raspberrypi:blackoutdetector
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raspberrypi:blackoutdetector [2013/11/10 00:33] – rlunaro | raspberrypi:blackoutdetector [2022/12/02 22:02] (current) – external edit 127.0.0.1 | ||
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===== Intro ===== | ===== Intro ===== | ||
+ | |||
+ | This are my first steps into electronics. I have power problems at my current home, | ||
+ | with random blackouts that are driving me crazy. These are specially annoying when | ||
+ | you are out of home (vacation) and there is nobody there to put the big | ||
+ | switch again on. | ||
+ | |||
+ | Instead of complaing to the gods for my misfortune, I tried to workaround this | ||
+ | problem in the nerd's way: I have constructed a blackout detector that sends | ||
+ | me a message to my phone when the power goes off at home. So, if I am outside, | ||
+ | at least I will know it. | ||
+ | |||
+ | ===== The idea ===== | ||
+ | |||
+ | I one of those fortunate guys who have an UPS at home. It is not a powerfull one, | ||
+ | but at least is enough to save your data and prevent a disaster. Having this and | ||
+ | a Raspberry PI, the only thing is a power detector to wire it to the GPIO bus and | ||
+ | I will have my blackout detector. | ||
+ | |||
+ | I did this by stabilizing a spare power source from an old phone and tame its output | ||
+ | to 3.3V, the voltage needed by the input pins of the GPIO bus. | ||
+ | |||
+ | |||
+ | ==== Ladies and gentlemen, the power source ==== | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | I've started with this power source, and my initial idea was to use a simple | ||
+ | resitor to lower the voltage to 3.3V, but when I went to measure the output | ||
+ | given, I received a big surprise: the output was 8V, very far from the 4.5 | ||
+ | expected. | ||
+ | |||
+ | I've asked around and I found out that you can lower this value in a safe | ||
+ | way by connecting it to an voltage stabilizer. It is a circuit that outputs | ||
+ | some voltage regardless of the input voltage you have. | ||
+ | |||
+ | In essence, this is made by an integrated cirtuit called LM317, a pair of | ||
+ | resistors and two capacitors. Here is the schematics: | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | Picking the values of the resistors is the most complicated thing. To ease | ||
+ | it, I've selected one fixed and the other a variable resistor: by trimming | ||
+ | it afterwars you can fix the voltage to a very precise value. Moreover, I' | ||
+ | discovered how handy is it when the output voltage changed when I' | ||
+ | enlarged the output cable. | ||
+ | |||
+ | Here is a picture of the resulting circuit: | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | I've bought a box to protect it. Here is the final product: | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | ==== References ==== | ||
+ | |||
+ | |||
+ | http:// | ||
+ | |||
raspberrypi/blackoutdetector.1384039989.txt.gz · Last modified: 2022/12/02 22:02 (external edit)