Esp8266 on falkp.no/blog

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

Solar panel to DC heater

Mon, 16 May 2022 00:00:00 +0000

In Norway electricity is the most popular form of heating for households at 96% (source). Pure 230V AC is a very high-level energy, and we don’t really need that precision for heating.

This is a project to see if easy, not-perfect, locally generated energy can be used to lower the heating bill.

Disclamer: this is mostly for fun. A more economic aproach would be insulation, heat pump, put on a sweater, etc.

# The plan

             ┌──────────────────┐
             │                  │
             │                  │
   ┌─────┐   │  ┌──────────┐    │
   │     │   │  │          │    │
   │ PV  ├───┼──┤ Heater   │    │
   │     │   │  │          │    │
   └─────┘   │  └──────────┘    │
             └──────────────────┘
                  House

A solar panel, with no controller or inverter, and a heater. Dumping heat in a basement that needs heating all year round.

# The problem

Solar panels have an optimal voltage, where they produce most power, and this changes based on light conditions. A proper controller (MPPT) is expensive, so I want to see if I can do without.

# Hardware

Specs of my first setup:

180 Watt panel (the most power I could get in a normal 12 Volt range)
100 Watt heater with fan (I’ve ordered a 180 W model too)
ESP8266 for statistics (with dht22, ads1115, acs712)

# Setup

The panel, wall mounted in a very sub-optimal location (shadows from people, walls).

Panel connections in
Current sensor
Relay to switch off
Connections out to load

The heater with fan. It’s tiny. The heater is a PTC, so I don’t think it will pose a threat if the fan dies. In front of it is a white temperature sensor, to see that we actually produce heat.

A micro controller, with an external ADC. The micro controller generates graphs and control the relay. The resistors by the ADC are a voltage divider, to scale down the ~23 Volts the panel can deliver to a safe 5 Volts the ADC can measure.

Unloaded the panel will be at ~22 V. With this load one can see that the output is only good when the potential keeps between 12-14 V. I have no way of controlling the voltage, except for changing to a smaller load (less effective heater).

Graph of power output. Totally this gave around 600 Wh on a mostly sunny day.

Green line is the temperature sensor next to the heater. Measuring right next to the fan, I’ve seen it at ~60 °C, but this one is placed a bit away. The orange line is a temperature sensor elsewhere in the room. The room seems to rise about 2 °C during a day. The gray field is cloudyness in percent.

# Conclution

So far this seems to generate heat as it should, but it will have to run for a pretty long time to earn back the ~1700 NOK I paid for the panel. I will test with different heaters to see if I find something that works better. A posibility is also to have several heater that can be switched on with relays based on the power available. A kind of very crude MPPT.

# Thermal

The panel seems to have some significant hotspots. Normal? Cheap panel?

The relay is producing heat, but waste heat isn’t a problem in this case. =)

The relay is pulling more current than a GPIO from the ESP is rated for, so it’s voltage regulator is getting very hot. Should probably fix that.

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. =)