LED lights up when something gets too hot. Works between 9-18 Volt. Simple schematic.
Please read the description/textbox first. Easy to make (with 2 NPN transistors (2 x BC 547) + a 5 cent Si diode) a warning light that indicates when something gets too hot.
CORRECTION to the video: somewhere I talk about "a silicon or germanium transistor", when I point out to the diode in the schematic. Of course I am talking about the properties of Silicon and Germanium DIODES (!).
The circuit is made with easy to find and cheap components, working between (say) 9 Volt and 18 Volt. Can be aligned/tuned. I found that even in some expensive cars (2022) that there was no warning light when the motor got too hot....
Or only when it got really too hot: thus when the motor could be (or was) damaged anyway (......). Say no temperature indication, at least as a minimal first warning.
This analog LED unit can help. It will, at first (you can set that with the 47 K potentiometer) show a faint glow, but it will/can surely show up when the motor gets too hot.
Of course: when you bind/strip the detection diode 1N4005 to the right place where you want to measure the heat (!). If not: the indication will not be OK because the diode (= sensor) is not heated up enough. That is logical.
Of course the wiring to the Silicon detection diode (the 1N4005) must be completely isolated, from the beginning to the end, where you strap it to a motor or a water tube inside that motor or the "block" or whatever appliance where you want an indication of a too high temperature.
And you have to interpret the light of the LED, that is analog technology.
So fasten the 1N4005 diode (5 cents) via that 2 meter insulated wire say to a water hose, or somewhere to the block of a combustion motor, the block of an electromotor and align the potentiometer of 47 K to “what you want to see when the material (motor or whatever) heats up to temperature X”.
That alignment via that 47 K potentiometer depends on what you want to see and what you want to watch over. Use a 47 K potentiometer of a high quality to get the best results, say a precision trimmer, that can be aligned with a mini screwdriver. High quality potentiometers are available everywhere, also in this value (47 K).
When HF stray fields of the (a) motor or of another HF source influence how the diode (and the Darlington) acts, try to damp HF influences with 100 N (300 V) capacitors. Is showed in the video.
That effect was not tested, sorry, but that is the direction in which to think when EM pulses influence the LED/Si diode temperature indicator.
Don’t worry by the way. It works and was tested. I am always interested in your evaluations.
And: use a bright RED LED, that will be visible during the day and the night.
To read the temperature and (possible) overheating of the motor or whatever appliance.
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