Yup, using a nRF24L01+. Transmits between every minute and, er, 7 or 8 minutes. Depends if the temp has changed since last check.

Oh no, it's gone down by 0.1V. Not bad after 3.5 months. Not sure if it would have lasted slightly longer if there wasn't a power outage the day before yesterday and the sensor was trying to send to a switched off Pi for over 24 hours.

I'm in the process of doing some work in my loft - boarding it and opening up the loft hatch so it's much bigger.

Hatch was been made bigger today, it's massive and maybe a bit too big (nj). Gone from 35cm x 51cm to 78cm x 90cm.

I'm trying to figure out the best way to work the ladders and hatch. Motorised ladders cost an absolute fortune so I'll be going for some regular loft ladders. But a motorised hatch door seems like a reasonable possibility. The hatch will be over 3m high so that's why I like the idea of it being motorised.

I'm thinking an arduino, a motor and 433 MHz receiver (plus 433Mhz 2 button remote).

The door will be opening inwards into the attic, rather than down into the landing space. It will also be able to fall against the wall next to it, rather than open to 180 degrees flat.

Something like:

               |
              /|
       Door  / | Wall
            /  |
           /   |
__________/    |

What would be the best sort of motor for this sort of thing? A stepper motor so I can move it a specific distance?

The hatch door will be made out of MDF and will probably be a decent weight.

A simple case of having string/rope attached to the door and winding/unwinding it around a spool?

But with it going past 90 degrees that means I'd need something to get it past the 90 degree point to shut it. That might be difficult to do all that without it slamming and/or putting a huge strain on the motor.

Or I put something in place to prevent it going past 90 degrees and maybe have an electromagnet to hold it open. 
 

                  |
          |       |
      Door|__ Post| Wall
          |  |    |
          |  |    |
__________|__|____|

Or I just get a really long post to push it open (yj).

Could you have the door on the back on the ladder, like this:

Where's his helmet and safety harness?

Windscreen wiper motor.

Indeed, for a man who stores his dustpan upright on a shelf, he should know better... he'll have a boiler suit set aside for DIY matters, a utility belt/kilt for demanding jobs and his screws all sorted into individual compartments in a wall thinger.

And just run it for x seconds?

It is a nice idea, but I think they're still too expensive, pretty tight budget.

Mine are piled in cardboard cartons -- when I remember to put them back.

Or I could use a hall effect sensor or two to detect whether it is open or shut.

Mine are in an old Fairy tub. :J

They use a mechanical linkage which reverses direction (motor runs continuously in one direction), so just install it so that turn in direction coincides with the max open position of the hatch, then add a limit switch to stop the motor when it reaches there.

They use a worm gear in the gearbox so produce substantial torque, but I've no idea if it's enough to lift a MDF door from horizontal. If there was torque figure available somewhere it's fairly trivial to work it out, though. Or just try it and see, if I doesn't work you have a spare motor for making a robot.

Is it finished?

Which bit?

It's half boarded and the hatch frame is in. Should get it pretty much finished tomorrow. Then I'll design some ridiculous way to open the hatch door.

What about having a piece of hanging 'art' on the wall beside where the hatch is?

Use it as a counterweight, if you want to open the hatch then just give it a gentle tug downwards and marvel at your secret entrance skills :D

My dad has suggested a counter-weight method too, with the weight in the attic.

It would still require the door to be pushed (at least initially), but it would make it much easier.

We've also realised that with a top opening door it may need some space for the loft ladders, unless the door actually goes within the frame rather than on top. Anyway, I've got enough MDF left over to sort that.

Spring(s)?

Have you got any pictures of what you've done so far?

Whenever anyone's telling me about their DIY projects my mind automatically imagines an Ikea-like paradise where everything fits neatly, walls are perfectly straight, you've got all the right screws to hand and there's never a dead battery, all in a room lit by white light coming through diaphanous curtains. I don't know why, 'cos my own DIY projects are usually messy affairs covered in filler, caulk, paint, blood and much swearing.

My DIY project sounds very similar to yours. I've taken a few photos of the hatch progress, I'll put them up later. I'll take a photo of the finished flooring once it's done. I was going to put a camera up there and timelapse it, but it's so so filthy.

My dust mask from yesterday