Collection of smaller projects 2

published: by Maarten Tromp.

After writing the first collection of smaller projects I realized there were many more projects I've hacked together over the past years. Just like in part 1, some projects are old, some are unfinished, some failed miserably, but I would like to share them anyway. Each of the projects by itself would be too small for a full article, so this is a another collection of short articles.

Universal Cereal Bus

project date:

With this recently introduced USB standard, I realized the following:

Q: where do you put your breakfast cereal?
A: in the Universal Cereal Bus.

Realization and printing the label happened during breakfast around 2002.

Alarm clock switches computer on

project date:

My student room was a single room. I had a huge self-assembled computer, but it was so noisy I couldn't sleep with it powered on. So in the evening I powered down the computer, go to sleep, and in the morning, get out of bed and power it up again. Now how can we optimize this? If my computer were to power up automatically in the morning, that would save me one step. The BIOS had an option for that, but it could only power up on the same time every day. Since my schedule was more flexible than that, I needed a more flexible solution. There is however a device that knows exactly when I should be getting out of bed; my alarm clock. So why not switch the computer on when the alarm sounds?

I opened up the alarm clock. There were only a few parts inside; transformer, buttons, display, piezo speaker and a black blob chip. Given the options I choose to use the piezo speaker as trigger. I mounted a 3.5 mm jack chassis in the side of the alarm clock and wired it in parallel to the piezo speaker. From there I ran a wire to the computer.

Inside the computer I connected the wire directly to a TIL111 optocoupler from the parts bin. The optocoupler output was connected in parallel with the power button. If I recall correctly this was all the circuitry there was. No smoothing, no debouncing, no current limiting, just a single optocoupler. Now if everything would go according to plan, the alarm clock would drive the optocoupler as well as the piezo speaker, tricking the computer into thinking that someone had pressed the power button.

The setup worked first try! Since that day I woke up to the sound of my alarm clock and my pc. And since I could not sleep with the computer powered on there was nothing else to do than get out of bed. Talk about win-win.

However, as I found out later, snoozing the alarm would trigger another alarm 9 minutes later. This would simultaneously be transferred to my computer which registers it as another power button press and starts to power down again. This was clearly not the intent.

To counter this effect I could wire the alarm clock to the wake-on-lan port on the network card instead of the power button. This would provide the power up functionality, without the power down side-effect. But before I got around to do this something unexpected happened. I replaced the hard disk with a bigger one. But the old hard disk, being some old server disk, was the reason why my computer was so noisy in the first place.

With the computer much more silent I could sleep with it powered on. There was no more need for the alarm clock power switch. So soon I started to work on a script that would play music in the morning to get me out of bed.

Trunk lid lock protection bar

project date: , project by Maarten Tromp and Kees Stein, article by Maarten Tromp

My first car was a Peugeot 205 Terberg. The model is like a regular 3 door Peugeot 205, but fitted with a plastic extension on the top and back to make it into a light van. It was perfect for me. A lot of stuff fitted in the trunk (sound system, servers, furniture) and the car had room for a single passenger. It was cheap, light, fast enough and fuel efficient.

However, one part of the conversion was not thought all the way through. The way the trunk lid closed was a bit silly. The lid had a normal lock that grabs a pin. So far so good, but the pin itself was sticking straight up in the door opening. On a normal Peugeot 205 the pin sits at an angle, because the trunk lid is at an angle. That way you never hit the pin while loading stuff in the trunk. But with the conversion the trunk lid is vertical and so is the pin. Everything you lift in the trunk hits the pin. And since the pin sits on an flimsy angle bracket, it would bend inwards and then the lid wouldn't lock properly. It took me a while to figure out what caused the lid not to lock at times and started to use a bungee cord to hold the lid closed instead. When I finally found the culprit I wasn't sure how to fix it. I kept bending the pin back up, but it kept bending down again. Clearly a better and more permanent solution was needed.

Luckily Kees, my stepdad, is a mechanical engineer. He has experience with with metal work and was willing to help me come up with a solution. We decided to make a metal protection bar to go over the pin.

First we bent a metal bar, formerly part of espagnolette window lock, into a U-shape. Heating it up over the furnace in the kitchen and then bending it over some bricks were things I, being an electrical engineer, would have never thought of. Then we welded it on a piece of angle profile. This was also something I had never done before. Who would have thought mechanical engineering would actually be this useful? Last we mounted the angle profile on the bottom of the trunk, so that the U-shaped bar sits over the pin. With a little paint it wasn't even all that visible.

This protection worked flawlessly. The pin never bent again. After years of use I can say this hack worked perfectly.

Circular saw case

project date:

The circular saw I had bought, didn't come with a case. Just like my microscope, but several years prior to that. At the start of 2008 I was looking for a simple project and building a case for this saw seemed just right.

The case is designed to fit snugly around the circular saw and be as compact as possible, even though the saw has handles and bits sticking out on every side. The enclosure is made from 12mm birch plywood, maybe a bit overkill for this case, but beautiful to look at and really sturdy. To not spoil the looks with screws, all joints are glued. This was an experiment for me but the case proved strong enough to stand on.

