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I bought two switch relays, and connected them up to my Raspberry Pi. I can turn any device on and off, at my will! How, this person online has a more complicated schematics:

https://www.circuitbasics.com/wp-content/uploads/2015/11/Arduino-Temperature-Dependent-Light-Bulb-With-5V-Relay-Updated.png

He says:

"The thermistor part of the circuit is set up as a voltage divider. The value of the resistor should be the same order of magnitude as the thermistor. For example, I’m using a 10K Ω thermistor, so the resistor should be 10K Ω as well. If you use a 100K Ω thermistor, use a 100K Ω resistor."

What is a voltage divider? I am trying to follow the wires on the breadboard and it's doing my head in. Do I need to know about voltage dividers, and if I wanted to, is there a simple practical guide about them?

Thank you!

Merc
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    Have you tried searching for the term? – joan Jun 30 '22 at 13:45
  • That is why engineers use schematics, they are much easier to follow and generally impart more information. – Gil Jun 30 '22 at 14:53
  • In this case, a voltage divider simply acts to bring the voltage down into a range that falls withing the range of the Arduino's analog input. However, that's not relevant to the RPi as it has no analog inputs. – Seamus Jul 02 '22 at 01:20

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Citing https://en.wikipedia.org/wiki/Voltage_divider:

In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (Vout) that is a fraction of its input voltage (Vin).

Referring to the shematics in the Wikipedia article, red is Vin , black is ground, blue is Vout .

Red and black are also connected to the relay board as power supply, and green is the control signal for the relay board.

Your circuit may work without knowing anything about a voltage divider, but this knowledge might be useful for debugging if it does not work as expected.

I recommend to use a lightbulb for safe low voltage instead of connecting this to mains voltage. Use mains voltage only if you know what you are doing and have sufficient equipment for your own safety.

Bodo
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