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--- raspberrypi:blackoutdetector [2013/11/10 00:41] – rlunaro
+++ raspberrypi:blackoutdetector [2022/12/02 22:02] (current) – external edit 127.0.0.1
@@ Line 2: / Line 2: @@
 ===== 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 ====
 {{ :00.jpg?direct&200 |}}
+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:
+{{ :raspberrypi:03.png?direct&500 |}}
+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've
+discovered how handy is it when the output voltage changed when I've
+enlarged the output cable.
+Here is a picture of the resulting circuit:
+{{ :01.jpg?direct&200 |}}
+I've bought a box to protect it. Here is the final product:
+{{ :02.jpg?direct&200 |}}
+==== References ====
+http://www.learningaboutelectronics.com/Articles/LM317-voltage-regulator