A view from the fridge

Why the fridge? Well, having built various things for the tortoise, your normal host has been doing a good amount of research about hibernating Tilly. You need a good stable temperature of somewhere between 3 and 7 degrees which, you may well know is the sort of temperature a domestic fridge maintains. If you are shocked about the prospect of putting a pet in a fridge, don’t be, it is a widespread practice. Keeping a constant is important but getting too cold is not going to be good for her and too warm risks her waking up which also causes problems.

While a fridge aims to keep a good temperature, its own control system gives some variation and opening the door of course lets in warm air. The quest set was to see how stable the temperature is and what makes it vary. This is where some Shed Engineering comes in. You can buy various devices for simple temperature measurement which gives you maximum and minimum but if you want something that logs temperature, you are into industrial controls territory and lots of money. After being given a Raspberry Pi for Christmas a couple of years ago, there have been a couple of ideas for small projects that are in various schemes in different stages of development so why not have a go at another one.

Objective: measure the temperature of the box of soil in the fridge and record it so that worried tortoise owners can check on it.

I had already got a thermocouple unit so that we could calibrate the Rayburn oven temperature so as to burn the cakes less so we had a go using that. While that is good for very high temperature ranges, it is not great for sub-degree accuracy and early results showed things to be reasonably stable but not with the certainty needed.

The wonderful world of internet searches and open source development pointed me at a little device which would link up to the Raspberry Pi, allow regular, accurate measurements and be able to store them to look at them over time. The assembled nature of each of the hardware items meant very little construction was needed for the test and the various software tutorials  pointing you to the library files for the temperature board enabled very simple program to give spot readings. The Raspberry Pi Zero board shown below is the core of things for the processing and here is seen dwarfed by the cable connectors for the prototype.

The Pi

The fact that the operating system that is fairly normal for Raspberry Pi allows you to automatically run a program however frequently you like (a thing called Cron Jobs, which always takes me back to the time travel machines called the Chron-o-John in Day of the Tentacle, a game which distracted us from our final year studies for far too long, but that is another story) and has the ability to access web pages all means that we had something that sampled the temperature every minute and stored it in a database on a website for easy viewing where every you are.

Looking at a list of numbers is not that great. As much as selling my soul to Google goes against most feelings I have on the matter, looking for an easy way to turn lists of numbers into a nice graph without hours of coding led me to Google Charts which did just the job.

Having looked at the general temperature of the fridge, the box for Tilly was put in place and the measuring device refined slightly to make it suitable for being buried in the soil. This involved adding a small metal plate to one side to contact with the temperature measuring chip on the board and encapsulating the rest of the device so that it would survive being buried in soil which may be slightly damp.

Going Underground

The early results were promising in that the fridge appeared to be, and stay, within the required limits.

First Tests
It did, however, highlight a few obvious things.

The fridge has some sort of defrost cycle so every eight hours or so the temperature rises up a couple of degrees before settling back to its gentle wobble around its target temperature, varying just by the hysteresis in its control system.


Putting stuff in the fridge which is warmer that the bits already in there has an impact on temperature, but not necessarily in the way that you think. If you put something room temperature in the fridge, you would think that the temperature inside would go up. True there is more thermal energy in the box. However, it very much depends where you put the item as to what happens. If, as we found (and is actually blindingly obvious) you put the warmer thing near where the fridge has its temperature sensor, it will think that things are warming up and run the compressor for longer to overcome this. The result is that the already cold bits of the fridge get very cold until the vital area gets cool enough to register all is well. While it does not matter if your milk gets a bit of ice on it or a small corner of your salad drawer gets a little frosted, your tortoise is a bit more picky and wants to avoid permanent eye or brain damage.

Too Cold

A few months of observations and experiments led to the happy position of a bottle of water always stored next to the sensor to give a) a cold mass to generally act as a sink for things going in and out and the air changes when the door opens (acting as a temperature dampener) and b) a physical reminder that you do not want to put a room temperature thing next to the sensor. A bespoke device was rustled up to make sure the appointed bottle does not roll away.

