Power outage alarm

RE: Power outage alarm

kmikemoo — Sun, 27 Jul 2025 17:23:21 GMT

EdgarAndre I'm sorry to hear that you had to return the sensor. It has a 4.3 of 5 rating with over 2,500 reviews. Also remember that people are much more likely to leave a negative review than a positive one. The system is skewed towards the negative.

You can replicate what this was going to do with you Pico and a temperature sensor - such as the DS18B20, DHT11, DHT22 or LM35. I'd still go with a small piezo alarm. Since it seems like you really want to build one, pick up a LiPo battery and charger module (TP4056). Use that to power the Pico and charge the battery. A single 18650 battery should be sufficient. With normal power available, the system runs off of the wall wart. If the power goes out, it runs off of battery. The only downside is the cable that goes into the fridge and/or freezer for the sensor.

RE: Power outage alarm

EdgarAndre — Sun, 27 Jul 2025 16:36:46 GMT

I just returned the freezer and refrigerator alarm I bought on Amazon because one of the sensors wasn't working. I also reread the comments from other dissatisfied buyers and there seem to be reliability issues with the thermometer's accuracy and overall build quality. However, I found a circuit that seems interesting and I'll give you the link. If you have the time, I would appreciate your feedback. Leaving a light on isn't ideal, but since I would only be using this alarm at night for severe storm warnings, it's acceptable. I will obviously use the smallest Dell bulb possible.https://www.instructables.com/Power-Outage-Alarm/

RE: Power outage alarm

EdgarAndre — Sun, 27 Jul 2025 16:22:19 GMT

On this alarm you can set the temperature at which the alarm will sound. So I can sleep easy knowing that if the temperature of my freezer rises to -5 celcius (23 F) the alarm will sound.

RE: Power outage alarm

kmikemoo — Fri, 25 Jul 2025 16:13:20 GMT

EdgarAndre Good choice - both on the device and the decision to use an off the shelf product. Now you have the protection AND you don't have a time constraint to experiment with your Pico. You also have expanded your project. Do you just stick with the temperature as a trigger or do you still pursue the time after power failure route? Welcome to electronics - where every project begets at least one additional project.

RE: Power outage alarm

EdgarAndre — Thu, 24 Jul 2025 20:42:18 GMT

I want to thank every one for your suggestions and help. Here is what I ordered for now and it might be a permanent solution if the product is good.

https://www.amazon.ca/ORIA-Refrigerator-Thermometer-Wireless

RE: Power outage alarm

EdgarAndre — Thu, 24 Jul 2025 20:34:33 GMT

I just orderd thi freezer alarm from Amazon. This might solve my problem. But since i bought a Pico 2 Starter kit, I will start learning the basics when the weather is bad outside. Thank you for your help. https://www.amazon.ca/ORIA-Refrigerator-Thermometer-Wireless-Restaurants/dp/B07B9QF64N?crid=3UFJ7T6Q9FI3C&dib=eyJ2IjoiMSJ9.b7EA6KGf2SVSRMGHCiX3e2uweqKHN7wxVytXzAykKVXO-6WQ-jBt-DL9F0saGYpCfFVD5XYryGSUkAvh8NuqDAIx_XAmsQBpAHeFrOo-A2lTckZ7KI5RwoDSWmEq9W59DYPIEnSBHKp6CRktTBuqvaoU410LMTiHXoSVu7zyWbbb2s55gVjzk_jtbLEuzjyaiL9up5v4rvzApHKYtob5Px_3TSAGHn6_1bfv_Mq-KMZx3b8xGwFcotZl_XPrRFLIb-UqFiHdLVqbFPJw_LfddJMnSFt1CNVjQHlFFtx3GjI.cQkrAV0WciOPkDIc8c2Q1LncWYbIZgYyv1XVfi2rzE0&dib_tag=se&keywords=oquimax%2Bfreezer%2Balarm&qid=1753388793&sprefix=oquimax%2Bfreezer%2Balarm%2Caps%2C82&sr=8-9&th=1

RE: Power outage alarm

EdgarAndre — Thu, 24 Jul 2025 14:44:00 GMT

I dont want to to be awaken as soon as there is a power alarm. Not even for a 10 minutes. Two hours is when my freezer needs to get cold again. Hi like the solution from Beacon_Dave and will try it.

Could perhaps just use a Wallwart PSU into a relay to do similar. Power goes off, relay drops connecting battery power to the Pico, which then starts a 2h countdown timer to trigger a buzzer. If power comes back on before the 2h elapses, the relay closes, power is removed from the Pico.

