Water Level Monitor

Water Level Monitor

We've got a rainwater harvesting system that consists of a tank holding rainwater and a pump that supplies toilets and the washing machine. The system came with a mechanical water level meter which is fine, but it requires a trip to a cupboard and some hand pumping. The pumping creates high pressure air which runs in a pipe to the tank. The higher the water level in the tank, the higher the pressure. A pressure gauge in the meter shows the capacity in percentage capacity.

The reading is the height of water in the cylindrical tank. As the cross section of the tank is circular this doesn't quite represent the amount of water in the tank, but it's fairly close.

I started looking at an electrical version a few years ago. Using a pump instead of the mechanical hand operated piston was an obvious way to do this.You could then have a pressure sensor which gives you the same reading as the mechanical system.

The first problem was the pressure involved. The tank is about a meter and a half high and that leads to quite a pressure. The pump needs to generate at least this pressure and the pressure sensor needs to be able to read that pressure. I couldn't find either a pump or a pressure sensor that would work at the pressure I needed.

I left the project for a while, then I came across a cheap blood pressure monitor. This has a pump and a pressure sensor and performs a very similar task to the water level meter I wanted to create. The pressures involved looked promising as well. I dismantled the monitor and extracted the pressure sensor and pump. I reverse engineered the circuit for the sensor and recreated it on an arduino Uno format shield.

You can see the sensor below the IC, it attaches to plastic tubing.The pump drive is a power transistor driven with a PWM signal so I have speed control. If the pump is driven at full speed then it is a bit noisy. Running at a lower speed still gives a high enough air pressure and it's much much quieter.

The final system is mounted in the same cupboard next to the manual meter:

The electronics are in a 3D printed case,  the pump is on 3D printed brackets. The manual meter reads the air pressure when the pump is energised, so you can use it instead of the manual pumping system.

The manual pumping system (below the electronic system) still works exactly as it did before, so there's a backup in case the electronics fails.

The code is set up to energise the pump once an hour, it then stores up to 1000 samples which are offloaded to my laptop using a cron job. I can then graph the samples as needed.

There's a Global Shortage of Toilet Paper

There's a Global Shortage of Toilet Paper

But more importantly there appears to be a global shortage of PLA. I've been printing a fair few things recently and thought it'd be a good idea to stock upon PLA filament. Unfortunately I found that lots of suppliers were out of stock and the price had risen to about double what I last paid. I managed to buy some PLA at a higher price than my last purchase, so I have some in stock.
I had a look around and found that PETG was an odour free plastic (not biodegradable though) that seemed to be similar to PLA. More importantly it was available. I bought some as a sample.

My fisher 3D printer doesn't have a heated bed. This hasn't caused me any problems with PLA other than a slight warp on some larger prints. The bed has Buildtak (BuildTak?) on it which is a very nice surface. PETG seems to need a heated bed according to the internet. Anyway, the PETG arrived and I had a go at printing with it using my normal PLA settings and no heated bed (I've ordered some parts but they won't arrive for ages).

First, the robot that came with the printer:

He didn't print very well, in fact his foot half fell off, but it wasn't a total disaster. I then realised that the file was an STL that was on the SD card and it has a print temperature of 200C. I don't print PLA at that temperature, for some reason all my printers work best at 220C. PETG seems to have a slightly higher print temperature than PLA. I tried a couple of my smaller parts with PETG at my PLA temperature: 220C:

That's a dehydrator knob and a thicknesser latch thingy and both printed fine. No problems at all.

The layers look very similar to the PLA versions. The part does seem to have a little more flex in it compared to PLA.

My Panasonic lens fix was a success until I dropped it again, I then printed another part and fitted it, but it was a slightly different design and had a hole in it which caused too much flex for the contacts on the lens to reliably engage with the camera. It finally got to the pint where I couldn't use th elens, so I decided to fix the problem. I altered the model and printed a new part in PLA and an identical one in PETG. Of course, it's white not black as that was the PETG colour I bought:

The PETG part seems to be a bit more 'slippery' and this is useful on a lens mount, so the PETG part is better than the PLA one in this respect.

The PLA part doesn't seem to be quite as tidy as the PETG, but the difference in colour doesn't help the PLA.

The lens is now working with the PETG part, which is what I wanted. It looks like PETG is going to work for me in the same way I use PLA. Excellent.

Dehydrator Knobs

Dehydrator Knobs

To go with the new front panel, some knobs:

3D printed and then hand drilled to size so it fits nicely on the shafts. The printer didn't seem to be able to print the splines that were on the model. They stiil fit though as the hole was snug.