Below the saw are three supports. Two L-shaped pieces, one on each side of the saw blade, and one U-shaped piece supporting the motor. There is some space left for the power cord and a ruler. The remaining parts, butterfly lock, handle, hinges and rubber feet, are actually flight case parts. These were more sturdy and elegant than what was available at the local hardware store. These bits were riveted on, to complete the flightcase-look. One thing I particularly like is the handle on top is mounted right over centre of gravity, which differs from the geometric centre.

The case is in use for over a decade now, but looks hardly worn. Only the metal parts oxidized a bit during those long cold winters sitting on a shelf in the shed.

Laptop lid mod

project date:

My laptop wasn't all that recognizable. It was a run of the mill Dell and easy to lose it between other laptops. I would like something a bit more me.

Then I realized that the backlight on the screen probably leaks out the back as well, so if you were to drill a hole in the lid, light would shine out. This was easy to test and indeed if you take the cover off, light is visible around the back of the screen. I decided to drill a '#' as it's a relatively simple shape, symmetric and symbolizes a root shell. Drilling and sanding 136 holes later, the pattern was there to stay. Unfortunately there were some plastic supports for the backlight that would block some of the holes, so I cut those.

The trick worked perfectly. Whenever the screen of the laptop was on, a beautiful lighted hash-sigh would be visible on the lid. I was planning to add a greenish colour filter, for the genuine terminal feeling, and to keep the dust out, but I never got around to actually do that.

Unfortunately I didn't take any photo's of the laptop at the time and the laptop itself has long been retired and lost.

Password manager

project date:

When looking for a simple password manager that would work over ssh, I could find none. Everything seemed to be graphical, web based or complex. So I did what any hacker would do, I made one myself.

My password manager is a simple GPG wrapper script. All passwords and login details are in a single encrypted text file. The script decrypts it for you, starts a viewer or editor and re-encrypts afterwards when needed. It takes care of temporary files, backup and shredding plain-texts. This script fitted the need I had for a simple tool that would work over ssh and has done exactly that for the better part of a decade now.

The script can be found in the downloads directory.


project date:

We happened to have a surplus clothes iron. I have used it in the past for making PCBs, but with my new printer it never worked quite right. It seemed like such a waste to throw out the iron.

A while later, while browsing the Hack42 website, I came across Aequitas' and Moem's Strijklicht. Now that is creative use of an old clothes iron, so my build is shamelessly copied from inspired by this hack. The word strijklicht is a play on words. Strijken means to iron clothes, licht means light. Combine those words and you get strijklicht which means something completely different; the light just skimming over a surface. One might call this a word hack.

When I opened up the clothes iron, I removed the water reservoir and heating element. Surprisingly it turned out not all holes in the sole were connected for steam. A considerable amount appears to be there for decoration only. The ones that were reachable from the inside I drilled out to fit 5mm leds. To get the leds just right I ordered some extra bright, warm white leds on Ebay. The leds turned out to be almost yellow, but I didn't want to go through the order-wait-test cycle again, so I used them anyway. Under the temperature dial I fitted a pwm dimmer, also from Ebay. Now you can dial in the brightness with the old knob. The spray nozzle, barely visible on the photo, holds another led. To power all this I managed to squeeze a compact 5V wall wart in the space previously occupied by the water reservoir in base of the iron. Now this enlightened iron can even be powered via the original braided power cord.

Teapot lampshade

project date:

The teapot at the office was leaky. Instead of throwing it out, I offered to adopt it. With the recent conversion of a clothes iron to lamp I thought I might also give the teapot a second life as a lampshade.

First I started to cut the bottom out with an angle grinder. The teapot turned out to be a double-walled affair and quite a bit of trapped tea came out once there was a hole. When everything was dried up again I found out that cutting neatly around the edge of the bottom was difficult. I wanted to get as close to the wall as possible, but without damaging the wall itself, and an angle grinder is not really a precision tool. I ended up cutting away tiny triangles and using a sanding disc to clean up around the edge.

With the bottom cut out, I started working at the top. The lid needed to be fixed so it wouldn't come off when the lamp was hanging. So with the lid closed I tried bending the edges of the lid outwards. This didn't work since there was limited space for me to work and the edges turned out to be very strong. Then I tried soldering the lid closed, but that didn't work either. My soldering iron didn't have the power to heat up all the metal to soldering temperature and I was afraid for discolouring the outside if I were to use more powerful tools such as a blowtorch. In the end I glued the lid in place and that worked just fine.

To hang the lamp and feed the power cord in, I needed a hole in the top of the teapot. So I unscrewed the black knob form the top and drilled through the threaded hole with a slightly bigger diameter. The metal part of the lid had a threaded rod sticking out the top, so I drilled from the bottom instead. All that was left to do was feed a cord with light socket through the top and hang it.

