Gina

I have sucked up resin into a 20mL syringe and also taken a 2mL syringe with needle and poked that into the bag of hardener and sucked up 2mL of hardener. I sealed up the bag again where the tiny hole is with Sellotape. The resin was too viscous to suck up with a needle on the syringe even though it was quite a big needle. I had to cut the needle off the syringe as it was stuck firmly on - that's why the tube is shorter than usual. Two photos - 1. syringes filled and 2. after cleaning off and piece of balse wood to seal the hardener needle and prevent a nasty accident.

I'm sorry but after an extensive search, I can't find the link to the Farnell Peltier TECs I'll post if I come across it.

Yes, quite sufficient. I'll look for the link to the Farnel ones.

Now received the epoxy potting resin from Maplin and started transfering to containers. These two photos show the resin pack as supplied and the resin part of the pack transferred to two plastic pots with screw lids. Or most of it there is a little bit left in the bag but I don't think it's worth pushing it. I may put the hardener straight into a syringe or another pot - not sure yet.

I've just checked the figures my Arduino sketch is providing with an online calculator for dewpoint and the calculator shows about -25C whereas my sketch is showing -11 for temp of 18C and RH of 13 I got the DP calculation sketch from the Arduino web site!

So it would seem Tested the 1100D with cold finger in normal mode with SD card and battery, and although it apperared to work normally there was no image on the SD card. So I'm going to bring the laptop in from the warm room and test it with APT. Just realised that I probably turned off "Save to SD card" in the optiond Didn't think of that when I tried it last night - doh

Found the other 1100D body with the cold finger coming out the back So one option is to use that and perform all the removal of unwanted parts anew. However, I should have all the bits that went into the last cooled 1100D system and that would save work and laeve some complete parts (as it were) for selling off (if I can be bothered ). I've also found another complete untouched 1100D body that appears to be in full working order. BTW - I am imaging tonight - adding Ha to the M51 data Still upping the exposure time to get more data ah the signal is much lower with Ha even binned 2x2.

Thank you Cath

Yes, I remember reading that. I don't think there's any doubt that I can get the humidity low enough. Next thing I'm working on is the cooling. Now where's that 1100D with the cold finger hiding???

With the box sealed and 8 bags of silica gel in it the dewpoint has now reached -10C after 30m. It is still slowly going down so I'm hopeful of reaching -15C in time I think this will be quite sufficient. In my tests a year or two ago I went down to -20C but the noise reduction between -10C and -20C was small. I am now content that I can achieve low enough humidity - next I need to perfect the machanism for replacing the cover glass within the dry box. It may not be necessary to use that many bags - the main point will be to reduce the amount of free air. In that way the amount of moisture in the box after closing the lid will also be reduced.

A small advance on the cover glass replacement mechanism design. A soft sponge pad connects the cover glass to a flat piece of plastic or metal which in turn is attached to the shaft. If I don't have the 3D printer I plan to use a sleeve on the shaft with the flat plate glued to it. If printed in plastic this can be all one piece - a tight fit on the shaft. The pad, placed in the centre of the glass will provide equal pressure all round the edge to ensure it sticks well, allowing for a slight misalignment.

There may be a slim chance of imaging tonight - keeping fingers crossed I shall do my best to try and provide as reliable a method as possible - I realise that others may follow my example and the responsibility this entails

It seems that after an hour the RH has stabilised at around 15% at 20C giving a dewpoint of -7C. I think the limit may be due to the fact that there is currently a gap where the wires to the DHT22 go past the box top seal. I shall have to seal the box before any futher testing to be meaningful.

A bit later and the humidity is getting back to where it was but with a lower temperature.

You may be right but I opened the lid in the living room and changed the air and immediately got RH or 47% at about the same temperature when the lid was back on. I think the silica gel held the temperature.

Not true actually - RH = 74% for air from freezer Living room RH = 43% according to my wal thermometer and humidity meter.

OK I'll try that

Thought I'd try an experiment so I unplugged the USB lead and put the box and Arduino in the freezer for a while. Then brought it back into the living room and reconnected to the PC. Here are the results for the first 15 minutes. This shows how the dew point depends on temperature as well as humidity.

Oh yes, I think so. However, this is with just two silica gel bags and I shall put as many in as I can. If I can print the parts I can arrange to keep the bags away from the mechanism - barriers with holes in. Here's a screenshot of the serial output with another couple of bags added.

Another 20m of drying.

I've set up a drying test with the box, DHT22 T & RH sensor and Arduino. Here's a screenshot of the first few minutes of drying and a photo of the setup.

Here are a couple of screenshots from SketchUp showing the idea. Front side of box removed for clarity. Also, I haven't shown the grommets or the box details. This is just a rough sketch but it is to scale. The arcs show the path of the cover glass as its fitted onto the sensor frame. The shaft shown is a 6mm aluminium rod but I may choose a different size depending on the size of grommets - I have quite a variety. I might use silicone grease on the grommets to aid sealing. I still have to work out how the sensor assembly will be held in the right place and orientation and also the lever on the shaft and attachment to the cover glass. It will be next week (or later) before I'm ready to replace the cover glass on the working sensor, as there's plenty to do before then so I might wait until I get the 3D printer working again. Then I can print parts with just the right dimensions, angles etc.

Yes, I should think so I was thinking of mounting the lever on a smooth shaft going through grommets. With a nice close fit of course to make a seal.

I'm still thinking about the lever - I have some ideas but not decided yet. I may do a SketchUp model. Trouble is SketchUp doesn't cater for a moving model AFAIK. Also, I don't know when I'm going to get the replacement control board for my 3D printer so I may have to build it the hard way. The sort of thing I have in mind is to hold the sensor assembly with the sensor facing slightly downwards so that any dust doesn't settle on it. And the cover glass with the inside face also facing slightly downwards. Then the cover glass swung round and onto the sensor frame once the humidity has dropped sufficiently. We haven't had a fire for a few days now so I'm hoping the dust level indoors is suitably low

Thanks They look similar to the ones in my kit but I've ordered one to see. Shold be here Friday or Saturday.