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MOSFET transistors are excellent choice for driving high current devices such as motors or high power RGB LEDs. They offer very low switching resistance and very small heat dissipation compared to bipolar transistors. This guide is designed to explain how to drive N-Channel MOSFETs with a microcontroller such as PIC or ATMEGA. Transistors heat up when driving large loads because they have a voltage dropped over them (Vce), and Heat (Watts) = Voltage * Current. This leads to thermal runaway within the transistor, eventually driving the device to destruction if not handled carefully. FET's are like digital switches, capable of turning on and off between the Drain and Source via a voltage potential at the Gate. When a FET is on, it usually has a resistance of less than 0.01 ohm, and when off, its like an open circuit. Because of the low resistance during the FET's on state, it can allow large amounts of current to pass through it without heating up. FET's turn on by voltage potential, not an electric current, and in return they have a very high input impedance. With this in mind, you only need a voltage to turn them on, perfect for digital electronics.

MOSFET transistors are excellent choice for driving high current devices such as motors or high power RGB LEDs. They offer very low switching resistance and very small heat dissipation compared to bipolar transistors. This guide is designed to explain how to drive P-Channel MOSFETs with a microcontroller such as PIC or ATMEGA. There are a couple of tricks to remember when using them. P-Channel MOSFETs are useful for switching positive supply of a target circuit on and off. Particular attention must be placed to the target circuit if the supply voltage is greater then the micro controller's logic voltages. If for example, your target device is being powered by 12 volts, and your logic high state from the micro controller is 5 volts, then the MOSFET will never turn off, as voltage will either be -12V or -7V (remember that this guide is designed for logic level MOSFETs). Anything over -3 volts will generally drive the logic level MOSFET on (varies between types of LL MOSFETs).

Here is the circuit diagram of an ultrasonic mosquito repeller.The circuit is based on the theory that insects like mosquito can be repelled by using sound frequencies in the ultrasonic (above 20KHz) range.

As shown in the schematic, temperature sensor of our electronic thermometer is LM35DZ. There are some kinds of LM35 IC, since it is cheap and easy to find we used LM35DZ in our project. It measures from 0°C to 100°C with a very linear output graph.For one degree change, it increases its output 10mV. On the Electronic Thermometer Schematic other hand, this circuit measures temperature values only between +10°C and +39°C. 2 numbered (middle) pin of the sensor is connected to the 5 numbered pins of LM3914 ICs. So every IC determines how many leds of bargraph will bright due to the analog signal received from the sensor. 2.2 microfarad tantal capacitors are connected between the 2 and 3 numbered pins of LM3914. Resistors in the circuit have %1 tolerance values.

Finite State Machine based Programmable Logic Controller * 7 Inputs * 8 Outputs * Simple IF/THEN/ELSE based compiler language generates direct EPROM files.

The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon is employed here for sensing the fire. The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output(pin 3) of IC1 is couples to base of transistor T3(SL100), which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2. Capacitor C1 charges up to the positive supply voltage and increases the the time for which the alarm is ON.

Using the GPS Satellite system offers the advantage of very accurate timing and by extension, frequency control. The long term error is to all intents and purposes zero, with time and frequency accuracy being comparable to the international standard. The traditional route is to use a relatively low cost GPS receiver module which outputs a 1 Pulse per second signal (1 PPS) aligned to UTC. Basic GPS modules such as the Garmin GPS25 and Motorola Oncore have been around for some years and are available at low cost. It is possible to phase lock a divided down crystal oscillator to this 1 PPS signal and transfer its long term stability to , say, a 10MHz reference which is subsequently used for deriving any LO and beacon frequencies. The subsequent PLL system is usually described as a GPS Disciplined Oscillator rather than locked, since it is not, strictly speaking, actually ‘locked’ to the GPS system at all; just controlled by it via the 1 PPS generated by software in the receiver module.

A very high quality intercom, which may also be used for room monitoring. This circuit consists of two identical intercom units. Each unit contains a power supply, microphone preamplifier, audio amplifier and a Push To Talk (PTT) relay circuit. Only 2 wires are required to connect the units together. Due to the low output impedance of the mic preamp, screened cable is not necessary and ordinary 2 core speaker cable, or bell wire may be used.

Nowadays, metal detection has become a hobby of many people. Besides as a funny and interesting hobby for them, they also wished indeed a treasure that is embedded in the soil when excavated. For this one hobby, you have to have a tool known as a metal detector. To undergo this hobby is quite expensive to buy. But for those of you who want to try to make yourself a metal detector, the following will be presented a simple schematic that relates to metal detection. The operation of metal detector is based on superheterodying principle, which is generally used in a heterodyne receiver. This circuit uses two RF oscillators. Both oscillator frequency is fixed at 5.5 MHz. The first RF oscillator comprises transistor T1 (BF 494) and 5.5 MHz ceramic filter commonly used in TV sound-IF section. The second oscillator is an oscillator Colpitt realization with the help of the transistor T3 (BF494) and inductor L1 (follow the details of construction) was driven by trimmer capacitor VC1.

This device is designed to measure the torque in an automobile drive shaft and provide an output to a vehicle data recording system or a portable computer via an RS-232 interface. The received data can then be combined with RPM measurements from the data recording system to calculate horsepower. It consists of the sensor unit, (Figure 1), which attaches to the driveshaft, and the receiver unit, , which provides the serial output signal. The sensor unit is battery powered and communicates with the receiver via a 433 Mhz RF data link.The receiver unit is powered by the vehicle electrical system. Circuit operation is shown in the diagram.