Remote thermometer

It really does depend on the distance from transmitter to receiver.

I bought something similar from Maplins 4 year ago but the transmission range is limited, OK for my back garden but I don't know whether it would be useful to you.

I will dig out the instructions and check max range.

Potty

Easy, find someone sleeping rough localy, offer him a bed under your staging in green house provided when you call him from your back door he shouts out the relevant temperatures.

A powerful telescope?

I've got an Arexx sensor in my greenhouse, and a USB base station in my home office. Dunno if that works out cheaper than Maplin's "Fine office" weather station *(currently discounted to 60 quid).

Arexx do a sensor that copes with a longer distance, but mine is only just 50M and its a bit touch and go - greenhouse glass, a hedge, and my office window to travel through. Having said that, it gets enough readings that you can see the shape of the graph, its not as though the temperature changes every minute.

TEMPERATURE LOGGER

The Arexx system looks good if the range is suitable, currently around £80 for the base station and 2 sensors but you can add more as and when you like. An Am@zon reviewer indicates that he increased range by improvising with a wire coat hanger.

I know the RasPi would work but I don't know enough to know how it would work, we have one at home but I'm new to Python and electronics, but as I understand it the problem of using the pi remotely is maintaining a stable power supply? We're about half a mile from the plot so if you could expand on this bit I'd be really grateful!

The Arexx system looks like its a good 'off the peg' solution. Standard sensor is up to 40m which i think would reach the greenhouse but might be pushing it for the hotbox. System with 2 sensors is about £60 and £15 for a similar sensor or about £30 for an external long range (90m) sensor.

So assuming I had:
Base (£60)
Greenhouse Air Temp (£0)
Garden Air Temp (£0)
Hotbox Air Temp (£30)
Hotbox Soil Temp (?? ideally a wire probe) ??(£30)

Plus I'd need to have some form of permanently on PC which if it'll work on a RasPi will cost £30, or if not I need a windows PC...

Mmmm...

The build my own option: TinyTX Wireless Temperature Sensor PCB seems like it may be much cheaper... but need to work out if I have the time ti spend on the build given that the hotbox is filling this weekend and so I have about 3 days before the temp should start to rise...

Arexx do have a sensor with a remote probe. Not sure if it is suitable for soil rather than air though (or even if there is a difference!)

If you are rolling-your-own then the 1-wire sensors might be worth a look. Remote wireless transmission is a bit of a bear with them ... but I have done loads, daisy-chained on some CAT5 (bell wire might well have been good enough ) and that worked well for logging temperature from multiple sensors.

Sorry must have been composing my post while you posted yours.

If I was going to use the Fine Offset unit that I've used before I'd have put it in the greenhouse with a Pi in there and then WiFi'd the Pi back to the house as that should be well in reach of WiFi. That meant the only remote power I needed was for the Pi (FO has battery power or USB).

Hadn't done any calculations on that I was assuming a couple of 7Ah 12V batteries and a solar panel would sort it out. My only solar experience is on a caravan which is only used at weekends during summer. However having now looked here: Solar Powered Raspberry Pi - Raspberry Pi I can see that solar power will be a very expensive feature... Especially as the FO doesn't do what I want as its only got 2 temp sensors and I want 5 or 6!

The only difference is it would possibly need waterproofed but thats easy enough.
From what I see of their probed unit its a seperate unti for the probe. Would have been good if the probe box had an air temp sensor in it too..

I can't wire directly to the house. I could wire all to one point on the plot and then 'beam' it to the house. Would need to learn how to beam it!

Would suspect I'd put a Pi in the house to receive the beam as that doesn't have a PSU issue...

Advantage of Roll Your Own is if I want a humidity sensor in the future I'll have the ability to upgrade. Or a soil moisture meter. or a robotic arm to open the green house window controlled by my Smart Phone... Possibly for little extra money?

The (battery powered) Fine Offset base unit will store entries on a round-robin basis - so you could rely on that storing them until they are "asked for" perhaps?

Will the Fine Offset transmit that far? If so then job-done. Base unit in the house and each time PC turned on it can download the data (I use Cumulus [freeware] software as the stuff that comes with Fine Offset is "sub par" ! )

Perhaps CONFIG the Fine Offset to log entries more frequently than normal? Cumulus will query it however frequently you like, but when PC is off then you only get the granularity that the Fine Offset is Confg'd for. Bit of a bore if you get a power cut because of some exciting weather event and the Fine Offset reverts to twice-an-hour and you miss all the juicy bits of the data! (More frequent readings will fill the buffer more quickly, and force the Round-Robin to overwrite, of course)

Thanks for that, and for the great link as well.

