Repair Cafe Update - November & December

A couple of months have passed quickly by and the November and December repair cafes have been and gone.

November

To start with there was a jammed paper shredder. Having taken it apart we found that the jam had caused the motor to flatten the teeth of one of the gears. Given the lack of available replacement parts, it seems like it's not going to be repairable.

The next item was an oscillating sander that wouldn't turn on. An initial suspicion of the motor brushes being worn was scuppered when the screw terminal on the PCB that connected the main cable, fell away during disassembly. It looked like the pins had just corroded through. There was enough left of the pins that it was possible to scrape the corrosion away and re-solder the connector.

Third up was a lamp. The issue became obvious when unpacking it, as one of the pins fell of the mains plug. The power adapter was disassembled, but turned out not to be salvageable. However a replacement shouldn't be too hard to find.



Finally a Technics Hi-Fi received was brought in with reports of the radio not working, and volume dropping intermittently. There was no obvious way to replicate the problem, but it did seem that the radio might have been badly tuned, and some cycling of the volume control seemed to sort the volume issues. Given that nothing was particularly done, yet the problem seemed to go away, it's hard to class it as a win or a loss.

Scorecard

	This month	Total
Wins	1	2
Draws (Workarounds and partial fixes)	1	3
Loss	1	1
Needs parts	1	3

December 

I managed to find a replacement power adapter for the lamp that was brought in last month, so was able to turn that into a quick win.

Second up was a dumpster-dived angle grinder that was just not powering on.
After checking the usual electrical culprits it was a case of the plastic switch being decoupled from the actual electrical switch - all it required required being clipped back into place. Unfortunately the nut that holds the disc in place was gone, but I'm sure a spare can be found in time for next time.

Unsurprisingly, there was a set of Christmas lights. Unfortunately not salvageable as it looked like there'd been an attempt to glue the bulbs in place.

Finally, a family brought in three lamps - I took two of them, one of the volunteers took the other. The first of mine was just a fuse replacement - easy win.
The second was also a fuse replacement, but it wasn't the plug fuse, it was a smaller device fuse on the circuit board of the lamp. With no replacement available, all we could do was advise them of the fuse that was needed and I showed them how to replace it.

Scorecard

	This month	Total
Wins	2	4
Draws (Workarounds and partial fixes)	0	3
Loss	1	2
Needs parts	2	3

That was the end of the repair cafe for the year, and although I've only been part of the repair cafe for the past three months, I was pleased to hear that a total of 650 kilograms of electronics was repaired in 2019, and I'm looking forward to trying to beat that record next year.

Glass display tray

Last Christmas I was given a nice set of drinks glasses.
In order to keep them safe, I keep them in their original cardboard box, which keeps them safe, but isn’t aesthetically great and keeps them hidden, so this was a quick project to create storage for them that is better looking and more permanent, and would fit in with the display stand I created earlier.

The box itself is made from iroko scrap. The outer walls are simple butt joints, and the dividers interlock each other as shown in the animation below.
For a finish, the wood was treated with danish oil.

Obligatory TL;DR finished project pic:

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read on for a description of the build (and me practising my 3D skills in Blender!)

Thin foam was cut to squares as a base in each of the six segments.

Thin strips of foam were then wrapped around the glasses and they were placed into the box, where the edges of the box act to hold the circle of foam in place, and finally small triangular segments were cut and placed around the circle to pad the corners. This creates a suitable fit, and the foam has an almost velcro-like quality that holds all the bits together without needing adhesive.

Drinks display stand

This is another small part of a larger modular project.

The aim is to create a display for drinks bottles and miniatures, which will present them nicely, while at the same time securing them to protect against small amounts of movement. i.e. I'm not expecting them to be secured if the whole stand is tipped over, but they must be able to tolerate the stand being wobbled side-to-side without the bottles clinking or falling over.

There is also the need to balance the trade-off between the display aspect of the unit, and the amount of storage it provides.

