My sons have large Lego minifig collections but most of it is lying in a large box. The older son wanted a cabinet so he could display (part of) his collection better. These cabinets can be pricey so I decided to make one myself. I’ve done some laser cut projects recently, such as the Darth Vader Chest Box and the Valentine’s Heart, so I decided to use the same technique for the cabinet.
The last month I’ve been working on my Darth Vader chest box. I’ve designed and built my own circuit with the Holtek HT8950A voice modulator, I create a laser cut case and designed 3D printed parts for the chest box. Since I had to learn a lot of new techniques, e.g laser cutting and 3D printing, this is by no means an easy project for me. With the project in its final stages now some design problems turn up that need fixing.
Soldering the board.
This week I soldered the components to the board. First I soldered the voice changer components and made sure this part of the circuit is working. Next I soldered the amplifier. I tested the total circuit and it worked the first time which is always a joyful moment. I find the Adafruit perma-protoboard very easy to work with since I’m able to copy the layout from the breadboard. Next I grouped all the buttons that operate the HT8950A on a board and soldered them to a piece perfboard. The buttons on the perfboard fit nicely into the laser cut side panel that I already made. Operating the chest box is easy with this (a major issue with my previous chest box).
Last week I made 3D printed parts for the front of the chest box. Unfortunately I found that these parts didn’t look good with the laser cut box. The plastic parts just didn’t do justice to the laser cut plywood. I therefore decided to laser cut all the parts that sit on the from of the box with I think is aesthetically more pleasing.
Another problem arose with the female audio jack connector that I need to plug in the microphone. The thread of this 3.5mm connector just isn’t long enough to be fitted onto the 6mm thick plywood. I designed a container to solve this. The audio connector fits into this container and the container is screwed to the case. Hopefully this container solves the problem.
Yet unsolved problems
I need to attach a nylon belt to the chest box. I’m thinking about popper snap fasteners attached to the belt to open or close the belt.
The HT8950A works fine with a proper audio signal as input but the microphone that I have, a small electret microphone, doesn’t give any audible output (except for noise). I assume that the signal is to weak and therefore needs amplification.
The last couple of weeks I worked on a homemade voice modulator that is easy and cheap to built. First I’d like to mimic the Darth Vader Voice Changer, but with the press of a button it can be changed to robot or helium kind of voice effects. Last week I’ve steadily continued my work. The project has two main parts, the electronics and the case.
For the project I choose the HT8950A voice modulator from Holtek as the heart of the circuit. It is cheap, versatile and easy to work with. I previously had the voice modulator working. I only had to amplify the signal which seemed simple enough. Well, that turned out to be a bit more troublesome than expected. After connecting the LM386 to the circuit and powering it up an annoying hiss was introduced. After some experimenting I figured that the breadboard was to blame and decided to copy the circuit to another breadboard. Although on the new breadboard the hiss appeared somewhat reduced but it was still at an unacceptable level. Even when I removed the input signal from the LM386 the hiss continued. I connected the HT8950A with a audio-jack to an external amp. I wanted to make sure that the hiss was coming from the LM386. With the external amp the hiss was gone. The fact that I had hiss without an input signal indicated that the supplied voltage wasn’t clean. To clean it up I placed a small capacitor (10nF) from pin 6 (V+) to ground and voila the hiss was gone (see schematics below). It took me some time but I’m almost ready to finish this circuit and solder it to perfboard.
Two (almost identical circuits) with the Holtek HT8950A voice modulator and the LM386 amplifier. Both circuits gave a hiss which was unacceptable. Eventually a simple 10uF capacitor from pin 6 to ground did the trick for me.
Schematics of the Darth Vader voice changer. I was able to eliminate all the hiss and noise from the LM386.
Printing the case.
I decided previously to make a T-slot plywood case for the Voice Changer but I’m not satisfied with the result. First I made a beginners mistake with the tab width. It was chosen poorly resulting in fragile edges of the case. Also I discovered that a T-slot case is not the best choice for this project. The case needs to be sturdy and the T-slot isn’t. I’m afraid it will fall apart when in use. Therefore I’ll made a regular finger joint that will be glued together. This new case was much better. Gone are the fragile edges and I’m confident that glued together it will be very sturdy.
Laser cut case made out of plywood. I first used a T-slot type of case but made a beginners mistake with the tab width and positioning. As a consequence the edges become very fragile. The front of the case has engravings for the positioning of large controls of the voice changer. These controls on the front will we dummies just to mimic the look of a Darth Vader voice changer. The actual controls will be on the side of the box.
Laser cut case with regular finger joint. This attempt is much better.
The first voice changer that I made had a handmade 1/2″ thick plywood case. Making it was very time-consuming and it’s a bit heavy. I felt I could do better. This year I got interested in laser cutting but until now I only read about it. The laser cutter isn’t as widespread as the 3D-printer. The laser optics combined with the CNC bring a whole range of possibilities when compared to creating by hand. First of all you can design with a computer and then send your file to the laser cutter greatly increasing the precision of the case. Second I can make casings that I never thought were feasible, e.g. it is possible to curve the wood by cutting in certain patterns, make complex wood joints normally the territory of professional carpenters or create detailed engravings in just minutes, just to name a few.
In the area where I live there is a FabLab that provides me the possibility to use their laser cutters for a modest fee. I’ve already been there to test the equipment. To create a case I started with an online tool called Makercase. It’s an easy to use tool that, once you’ve entered the parameters on length, width, thickness etc, provides you with an svg-file. The svg-file can be opened and changed in Inkscape, a free vector drawing program. Adobe Illustrator and Corel Draw are fine too but they are expensive and proprietary programs. Inkscape has a learning curve so I have spend the better part of the week to get acquainted with the program. I nevertheless made good progress and hopefully I’ll be able to have the case ready this week.
Image of the by Makecase generated svg-file. I choose the T-slot design and a thickness 1/4″. This is half the thickness that I used for the earlier version of the Darth Vader voice changer.