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Table of Contents
Notes for BCSS Southampton branch
Notes on sensors etc.
for the meeting on Tuesday 5th May 2026
Outline
- 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.
- Or you might look at the weather forecast and hope it's correct.
- 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.
- Some companies started to develop their own different protocols, but these would lock you into using only their products (just like Apple does).
- 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).
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, unconnected) from lounge
- Ohio Scientific display unit and remote sensor
- Large laptop (Crocus) with Samsung monitor
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:
- hysteresis
- “many thermostats on the market leave a very great deal to be desired”
- “Many seeds need a diurnal variation in temperature to germinate.”
- Heating pads and soil warming cables
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.
Add a link to the article.