This project was born out of constellation of things and desires :)
I've always wanted to make up a CMOY amplifier, just because I think it is a cool project and I always wanted to see if the headphones amplifier makes sense. I did buy my components, but never got to actually making it.
Next, while looking through my stuff recently, I've came across these 16340 cells that I bought for some reason. And finally, being a long time user of PCB sensors (excellent btw), both in the academy and in the industry, I wondered if we can find a "better" use for their sensor boxes other than...well.. holding sensors :)
It all boiled up to the point when I decided to fit a CMOY amplifier inside one of these boxes. Since we are in the modern age, of course it will be powered from rechargeable lithium battery which can be easily charged and used for charging phones and stuff. And being in the modern age, why not fit an additional Bluetooth speaker to the device?
The merit for this is as follows: the main functionality is to be a headphone amplifier (it is worth it by the way). Then, every once in a while you will need the bluetooth speaker, so just flip the switch and use it. And along the way you will want to charge an occasional phone. This device will give the answers for all three.
So, here it goes, I hope you will enjoy this instructable.
Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.
Step 1: Schematics, Parts List and Tools Needed
These are the parts I've used in my build. You can reference this and create your own variations, you will need the following parts:
1. Box - I used the PCB sensor box, it is a square box 87mm by 87mm, with 30mm height (outside dimensions)
2. 16340 cells, I don't believe they are more than 1000mAh, but all kinds of stuff is printed on them, here are some options:
3. Micro USB charger board, this will charge your cells from standard cable:
4. Booster board to 5V including USB socket:
5. Bluetooth receiver + amplifier board:
6. Voltage booster 2A - to power the CMOY:
7. 2 position switches:
8. 3.5mm stereo sockets, these are very nice:
9. Various LEDs - I used red blinking led and a green one, your choice may vary.
10. Two small speakers, I salvaged mine from an old laptop. Weirdly they were not identical, but I used what I had.
11. Parts for CMOY amplifier, will talk about it later
You will need the basic tools:
1. Soldering iron
2. Dremel tool
3. Hot glue + gun
5. Files, knife, the usual stuff...
Step 2: Get the Charger Indication LEDs Outside
The USB charger has two indicating LEDs that tell you the status of the battery. Red one which indicated charging state and the blue one which indicates full battery. I wanted them to be visible with closed box. For this reason I added two more LEDs with wires parallel to the existing ones on the board.
First, verify your polarity, it matters where is + and - on the LED. Then solder the wires to looase leds with proper shrinking. Lastly, solder them carefully to the board.
I used a small flashing red LED for the charging status, and solid green one for the fully charged indication.
Step 3: Prep Your Base, Determine the Layout, and Fit Things to the Base
You will have to determine which component goes where. This determines your battery layout and the placement of all parts. In my case I had to add two more cells at side of the existing four.
Solder the batteries in parallel.
Don't forget to add leads to your battery pack, you will have to connect it to the charger, have one output for the USB port and one output for the CMOY voltage supply. The Bluetooth amplifier is fed with 5V which I extracted from the USB out board.
Drill your holes and openings for the things, fit the LEDs and wire everything. The components are glued in place with hot glue.
Your base is ready.
Try charging and output, validate all functionality (red is blinking in pictures).
Step 4: Fitting Things Into the Lid, Prepping the Switches and BT Board
After finding the place for every component that sits on the lid, drill the appropriate holes.
There are two for the switches, two for 3.5mm jacks and "grill" for the speakers.
Next, because this box is intended for life in backpack, I did not want any accidental on/offs. For this reason I shortened the levers on the switches with Dremel cut off wheel.
Next, remove the unnecessary plug hub from the BT module, I will solder the speakers directly.
Step 5: Fit and Hot Glue Everything That Is Not CMOY
Wire and fit everything into the lid.
We are left with CMOY amplifier assembly, wiring and fitting.
Step 6: Soldering the CMOY Amplifier
This amplifier needs no introduction and explanation. This link was really helpful:
Also, I used this resource for advice and information: https://tangentsoft.net/audio/cmoy/
I did use the BUF634 in order to stabilize the virtual ground: https://tangentsoft.net/elec/vgrounds.html
I'm adding my schematics, due to the simplicity and straightforward layout, it helped me a lot.
During the fitting and idea process, I've built this circuit on a separate pcb. Later, I redid it with cleaner installation.
You can make the circuit more compact, but I had to do it more flat in order for the box to close.
Once the circuit is ready, add the in and out 3.5mm jacks, with appropriate wire length.
If you want the parts for this amplifier, please send me a message. I'm still left with stuff and I'm looking into thinning my inventory :)
Step 7: Fit Everything Inside, You Are Done!
Dry fit all, then hot glue everything.
Add the 3.5mm jacks.
Validate the lid closing.
This box is cool!
It actually looks way cooler once opened, for this reason I wanted a really clean installation inside, I think I made it.
The music does sounds better once fed through the amplifier, it is "deeper" - the best description of my non-audiophile ears :)
The speakers are not very loud but can be a solution in occasional group meeting.
The CMOY and BT speakers can be operated independently with appropriate switches.