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Tuesday, 9 January 2018

Sinclair Memory Calculator Tear-down

I've bought a Sinclair memory calculator. It's in a bit of a state, but that's good, as I bought it to tear it down. The videos are here:

Part 1:

Part 2:

Friday, 5 January 2018

Radioactive Junk

I buy the odd piece of interesting junk now and again, and I've been a bit wary of some of them maybe being around radioactive materials. So, I have finally got hold of a Geiger counter. Well, bought a kit and assembled it.

The kit is one from this site:

I got a GK-B5, which for now lives in a temporary case, namely the cardboard box that it came in:

The Geiger Muller tube is an SBM20 and has about 500V across it, but it's not dangerous as the supply has a very high output impedance. The kit works well, and registers a count of about 25 per minute for background radiation.

Have I found anything radioactive? Well, yes, but I was deliberately looking for something so I scanned a couple of local junk shops. I found four pieces of uranium glassware. It's a pale green glass, the pieces I found were in the form of a jug, two bottles and a tray. So did I find any of the junk I had bought to be radioactive? Well, no, none of the bits I had concerns were radioactive. But, I did find that one of the objectives I had bought for my microscope had a count that was similar to the uranium glass I found. I suspect that it may have been used to look at uranium ore and a piece has lodged in the objective. It's not too concerning but at least the Geiger counter has served it's purpose.

Olympus BHM Microscope LED Light

The BHM microscope that I bought recently was fitted with a light source that was an incandescent bulb. It is driven by a variable transformer PSU. The PSU is quite nice, the bulb not so much. I have a suspicion that the bulb is a replacement that isn't quite the right voltage as it has never been more bright than a bit dim. I decided to build an LED replacement, so ordered some Cree LEDs and set about making a mount for them.

I had a cylinder I had cast from some melted down scrap, and turned it to the diameter of the lamp holder that fits on the back of the microscope.
After it was the correct diameter I drilled some holes that will hold the LED into place:

 The LED is then fixed in place with three screws:

The cylinder acts as a heat sink. I had bread-boarded the circuit and checked how hot the circuit and LED got and it doesn't get very hot at all. It's a 1W LED so there's not a lot of scope for dissipation. The connections for the LED run in a milled channel down the cylinder. I put a block of aluminium on the end as a mounting plate for the circuitry and as extra heat-sinking outside of the light holder.

The PSU outputs a.c. which is fine for the bulb but not so good for the LED. I added a bridge rectifier, some dropper resistors and a capacitor to convert the a.c. to a d.c. supply. This mounts on the block on the end of the assembly. Initially I used bits of wire to connect the circuitry to the PSU:

3D printed stand-offs hold the circuit board away from the aluminium block:

I wasn't very happy with using bits of wire to connect the PSU and didn't fancy hunting around for a suitable connector, so I made one. I turned a couple of pins from phospher bronze:

And 3d printed a shell in two parts. The pins have a shoulder that holds them in to the shell. The pins turned out nicely:

Here's the light in place and generating photons. The LED is positioned very close to the position the bulb filament would have been in and I end up with a pretty even illumination across the field of view.

 The light and the connector look like this when assembled:

I may add bolts to hold the connector together, but the pins are a tight fit so I may not. Here's the original bulb in it's holder as a comparison:

The LED leads are soldered across a capacitor for now, I'll tidy them up later. Once I've run this for a while I'll  make a PCB to mount the components anyway, so this is probably temporary.

Monday, 25 December 2017

Making Tins More Useful

The food for the ongoing project comes in large metal tins. They look like they might be useful for storing things, but they have two drawbacks. Firstly, they are big. Well, tall. They take up a lot of space and whatever you put in them would end up jumbled together. Secondly they have a lip around the inside just below the top. This is to help in levelling the scoops of food so that they are all the same volume. It makes the tins less useful, though as the lip just gets in the way. So, what to do? i decided to chop them down to make them shorter:

I'm going to make a few different heights of tin, for storing different sized items.

Sunday, 24 December 2017

I bought a Casio fx602p and found a puzzle

I bought a Casio fx602p and found a puzzle

Well, it might be a puzzle, or it might be a coded shopping list, or something completely ordinary. It's a puzzle to me though.

The numbers don't appear to all be primes, so I don't think the calculator was used with a program to find primes. The other card doesn't have all the letters of the alphabet on it, so can't be used to code words. At least it can't code all words.

Here's the cards in close-up:

What are they for?

Friday, 15 December 2017


In the spirit of the season one of these was created:

Six millimetre plywood cut on the bandsaw and hand finished. Screwed together, so easily serviced in the future.

Tripod Fix Adjustment

I fixed my tripod a while back:

The clamp works by pressing onto a small rectangular block which stops the leg from collapsing. The 3D printed clamp wasn't quite the same size as the original on one of the clamps, so it didn't push very hard on the block. this meant the leg wasn't very firmly held when extended. Eventually the clamp slipped over the block and I lost it.

So I machined a new larger block out of nylon. This has fixed the problem and the clamp is now very firm when latching the leg.