Heat Sensor Circuit

This is the simple heat sensor circuit. It can be used to control any device using heat sensor. In this circuit a thermistor and a resistance is connected in series. This arrangement makes a potential divider circuit.

Here the thermistor is Negative Temperature Coefficient type. So when the room temperature is increased its resistance decreases simultaneously and more current flows through the resistor and the thermistor. We find more voltage at the junction of the resistor and the thermistor.

 

Our thermistor resistance value is 110 ohms. Suppose the resistance value becomes 90 ohms after heating the 110 ohms thermistor. Then the voltage across one resistor of the voltage divider circuit equals the ratio of that resistor’s value and the sum of resistances of the voltage across the series combination. This is the concept of voltage divider. 

The final output voltage of the voltage divider circuit is now applied to the npn transistor (BC548) through the base resistor (3.3K ohms). Here the emitter resistor is replaced with a zener diode. Emitter voltage is maintained at 4.7volt with the help of zener diode. This voltage is used to compare voltage. Transistor conducts when base voltage is greater than the emitter voltage. Transistor conducts if it gets more than 4.7volt of base voltage. Then the circuit is completed through buzzer and it gives sound.

 

Active FM Antenna Amplifier of FM Booster

FM booster is one kind of a preamplifier which can be used to listen FM radio programs from distance FM stations clearly. The circuit comprises a common-emitter tuned RF preamplifier which tuned RF preamplifier wired around VHF/UHF transistor 2SC2570.

Serial	Parts Lists	Value
1	R1	27kΩ
2	R2	270Ω
3	R3	1kΩ
4	C1	5.6pF
5	C2	5.6pF
6	C3	1n
7	C4
8	C5	10pF
9	C6	0.1µF
10	VC1	22pF Trimmer capacitor
11	L1	1T FROM BOTTOM END
12	L2	3T, 20SWG 5mm DIA, AIR CORE
13	T1	2SC2570

Adjust input/ output trimmers (VC1/VC2) for maximum gain.

3 digits Digital Ammeter using Microcontroller

Digital Ammeter is needed to do any kind of electronics circuit making. It is very much useful who is interested in electronics projects. Now-a-days there are many kind of digital or analog ammeter which are found in the market. But if you make such kind of digital meter then you have no no bounds happy.

The bellow circuit is digital Ammeter based on PIC16F684 and ACS712 current sensor. Here the measured ac/dc current will display on three digit 7-segment  with resolution 100mA. In this project current sensor is ACS712ELCTR-30A-T . This circuit can measure the ac or dc current up to 30mA with 66mV/A output sensitivity. 

The micro-controller PIC16F684 is used to read analog value from the ACS712 current sensor output and micro-controller convert to current and displaying on 7-segments display. For this circuit all 7-segment displays will be common anode type and it driven by PNP transistor BC557. Originally, this circuit is suitable for measuring DC current.

Remote Control Using the NE 555 and LM 567

Remote control circuit consists of two parts, one is transmitter and the other is receiver. A simple diagram is schematic remote control. The transmitter circuit’s transmitter IC is controlled by NE555. Receiver circuit works by the signal emitted frequency which is emitted by that transmitter circuit. Transmitted signal frequency must be equal to the frequency decoder of the receiver circuit. The NE 555 generated frequency is same that receive frequency of IC LM 567. 

The output frequency of the transmitter circuit is f,

f = 1.44/(Ra+2Rb)C

The resistor R1 is a receiver variable to facilitate the process of tuning. The system works well when the circuit is ready. The first step is tuning by way of the transmitter is turned on continuously, while the receiver R1 to set the value to be able to detect the signal transmitter. The second part is the receiver is controlled by LM 567. The following is a schematic drawing recipient.

f = 1 / (1.1 xR1xC1)

This frequency depends on the value of R₁ and C₁.

In the picture on top of each channel is designed with a different frequency. By considering the bandwidth of the frequency detection signal LM 567, inter-frequency channels should have a big enough difference, let’s try with a difference of 5 KHz.

IR Remote Control Circuit using Op amp 741

IR circuit is called Infrared Circuit. Remote controls are very much popular now-a-days. It is specially called cordless circuit. This circuit is very simple and low cost cordless remote control circuit which is based on infrared   rays.

Figure 1 shows the transmitter circuit. The transmitter produces infrared rays and that can be easily transmitted up to 4 meters with a special convex lens and a twin LED arrangements.

Figure 2 shows the receiver  circuit. Op amp IC1-741 generates high frequency squire wave which provides the gate pulses for SCR1. IC1’s output current flows through  SRC1 and it is conducting current and enables the LED to emits infrared rays. The output frequency of Op amp IC1 depends on the variable resistor VR1, which in turns varies the output radiations of the LED.

When IR rays fall on the photo-transistor T1 of the receiver, then base of the photo-transistor’s base produces charge carriers at a rate depending on the rate of arrival of incident radiations at the pn junction of the transistor. Then the resulting emitter voltage is amplified by Op amp IC-2 . The amplified signal is rectified by D2. Finally the amplified signal is to drive the relay.

Parts List: