viljamiP&S

I'm Viljami Pirttimaa and I post about some of my projects and solutions to small everyday problems. Some of the projects are done and in use, other are unfinished and waiting to be continued. This blog is not meant to be a guide to replicate any of the projects but if you need help or more information, feel free to ask.

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P: Adding external speaker to a Sonos system S: Ikea sells Sonos compatible speakers for 100 €. The speaker has a stereo amplifier whose two channels are used to drive a tweeter and a woofer. Crossover signal processing is done digitally by the Sonos system before the signal is sent to the amplifier. With some reverse engineering of the PCB I found the line level signals. I added a small op-amp circuit that mixes the signals and outputs it to two RCA jacks I added to the back of the speaker.

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P: My NAS was running quite hot inside my closet. S: I designed and printed a manifold that guides the exhausted hot air out of the closet through a vent that I installed to the side of the closet. Temperatures of the hard drives dropped by 10°C and the noise level didn't increase much. Hopefully my landlord doesn't mind the vent. CAD files on Onshape: https://cad.onshape.com/documents/0dd9dc2a8b62412346458d8d/w/ecc2b8e333d2a76af4380024/e/00393c9644a2aac2b6a8ff82

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Shuttlecock launcher that was built on a Machine Design Project course at Aalto University. The machine was designed and built as a group project. My task was to design the launching mechanism that consists of the two DC motors, two motor arms and the slide that guides the shuttlecock to the spinning wheels. The largest challenge was the violent vibrations caused by the cheap unbalanced wheels. Had we had a little more time we probably would have turned our own wheels on a lathe. In the end we had to run the motors at half their rated voltage but the launcher worked quite nicely. The documentation of the project can be found here: https://drive.google.com/open?id=1n7NWDvyfS5r9suAHYqp7zvVqkKHslrm9

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P: I needed a teleprompter for a school assignment. My dad has a Parrot teleprompter that uses a phone as a screen. It has a 77 mm lens filter thread for mounting it onto a camera. I needed a new mount to use it with a webcam on top of my monitor. S: I designed and printed a simple holder that replaces the lens filter mount. I added some closed cell foam to the side that sits against my screen to prevent scratches. CAD files on Onshape: https://cad.onshape.com/documents/5c6e407f059bf7079a335365/w/85356f6629a17c794aca2aa0/e/5cebaff5fcd4f8eccc88c617

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P: Pocket sized roll of Gorilla tape collects dust and dirt if I keep it in my backpack. S: I designed a 3D printed case for the tape roll. The two pieces are held together with a printed thread. Both pieces have a taper that tightens against the cardboard core of the roll so it doesn't rattle inside the case. CAD files on Onshape: https://cad.onshape.com/documents/347f99ad600713e91e4eab76/w/d43f0dd02a031ef17837960a/e/008d7f345e16d173b3279714

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P: I got myself an electric standing desk whose rated capacity was 120 kg. When I put all of my lab and computer gear on it got quite slow and it sounded like it was struggling when I drove it upwards. S: I estimated that I have about 125 kg of load on the table. I decided to buy a third leg to gain an extra 60 kg of lifting capacity. I didn't want to take all of my gear off the table so I used some Ikea trestle supports to lift the legs up. Then I was able to remove the tubes under the desk and slip the third leg in the middle. I didn't want to use the large foot on the middle leg as it would hit my legs when I'm sitting. I decided to 3D print a small foot that is the same heigth as the original foot. I used 100 % infill and PLA filament. It seems to handle the load without problems. CAD files on Onshape: https://cad.onshape.com/documents/ad45721d45c539f683473892/w/d88c4e11f755674a64cf7d23/e/ea22e2f2427e3dee141be069

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I built this robot as group project for a course at my university. More details, including a better die detection algorithm, are described here: https://wiki.aalto.fi/display/MEX/Kimble+Robot

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P: I needed to build a computer vision system for a robot that plays the Kimble-board game. The plastic dome over the die distorts the pips and is prone to reflections. The die sits on a reflective metal spring that makes thresholding the image a lot harder. These issues make the detection a lot more difficult. S: The detection is done in five major steps: 1: The image is captured with a webcam whose position is not constant with respect to the Kimble board. This is done inside the captureImage.py file. 2: A transformation matrix is calculated with homography. It matches similar points between the distorted camera image and a straight reference image and then calculates the needed transformation to straighten the camera image. All of this is done inside the findPerspective.py file. 3: The die is always in the middle of the straightened image. The image from the previous step is cropped, made grayscale and noise is filtered with a bilateral filter. 4: A gradient of the image is calculated with the cv2.laplacian() function. The gradient shows the rate of change of the image brightness across the image. This means that all sharp edges like the ones between the pips and the white body of the die show up. This image is then thresholded and cleaned up with erosion and dilation. 5: Small white circles that are likely to be the pips on the die are searched with cv2.findContours(). The image is then cropped around the middle of all such points. That cropped image is smoothed, and its contrast is adjusted with the CLAHE method. The pips are then recognized with a simple blob detector that filters by area and circularity. Lastly the minimum bounding box around all the detected circles is calculated with cv2.minAreaRect(). If the dimensions of that rectangle match typical values for the amount of pips detected the detection is likely accurate. If the box has dimensions that differ more than 10% there is likely a blob that was falsely detected. Each blob is removed one at a time and a bounding box is calculated for each combination of blobs until a bounding box of plausible dimensions is found. Developing this software would have been almost impossible without implementing some automated testing. The nature of the problem is such that fixing an issue affecting one image is likely to break the detection on other images. By running the automated test I could see the big piture and focus on fixing the issues affecting a lot of images. It took me a few hours to get about 70% of the test images detected correctly. Bringing that up to 100% of the test images took about 20 hours. It could even reject my two fake dots on a die that had three in reality. This was a test of the algorithm rejecting falsely detected reflections on the dome and the spring. The source code is available on GitHub: https://github.com/viljamip/kimble-die-detector

