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--- raspberrypi:blackoutdetector [2013/11/10 00:03] – rlunaro
+++ raspberrypi:blackoutdetector [2024/10/05 17:02] (current) – removed rlunaro
@@ Line 1: / Line 1: @@
-====== A blackout detector for the Raspberry PI ======
-===== 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 |}}