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Author: dvalin
To: dng@lists.dyne.org
Subject: Re: [DNG] question on programming (maybe OT???)
On 23.03.24 08:08, o1bigtenor via Dng wrote:

> Now if the more reasonably priced sensors actually used RS485 or

> 20 mA systems then this would be quite a bit more straightforward.

> As it is - - - well at present for me anyway - - - its going to take a

> ucontroller with  something like a LAN8270 board (IIRC) attached to

> the sensor to get the information transmitted. There is a severe trade

> off between lower cost sensors and high cost sensors re: connectivity

> options -- - - - unless you know of some options (would be very eager

> to hear of such!).

Well, if +/- 0.5°C is OK, then just a cheap LM35 temperature sensor on

an arduino ADC channel will give 10 mV/°C. You could calibrate it in

icewater, then boiling water, and store correction factors in EEPROM to

maybe improve that a bit. Averaging repeated measurements helps

eliminate noise if running longer wires to several sensors for barn-wide


Commercial humidity sensors seem to be either cheap or good. A DIY unit

can be made from two temperature sensors, one dry, the other wet. A

wicking cloth in a jar of water can supply the moisture. One unit I saw

decades ago use a small block of plaster of Paris standing in water.

That would probably crumble too soon, and it might be best to epoxy the

LM35 inside a very small glass test tube to avoid corrosion. A humidity

conversion table in program memory would be needed, but it would be

cheap and potentially as accurate as anything else easily acquired.

Mind you, an HDC1080 measures both humidity to +- 2% and temperature to

+- 0.2°C, and interfaces to your arduino via I²C. It draws about 1.3 uA

while giving 11 bit measurements at 1 sps.


> Hmmmmmm - - - solar - - - very useful if you have lots of solar energy - -

> - here - - - not so much from end of Nov to mid Feb absolutely not

> unusual to have 30+ days that are overcast - - - means when needs is

> high there is little available energy.

Ah, here in Australia, high energy need is only in Summer, so solar is

usually there when needed. But wait and you'll have a warmer climate too.

In 1896, the Swedish physicist Svante Arrhenius wrote a paper predicting

5°C to 6°C global temperature rise for +50% CO₂. We now have 425/280 ppm

= +52% CO₂. I don't expect it is possible to turn it around below +3°C,

so it's best not to overinvest in defeating cold - it won't last.¹

Greenland is now losing ice at 30 Mt/h = 5 km³ per week, according to

the Guardian. (That's in Jan 2024. Don't quote me for year's end.)

> Some very very interesting ideas - - - I do understand that I'm not

> doing anything real new - - - rather I'm trying to do more of this as

> DIY rather than opening my wallet a long ways!

Anything you can do to produce food in a trying climate, without complete

reliance on an always functioning electricity network, will be a service

to all, I figure. Resilience is the keyword for the coming centuries. As each

+1°C allows the atmosphere to carry 7% more moisture, and cyclones are

steam driven, +3°C is 21% more atmospheric shenanigans even if it's only


¹ Unless you're in northern Europe and the circumpolar aircurrents lose

stability and let the arctic cold through. Granted, that's a risk.

Enjoy the tech, especially the DIY. At least you then know where to go

for repairs.