Electrical & Power Electronics Projects


Hybrid Solar Charger

Efficiency of a solar charging system depends on the weather conditions. Usually the solar panel gets four to five hours of bright sunlight in a day. If the weather is cloudy or rainy, it affects the charging process and the battery does not attain full charge. This proposed hybrid solar charger can solve the problem as it can charge the battery using both solar power as well as AC mains supply. When output from the solar panel s above 12 volts, the battery charges using the solar power. When the output drops below 12 volts, the battery charges through AC mains supply.


The objective of this project is to develop a low cost, compact and high reliable device for the hybrid solar charger. The project design involves a 10W solar panel, operational amplifier , transistor BC547, 12V single change over relay , step-down transformer and a few other components. In bright sunlight, the 12V, 10W solar panel provides up to 17 volts DC with 0.6-ampere current, When output from the solar panel is 12 volts or more the battery is charged by solar supply through enegises relay and this charging status is indicated by a LED ON. When output from the solar panel drops below 12 volts, output of the comparator turns low and the relay de-energizes. Now the battery gets charging current from the transformer-based mains power supply through the normally- closed (N/C) contact of the relay. The operational amplifiers as comparator and zener diode used which comprises the solar voltage for chargable voltage limit 12v. There are a rectifying diode and smoothing capacitor provides charging current from mains while solar power goes below 12v. Thus a battery is kept in continuous charging even if low solar light using this hybrid solar charger.

Temperature Controlled LEDs using LM35

This project proposed a building a simple yet very useful circuit using Temperature Sensor LM35. In this circuit, we are going to control the LEDs according to temperature around. If temperature goes beyond a particular level (50 Degree in this circuit) then Red LED will glow automatically, otherwise yellow LED remains on below that particular temperature. This threshold temperature value can be set by adjusting the Variable resistor in the circuit, according to requirement.



This Temperature controlled Lights circuit can be useful in many ways, like it can work as temperature indicator or it can trigger any device like fan or alarm beyond a particular temperature. It can also work as fire alarm if you set the threshold temperature very high like 100 Degree Celsius. In this circuit you will also learn about how to use LM35 sensor in any circuit. LM35 is very popular and inexpensive temperature sensor generally used as digital thermometer or to measure temperature.

Temperature Meter Display

This temperature meter uses the precision micro power centigrade sensor IC LM35. The output voltage of the IC is linearly equal to +10Mv per degree centigrade. The temperature level is displayed through LED readout.

The circuit uses the precision temperature IC LM35. This three pin transistor like IC give output linearly equal to +10mV per degree rise in temperature. It can measure temperature between -4 degree to +110 degree centigrade. Its related type LM34 is Fahrenheit sensor and its output is equal to -10mV per degree Fahrenheit. Output of IC1 is directly given into the input of the display driver IC LM3914. It is a monolithic integrated circuit with 10 active low outputs that can drive 10 LEDs directly without a current limiting resistor.

The internal circuitry of the IC adjusts the current passing through the LEDs. The input of LM 3914 is very sensitive and its outputs 18 – 10 sinks current one by one as the input receives an increment of 125 milli volts. Here only 6 outputs are used to drive 6 LEDs. More LEDs can be included in the remaining outputs if required. As the IC LM35 senses temperature rise, LEDs one to six light up. If the sensitivity is not high, VR2 can be omitted. Then output of IC LM35 should be directly connected to the input of IC LM3914.

Over Temperature Detect Fire Alarm

At the heart of this overhead detector (fire alarm) circuit is a precision integrated temperature sensor type LM35 (IC1), which provides an accurately linear and directly proportional output in mV, over the zero to +155 degrees C temperature range.

This can be used as part of fire smoke detectors but do not use it as a home fire alarm system. The LM35 develops an output voltage of 10 mV/K change in measured temperature. Designed to draw a minimal current of its own, the LM35 has very low self heating in still air.

Here the output of the LM35 is applied to the non-inverting input of a comparator wired around a CA3130 opamp (IC2). A voltage divider network R3-P1 sets the threshold voltage, at the inverting input of the opamp. The threshold voltage determines the adjustable temperature trip level at which the circuit is activated.

When the measured temperature exceeds the user-defined level, the comparator pulls its output High to approx. 2.2 V causing transistor T1 to be forward biased instantly. T2 is also switched on, supplying the oscillator circuit around IC3 with sufficient voltage to start working. The 555 set up in astable mode directly drives active piezoelectric buzzer Bz1 to raise a loud alert. Components R7, R8 and C4 determine the on/off rhythm of the sounder.

Temperature Active Cooling Fan

Heat activated cooling fan controller is a simple project which operates a brushless fan when the temperature in a particular area goes above a set point, when temperature return normal, fan automatically turns off. The project is built using LM358 Op-amp and LM35 temperature Sensor. Project requires 12V DC supply and can drive 12V Fan. This project is useful in application like Heat sink temperature controller, PC, heat sensitive equipment, Power supply, Audio Amplifiers, Battery chargers, Oven etc

The LM35 used as temperature sensor, LM358 act as comparator and provides high output when temperature rise above set point, high output drive the Fan trough driver transistor. The LM35 series are precision integrated-circuit temperature devices with an output voltage linearly-proportional to the Centigrade temperature. The LM35 device has an advantage over linear temperature sensors calibrated in Kelvin, as the user is not required to subtract a large constant voltage from the output to obtain convenient Centigrade scaling. The LM35 device does not require any external calibration or trimming to provide typical accuracy of ±¼°C at room temperature. Temperature sensing range 2 to 150 centigrade. LM35 provides output of 10mV/Centigrade.