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Notes for BCSS Southampton branch

Notes on sensors etc.

for the meeting on Tuesday 5th May 2026

:NOTE: Tom Radford showed a small battery-powered data logger (similar to or identical to this one: https://www.amazon.co.uk/Temperature-Elitech-RC-5-Calibration-Certified/dp/B075B88C5B; there is a more expensive orange version which might differ only in having PDF export) which recorded temperature readings which could be downloaded via USB. He said they are certified for accuracy within a part of one degree, and are widely used in the chilled meat industry. The difference between such a data-logger and my approach is that the latter allows for remote monitoring and for actions to be taken either manually or automatically in the light of the data obtained.

Outline

"Stand-alone" sensors

They can tell you what's happening, if you remember to look at them.

  • Show an alcohol thermometer. You might have one of these in your greenhouse.
    • More sophisticated ones can be digital (show one of mine)
    • You need to go into the greenhouse to read it.
    • It's no use if you are at work or away on holiday.
      • A max-min facility can be useful if you can look at it at some time every day (the digital one here shows the minimum and maximum temperature and humidity for the last 24 hours, which removes the need to keep resetting it).
    • Or you might look at the weather forecast and hope it's correct.

Remotely readable sensors

So you don't have to go out to your greenhouse in the pouring rain.

  • Some sensors can be read remotely
    • Oregon Scientific uses radio waves (like Wi-Fi but using a proprietary protocol) to communicate with remote temperature sensors. Show mine (if I can get it to work reliably). This is what got me interested in the possibilities for remote sensing. I had two or three remote sensors in my greenhouse (actually a conservatory) for many years.
  • As well as sensors, some devices can be controlled remotely.

Remotely controlled devices

  • TVs have contributed to national obesity levels by the invention of the remote control, saving you the effort of levering yourself up from the sofa.
  • This where I got interested in remote controls - my mother's light switches.
  • Switch the light on and off using the IKEA Rodret push-button switch.

Multiple sensors controlled from a base unit

  • Some companies started to develop their own “smart home” systems, using their own different proprietary protocols, but these would lock you into using only their products (just like Apple does).
  • Some more recent devices from some companies appear to lock you in, but in practice they don't.
  • Recently, more open public-domain standards have been introduced, so that devices from different manufacturers can be more interoperable. These standards include Zigbee and Z-Wave (using the same radio frequencies that Wi-Fi uses, which don't need a licence for low-power use) and i2C (for daisy-chaining devices together by wire).
  • These standards mean that you don't have to become wedded to a single manufacturer and not be able to mix and match.
  • They also mean that it is possible for software companies and other groups of enthusiastic software developers to design and create sophisticated monitoring and control systems. These started to be called “home automation” systems, but that sounds rather like a 1950's view of the gadgets of the future. The preferred term nowadays seems to be “smart home”. (When I was young, that meant that your front doorstep was polished, your front gate was recently re-painted and you had net curtains in your front-room window.)
Smart home systems
  • Commercial:
    • Samsung SmartThings
    • IKEA (which uses Zigbee)
  • Independent, open source:
    • The advantage of open-source projects is that (if the members maintain their enthusiasm) they can react quickly to new ideas and add new features and support for new devices
    • Home Assistant (also Domoticz etc.)

Home Assistant appears to be the leading

Items to include

  • Sensors for temperature, humidity, light, CO2, soil moisture …
    • Battery operated / USB-C power / mains power
    • Communication by wire (incl. I2C, QWIIK), Wi-Fi, Zigbee, ZWave
    • Remote services e.g. local weather reports, forecast, etc. (basically using other people's sensors)
  • Hub(s) to receive data
    • Data storage and display
  • Control incl. mains sockets
  • Demo (with IKEA mini greenhouse)
    • Laptop (and Raspberry Pi) both with Home Assistant
      • with Zigbee dongle(s) connecting to
        • temperature and light sensors
        • soil moisture sensor in a pot of compost
    • Display temperature changes
    • React to high or low value
    • Control a fan and lights
    • Large (Samsung) and 17“ monitors for display
    • Internet using phone as Wi-Fi hotspot
      • to allow access to weather data
      • to present display on (this) website for view on mobiles at meeting
      • to serve readings, show dashboard and control devices from mobile phone

Things to sort out and test

  • Test the Ohio Scientific display unit and remote sensor
  • Test the weather station and (? Zigbee) hub
  • Install Home Assistant on laptop
  • Choose a Raspberry Pi and install Home Assistant on it
  • Test 17” as well as Samsung 22“ monitors on Crocus (and Raspberry Pi)
  • Use remote slide changer to make the laptop
    • change slide in presentation
    • move from one page to another on the web or in a Home Assistant dashboard
    • ditto for Raspberry Pi

Things to bring

  • Thermometer (alcohol) from hall
  • Thermometer (digital, max-min, with humidity, unconnected) from lounge
  • Ohio Scientific display unit and remote sensor
  • Large laptop (Crocus) with Samsung monitor
  • Zigbee sensors:

Notes on heating, lighting, etc.

for the meeting on Tuesday 7th May 2024

Heating

Carl Garnham's article is aimed mainly at seed raising, i.e. heating small spaces rather than an entire greenhouse:

Full article, including links to references and equipment: Thoughts on heating by Carl Garnham, SABG Newsletter no. 49 (August 2023)

Lighting

Growers of South African bulbs probably get more worried about light levels than succulent growers, because the former plants tend to grow in winter.

1. Always keep greenhouse glass, inside and out, as scrupulously clean as is possible.

2. If any particular plant/species is associated with shade in habitat, think carefully about possible lighting levels habitat v. inside a UK greenhouse.

3. Within a UK greenhouse, in winter, with clean glass and bubble insulation in place, light levels and insolation will be a small fraction (10-20%?) of the level in winter, in habitat, in RSA.

4. Remove bubble-wrap insulation when not required, although it may be needed during the winter, the time of least natural daylight (insolation) in the UK.

5. Providing truly significant supplementary levels of growth-promoting lighting (PAR) beyond sunlight in a UK greenhouse is neither simple, nor cheap, more so if using anything but commercial horticultural designs and very much so in winter.

6. Stimulation of flowering/extending photoperiod does not require major levels of lighting.

7. Experiment, with winter photoperiod, lamps, reflectors and positioning of lamps, and perhaps colour of lighting – there is no data out there for any plant that we choose to grow, so far as I have been able to find. (Just a prompt – is the glaucous colour of some plants seen in nature, which is seldom seen in many plants in European cultivation, triggered by total insolation, or by high levels of just one colour? It would be comparatively easy to massively boost a narrow band of colour if that was all that the LED produced (assuming that LEDs are available that produce that colour), which is what commercial horticultural lighting does.)

8. If anyone experiments, to come closest to understanding what is going on, a measurement device is needed; you cannot trust your eyes (a consequence of the amazing biological engineering that eyes represent)

Full article, including links to references and equipment: My first tinkering with artificial lighting for plant growth by Carl Garnham, SABG Newsletter no. 50 (March 2024)

Composts etc.

In an earlier SABG Newsletter, there is an article on cat litter as a potting medium.

FIXME Add a link to the article.