Bottle Stop

A couple of other refinements were made along the way.

Wrapping the box up in foil covered insulation gave the box an even slower response time to changes in the fridge so gives a very smooth profile.


The link to the website also gives a few more possibilities. The script that uploads the data checks the information to see if the temperature is within limits. If it is not, you can have an alarm condition to send you an alert. This is set up to be via e-mail and text message. E-mail is straight forward from the web hosting and there are many SMS applications that allow you to send text messages. Most have a free introductory offering but inevitably, there is a small cost to an ongoing service. Hopefully things will be stable enough to mean that we do not eat through texts as too fast a rate. The tests so far look good.

Given that you can run cron jobs on the web hosting too, it is set up to check every ten minutes whether readings have been posted (they should be there every minute). If there has been no activity, it sends an alert warning of system failure. This is not 100% sophisticated in that the fault could be that the Pi has stopped working or that the home internet which links it to the page has dropped out or that the reasonable value web hosting (which incidentally is the same used to host this blog) is having an off day. It may also be that the power to the house has gone off (and hence so has the fridge). However, given the relatively slow response time of the soil mass in the fridge with a reasonable amount of thermal mass (the general stuff and extra bottles of water), a Pi Failure alarm will not require urgent response as it will take a few hours to rise up to anything worrying if the fridge has failed as well. Anyway, the alert is there and someone can look into it.

The Finished Article

Tilly is just preparing for hibernation now – no food and waiting for her insides to be empty before a bit of cooling down next week and into the box thereafter. If you want to see her comfort levels (if you can call 5 degrees C comfortable) have a look at the Tilly Temperature. Don’t fret about some of the variations in the past weeks and months, these were the various experiments. Hopefully it will be a smooth line over the next couple of months.

Here is the display squashed into a small box on this screen. The real page is a bit clearer.

In which there is a UFO (and a flying saucer)

Here is the flying saucer:img_5566-copy

The UFO being the Un-Finished Object:img_5565-copy

Complete with purple boots because why not? This one is for Small after Tiny nicked the flowery one. I’m not too sure about it – the tension is very loose, it is coming up the size it’s meant to I think but it’s a bit gappy, the overall effect is better than the individual pieces so it’s a sort of impressionist space blanket. He’s pleased with it anyway and he has inherited his father’s lawn sprinklery sweatiness so maybe a lightweight blanket is better… Us chilly people, however, need a monster like this to snuggle up with (excuse the cat, she is a law unto herself and wouldn’t be in the picture if I asked her to but insisted on being there when I didn’t want her):img_5567-copy

Having almost finished covering all the beds in the house with crochet I’d better start some Christmas knitting if people don’t distract me with things like this, (thanks Pip!), they’d need testing first before I made any for Christmas presents, wouldn’t they? And my slippers are always broken (except when they’re not). And these would be much easier to fix when they wore out. Plus there’s a small person who I promised a birthday jumper to last year and he has doubled in size now so I’d better do it quick before he grows any more! Time to cwtch up with a big blanket and Ravelry this evening and do some planning.

In which there is nothing much happening

I have been really bad at taking photos of things: Grandad’s jumper is finished, maybe he’ll have worked out how to work his new camera and send me a picture by the time it is cold enough to wear it. The grey cardigan is properly finished, it is cold enough to wear that but am not capable of taking a photo of myself whilst wearing it.  A blanket for Small (because Tiny nicked my pretty flowery one and he said it wasn’t fair) is started but I haven’t taken any photos of that yet either. Here is an obsessive photo of some beans.


Aren’t they nice?

In which there is a lot of catching up to do

I remembered my WordPress login, I updated all the stuff that I haven’t updated since March and I tried to upload some pictures but they are all bigger than 2MB and the silly thing won’t let me so now I have resorted to writing the words and hopefully the Man in the Shed will fix it for me later…*EDIT – He fixed it because he’s clever like that. Yay!*

Oops, I was going to write a new post in half term and it whooshed by like all the other weeks and I didn’t. This term has mostly been blankets, there was this one for a soon to be new baby which started off ok and then got ridiculously huge until there almost was no room for my lunch in my bag because it was full of blanket.


