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I'm new to electronics and I want to control a device using a temperature as an input.

Right now I saw this video on youtube and want to follow it as well as know what the components are for.

https://www.youtube.com/watch?v=PkRJBQgjLrc

From the video I know that the NTC MF52-103 is the temperature sensor and that its output is a resistance. I just don't know how to set/configure the resistance to the temperature I want to control as well as what are the purpose of the two other transistors.

Fan circuit 'diagram'

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    \$\begingroup\$ I'm not going to watch a video of unknown length, and look for the schematic diagram and the parts list. Please post a screenshot of the circuit and a list of parts. \$\endgroup\$
    – JRE
    Commented Aug 8, 2019 at 5:57
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    \$\begingroup\$ Youtube videos are the last place to get this kind of information. Written descriptions with clear drawings are much more useful and easier to work from. \$\endgroup\$
    – JRE
    Commented Aug 8, 2019 at 5:58
  • \$\begingroup\$ Like this one that includes a description of how it works, and a clear circuit diagram. \$\endgroup\$
    – JRE
    Commented Aug 8, 2019 at 6:02
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    \$\begingroup\$ What is it you want to do? You say you want to follow the video, but I watched it for about 30 seconds and it had no schematic (except a very crude cartoon) and had a fan going all the time. Is this what you want? Or do you want something to turn on at certain temperatures, or maybe off at certain temperatures? If so, what? You need to describe your goals a bit clearer. You should edit your question, stating your goals at the beginning, then say what you have tried, which can include the youtube video. Depending what your exact goals are, the circuit in that video may be no good for you \$\endgroup\$
    – MCG
    Commented Aug 8, 2019 at 7:49
  • \$\begingroup\$ I added the closest thing that the video had to a schematic. For more information about what a schematic is, if you are unfamiliar, please see: electronics.stackexchange.com/q/105136/2028 \$\endgroup\$
    – JYelton
    Commented Aug 8, 2019 at 22:20

3 Answers 3

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You could do something like in the schematic below. Let R2 be your NTC. It's probably best if you replace R5 with a potentiometer do be able to adjust your threshold. As long as V+ of the OPAMP is lower than V-, its output is pulled low so the LED will not be lit. With the temperature increasing, the reistance of R2 will drop and V- will sooner or later be lower than V+, so the OPAMP will pull the output high and the LED goes on. This just works well if you have one specific temperature threshold wo which you can calibrate the circuit. Keep in mind that NTCs have non-linear characteristics.

schematic

simulate this circuit – Schematic created using CircuitLab

In a next step you could replace the simple comparator with a so called Schmitt Trigger to prevent the LED from flickering when the temperatur is exactly at your threshold.

Edit: I just saw that the video is a fan controller and not a temperature depending LED, so what exactly do you want? The video explains pretty clear what components are used and how they're assembled.

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I'd throw an ATTiny at it: use an ADC input to measure the NTC resistance, convert that to a PWM value to drive the load (LED or fan? OP isn't clear.)

Here's a whole appnote doing just that: https://www.microchip.com/wwwAppNotes/AppNotes.aspx?appnote=en592120

Don't want PWM? Change the code to make the two PWM values: 0 and 100%.

ATTiny also has an internal thermal diode, so no need for the NTC if you don't care about exactly where the temp is being measured.

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This circuit will do that

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ This is not a very useful circuit for OP. The question states they are a beginner, and states they are unsure what the purpose of transistors are in the youtube video of a simple circuit. This is clearly going to be way beyond them to understand. \$\endgroup\$
    – MCG
    Commented Aug 8, 2019 at 8:25

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