Mending Jeans

I bike to work regularly, even during winter. As a result my jeans wear off often, every time in the same place, let's call it "the saddle area". I used to take the jeans back home and ask mum to do it. She would just go to her "work room" power up her good old sewing machine and get it done in no time.


Since we decided last year to buy a sewing machine, I thought I could try and do it myself. It is very easy and hardly noticeable once the patch is made.
You will need a pair of jeans to fix, a jeans patch a bit bigger than the hole (+2cm, 1 inch) and thread.


There's a trick about the thread (thanks mum), use grey or light grey thread. Using blue thread, even if it's the same colour as the jeans will produce a noticeable patch.


Place the patch on the inside of the jeans and secure it with pins, take care to stretch both the jeans and the patch.


Load the top thread with the grey coloured thread (the under carrier is not so important), select a wide zig-zag stitch (5mm width) and reduce the length (advance) to 1 to 2mm (a bit like the bottom right stitch of figure 2 here).
Lock both fabrics under the zig-zag presser foot starting from 2cm/1 inch outside the hole to cover, sew until 2cm/1 inch the hole end. Repeat in reverse.


When you reach the place where you started, move the needle to the top most position, release the feet, move the fabrics 5mm (about the width of the stitch) to the side, press the feet and repeat until the hole is covered.


Here is the patch finished. The good news are it is hardly noticeable, the bad news are, that usually if you do this in one leg, chances are the other leg's fabric will also fail in a few weeks.

Weller WTCP-S Repair

This week as I was about to start soldering my boards my old trusted Weller WTCP-S started to fail, first ocasionally it wouldn't heat up until shaken, lattely not at all.
Wanting to fix it (if possible) I opened it to check the famous "Magnastat", these Soldering Irons operate on the principle of the Curie Temperature, where a magnet loses its magnetic properties at a certain temperature point.
Inside the casing there's a ferromagnetic piston and the tip is also magnet with a predetermined Curie point (the number on the bottom of the tip), when the temperature is reached the magnet losses its properties, the piston is no longer pulled and the contact at the bottom opens, opening the heating circuit.

I had to open the contact casing and clean the contacts, put it back together and test....

While cleaning the contacts the wiring came loose, so now I was facing a chicken'n'egg problem, how to solder a soldering iron?, the local hackerspace was the answer, I meet some really nice people in really nice location and they had a spare soldering iron I could use in their "electronics shack".
Anyway got home, tested it and it works for now... but I expect it to fail again soon... I'm ordering a replacement today...

Arduino NG rev. c

About a year and a half ago I bought my first Arduino, it was a Arduino NG. At the time it was quite new by the fact that it had a USB port. I did a lot of experiments with it, borrowed it a couple of times and now it is back home.
I never used it with external power until one day I wanted to do an autonomous robot. I programmed some test code, removed it from the USB port, powered the auxiliary power supply (a.k.a 9v battery) and nothing...
The usual debugging technique followed:
- test program with USB, it worked.
- remove from USB, change switch to external, power external and wait...wait..nothing.
- check the web... I found here that the problem existed and already had a solution.
- while browsing "problem Arduino NG" I also found here that the "autoreset" feature of the diecimila had been implemented.
So I picked up the soldering iron, my pack of SMD components and went on to hack the board. So I changed the 3rd resistor from the top and I placed the capacitor just below the RX Led (a reader told me it was very clear what I had really done to the board...)
Here is the final result:

Humidifier Reloaded (Hacked)

Pedro had a problem with his Venta Humidifier, although it has a nice "discrete" design it lacks one important feature: an external water level indicator. Pedro drafted a small specification of what he wanted, two indicators, one for "almost empty" and another for "empty", if possible when empty stop the motor i.e. cut the power.
I checked the price of a new one (just in case I ruined it beyond recognition) and after taking note of the 114€ price (and they weren't able to add a simple level indicator... shame on you product designers), I went to work.
My first idea was to use a buoy and a lever to externally indicate the level, but it appeared to be too fragile to store and to align the top of the Humidifier, then I though of building a buoy with a magnet and placing Reed switches on the outside of the case.
Having a small tube glued inside was very easy, I had to use hot glue as special PVC glue (in the picture) did not work with the case (clearly not PVC!!).


My original magnet was too heavy, it weighted about 7g and for that I needed about 7cm² of foam supporting it, too much!Then I tried 3 and 4 smaller magnets, about 1g each. Here is a picture of the magnet with the floater and the REED switch on top.

After having the level system I went out to design the electrical system. Initially I planed on using a normally closed reed switch for the power but a switch capable of cutting 230V 0.35A inductive load is impossible to find.
So I had to resort to an additional battery and a relay to invert the signal, the use of the battery made me use an extra power switch to turn off the detection circuit when the Humidifier is stored away.
Two normally open switches, one lighting a green LED when the level is almost at the bottom and a red LED lighting when the level of water is at the bottom and cutting the motor when this happens. The Relay contact is normally closed so that if the battery runs out or Pedro doesn't want it to operate just remove the battery and let it work as previous.

Here's is the finished "product", with the boxed closed and the LED visible.

Here's another picture, just to show the chaos during the creative process... :-)