Shredder switches

 I did manage to fix the shredder - a little victory but was bamboozled for a while by why it wouldn't turn out. Turns out that there are 3 switches that must be wired in series. The switch you press to turn it on is A. Switch B means that the rotor won't run unless there is paper in it. The paper pushes down at B on the black plastic arm that pivots, pushing inwards to close the switch. When that paper has shredded, the arm pops back out and the motor stops.

But there is a third switch that is only activated by putting the shredder into the waste tub so you can't operate the shredder away from that tub.

Shredder induction motor

 The shredder got stuck and needed surgery.

Looks like an induction motor. It has an ac supply so the electromagnet coils produce an oscillating magnetic field through the rotor coil. This induces a current which pushes against the magnetic field by Fleming's Left Hand Rule..

Cleaning the waste ink pads on a Canon Pixma MG 2950

 My Canon MG 2950 was a sturdy and dependable printer. It lasted for years. Then I got the waste ink pads full message. It is possible to keep going after that by pressing the black print button when prompted. But that finally ended last week. So faced with the option of having a go or giving up and buying a new one, I had nothing to lose so I decided to see what the fuss was about. I got in by taking out the two screws by the paper feed. Then you unhook a catch above where the paper comes out and push the top back to release two further catches. The electric feed ribbon to the top comes out. The waste ink pad is A. Undo screw B to release.

I tried soaking in a bowl - lovely diffusion experiment - but under a running tap was best.

This is it dry.

This is it back in.

Wonderful chromatography.

Sadly I then got code 5012 which was terminal. If you get code 5B00 then there are good instructions online for a reset. Sadly didn't work for me but it was fun trying.

Mid-winter sky

Mrs B found this wonderful APOD last week covering the part of sky in the photo and showing the nebulae. Our southern sky is the one with street lights so I'll have a better look when we are somewhere with a darker southern aspect.

 

Large fuse

I was shown the fuse that covers the whole household electrics. I was amazed that it is a huge version of a domestic cartridge fuse.

Migrating toothbrush

When turned on and stood on the table, this electric toothbrush moved left in a more or less straight line. Here's my theory as to why. The brush head twists backwards and forwards - not whole turns but a bit clockwise and a bit anti-clockwise. The head is not on the axis of the brush so it creates a torque. There is a reaction torque, equal and opposite as the friction on the base pushes back. This nudges the base around a little bit. Done alternately, this seems to add up to a linear motion, a little like shuffling.

Needle felting and cross-linking

My first go at needle felting. You start of with the wool above that can be teased apart. Lots of parallel strands.

Then the needle has a series of tiny barbs near the tip. You poke down through the wool and pull out. It drags bits of deeper strands back up across the nearer ones and thus binds the whole thing together.

This seems like a good analogue for cross-linking in polymers to make them more solid. You can see some of the cross-links in the yellow wool.

Dyeing and pH

My friend was using madder to dye her wool. She said that changing the pH by adding bicarbonate of soda changes the dye colour. That sounds to me like a more lasting version of the red cabbage indicator. The reaction must change the electron energy levels in the molecule so that different photons are reflected back.

Bill Gates gives data on planting trees

Having planted a fair few trees, I've always wondered what the data on tree planting as a solution to global warming looks like. Bill Gates provides this in his book on pages 128 and 129. He gives a rule of thumb that a tree absorbs 4 tons of carbon dioxide over 40 years. He points out that if the trees in the picture weren't planted but some just grew naturally, there will be no extra carbon absorption. It is extra trees that count. Also it matters where the trees are planted. The tropics is better! He then calculates that 50 acres of trees would be need to be planted extra in the tropics and maintained in perpetuity to offset the lifetime carbon emissions of the average American. This would mean half the world's land mass for just USA alone. 

Equipotentials in fairy lights

I liked the curved line pattern above the door. It reminded me of contours or equipotentials. It might be like taking point measurements of potential and plotting them, then joining to get equipotentials. 

LED threshold voltages

We had a problem with the fairy lights. It was solved by replacing the batteries. The one on the left below had batteries replaced and the one on the right didn't.

With fading batteries, no matter which colour you press on the remote, you get red.

I'm not sure how they are wired inside but my guess is separate LEDs. Red LEDs have the lowest threshold voltage and would be the last to be still working as the output pd of the battery faded. This is connected to the photon energy hf - so colours with higher frequency have higher energy photons and need a higher voltage to get that energy. Full theory is here.