Intro: Cheap, Awesome Rechargable Sound System $100 and Better Sound Than Big Jam Box.
So, the other day, my friends said they were about to leave our loft and go outside for a walk. I figured that meant that I had about two hours to "Get ready". Since I was already dressed and showered, I thought about it for a moment and realized I would want music to share.
This project is a work in progress. I intend to add a bit more in early March.
I'm also still adding some details to the Instructable - somehow this is my first one but I am enjoying it.
The overall idea is to combine some good value/open box speakers with a 50 watt audio amp board and some Lithium Ion batteries and a bluetooth audio receiver to make something like a "Jambox" but better sounding and cheaper. The project is very modular and some pieces are optional.
This instructable isn't meant as from the ground up walkthrough - I want it to be general enough so that you can make it from what you can find. But if you need help, leave a comment and I will try to assist.
The general idea should work with differing components as long as things physically fit.
I even made a back strap out of a used rubber bike tube, so it can be worn like a backpack.
Step 1: Parts
• "Passive" un-amplified speaker, or speaker with a broken or removed amplifier. I used Yamaha AW350 indoor outdoor speakers which are approximately $100 a pair from Amazon - But they have "warehouse deal" scratch and dent for $70/pair. These sound pretty decent, have good bass, and are lightweight and fairly durable.
• (Optional - you can also just use a wire) Small bluetooth audio receiver - Lots of options here but you want something specifically for music to make sure it sounds decent (Bluetooth speakerphone profile has a lower sample and bit rate) I used a Belkin music receiver
• Optional (but needed for Bluetooth) 24v-5V dc/dc converter
Something like this:
•Class D 50 wattX2 audio amp. Right now we are just using one channel - but we did buy two speakers....But I will get to that in a future update. I got this one.
• 6x 18650 batteries and charger 3.7 volt batteries, connected six in series give us about 22 volts. Probably these will have somewhat overstated capacity compared to reality unless you get name brand like Panasonic. The say 5000 mah, but divide by 3 for more accurate measurement, about 1700mah. We multiply 22 volts * Milliamp Hours and we get Watt-Hours of about 37. Experimentally this seems to give perhaps 6 hours at decent volume.
• A round hole rocker power switch
• Some hook-up wire
• An old audio cable with 1/8" headphone jack attached that we can cut and solder to. You want to find something like a "Y" cable, headphone male to dual RCA jack and cut off the RCA ends. The wire in headphones is specially treated to be flexible and strong and is really annoying to solder to.
•Some clear polycarbonate tube or similar that the 18650 batteries will fit inside, mine is 1" OD
Step 2: Open the Speaker and Look Inside.
The metal cover protecting the speaker drivers is held on by some adhesive along the edges. Gently push it inwards and using a flat head screwdriver, carefully work your way around the edges and pry it off a little at a time.
Once you get the front cover off, there are 6 phillips screw holding the back cover on.
Undo these six screws. I used the metal cover as a parts holder as I was working.
The back cover also has some adhesive, so pry it apart with a screwdriver similar to the front metal cover.
When it starts to separate, be careful as the wires inside connect the two halves and we don't want to pull them out until we are ready.
I labeled the speaker wire connectors with the letter of the color so it's easier to remember where they go later.
The wires from the woofer and the tweeter both lead to the crossover and connector board.
This is where we will connect to the speaker.
The red and black wire leading outside the case is the input. We will disconnect these wires from the terminals normally used to connect to the speaker, and use them to plug into the crossover with our amplifier.
Step 3: (optional) Bluetooth Module for Wireless Audio
If you are using the bluetooth module, you will also have to add the DC/DC converter to get 5v. But this can be used to charge your phone and add Arduino controlled lights later.
I pried off the cover, and located where the audio in (1/8" female jack) is, and where the power comes in.
By using a multimeter on continuity mode connected to the 1/8 to headphone jack cable, I found the audio ground. I plugged in the audio cable to the bluetooth adapter, touched one probe of the multimeter to the ground on the cable and probed the connections coming from the audio jack until the meter beeped. I marked which of the connectors was for ground.
In my setup, I soldered the 3 pin connector that came with the audio amp board directly to the bluetooth module.
I removed the PC Board from the enclosure to make it easier to work with.
Step 4: Wiring to the Speakers
If you aren't using the Bluetooth option, you take the 3 pin JST connector and solder it to the cut 1/8" audio cable.
When you cut the cable you will be able to see braided metal, which is the ground, and generally a red and white wire which are the left and right audio signal.
The ground connects to the black wire on the 3 pin JST, and the red and white connect to the same colors.
We connect the red and black wires that go to the crossover board to one of the two speaker outputs on our amplifier board (see image for connection locations).
Step 5: Build the Battery Pack.
Here's the simple way I came up with to make a battery pack.
It's inspired by the way flashlights hold batteries: A tube with batteries end to end (in series, so the voltage adds together), a spring on one end and contacts on both ends.
By making two of these 3-cell holders, and putting them in series we get 22.2 volts.
That's about ideal for the specific amp I used.
I used some 1" outside diameter polycarbonate tube I have from a project.
I cut it a bit longer than the three batteries, and drilled some holes at each end to put some M4 hardware at one end as a contact, and aluminum wire and a spring at the other end as a contact that keeps pressure on the wires and batteries so power stays on when the unit bounces around.
I put the two of the three battery packs next to each other facing opposite ways, and connected one end to make six batteries in series.
DON'T Connect both ends to each other. This will create a time paradox... no... wormhole.. no...
it will create a Short Circuit, and that could burn you or start a fire. We don't want that.
Step 6: Wiring, and Add a Power Switch
Find a "normal" SPST, SPDT or DPDT switch, and solder two wires to it.
SPST is simplest - only two connections.
SPDT, connect to the center connection, and one of the outside connections
DPDT, Connect to a center pin and an outside pin on in the same "column" when held with the axis the switch moves in held in up/down orientation.
We take the positive and negative wires coming from the battery pack. The negative goes into the amp board directly (and also connects there to the DC-DC converter).
The positive wire goes through the switch, so we can disconnect the power from the batteries and shut the system off.
Step 7: Put It Back Together.
First, whatever we did - let's test it.
When you are turning a project on for the first time, or after repair, it's good to pay special attention to you wiring, check for any reversed polarities and make sure you haven't accidentally plugged to high a voltage in to anything.
Be ready to disconnect power things if anything seems weird.
Since this was a very quick project (<2 hours... it's taken longer to write the Instructable)... I just sort of wrapped things in electrical tape and gaffe tape to make sure they don't move around when I'm walking.
You may want to do a better job, maybe with some hot glue etc.
But keep in mind - we haven't added a way to charge the batteries without taking it apart - I still have to do this to mine, will up date the Instructable ;)
Make the electronics and batteries so they don't move but also don't get in the way of re-assemby.
(In my case it was a little tight but worked out OK)
Screw it all together and re-affix the speaker grill.
See if it still turns on (I check to see if the bluetooth device is there).
Plug in, or bluetooth in and rock out!
If it doesn't work, recheck your wiring.
Trace power with a multimeter, and make sure the right voltage appears at the amp board, an at the output of the DC/DC converter if installed.
Hopefully it's working now. If you get stuck feel free to post a comment and I'll try to help.
I'm working to make mine better, and will add more.