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P: Milling makes a mess S: I designed an air pistol that swivels on a ball joint. The ball is a suspension part from a car. Top and bottom plates are machined from POM (Delrin) to mate the ball. The air pistol is mounted on top of the eclosure. This setup allows me to keep the doors closed and blow chips to the dust extraction funnel in the back corner. The vacuum helps to seal the doors and keep the chips in. CAD files on Onshape: https://cad.onshape.com/documents/ba3b1182d229dbf4aadb7515/w/1f64538b96b2f396e0333770/e/fe534ce7d6868de2cc48eb23

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P: My friend's guild at school did not have enough keys for its members. They needed a way of sharing a key with every member of the guild. S: Me and my friend Marton made a prototype of safe that can be opened with Telegram messaging service. I did most of the electrical and mechanical design and manufacturing. Marton did most of the software development. Inside a laser cut acrylic box it has an ESP8266 microcontroller with WiFi, Nema17 stepper motor and a 3D printed rack and pinion for the linear movement. Mechanical locking is done with a solenoid.

CAD files on Onshape: https://cad.onshape.com/documents/f366d068354acfe174802381/w/ba0ea47974a01133c210c260/e/3963479bea16442e9843a653

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P: Stepper drivers needed a bit of extra cooling S: As the xPRO CNC board conveniently has two pin headers on the opposite sides of the drivers, I decided to use them to mount a fan. The 6 pin ISCP header has 5V and GND pins which power the fan. The final design is quite compact and easy to install. CAD files on Onshape: https://cad.onshape.com/documents/9c124d1502f4031b1e0a1865/w/1c0b8a66fcd19e05899220f6/e/897f7a3262bf63e7283b9811

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P: A robotic lawn mower needed a home S: I designed a tiny house with a door mechanism that operates with springs. When the robot starts mowing it pushes the door open and spring tension keeps the door up. When the robot gets back home to the charger it pushes on a bar that pulls the door shut. Spring tension keeps the door securely shut.

CAD files on Onshape: https://cad.onshape.com/documents/d541c8e7b6ce76f6978c73a9/w/cd2a3f9787ccfedbb18261bf/e/fa53fc9ed853d52072cca5a3

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P: I broke a tap in a piece of aluminium I had spent quite a while machining. S: Luckily Youtube has a solution for everything. I bought a kilogram of alum from a local crafts supply store. It dissolves steel but doesn't touch the aluminium. Here is what is left of the tap after it had been 1 h 30 mins in the boiling alum solution.

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P: Dishwasher's plastic part had lost its rigidity and it caused the basket to drop down all the time. S: I could not find a matching spare part online so I had to make one. I put the part to a regular office scanner and measured a few things to make a CAD-model. I printed it in ABS for heat resistance and acetone smoothed it to minimize bacterial ingress. It took three iterations to get every detail just right. The last image shows the printed part 17 months later. It looks a bit ugly but still works just fine. CAD files on Onshape: https://cad.onshape.com/documents/eab1f7b2c537e1fc5b41adde/w/1bbe57dfe36e41b5e0621d86/e/966cfc227240010c9571ab45

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P: An infrared heater needed a timer. S: Timers for coffee makers are cheap. I designed and printed a wall mount for a timer bought from Clas Ohlson. It simply has Schuko sockets on the top and the bottom. CAD files on Onshape: https://cad.onshape.com/documents/e978f2e75a795bc7e07ea30c/w/87a4150438cfc191d55aa2c4/e/44a02d8581c2957d1e7b27eb

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P: I didn't have a good place to store small electrical wire. S: I designed and printed a hanging spool holder. It has a notch to keep the loose end of the wire secure and a snap fit to make changing spools easy. I printed in ABS and used acetone smoothing to make it a bit stronger and it also looks a bit nicer. CAD files on Onshape: https://cad.onshape.com/documents/ed5164bec301cb212265326d/w/21f66215ea0ef3a2b23525ab/e/b8ad2dfacd1df8b8ba2ef4f6

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P: It is very hard to fill a Peugeot pepper mill S: I designed a snug fitting funnel with a narrow pouring spout. Now it is easy to fill the funnel, shake a little and pour the excess out without making a mess. CAD files on Onshape: https://cad.onshape.com/documents/1b4925daaba3454b400b88b6/w/b20ca76db4babd384b3f8e1b/e/420be7c7651d1833ca136d73