There was this one which was a Stylecraft Crochet Along thing which just had to be made because it is so pretty, you can still get the pattern on their website but I’m too lazy to look up the links, I’m just going for speed and actually getting round to posting something. That was a much more sensible size for my work bag because it is made of small hexagons. It has since been commandeered by Tiny for a bedspread although it isn’t really big enough. I added a couple of rows to the border because I had quite a bit of yarn left over and why would you end with a red and pink row if you could end with purple and blue?


There was this one which I started before the first blanket (but it isn’t a blanket) and then it got postponed in the middle to start the flowery one which in turn got put aside to do the rainbow one but they are all done now except the pockets on this. It isn’t meant to have pockets but I am incapable of leaving my phone in my bag and people tell me off if I keep it in my bra. It has got some nice cables on the back but you can’t see them because I put it up this way to dry.


The holidays so far have mostly been making hats, very good stash busting hats. There is a pattern somewhere, I can look it up if anyone wants to know but I am being lazy, as I said, this is also why the photos are wonky and not cropped and well, never mind, at least there is a post. The rainbow one is mine, the striped one is Tiny’s, the scary red one is Small’s and the white one that isn’t finished is for a friend who ordered a lacy one. The Man in the Shed declined to have one made for him, not sure why…


The Man in the Shed has been busy making an outside box (he didn’t do the bricks but he did do the cat proofing) for the So-Called Tortoise (so-called because she does appear to be a tortoise, I keep checking in case I’ve been mistaken and she is really a cocker spaniel or a greyhound but she remains stubbornly tortoise shaped) after only sixteen months stuck inside, poor thing, she is thoroughly enjoying it and I am deliberately planting weeds which goes against the grain a bit. She has been happily stumping around and sitting in the sun enjoying the flowers, I am starting to wonder if I am secretly a tortoise, we have a lot in common.


I’m nearly up to date now, I had about nine months of housework to catch up on so the first week and a half of the holidays was mostly cleaning and getting haircuts (Tiny is very pleased with hers and mine is at least tidier than it has been, I’ve only been psyching myself up to get it cut again for three years this time…) The place is nowhere near pristine but I made enough of a dent in it to show willing, both the small people’s carpets have been visible enough to hoover this month and there isn’t that much washing left.

The second week was swimming, tiling the utility room and waiting for the rain to stop among other things and I managed to sort out some new uniform before the week before school starts this year. When I say ‘sort out’ you realise I mean that there is uniform that fits in the house, I still have a thousand and thirteen iron on name tags to do… Ooh and we accidentally managed to sort out school shoes on a day out in Cheltenham which means I don’t have to drag the Smalls into Cardiff, hurrah! I just hope they don’t grow now.

Now it is the third week, it is the first and only week on the calendar with nothing on it, the sun is shining and the garden is calling, it’s a jungle and the vegetables have all gone to pot, mainly because I left them in the pots and didn’t have time to plant them out – the tomatoes have just about recovered but the brassicas didn’t make it out of the greenhouse thanks to a bumper harvest of slugs and snails despite the slug pellets and going out in the dark with a bin bag to catch them (that was a lot of slimy creatures in one night), I forgot to dig up any potatoes while they were growing and had to harvest the whole lot in one go yesterday (ooh, that hurt!)


I have finally managed to do some weeding (not very much yet but I managed to hack a path to the compost bin so that’s a start, I’m going back out as soon as I have written this) aided and abetted by my lovely and extremely thorough dad who started it off last week for me – there is one border which seems to have been all weeds and no shrubs by the look of it after he had finished but it is full of So-Called Tortoise friendly plants now: pansies, snapdragons, sow thistle and I’m trying to persuade some honesty to grow which I pinched from my grandparents in Hampshire but the soil is very different so I don’t know whether it will work. A couple of weeks ago he attacked a mountain of bindweed for me as well but I’m making him a jumper so I think we’re square.


