usually injected into the line by nearby equipment.
Frequency instability: defined as temporary changes in the mains frequency.
Harmonic distortion: defined as a departure from the ideal sinusoidal waveform expected on the line.
- ECG Monitoring
- PH monitor
- Glucose rate monitoring
- Heart beat Monitoring
- Blind stick
- Body resistance monitoring
- Finger print scan
- Iris Recognition
- ultrasonic collision detection for blind person
- Galvanic skin resistance system
- Body temperature monitoring system
- Accelerometer based handicapped wheel chair
- Nasal sensor respiratory system
- heart rate temperature monitoring with gsm
- Wireless alert for nurse using RF communication
- Baby incubator system
- Automatic steam for patient
- Spinal disk problem patient relief system
- Artificial parts based sensitive system for patient
- text to speech system
- symbol based identification for patient