Heat Sensor Circuit with LM741

This circuit automatically fan or a fan for your computer, electronic project, the circuit is only valid for your project.

This circuit is known as a thermal sensor. In principle, this circuit or NTC thermistor as a sensor. This diagram, where the temperature is almost simple sensor data subsequently amplified by Op-Amp 741, which is then compared with pl P2, etc. served as governor of sushi, then transistor Q1 to move Relay.

heat sensor circuit

Transistor Q1 is a 2N2222 (A) 2N3904, NTE123A, ECG123A, etc. Not all are critical. Only acted as a relay for each type of work, therefore, deconvolution, the length of the energy needed to activate the power coils. D1, 1N4148, acts as a spark arrester on the relay contacts open and abolishs to false trigger. Feel free to use another type of matter, such as 1N4001 or something. Solder directly on the ‘+’ and ‘-’ relay terminals.

Electronic Part List:

IC1 = LM741, LM741CN-ND, LM741CN, NE741, μA741, etc.
Q1 = 2N2222 2N2222 2N3904-ND
D1 = 1N4148
Th1 = 10K
Re1 = 12V relay
R1 = 47K
R2 = 150 – 390K (if ralay “chatters”)
R3 = 1K8,
R4, R5 = 2K2
P1 = 50K Trimmer Pot

Heat Sensor PCB Diagram

How to work
Th1, 50K thermistor is a standard type. I was looking for a bar or rectangular thing. Available from Tandy Radio Shack. Almost every kind will do. I experimented with different models from 22K to 100K, and everything worked fine after replacing the trimmer pot and a small “tuning.

Which was used in the above figure is the circuit model under 50K Fenwal (# 197-503LAG-A01). 50K was measured accurately at 25 ° C and 10% tolerance. Increasing resistance temperature drop. Tolerance for my purposes (cooling power coolrib wide) is 10%.

Heat Sensor Part On PCB Diagram

Another name for this thing is “NTC”. NTC means a negative temperature coefficient “, which means that when the temperature decreases the resistance of the thermistor increases. You might have to buy at the lowest price. Some are thermistor, at least $ 4.00, but for $ 55.00 Canadian dollars for the type of glass encapsulated (the best).
I replaced my 60k thermistor type of glass hermetically sealed, such as the environment, and so my question corrosive particles that may affect future performance include.

BOURNS trimmer P1 is a simple rule, and wide temperature range of this circuit. I used a 10-style in the mood for some fine tuning, but the nature of regular use.

R1 is the “safety” resistor P1 trimmer pot is completely adjusted to “0″ ohm. Just then, the thermistor will receive a full 12 volts, and so hot that it puts blisters on your fingers …
R3 feeds back a bit in the differential op-amp relay to rattle when thermistor temperature reaches remove. Depending on the application and the type used in the 1 Re1 quarter and starts around 330K and reduce its value to the desired result. 150k value reported in the system worked for me. Impairment of hysteresis R2 more resources, but use more than necessary. Or temporary use of the trimmer pot and read the value. 120K worked for me.

Transistor Q1 is a 2N2222 (A) 2N3904, NTE123A, ECG123A, etc. are not critical. Acts as a relay switch in almost every type of work, and could provide the current necessary to activate the relay coil.

D1, 1N4148, acts as a spark arrestor when the relay contacts to open and eliminates false start. For my purposes, 1N4148 is good for the relay I have a little amp. However, you can create a number of diodes used here, my next choice would be regular target 1N4001 or something to be used as a kind of relay connected to the control process more than 1 ampere.

Digagram circuit and PCB layout are current C1, C2, R7 and LED. C1 and C2 are new to the relay switching noise in some applications to remove. Optional LED and resistor was added to the circuit and layot for your convenience. Relays used in this kit is a type of small 12V/0.5A. If the relay clicked increase the feedback resistor R3 to 180km or something “higher, and a small ceramic cap coils connected in parallel with diode D1. Diode 1N4148 is designed for small relay. When using relays as 1N4001 or 1N4004.

If you want to create a custom PCB, try the following. PCB is equipped with holes for the relay, but not your specific relay. It was designed for one type of arene DC12V HB1. Diversity and the relay model is for adults only. How to join? Well, I had a lot of space on the board mount relay. You can also mountain, and connect various cables. Use of silicone adhesives, cyanoacrylate ester (crazy glue) or double-sided tape on his relay place. Works well. Note that the PAC and the imposition Page Not according to the timetable for drawing fans. PCB is about 1.5 x 3 inches (4.8 x 7.6 mm)
If you print inkjet PCBs probably not to scale. Try 8-pin IC socket for mounting on a printed copy to ensure that it matches the scale for printing on a sheet of transparency and PCB …