Bad battery choice

Sat, 21 May 2022 00:00:00 +0000

Shelly sells a smarthome sensor called Door/Window2. It works well, use wifi, is very configurable and can be used locally, without cloud. Unfortunately they’ve chosen a weird, expensive battery option, CR123A. It can cost around 70 NOK (~10 USD), and does not exist as a rechargable option. And you need two of them! So what do you do if you only have one left?

Use a single, abundant 18650 instead!

It fits almost perfectly, has higher capacity and can be found in any discarded electronics. They are always rechargable, and most have an included protection circuit.

The CR123A is 3 V, so two gives 6 V. A standard lithium-ion is 3.7 V (2.7-4.2 actually), but this still works. The ESP8266, which the sensor is based on, can in theory run on 1.7-3.6V.

Unfortunately the cover is just a bit too narrow for them. May need to design a new one suitable for 3D printing.

Edit: Never mind, someone beat me to it! Shelly DW2 18650 Case

Non-invasive graphing of energy usage

Wed, 01 Apr 2020 00:00:00 +0000

“If you can’t measure it, you can’t improve it.”

Reducing energy usage is hard if you can’t see it. Here’s a cheap way to graph home or office energy usage.

By reading data from the energy meter, one can get super accurate, real-time usage data.

I’ve used:

A smart home controller, Home Assistant
A graphing system, Grafana
A micro controller, esp8266, ~$5
An LDR sensor, $1

You need some familiarity with all of the above to set this up.

Here’s my energy meter:

It doesn’t matter which one you have, as long as it has a LED that blinks each X kWh used. I’ve written software for the esp8266 in MicroPython, called esp_energy_meter, that measures the time between each blink. It works great, and I’ve had it running for several locations for years. See the gitlab repo for more info on setup.

When you have this set up, you can combine it with real-time energy prices to get full control of your energy usage. And then it’s time to adjust your usage based on pricing. =)

Smarthome on falkp.no/blog

Bad battery choice

Non-invasive graphing of energy usage