After iterating over a number of designs I settled on the idea of having a central area which would display a number of larger bottles, with a frame/shelf element around the back and side edges to hold miniatures (the front would need to be left open to allow access to the bottles).







The base

The base is simple plywood, with foam to support the larger bottles. The foam is spray-glued to the plywood, with cut-outs to place the bottles, and is wrapped in fabric - also spray-glued and stapled.

The frame

The frame is oak, attached through the bottom of the plywood, and supported by the miniatures shelves and the top frame, which is mitred, and screwed to the uprights with dowels to cover the screw holes. The sides are left open, but the back is enclosed with iroko (there is a logic to this that will become apparent later). The mixture of woods creates a nice colour contrast and adds additional support. 
 

The miniatures shelves

The basic idea behind the miniature shelf is to use a forstner bit to cut out grooves for the bottles to stand in. But this alone raises a couple of problems

• If they're just sat in holes, it won't be possible to see the labels and know easily what they are.
• There's no definitive standard size/shape of the bottles.

The latter question has an easy answer, just pick the smallest forstner bit that covers the most bottles that I have to hand - this turned out to be 41mm.

The solution to the first point is to cut the groove off centre, so that it has an open front, allowing the label to be seen, but again, this raises the next question - if the groove is open-fronted, then what's to stop the bottle just falling out?

I'd already planned to line the bottle slots with leather to prevent rattling. By over-sizing the corners of the leather (see below illustration), the leather also acts like a clip to hold the bottles in place, with a sturdy leather disc glued in the bottom to provide extra support.

The finished display
 

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Repair Cafe

I recently started volunteering at a local 'repair cafe'. It’s a community environmental initiative where people in the local community can bring in small broken consumer electronics, and the volunteers will see if it can be repaired, at no charge, in order to keep items out of the waste stream.

If items can’t be fixed on site, advice is given whether it’s worth repairing, and if so what parts, etc. might be required. If they can be fixed, they’re tested to ensure they’re safe, and weighed so that the organisation can monitor the amount of material kept from landfill.

The other volunteers have a wealth of experience in a number of technical and scientific fields, so I also see it as an opportunity to learn and improve my skill set.

I’m also going to keep a record of the repairs I do, and document them here in the hope that it provides a DIY reference for others who may need similar fixes but aren’t able to access a repair cafe in their area.

So, these are the repairs I was faced with on my first day:

• An automatic cat feeder – a simple mechanical clock device turning cogs which in turn allowed a lid on a good tray to open after the set time. The mechanism was reported as being slow. Observation of the device over a couple of minutes didn’t really show any sign of being off, and a test over half hour showed some drift – about an extra minute. The device was far from being a precision instrument though, so suggested that they observe the amount of drift over the time period they’re after and adjust the time they set accordingly.

• An electrical beard trimmer. The mains wire was disconnected. Soldered in place and fixed.

• A DAB digital radio, on which the LCD display wasn’t functioning. Managed to disassemble and retrieve the faulty part, so that a replacement could be found.

• A toaster. The lever to push the toast down was stiff. This seemed to be a design flaw in the toaster, where the lever being pushed down would effectively pivot on the rail where it’s mounted, causing it to bind.
  

  

  
  There wasn’t much that could be done to repair it, but was able to advise the user how to workaround it by keeping the lever flat whilst it was being pushed.
  
  
  
  
  
  
  
  
  
  
  
  
  
• A halogen cooking lamp thing. The timer and the fan would run, but the halogen lamp wouldn’t turn on. Testing showed no power to the halogen connector.
  Tracing the problem back showed that a potentiometer device (pictured) which set the halogens temperature had broken part.
  
  Advised the user of the broken part so they can try and get a spare from the manufacturer to attempt a repair next time.
  
