Recently we at @ttncat had to prepare a crash course on LoRa, LoRaWAN and The Things Network for a professional school in Barcelona. It was a 15 hours course that covered from the very basics to some more advanced topics on RF like link budget, attenuation or impedance matching. It was fun to go back to my years at college and revisit and update some of those topics. And at the same time it was a great opportunity to upgrade my toolbox.
I’d like this to be the first of a series of posts about radio frequency. Talking about tools and devices I already had and some of the new ones I now own. I think they might be of some interest for newbies and makers since -due to my budget- they tend to be low cost devices. At least I hope you will find it interesting to know they exist.
I don’t pretend to write these posts in any specific order but I’m just starting with what I feel is one of the most basic concepts, and it’s that a radio device outputs energy. So maybe one of the first questions is “how much energy?“.
So RF power monitoring is the first step to analyze how a certain radio sends data by quantitatively measuring how much energy it outputs. You probably know this is called “power” and power is measured in Watts (W). Radio Liberty (a CIA-founded organization meant to broadcast anti-comunist propaganda) had a facility in Pals, Girona, from where they could reach as far as Moscow. The facility consisted on 6 radio towers with an overall output of 1.5MW (that’s megawatts).
Some time ago I worked on a home project to get a notification when my washing machine had done its job based on monitoring its power consumption. There was a good reason for that, the machine was outside the house and I had already forgotten about the laundry several times. And when that happens your only option is to wash it again, because it really smells musty…
Monitoring your appliances
Use ESPurna 🙂
OK, there are different ways to get the info about power consumption. But since we want to be able to process the data ourselves most commercial products won’t be suitable unless we modify it.
Alternatively, those that use radio communication to send data from the meter to the base station might be suitable for a man-in-the-middle hack. For instance, if you own an Efergy power meter you must know you can sniff the data it sends using a simple RTL-SDR dongle.
But for most cases, your best chance is to get your hands on a commercial product with an ESP8266 chip in it and change the firmware to suit your needs. You can write your own or use an existing firmware like ESPurna, that already supports a bunch of power metering smart switches.
What info do you need?
The idea is to report (via MQTT) power data from each individual appliance very minute. You can then use Node-RED along with InfluxDB and Grafana (or Graphite) to receive, persist and graph your data like in the image below.
Lately I’ve been quite busy with the ESPurna firmware. It’s growing bigger and gaining some momentum. It’s really fulfilling to see other people using it and reporting back. But at the same time it’s very time consuming. Last Saturday I released version 1.5.0 with some new functionalities and bug fixes and I decided to use some of my free time over the weekend to work on a project that’s been waiting for a month in the shelf.
A few weeks ago I was playing with the Sonoff TH and I wrote a post about its sensor interface and the possibility of using lots of different digital sensors, including I2C sensors since the board can be easily hacked to export 2 digital pins over that interface.
And having I2C not only increases the number of potentially usable sensors but also opens the possibility of using I2C Analog to Digital converters to overpass the lack of analog inputs in the device. Here it comes the Texas Instruments ADC121 (datasheet), an 12-bit precision ADC with I2C support priced 2.74€ in quantities of 1.
Have you ever forgotten your wet clothing inside the washer for a whole day? I have. Even for two days. They smell. You have to wash them again and you know you might end up forgetting about them again!
Actually that is happening to me since me moved to an old house in a town north of Barcelona. Instead of having the washer in the kitchen, like we used to, now we have it in the cellar, in a place I don’t normally pass by to notice the laundry is done.
So I started thinking about monitoring the washer to get notifications when the laundry is done. And since I was at the same time playing with ITead’s Sonoffs, which has an AC/DC transformer and a powerful controller with wifi, it looked like a nice project to put together.