Tuesday, 26 May 2020

Tray Stand / Foldable Table

While lockdown has prevented me from being able to get back to many woodworking projects this year, I did manage to cut a few offcuts to size and sand them in order to fashion a stand for a bamboo tray. The idea being for it to be a temporary table or drinks stand in our small patch of outside space.

The construction is a simple X-frame, with horizontal bars at each of the four points - 2 to support the tray, 2 to act as feet. These are joined to the X-frame using a 3D-printed bracket - the SCAD file for this is up on GitHub.

In order to stop the frame from spreading out and collapsing under the weight of the tray and it's contents, the feet were joined with some denim fabric, courtesy of an old pair of jeans. This allows the stand to be folded up, but providing plenty of rigidity during use.

Sewing things other than leather is a pretty new thing to me, my only prior sewing-related project being the lanyard I made a while back. So I'm the first to admit it's not the neatest work, but it does the job, so can't complain.

With the benefit of hindsight, the hinges allowed a bit too much flexibility, allowing the cross-bars to roll. The fabric on the feet alleviates this at the bottom. On the top, the base of the tray has a small lip which helps latch onto the cross-bars - whilst they still roll, it's impact is minimised and the tray/table works fine.

Thursday, 30 April 2020

Yarn slack winder

This is another of the lockdown projects where I'm trying to keep myself occupied during the Covid-19 lockdown by challenging myself to a project per week, using only materials from my workshop junk bin.

I don't crochet or knit, but my partner does, and I often end up watching TV whilst having been delegated to idly unwinding a ball of wool.

So, apparently, when crocheting or knitting, it's important to make sure that there's some slack between the workpiece and the ball of yarn. This usually means stopping every so often to pull more yarn from the ball. It can lead to inconsistent tension in the workpiece, making the work uneven.

This gave me an idea to create a yarn dispenser that could be hands-free, and unwind small amounts at a time, to maintain slack.

The OpenSCAD model
The design

The basic principle is to repurpose two rubber rollers (grey) from a printer. The bottom one is attached to a motor, which is housed in the case (red), and supported at the other wide by a support (yellow).
The top roller is attached to two mounts (blue) and is free-rolling.

The two mounts will be attached to their respective parts of the case by screws, where the tightness can be adjusted to allow more or less gap between the rollers, to vary the grip depending on the thickness/density of the yarn.
The yarn will be sandwiched between the two rollers, so that when the motor is activated by a foot pedal, it is pulled between the rollers.

To keep the two sides of the frame separate, they were mounted to a small piece of scrap acrylic I found. It's not a perfect size, but it's functional enough for this prototype.

The 3D printed models are pretty basic, but should anyone want to use them, they're up on GitHub.

The electronics

The motor is some generic DC motor that, like most things in the junk bin, was probably pulled from an old printer.

Most of the circuit for this was was salvaged from the old Smoke Machine project.

The SN754410 was de-soldered so that it would function in a more conventional way, powered from a 9v wall wart, and a TS7805 regular to provide 5v.

The circuit. The SW1 switch allows the direction of the motor to be easily switched. SW2 is the foot pedal that will be pressed to feed the yarn.

The electronics were built into an old business card box, similar to the USB KVM Switch.

With the circuit hot glued in place, a piece of a disposable pen was glued to the button to extend it's reach, so that it would sit slightly higher than the top of the box lid. This means the the circuit enclosure also doubles up as the foot pedal - pushing down on the lid pushes on the pen, and in turn presses the switch.

Finished product
In initial testing, it was discovered that the yarn would veer off to the side of the rollers and become tangled. As a quick-fix solution, I used a scrap of leather, punched a guide hole in the middle and tacked it to the input side of the rollers.

Tuesday, 31 March 2020

Simple USB KVM adapter

With the shadow of Covid-19 hanging over our heads, I, like many others, am now working from home.

Having my home PC set up right next to my work set up has been a bit of a pain - two keyboards and two mice competing for desk space. Plus the work keyboard and mouse was a spare wireless set I had kicking about - not really comfortable enough for long-term use.

The monitor I attached to my work laptop was the second monitor I use for my home set-up - thankfully it has two inputs, so that's an easy one-button switch.

I wanted to use my main keyboard and mouse with my work set-up as well as home, but didn't want to unplug/replug each time.

I also wasn't too keen or just ordering a USB KVM adapter (a device which lets multiple computers share keyboard, mouse and monitor), as recently some of our local postal and delivery works have fallen ill, and so I'm avoiding any non-essential deliveries - I don't like the idea of putting others at risk for stuff that's a 'nice-to-have'.

