Signal Generator Housing Box
Description
This model is a box I designed to house a small signal generator kit available from Aliexpress (link in parts list). The kit includes the PCB and all components needed to complete the kit. I buy these inexpensive kits simply to get more soldering experience. I usually try to make some kind of box to house the completed kit and make it usable as an instrument. It is certainly not a professional signal generator as it produces four types of wave patterns (square, sawtooth, triangular, and sine) at a single frequency; there is an onboard potentiometer to adjust the output voltage. Another reason for designing a box is to get more experience designing 3D models using FreeCAD. I include the FreeCAD file that generates the stl (step) files. Since I wanted the resulting build to be useful, I decided to dress it up with a USB-C socket for a power source, a power switch to be able to turn it off without having to unplug the power, and added a rotary switch wired to the waveform selection pins on the PCB. None of this is needed simply to test the build of the PCB; however, all of these activities add experience. I design the lids (or bottoms depending on how I want to mount the PCB) to exactly fit by pressing the lid down onto the bottom. A 3D printer that accurately prints the dimensions of the model allows me to use this tight fit; your mileage may vary. I wanted to have a dial for the rotary switch so that the position of the specific waveform would be visible. However, the box is too small to have many printable characters. I also designed the lid for this box with the top down on the build plate so it needed no supports and the 2mm inset would perfectly fit into the base. Because of that, I designed a separate dial that fits over the rotary switch threaded shaft and is held tight by the switch's mounting nut. Numbers on the dial are 0-4; 0 is no connection (i.e. no waveform is selected), 1 is square, 2 is sawtooth, 3 is triangular, and 4 is sine. The 3mf file is a Bambu Labs file containing all three bodies of the model; the dial has been painted for use with the Bambu Labs multicolor printing using the AMS. The dial is only 0.8mm thick, so a regular printer can be paused at 0.8mm for switching filament to another color. Or just print in one color and use a marking pen to highlight the numbers. One of the images shows the wired waveform generator being tested; another shows the box completed and assembled. Assembly: it is a tight fit to put the components in the box. In fact, instead of using Dupont connectors which have rather long terminals, I wired, it up using 25-gauge wire for the power (USB-C G to ground, USB-C V to switch, switch to V+ on the PCB), and the two wired for the output to the banana jacks (+ to red, - to black). Mount the USB-C socket first as the M2 screws are quite small and it is easier to connect the screws if nothing else is in the interior of the box. Then position the PCB in place and screw in the three M3 screws. Push the power switch into its mounting hole and solder up the power wires. Mount the two banana jacks onto the lid and bend up the solder lugs 45 degrees; then solder the output leads to the banana jacks. I used standard Dupont connectors to plug into the PCB waveform selector pins (top pins are common ground). For easy identification, I used wires red, orange, yellow, and green (matches the resistor color code) for positions 1-4 of the rotary switch. The rotary switch is quite inexpensive. One drawback is that there are absolutely no markings that indicate the pin to use for each position. This was determined by testing the switch with a ohmmeter. As it turns out, there is a small nib (nub?) on the switch bottom that is used to keep the switch from turning while tightening the mounting nut. The pin for the first position I call 0 is just to the right of that nib; you can see this in the picture named "SwitchWiring". Numbers 1-4 continue clockwise when looking from the front. Mount the rotary switch onto the lid placing the dial on before the nut. Them solder the 5 wires: black to common, then red, orange, yellow, and green to the correct switch positions. I used a knob that I came with a box of potentiometers; however, you can easily print a knob using one from the link in the parts list. Push the lid onto the base and you are finished. "BoxCompleted.jpeg" sho9ws the completed state of the box. Parts List: Waveform Generator: https://www.aliexpress.us/item/2251832865322054.html Banana Jacks: https://www.aliexpress.us/item/3256805556063878.html USB-C Jack: https://www.aliexpress.us/item/3256805611239221.html Power Switch: https://www.aliexpress.us/item/3256805374235793.html Rotary Switch: https://www.aliexpress.us/item/3256804365554680.html PCB Screws: M3x6 Socket Cap - need 3 screws. USB-C Jack Screws: M2x6 with nuts. Rotary Switch Knob, if needed: https://www.thingiverse.com/thing:1465938/
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