Dehydrator Update

Dehydrator Update

It was time for an update to a couple aspects of the dehydrator. Firstly, the trays I made to hold the stuff to be dried needed to be replaced. they were wooden and had warped really badly:

The replacement is a metal rod and 3D printed tray which hopefully won't warp. It also has a handle in the middle of the tray so lowering it into the dehydrator is going to be a lot easier.

Whatever is being dehydrated sits on a plastic mesh so that air flows easily through the trays:

The trays look a lot better than the wooden ones and I hope they will work a lot better as well.

The second update is an engraved front panel.

Which potentiometer controls what is now obvious, as is the function of the LED. This is engraved white on black plastic sheet. I need to make some nice knobs for the pots next...

Clock Bargain

Clock Bargain

What do you do when you see a clock for sale for one pound?
You buy seven, of course.

Then you attach them to a board and there you go, a timezone array clock thing (I'm still not sure what these things are called).

The location labels are CNC routed out of a plastic that I took ages to source that has a white layer on top of a black substrate. It took ages, not to find it, but to find it at a reasonable price. It's really nice when routed, and has an old-school type of look to it. This plastic was used a lot in the sixties and seventies for labelling electronic equipment controls.

The whole thing didn't cost too much more than the bargain £7 for the clocks, either. The board is made from scrap and recycled packing case material, and I bought more of the expensive label material than I needed here, so I will use that on other projects.
Seven batteries is a not insignificant cost, either.

Canon Selphy Printer Cartridge Transplant

Canon Selphy Printer Cartridge Transplant

I recently fixed a canon Selphy 740 printer, (see here). As the repair was successful I then needed some more cartridges for it. It doesn't use ink, it uses a dye sublimation process (I think) that takes a multicoloured film and transfers the coloured material to the paper in a sequence of passes. The cartridges are pretty expensive, so I bought some non-original versions as they were a bit cheaper. All was well and I printed some photos with the replica cartridges. Then I tried another cartridge I had bought and it didn't work. I tried the first one again and it was fine. After a few prints I worked out that two of the three cartridges I had bought didn't print reliably. Oh dear.

I contacted the supplier but didn't really want to go through the hassle of returning the cartridges. The Canon cartridges were very reliable so I wondered if the replicas were mechanically slightly different. Could I take the film from the replica and put it into an empty Canon case?

The cartridge case clips together so it is simple to unclip it and get access to the film:

I then swapped the film over and clipped the Canon cartridge together again:

The Canon part had a metal rod holding the film down, the replica had a plastic rod. I don't think this could be the cause of the problem I saw, I think it's more likely that the ratchet mechanism that is used wasn't unlatching.

Does the transplant work? Yes it does:

It takes a while to swap the film, but you get the cost savings and you can print. You do need a few canon cartidges first, though, and I only have two.

DIY "Digital" Watch

DIY "Digital" Watch

OK, it's digital in that it's made of bits. From ebay. It's actually mechanical and uses a movement, case and strap from ebay and a couple of 3D printed movement rings to hold it all in the case. The current setup is this:

I bought really cheap parts, and had a few adventures along the way but I have finally got somewhere. I started by buying a Chinese movement that might be based on the ETA 2824, or not. I also bout a case which is better than I thought it would be, and a bracelet. I also bought some hands to fit on the movement. For some reason that I can't remember I part dismantled the movement, I can't remember why. There must have been a reason as I intended to just fit the movement in the case. Anyway, in the process I managed to shear a screw (left and thread, I though they were marked with three slots?) and lose a click spring. I have subsequently managed to make a click spring and replace the sheared off screw with a new one, and the movement works again.

While I was wondering if I'd ever fix the movement I bought another one (even cheaper than the first), as a replacement for the broken one. It was about £11 on ebay and I found out that that isn't really enough money to make a decent movement. The move expensive movement was £22 and that does seem to be enough, just). The cannon pinion never worked properly and the movement kept awful time, simply because the minute and hour hands weren't moving. I eventually gave up on this movement, I may have another go at getting it to work sometime.

At the same time as buying the second movement I bought a correct sized dial, which was very nice. Unfortunately the dial doesn't fit the dial mount on the first movement so I can't use it. I may get another one if I feel like it.

The dial is held in the case with a 3D printed ring, you can see it in the photo above. The movement is also held in place with a 3D printed ring. The case has a clear back, which I didn't deliberately look for, but turned out to be useful when I was sizing and adjusting 3D printed parts:

The movement is automatic, so should and does appear to wind itself.

So, this is an alternative to the digital watches I've been trying to make, and stalled on for the time being, it tells the time, doesn't need batteries and shows the date. That covers most of what I want it to do.