In which I got slightly carried away making hats

I haven’t posted anything since half term. My life is now ruled by the school calendar more completely than ever. Counting terms it is a difficult habit to break when you leave school having spent three quarters of your life there, it was just about wearing off when my own children started school and it started to tighten its grip again but now, working in school, I am back to counting down the days of term until the next break. The Easter holiday starts tomorrow and I have time to catch my breath again for a little while.

This term I have mostly been making hats (and a green jumper that I started three times but I’ll tell you about that another day). One of the teachers at school is starting her maternity leave today and she asked me if I could make her some baby hats (I mostly sit in the staff room with my knitting to give me an excuse for avoiding eye contact), she said her mum would do jumpers and stuff but hats were too fiddly.

I have found though that the trouble with teeny hats is they don’t take very long and there are millions of patterns so it is very easy to get carried away and think, ‘That’s a nice pattern, I’ll just do one more…’, on the other hand the good thing about teeny hats is they don’t take very long, are very small and portable and good for knitting in the staff room without having to hide an enormous ball of green aran in the bottom of your handbag just to avoid accidentally giving someone a withering look when they are the fifth person that day to say, “Wow, that’s a big ball of wool!” (For the record it is 400g and a perfectly normal size for a 400g skein of acrylic aran.)IMG_4126

Anyway, I made a lot of hats and thoroughly enjoyed it and I even potted them up before I gave them to her. I haven’t done anything in the garden yet this year, is it showing? Sorting out the veg patch is on my list of things to do in the Easter holidays and I am hoping that BBC weather has got the forecast very wrong otherwise I won’t get far down the list.IMG_4128

My next mission which I had no choice but to accept (the enormous ball of green aran is on hold for a minute, at least for away from home knitting as it is a bit unruly but it was five pounds in Aldi and it is the sort of green that makes me think of Grandad so it had to be done) went something like this:

Me: What would you like for your birthday?

Tiny: A big teddy turtle.

Me: Oh. Right. Where are you expecting me to get you a big teddy turtle from?

Tiny: You can knit one.

Me: Yes. I could knit one.


Me: How big is a big teddy turtle?

Tiny: About this big. (Indicates about eight inches with hands)

Me: (Breathing a sigh of relief at how big ‘big’ is) Oh. Right. If I did knit one that is quite a small present, what would you like for your main present?

Tiny: (Looks around room for inspiration) A chair. I don’t like that one any more.

Me: Right. What sort of chair? Would you like a rocking chair?

Tiny: Yes, a rocking chair.

Me: Really? You’d like a rocking chair for your big birthday present?

Tiny: Yes.

Me: Right.

This child is unique. So now I am knitting a turtle (whilst investigating rocking chairs). So far it (the turtle not the rocking chair) has two legs, a body, a tail, half a head and no shell. We compromised on the colour – she wanted it to be red and pink and purple but we found one with welly boots and a rain hat so it is going to be green with pink and purple boots and hat. I drew the line at knitting a pink and red turtle.

In which I haven’t fallen into a black hole

IMG_4043No black holes, only that I got a job (a miraculous occurrence if you know anything about me and interviews) in October and haven’t been heard of since.

IMG_4044Time is precious, the last three months have wooshed by and there is little enough time to make things now, without stopping to write it down and take pictures.

I just about managed to finish the Christmas knitting. There were Vikings, Lego man gloves, Red Riding Hood/wolf costumes and I got them done in time, the people with birthdays in December and January were probably breathing a sigh of relief that they didn’t have to work out how to be polite about being given knitting again.

IMG_4047Now it is half term and I have almost found the bottom of the washing basket.

IMG_4048Christmas didn’t really count as a break because it had Christmas in it and was still busy although we managed not to have flu this year which is always nice.

IMG_4049We are decorating Small’s room at the moment, he wanted it red and orange.

IMG_4050We compromised, I said he could have one wall red and one wall orange if the rest were a very light colour.

IMG_4051At the last minute he decided to have red and blue instead and we found some blackboard paint which gave us an idea to make the blue wall more interesting.IMG_4053I think I’ve earned a cup of tea now.