RE: Power outage alarm

kmikemoo — Tue, 22 Jul 2025 16:26:24 GMT

shabaz Many years ago, I put my router on a UPS. The first outage proved that my ISP had NONE of their equipment on UPS's. 😆 Nor did they have backup generators. I can only hope that they have improved. 😂

RE: Power outage alarm

EdgarAndre — Tue, 22 Jul 2025 15:30:39 GMT

Thank You so much for your help. It is really appreciated. I will also use all the great comments from the other members to help me realize that project.

RE: Power outage alarm

BigG — Mon, 21 Jul 2025 22:13:39 GMT

For simplicity, you could buy an Adafruit Feather RP2040 board and add a lipo battery for back up power. Just plug a USB cable into a suitable plug-in wall charger and connect the Adafruit Feather RP2040 board to the USB cable. This will ensure the lipo battery if always fully charged.

Then just monitor the voltage on the USB pin using a voltage divider. This voltage will be 5V when you have mains power and 0V on power failure.

RE: Power outage alarm

BigG — Mon, 21 Jul 2025 21:59:29 GMT

Agree.

In my opinion, an off-the-shelf alarm is a good starting point, as you need a safe way to detect the mains power failure. Then you can modify the off-the-shelf product to suit your purposes.

A good starting point could be one of these power failure alarms (commonly available on Amazon).

https://www.amazon.com/dp/B0CLDKRG7W/ref=sspa_dk_detail_0?th=1

For example, I would disconnect the piezo alarm and use the alarm input trigger as an input into the Raspberry Pi Pico board to safely create your own logic and alarm output etc.

RE: Power outage alarm

colporteur — Mon, 21 Jul 2025 21:29:51 GMT

I just had cause to setup a NUT (Network UPS Tools) server on a Raspberry Pi. technotim.live/.../

The server is monitoring an APC 1100 UPS that carries the network's edge router. AC power fluctuations are common since we are a rural company. The UPS keeps the edgerouter up during power issues. It doesn't insure a complete network but does maintain the edge device. If there is a power issue the NUT server monitoring the UPS. When the battery is on its last legs. It then tells the edgerouter it has to shutdown.

If EdgarAndre project had access to a UPS that has a serial output, the NUT server provides all the management tools to deal with power. The electronics involved is a USB to serial cable, the current Raspberry Pi Lite 64 bit O/S and a network cable. Simple solutions with lots of capabilities.

RE: Power outage alarm

robogary — Mon, 21 Jul 2025 20:35:15 GMT

ROFL - I got qty 16+ of RPI Picos on a shopping cart to use for teaching a class at the library, and a Pico W. I ended up donating at least 10 to our local VoTech School, and still have a bunch of Picos. I still have a bunch of Arduino Nano clones that I bought many years ago for less than $2 each. I just keep recycling them, very few have failed.

I really really miss bi-monthly E14 project contests and Tariq shopping carts.

RE: Power outage alarm

shabaz — Mon, 21 Jul 2025 20:27:25 GMT

Interesting! I'd not heard of this issue. Poor squirrels!

I've done the thing beacon_dave mentions in the past, i.e. small plug-in mains adapter holding a relay energized, but for a different purpose, which was to maintain my home router during a power outage. The relays de-energized fast enough that it's possible to switch to a battery pack of (say) 8 x AA cells to have a backup 12V supply to the router (without the router resetting).

RE: Power outage alarm

kmikemoo — Mon, 21 Jul 2025 19:34:22 GMT

robogary The Pico 2 may be overkill, but at $5 each... they're quite affordable. 😆 I think I still have 5 left from my initial impulse buy when they first came out. And then there's still those "salvaged" original Pico's from the other projects I lost interest in.

RE: Power outage alarm

beacon_dave — Mon, 21 Jul 2025 19:12:00 GMT

Could also perhaps use something like a PowerBoost to act as a mini UPS if you want 'always on' processing power for future features.

Monitor the state of the USB power to start/reset the 2h timer.

The likes of a Feather RP2040 or similar might be a neater all-in-one solution.

RE: Power outage alarm

kmikemoo — Mon, 21 Jul 2025 19:11:20 GMT

shabaz I understand EdgarAndre's desire for the 2-hour wait. At the last place we rented, the squirrels would regularly trip the main feeder breaker. The outage would typically last 45 minutes to an hour. Why get woken up an hour or so before your normal alarm when you can't do anything about anything? ☺😆

These days, the battery backup sump pump alarms as soon as the electricity fails so no sleeping in there. We also don't lose the main feeder where I currently live. Maybe we have smarter or less conductive squirrels.