  
  
  
  
  Scorecard
  

  	Score
  Wins	1
  Draws (Workarounds and partial fixes)	2
  Needs parts	2

Empty roll warning buzzer

This was a commissioned project that went nowhere, but could easily be re-purposed for many different use cases, so I thought I'd share it.

The aim is to create a range finder device that can be mounted and aimed at a roll of material on an assembly line, so that the range finder can be used to determine the amount of material left on the roll, and sound a buzzer when the supply falls below a set amount, informing the machines operator so that they can replace the roll and minimize downtime.

The sensor is a Sharp GP2Y0A21YK0F. The datasheet shows that the voltage drops as the distance increases. In our particular use case, this means that as the material runs out, the voltage will drop, so we want to flag a warning below a set voltage.

Initially I thought about using a low battery circuit similar to the one I modified to use in the Keyboard Pedal project. However, I later realised that would be over-complicating it, and that the same result can be achieved using a simple comparator circuit.

The chip used is the LM358 op-amp, and the circuit is similar to the one found on page 6 of this PDF.

The key differences being:

• The voltage provided by the resistor and zener diode in their diagram is replaced by a potentiometer in mine, so that the 'trigger' value can be adjusted.
• The potentiometer in their diagram is replaced by the IR sensor in mine.
• The resistor and LED output in theirs, replaced by a buzzer.
• The voltage of my circuit is 5V so it can run off a USB charger.

With all those changes taken into account, the resulting circuit looks like this.

Note that RV2 is the IR distance sensor - I didn't have the symbol for it in KiCad so used a potentiometer symbol as that's essentially the behaviour it exhibits.

The finished circuit, fit neatly into it's enclosure.

The case

The circuit needed to be neatly enclosed for it's purpose. Often for electronics projects I'll end up re-purposing existing containers and boxes as enclosures, but as it was a commissioned project something more professional was in order.
The whole enclosure is 3D printed, based off a simple lidded box design with cut outs for controls and the IR sensor itself.

I also took the opportunity to turn the box into a simple parametric template so I can recycle it for other projects. the SCAD source code can be found on GitHub.

All that's needed is to supply the internal dimensions that are required and it'll create a thin-walled box meeting those criteria, using only stock OpenSCAD commands - no other modules required.

The lid fits snug - on my (admittedly by this point quite old) 3D printer, a nice unintended side effect of the rough resolution is that the ridges create a nice friction fit, allowing the box to be closed tight, but also popped back open with relative ease should maintenance be required.

The controls and buzzer

The sensor - the glue-filled part was to allow flexibility in angling the sensor, but was later found to be not required

The test

As I didn't have access to the factory where this was intended to be used, I whipped up a quick test rig using kitchen roll as the stunt double for the actual material.

The short buzzing before the alarm fully triggers is driven by the 'wobble' of the roll on the holder. In production use the material rolls are much more securely held, and so this effect would be minimised.

Powerful car jack linear actuator

Creating a powerful linear actuator by attaching a car jack to a motor is nothing new, but a lot of the demonstrations that I've seen neglect the fact that the point where the motor needs to mount to the jack (at the end of the threaded rod), will have movement both vertically and horizontally towards/from the middle of the jack. This makes it difficult to mount the motor in a fixed position.

So while this isn't a project in itself - it's a small part of a bigger project I'm currently working on, I thought I'd share my solution to this problem in case it is of use other others attempting something similar.


I found the best method is to focus on mounting the motor in relation to the threaded rod, rather than the jack, or the other frame/other parts of the project, as this is the only bit where the position remains relative.

The frame supporting the motor in line with the jack
(Jack body not illustrated)

This frame (yellow) goes around the middle of the jack, and hooks at the end over the threaded rod (green).

At the other end, the motor (red) is attached to the rod in order to turn it and mounted securely to the frame, allowing it to move with the rise and fall of the jack.


The downside to this mechanism is that the torque of the motor will cause the whole frame to rotate. This can be overcome by building the frame as close to the jack body as possible, to minimise the amount of rotation.


