Introduction: Temperature Sensing Using LM 35
Hello guys, this is YoungEngineerAS, having new instructable today. Let us see how to build your own custom Temperature sensing device using LM 35 sensor.
- A 9 V battery
- 7805 IC [5 V regulator]
- Bread Board
- Connecting wires
- LM 35
- LM 358 op amp IC
- A 1 kilo ohm resistor
- 10k POT
To build this, you need to follow simple steps ---
Step 1: Bread Board Connection
Plug the 7805 IC into the bread board. According to the pin numbers of 7805 - Pin1 is input, Pin2 is GND and Pin3 is Output when the hump of the IC is facing you. Give the input of 9 V across P1 and P2. Take the output across P3 and make the power rails with a 5 V supply. (More details regarding the bread board connections is available on the net).
Step 2: LM 358 Connection
It is a low power OPAMP IC which can amplify low level signals to readable high levels. It works on 5V supply and can give a max. Saturated output of ~4V.
1. OUT1: Output pin of the opamp1.
2. IN-: This is inverting input to the OPAMP1. Whatever input given, gets inverted to negative The IC has two set of Op Amps. Pin description is as follows: Value. Then output will be –ve. When this pin is used, the IN+ should be grounded when used in open loop mode.
3. IN+: This is non-Inverting input to the opamp1. The output is +ve when an input is given to this pin. When this pin is used, the other input pin, ie, IN- must be grounded when used in Open loop mode.
4. VCC: This is the main power supply to the IC. It can be 3V to 32V max. Depending upon supply voltage, the max output voltage varies. If, 5V supply, output can be ~4V. To this terminal, Positive of battery or source is connected.
5. GND: This is where we need to connect Negative terminal of the battery. If we use the IC for AC signals, then instead of calling it GND, we call it –VEE.
Connect Pin8 to 5 V rail and Pin4 to ground rail as shown in the picture.
Step 3: Setting Threshold Using 10k POT
Connect POT(10kOhms) variable pin to pin 1 and any fixed pin to pin 2 of LM358 opamp. Since we need to make the sensing above the room temperature,we will set the position of the variable end by turning the pot and adjust the LED to be having minimum glow later when battery is connected.
Step 4: Feedback Resistor to Op Amp
Connect a 1kOhm resistor between pin 2 and ground , which acts as feedback path.
Step 5: LM 35 Connection
Ground pin 3 of lm358 and connect pin2 of temperature sensor IC(LM35) to pin 3 of the OPAMP. Connect pin 1 of Temperature sensor IC to VCC and Pin3 of it to ground.
Step 6: Indicator LED
Connect an LED anode to pin1 of LM358 OpAmp and its cathode to ground(-ve) in breadboard.
Step 7: Final Output
According to the temperature increase, intensity of LED light increase.
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