Min Max Thermometer

Apr 08, 2025 Last reply: 1 year ago 12 Replies
S

We have a 'new' greenhouse (I put it up last autumn). I dug out an old-style mercury min-max thermometer and, whilst it does sort of work, when you try to reset it the "Max" pin resets, but the "Min" pin refuses to move.



Hence I want a new thermometer. Humidity measurement might also be handy but not essential. Remote sensing (readout in the house) also sounds like a good idea, but I would still need readings to be shown in the greenhouse itself.



I've looked at some of the remote sensor types, but I'm not sure if they would work, given our 22 inch thick stone walls and a greenhouse that is roughly 8 - 10 metres away (sorry about the mixed units).



Anyone got experience with these? Or any recommendations?



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J

Ours has always been reluctant. Try pressing and releasing the reset button repeatedly, or moving a magnet up and down around the marker.

I've had a few 433MHz weather stations with remote sensors. Range quoted usually 20m-ish, actual range about 4m through one external block wall. Radio control items always exaggerate the range possible. I built some Tx-Rx pairs using XBee modules with about one inch antennae, which could manage about 15-20m on 900MHz, but presumably most commercial thermometers use 433MHz.

Supply voltage matters a lot, the 433MHz modules available on Ebay and the like will operate over a fairly wide voltage range, but they need

12V for maximum range. Doorbells typically use some exotic tiny 9V or 12V battery to reach through a house. If the sensor uses a pair of AAAs, it probably won't have much range. We have some remote sockets with the controller using 3V, which reaches about 5m through one internal wall. Mostly.
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C

We got an indoor/outdoor thermometer a few years ago made by these people

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I can't see an illustration of exactly the same model but it has worked pretty well. The outdoor unit is seems to be able to transmit through several walls and about 20m distance without problems. It's only a thermometer with max/min over 24 hours, but it looks as if they also do hygrometers.

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J

Try swinging it at arms length (hold it tight!) letting centrifugal force do the moving. If that doesn't work a powerful magnet (neodymium) should move it. > Hence I want a new thermometer.

If possible put the receiver on a windowsill in direct sight of the transmitter. FWIW I can get reception from about 7m away through two brick walls.

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C

I've recently bought one of these

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off Amazon. Does most of what you want, although the outdoor sensor is 'dumb' and doesn't have it's own display. All the displays are on the indoor unit. I'm very pleased with it so far.

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J

I have something similar by TECHNOline. It works fine, but struggles at around 20m between transmitter and receiver.

I have a perfectly good Max/Min, but obviously not as precise. If the pin sticks and the push-button fails to free it then I take from the wall and whirl in circles and let centripetal force do the job. :)

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R

While we're at it, used one of these for a few years now:

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Works well with range down 3 floors to the cellar and outside to the garden, and records to an SD card - as you'd hope and expect for almost £200 . . .

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S

Now where did I put the bits from the last time I dismantled a spinning rust HDD? I knew it would come in handy one day. That said, if the pin sticks in place, I suspect it will carry on doing that.

I've looked at a number of 'indoor display + outdoor sensor' systems, and I am now divided between one of those or a simple analogue mercury min/max.

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N

Why not both?

(And then trying to work out which is right when they disagree!).

nib

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T

Are mercury thermometers still available?

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S

Given that SWMBO is a confirmed (and voluble) Luddite, I may do just that. After all, the greenhouse was built for her.

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C

Aren't they all alcohol these days? I also have a digital max/min - looks like an analogue max/min but no rising/falling liquid thread.

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