I like their in house solution using the DS18B20 waterproof sensors and uploading the data to Xively.

That would work for me for the greenhouse soil and air, outside soil and air and garage ambient and propagators.

Allotment is out of the question at that price although I do have 2 deep cycle batteries.

@Kristen snag with the FO is it is one outside temperature unit and one in the base unit. So I could use the temp in the base unit as a second temp (say in the greenhouse) but it only talks to the PC via USB so I'd be back to the problem of needing a PC (aka the Pi) in the greenhouse.

You can set it to store data every 5 minutes, although you can download every 48seconds. I use PYWWS to do all my work to it. Temp rarely fluctuates much and I was thinking 10 or 15minute intervals.

Even at 5mins the FO will hold 2 or 3 weeks worth in buffer.

@JohnJohn
I'm currently looking at using the 1-wire bus system as its expandable and extra probes are cheap which means I can have soil and air for very little money. So thinking: Hot box - Mid Heap, Soil, Air (?+Humidity); Greenhouse - Air (?+humidity), Soil, Outside - Air, Soil.

That would be controlled by something called a HA7S which can be directly connected to a serial port of a computer. Should make testing easy.

Then I think, I'm going to bridge the wireless bit using a CISECO's Slice of Radio on a RasPi and the SRF Radio at the other end. As I understand it that will talk to the HA7S as though its plugged directly into the serial port on a computer... ...remains to be seen!

SRF power consumption is about 36mA during transmit. HA7S about 3mA and each probe is about 1.5mA. You need to power the probe for about 1.5seconds to get the data back. Lets assume I have 9 probes (counting humidity as a separate probe). If I assume I need 5 seconds per probe thats 45 seconds and I'll be happy if it does the comms in <1minute, and I'm going to assume its messy and every probe is powered for that 45-60seconds. I'd just do 6 times an hour. ( 9 x 1.5mA ) + 3mA + 36mA = 52.5mA - I'm going to assume it consumes 60mA while running., 60mA for 1/10th hour = 6mAh. Was thinking of running it from 2 or 3 x AA 2100mAh rechargables - would last 210hours before reaching 40% charge. So nearly 9 days. If thats all I'm getting I'd look to put a small solar cell in to top that up. If in reality I can run it at under 40mA while transmitting I could increase that endurance and if I can trim back the transmission time to 15seconds I can quadruple that.

There is a background sleep mode that draws 123uA and a deep sleep that draw 0.2uA. I think I'd need to be in sleep mode so mustn't forget 3mA a day of background. But if it was sleeping and nothing else it would last 420 days! Just need to figure out how it wakes up!

Anyway reason for all this info is that the SRF has the option of a replaceable antenna which I've read can get you some pretty good distances covered - might be an option but I'll come back here once I've started playing and post results,..

Yes, I agree with all your points about Jerry-rigging a weather station. Not especially cheap, and some redundant bits - much wind in your greenhouse?

Dunno what your skill set is, so sorry if you are skilled-in-the-art, but I found a book called something like "Make your own weather station" (based on 1-wire sensors) very interesting. There is (or used to be) a forum dedicated to readers / followers of the book

Thanks for taking the time to go through this, as I said, I'm new to electronics but having looked online I get the function of the HA7S but I'm going to need to read more before I fully understand it!

That looks really interesting- The Slice of Radio suggests up to 1Km line of sight with a whip, the SRF over 3Km which I find astonishing. Having just done a rough line of site on google earth I recon we are about 700m from the plot so I would be very interested to know how you get on. Thanks again.

More than there should be when the windows have been blown out !!!

My skill set is I can wield a soldering iron and burn my fingers with it like the best of them!

In reality I'm a tech geek but generally confined to telling a computer to do something for me. I don't yet have a RasPi but its right up my street... ...been using linux systems for about 15 years, have various servers that I have built. Have a router at the Sailing Club linked to a FO Weather Station and a Web Cam that provides 'live' weather etc. But all that is plug and play, sorry plug and reconfigure loads of linux config files and eventually play! None has needed a soldering iron!

I designed a few low tech logic circuits a few years back and got some of them to work. Never done anything that interfaced to a computer.

one-wire was completely new to me till you suggested it.