While writing all this down I realized the teapot could do with a mains earth connection.

Electronics workbench

project date:

In our previous house I had made a desk to size for our study. It was bolted to the wall and shelves were made around it. There was no way that desk could easily be moved into the new house. So I started thinking what I would like to have instead. There was no shortage of ideas, ranging from buying a professional lab table to see what I can make from the scrap wood in the shed. I decided on the latter.

The resulting desk is 180 x 80 cm, which is more than big enough for me. It is made to be standing height, which for me is 91 cm. There is a shelf over the desk to hold some equipment. The shelf is 30 cm deep, 35 cm high and has approximately 29 cm of height under the shelf. The frame is made from 44 x 69 mm studs, left over from the attic construction. The top is made from bits of 18 mm plywood, once given to me by the neighbour cleaning out his shed. Everything is screwed together thoroughly since some of the wood is a bit warped.

With the base desk done, it's time to dress it up. I added two more supports for the shelf, which left exactly the right space for three 19 inch racks (not really a coincidence) at the back of the desk. For proper equipment mounting I installed three sets of 6 U racking strips. In the 19 inch racks went some 19 inch power strips without power switches. Everything on the desk and the shelf, is connected to those power strips which are are in turn connected to a big power switch on the top left corner of the frame. The switch acts as a "bench on / off" switch but also as panic button.

For the work surface I acquired an ESD mat, made to measure. Apart from being static dissipative, the mat provides a tough rubber work surface that withstands the abuse of sharp bits and soldering equipment. On the roof, over the desk, I mounted some led panels. They light up the desk nicely and also act as an indicator for whether the desk is "switched on" or not. Last I added some tool drawers. Now I finally have the space to organize my screwdrivers and pliers with room to spare.

Next to the desk are some Ikea Ivar shelves to hold parts and projects. Once again, more space than I can fill, or at least for now.

Shower hose door loop

project date:

The wire from the smart cat flap kept getting caught by the door. A simple problem, with a simple solution.

There are commercial door loops readily available, but why buy new when you have a shed full of parts? The loop is made from approximately 30 cm shower hose. Cutting it with a hacksaw is tricky because of the interlocking metal wrap. I'd rather use an angle grinder next time. Be sure to file and sand the edges, you don't want the edges to cut into the wiring. The loop is held in place with electrical conduit clamps.

The result is not the most beautiful thing, but it's practical, free and made quicker than a round trip to the hardware store.

Momentary latching switch

project date:

For my bass guitar effects board I made a ABY splitter. It feeds the bass guitar signal to either effects chain A, effects chain B or both at the same time. It has two buttons (A and B), one for each output. The problem with buttons is that sometimes you want a button press to be latching, and sometimes you need it to be momentary. That is why this splitter is special.

If a button press is shorter than 250 ms the switch will be latching. In other words, when you tap the button like you're used to on any other effects pedal, the output will switch on and off like you're used to. The box will behave exactly like any other ABY splitter. However, when a button press is 250 ms or longer, the switch will be activated momentary. The output will switch back once you release the button. It behaves like a doorbell now. This allows you to activate an output for a short period of time, say only a couple of notes, without having to repeatedly press the button.

As you might have guessed; there is a microcontroller in the box. The buttons connect to an Atmel tiny2313 AVR, which controls two relays. The processor times button press duration and decides whether to switch momentary or latching. The relays are Takamisawa AL5WN-K, 5V bistable type. This specific model was suggested in a thread. The coil is connected between two output pins of the avr, as suggested by another thread. There is apparently no need for a H-bridge driver, it all works just fine without one. Pulsing one output pin high, while keeping the other one low, will switch the relay on. Pulsing the other output pin will switch the relay off again. You need to keep the pulses to a couple of ms to avoid burning up the coils though, as described in the data sheet.

Source code, schematic and data sheets are available at the downloads directory.

Geek jewellery

project date:

For my girlfriend wife I have made some geeky jewellery over the years.

The first set of earrings I made her shortly after we met. It is made of ICs (Philips HEF4027BP, dual jk flip-flop, DIP). The legs are cut short to prevent them from getting stuck in your clothing. The hook is on a bit of thin solid-core wire that just fits between the IC body and the legs. Unfortunately it tends to bend a little.

Later, when we realized (and admitted) we are both Trekkies, I made some StarTrek TNG (The Next Generation) logo earrings for her birthday. These are cut from FR4 PCB material, since that was the only suitable material I had lying around.

Next pair of earrings are two sets of d6 dice I made for Sinterklaas (Dutch holiday). Since my girlfriend wife is a role player and general board game player, this seemed only logical. The dice were sourced from Ebay.

Since we share the hobby of drinking tea, I started looking for tea cup or tea pot related pendants. When I found some on Ebay, I made those into earrings again.

For our wedding I got a bright idea and made some earrings from bicycle light bulbs.

The most recent addition is a birthday present. It's a processor pendant (Motorola MC68HC000FN20, 32-Bit MPU, PLCC86) to go with the IC earrings.