So I figured I'd look through the electronics pile and see what I could piece together.

I did have a PS/2 KVM that I was hoping to adapt, but having read the datasheet for the bus IC that underpins it, it had a low maximum current rating - it might have been fine for just a keyboard or a mouse, but the keyboard I want to use has a backlight, audio controller and USB hub built in, and a brief look with

lsusb -v

showed that they would easily surpass that maximum rating.

Software options are also a no go - whilst they'd been fine when working locally, they won't work with my work's VPN, the the IT guys have enough on their plate without me adding to it.

So, I ended up going for the simplest of options. I had some relays - they were obviously meant for higher power application than this, but found that wired up in parallel, 5V was enough to trigger them. I was planning on powering it from a USB port, so 5V was the target.

A rough schematic of the switch

Unfortunately they had a weird footprint that put one of the pins in between rows on standard perfboard, so I ended up dead-bug soldering them.
A diode across each of them to prevent voltage spikes from the coils, some USB extension leads and a switch later, and I had a 4 channel switch.

I was a bit concerned at the lack of a protective load on this circuit, but adding any additional resistance from the power to the relays would prevent them from switching - as they're really designed for higher power applications, I reason that the coils have enough power requirement to prevent a short.

I have ran it for a few days under close observation and seen no temperature / magic smoke issues, and it's only ever powered when I'm sat right in front of it, so it should be fine. Obviously if this wasn't a "whatever's at hand" project, there'd be much more elegant ways of doing this (bus IC, 4 pole switch, more appropriate relays, etc), but here we are.

A gratuitous amount of cable ties, double sided tape and an old business card box provides structure and an enclosure. I'll probably tidy it up a bit more later as time allows, but for now it's enough that it works.

Thursday, 16 January 2020

Beko WDR7543121W Washer/Dryer Repair

Over the Christmas holidays our Beko Washer Dryer stopped working. It was fine for one cycle, and a couple of days later when we went to do another cycle, it just wouldn’t power on.

After checking the obvious things – fuses, sockets etc, I noticed that when first powered (at the wall), there’d be a faint beep – like the key-press beep, but much quieter.

The machine was pretty new, so the first port of call was see if it would be covered under warranty. It’s about 18 months old, so of course just out of warranty. I tried contacting the retailer anyway to see if there was any room for good will support. Of course there wasn’t – planned obsolescence is their business model, after all.

Some online research seemed to point to the mainboard being dead.
Hoping to get things resolved quickly, I found a replacement board and ordered it.

When it arrived the next day, it seemed slightly different to the original – the part number showed “G09” rather than the “G08” that was already installed. I also noticed that although the board layout was the same, some components were either added or removed.
The original board
Reasoning it to be a more up to date and optimised version of the same board, I swapped them out.
Booting it up, it seemed positive to begin with – it beeped, the display lit up, and all seemed well.
Everything seemed to work just fine… until I hit start, and nothing happened.

A local repairman who I spoke to advised me that sometimes these boards require ‘programming’ to work with a machine – which is something even he couldn’t help with, as only the manufacturers’ own contractors are able to do that. Basically, it’s like DRM (digital rights management) for washing machines.
Curiosity got the better of me, so I popped the PCB out of it’s enclosure to take a closer look.

On the other side, there was an Atmel ATMEGA – a family of microcontrollers that I’m quite familiar with. It got me wondering if I could dump the firmware from the old board, find what exactly is needed to get the new one working – my guess would be a serial number or other identifier baked in there that I might be able to transfer across to the new board.

However, when I was researching this board, I found another web page hidden away at WasherHelp. It's for a different model number, but I figured worth a shot.
There was references to a diode on the board that failed – The one labelled D7 on the PCB. I checked on my board, and found that the same diode is dead on my board.

I de-soldered the diode from my board, an SR110 schottky diode, and started looking up alternatives. I found that the 1N4002 diode is similar specification, but is a regular diode, not schottky. This was bumping up on the limits of my electronics knowledge, so I asked a friend who has more professional electronics experience, and he told me it would probably be OK, but would likely run warmer and be less efficient.

I also had an 1N4002 on an old PCB in my junk bin. I swapped it in, gave it a test run, and it worked.

I’m happy that I got this sorted, and hopefully will help others extend the life of their appliances. I’m a little disappointed though that I didn’t get a chance to mess with the microcontroller/firmware stuff though. Perhaps another appliance will give me a chance to explore another time.

Disclaimer: This is just what worked for me, and is in no way professional repair advice or instruction. If you decide to do something similar, remember that you, and you alone, are ultimately responsible for the outcome.