MakeVember the 1st

ESP8266 Temperature/Humidity MQTT sensor.

So… I noticed a couple of #makevember posts on twitter.

I struggle at this time of year. The shortening days leave me with progressively less and less motivation. Less drive to complete things and a generally low mood. I snap out of it sooner or later – there is generally a point where I consciously start to improve my immediate environment and that triggers a virtuous spiral of “doing stuff” which makes me happy.

So.. Makevember is about making something each day of November. It’s not a big thing, nearly 200 people follow the Makevember retweeter. I think it was more popular a couple of years back. The original manifesto is at…

I’ve been following the Make shit Mondays topic managed by and I’ve found it a really useful thing. It has encouraged me to look at the things I’ve been doing and to recognise that they are achievements – even small ones count. I missed a few weeks falling into my “shorter days” hole and well, I need to be a bit more disciplined.

So can I find things to make every day for 30 days ? I listed all the things I want to do or have half completed and there were a lot of them. Over 30. So I’m not short of things to be getting on with and I might as well do it with a bit of discipline and document it.

So, with that in mind… Yesterdays making was a little ESP8266 and DHT11 temperature and humidity sensor which reports its values over MQTT to a RaspberryPI running OpenHABian.

The OpenHABian install was faultless, very simple to do and has set up a whole plethora of tools that I don’t currently understand. However, I’ve got a Mosquitto broker on there and it is listening to values from my little sensor.

The ESP-01S (I’m a few years late to the party) is quite funky, and the DHT11 carrier board handles the power supply, etc. So all that is needed is the software and there are many examples for it – so it’s a download and flash thing.

So it all works and I get information from the sensor… I can even use MQTTExplorer to plot graphs of my useful information.

Temperature plot
Humidity plot
Voltage Plot

This is neat. However, it isn’t doing what I want it to.

The sensor polls continuously – this generates a data point every 10 seconds or so. There is no need for this granularity, every five minutes would be fine. Most likely every 15 minutes would be OK. The 18650battery I was using to power it doesn’t last a day at the moment. I’m sure it can be made to last a month given careful design.

The heat generated by running continuously means the temperature sensor gives an incorrect result. It wasn’t 20 degrees in my workshop yesterday. I’d guess it was nearer to 12 degrees.

This means I need to investigate the low power mode of the module and rewrite the firmware.

I’m really happy with the 3D printed battery holder, but the “9900mAh” cells are a lie. They’re probably best avoided.

At the moment the values are fired off to the broker, but nothing more happens to them. I need to implement some kind of logging system. And other stuff. As these sensors are so cheap I’m intending to put half a dozen of them at various places on the property and see if I can develop some kind of temperature model. Maybe something that tells me when it is going to be sub zero and high humidity in the wood room so I can avoid flash rusting all the woodworking machines… which happened last year.

Topics that I’ve learned today…

  1. How to flash an ESP01S
  2. MQTT library
  3. Neat 3D printed battery box.
  4. How awful cheap 18650 batteries are.

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