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I usually forget to turn off the geyser. To solve this problem, I want to create an alarm that will go off, 10 minutes after I have turned on the switch for the geyser. I'm a computer science student. So I'm not sure how do I even start. Any help would be appreciated.

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    \$\begingroup\$ Just set an alarm in your phone, it is the easiest one. If you want to create something just to get some experience with it, look around on the internet first and do some more research. \$\endgroup\$
    – JonathanG
    Commented Dec 16, 2020 at 12:54
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    \$\begingroup\$ Is this a 'real' problem you're trying to solve? Seems like an XY problem - why do you believe that it's necessary for you to be turning your geyser (aka water heater) on and off regularly? Surely it has a functioning thermostat and is reasonably well insulated against heat loss... \$\endgroup\$
    – brhans
    Commented Dec 16, 2020 at 13:11
  • \$\begingroup\$ @brahns This seems pretty common in developing countries. Even in an Airbnb apartment in a nice area of Mexico City I had to exit the apartment and start a gas water heater in the inner courtyard. \$\endgroup\$ Commented Dec 16, 2020 at 13:33
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    \$\begingroup\$ There are dozens of different ways to set an alarm: your phone, Amazon Echo Dot, alarm clock, kitchen timer, microwave oven or stove timer, etc. What about these are not working for you ? \$\endgroup\$
    – Hilmar
    Commented Dec 16, 2020 at 13:36
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    \$\begingroup\$ Buy an egg timer, mount the timer close to the geyser's switch. Set the timer to 10 minutes when you start using the geyser. You're underestimating how much effort it will take for you to acquire the skills needed to build your own timer. If you want to regularly build electronics projects then that is time well spend. If you just want to build this timer then it will not be worth your time. \$\endgroup\$ Commented Dec 16, 2020 at 14:02

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This is mostly a mechanical problem if you intend to start the alarm timer automatically. As we don’t have any information on that, I’ll assume that there is either a low voltage contact closure or mains is applied when the timer is supposed to start.

So now the problem is reduced to making an alarm indication 10 minutes after the start.

An easy solution would be to use an Arduino board. You could either program the board using the Arduino IDE or or use something like the gcc tool chain to write a bare metal program for the AVR chip.

All the program has to do is delay for 10 minutes and the generate whatever indicator you want, such as a port pin changing state to drive a relay through a transistor or a 2kHz signal to drive a beeper.

The program could be as simple as using library delay and PWM functions, or you could delve deep into the datasheet and use timer peripherals and interrupts. Adding a countdown display might be nice, though it starts to look a bit suspicious.

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