In addition, springs are mounted from the underside of the elevated surface to the frame, to add additional support and reduce vibration.

Electronically, the motor is driven by a H-bridge controller. Reed switches are mounted to the base - one on the base itself, another positioned in an elevated position to line up with the frame at it's highest point. Corresponding magnets are mounted on the frame, which line up with the reed switches to create a high level limit and low limit.

Control is currently provided by an Arduino with a single button input - each button press will either raise or lower the platform.

Code is below:

#define R_EN 13
#define L_EN 12
#define R_PWM 11
#define L_PWM 10

#define MAIN_SWITCH 4
#define LIMIT_LOW 7
#define LIMIT_HIGH 8


void setup() {
  pinMode(R_EN, OUTPUT);
  pinMode(L_EN, OUTPUT);
  digitalWrite(R_EN, HIGH);
  digitalWrite(L_EN, HIGH);

  pinMode(MAIN_SWITCH, INPUT);
  pinMode(LIMIT_LOW, INPUT);
  pinMode(LIMIT_HIGH, INPUT);


}

void loop() {
  if (digitalRead(MAIN_SWITCH)==HIGH) {
    runProcess();
    
  } 

}
void runProcess() {
  if (digitalRead(LIMIT_LOW) == HIGH) {
    while (digitalRead(LIMIT_HIGH) != HIGH) {
      lift();
    }
    freeze();
    return;
  }
  if (digitalRead(LIMIT_HIGH) == HIGH) {
    while (digitalRead(LIMIT_LOW) != HIGH) {
      lower();
    }
    freeze();
    return;
  }
}
void freeze() {
  analogWrite(L_PWM,0);
  analogWrite(R_PWM,0);
}
void lower() {
  if (digitalRead(LIMIT_LOW) == HIGH) {
    freeze();
  } else {
    analogWrite(R_PWM,0);
    analogWrite(L_PWM,255);
  }
}
void lift() {
  if (digitalRead(LIMIT_HIGH) == HIGH) {
    freeze();
  } else {
    analogWrite(L_PWM,0);
    analogWrite(R_PWM,255);
  }
}

Demo Video 

Leather-bound notebook

Following on from the pen and pencil projects I figured I'd continue on with the stationery theme.

Like most people who've ever taken notes, I have a lot of half-used notebooks gathering dust, leaving a large stockpile of perfectly good paper not getting used simply because it's bound to some other paper that did.

I'd been thinking about trying a book-binding type project anyway, so figured why not save a few steps and do some up-cycling in the process.

The candidate books are some school-exercise-book style notebooks.

These are great candidates because they are only bound by 2 staples and each book is a single stack of folded paper.

There's a detailed Instructable for this, which I used heavily for this project, so rather than reinvent the wheel, I'm only going to detail the areas where my process differed from theirs.

To start with, I removed the covers from 4 of the blue books.

To get the fabric for the binding, an old t-shirt was sacrificed.

I oversized the measurements for this bit, so that I could pin the fabric to a scrap backing board, to hold it taut while I mounted the folios.

I put clips each end of the stack of paper, painted some PVA glue onto the fabric, and then added the spines of the paper. Doing it this way around prevents the glue leaking between the pages and fixing them together.

The resulting object was surprisingly stable enough to move somewhere safe to dry.


In the meantime I started preparing the cover as per the instructables instructions. However the leather that I had for the cover was slightly too narrow to have the one inch border that it instructs, but still have enough material to wrap around, so I'd be working with narrower margins.

In addition, in order to be able to fold the leather over to create a neat edge, it needs to be thinned. I did this using a combination of skiving tool and sanding, to thin the material around the border.

After that it was just a case of following the rest of the instructable. For the lining paper I used some of the card I had left over from the Picture Frame that I did a while back.

To finish it off I added some brass corners, and that was it. Not perfect by any means, but very happy with it as a first attempt.

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