I also immediately went to Amazon to see how much a commercial unit would cost. None of them had a time delay. 😂😂

RE: Power outage alarm

robogary — Mon, 21 Jul 2025 17:02:41 GMT

because that takes all the fun out of it. I'd also agree that a a purchased solution is likely alot safer for someone that isnt well versed in electronics and electricity. Avoid the sparkies.

RE: Power outage alarm

robogary — Mon, 21 Jul 2025 16:58:51 GMT

good idea. that suggestion works and is probably about $100 less expensive than a TDAD relay.It relies on the author simplifying his functional spec. I had also given some thought too for using a quad 555 timer IC especially since likes 9V. one 555 for a 2 sec "blip beep" and another for a 2 hour "wake me up firehouse alarm". Pico 2 is way overkill unless someone wants to go full IOT Pico W or start sending emails.

RE: Power outage alarm

shabaz — Mon, 21 Jul 2025 16:55:16 GMT

If you're a beginner, you could just try some beginner projects, they may get you halfway there.

The first project is usually a blinking LED. If you can blink an LED then you can pulse a buzzer with not much more of a leap, using say a relay module. Try controlling the blinking with a button input. If you can do that then it's not too dissimilar to getting a power status signal to know when the outage has started.

Get familiar with loops, if/else and while statements, all of which are useful tools to build up the behaviour you may want.

If you're looking for a ready-made solution rather than developing it yourself, then there are fridge alarms for not a lot of money.

But personally I would want to be notified immediately, not after two hours, just in case I'm not home. But that entails a different solution.

We had a few brief power outages one morning last week. It was interesting seeing the complete lack of business continuity plans from some of the major retail chain stores near me.. they gave up and shut for the day. On the other hand, it was a bright, warm Friday, the staff probably were not too motivated to look for an alternative solution : )

RE: Power outage alarm

anniel747 — Mon, 21 Jul 2025 16:46:07 GMT

[deleted]

RE: Power outage alarm

beacon_dave — Mon, 21 Jul 2025 16:29:39 GMT

[quote userid="153409" url="~/technologies/experts/f/forum/55975/power-outage-alarm/229602"]You could also use that relay closure to power up the Pico 2 , and then provide the additional features you want without summing power supplies and attenuating analog circuits to check the power levels.[/quote]

RE: Power outage alarm

robogary — Mon, 21 Jul 2025 16:07:49 GMT

if you wanted to keep it simple and be successful, find a time delay after de-energization relay (TDAD) relay with the coil voltage and freq the same as the power supply feed for the fridge and freezer. One example is ABB 1SVR730120R3300 Time Relay, OFF-Delay, CT-ARS.21S, 24-240V AC/DC, 0.05s - 10 min, 1 SPDT. It doesnt have the elegance of all the features you want, but after 10 minutes of power loss, a N.C. contact can connect a 9V battery to a buzzer to wake you up and remind you to start the generator.

You could also use that relay closure to power up the Pico 2 , and then provide the additional features you want without summing power supplies and attenuating analog circuits to check the power levels.

This is the control power circuit for the RPi Pico 2. SYS input isnt rated for a 9V battery input, maximum of 5v. You'll need a buck power supply to step down the 9V to 5V ish and a blocking diode so it doesnt backfeed the USB.

RE: Power outage alarm

EdgarAndre — Mon, 21 Jul 2025 15:20:17 GMT

Thanks for your help. As power outages become more frequent due to storms, I need an alarm to save the contents of my freezer and refrigerator. I want to be alerted while I'm asleep after a two-hour power outage to start my generator and prevent these losses.

RE: Power outage alarm

robogary — Sun, 20 Jul 2025 21:25:22 GMT

Sounds like a school homework project. Here are some hints.

Firstly, you need to look at the pico power supply circuit.USB is 5v . Vin you are saying is 9v, but inside its converted to something else. There should a blocking diode provided so the USB volts doesn't backfeed the Vin if Vin gets lower than USB.

Use a voltage divider to attenuation the voltage of both USB and battery, and bring in as analog inputs. Use code to set limits and the levels for making low voltage alarms. You'll want to know if the 9v battery is OK.

Use a counter or real time clock for elasped time. The 2 second delay is easy code, proably an interrupt would be

Use a piezoelectric buzzer for the alarm. There are integrated circuits that find the buzzer resonance and drive it there so they are really loud.