Bluetooth Speaker and Powerbank

thingiverse

Bluetooth Speaker Rev 0 With all of the excellent bluetooth designs posted here, I wanted to add some additional functions to the various speaker designs, and keep within a budget of $30.00. My benchmark design is the color bluetooth speaker pictured, and this design audio performance matches or exceeds the benchmark! This is a basic quarter wave design, using a pair of chinesium 2" speakers rated at 15W 4 ohms, and a basic bluetooth 20w amplifier. It is difficult to take asian speaker manufacturer specifications at face value - the DC value of the voice coil is off by 25% and power ratings are usually wildly over rated! This may not be a problem if the impedance is high, but most of these measure low and this can cause heating in the amplifier. I swept several speakers over intended audio frequencies, and used the pair that is closest to rated spec. I also wanted a low frequency (fs) of as close to 100kHz as possible, and these are not bad at 130kHz. The electronics are all canned pieces from Aliexpress with modifications and are placed in the lid of the unit. This Rev 0 unit is boxy, some better lines will be on Rev 1. Some highlights: 1) Battery indicator specifically for 1S LiIon battery packs used as received 2) 4P battery pack provides charging and safety circuits with input connectors supporting MicroUSB and USB-C, and an output standard USB port to be used for charging external devices. This unit has buck/boost switchers for +3.3V and +5.0V output when the unit is active. I had to remove the USB connector and wired it manually onto the top panel. I also had to solder a 470 ohm resistor across the 5.0V port so the unit would not power off automatically. The 5 LEDs seen in the picture are mounted on the bottom of the PCB and are just a backup to show charging status. This board will cut output power when the battery voltage falls to around 2.5V. 3) I am using Samsung 18650 cells rated at 3Ah (yes, they actually provide 3 Ah!) to power the device 4) Bluetooth 2-channel amplifier with volume control. I removed the switch and wired to some keyswitches I had lying around the lab to give volume up and down as well as play/pause functions on the front panel. I used a light peg to display the blue connection indicator on the front panel. Annoying that it flashes constantly while operating. This particular board needs 12 - 24 V, and running from 12V with 4 ohm speakers gives the best performance - from a distortion and efficiency standpoint. 5) DC-DC converter - design to operate from a single LiIon cell and comes configured for 5.0V output. I removed the output USB connector to direct wire the output into the bluetooth amplifier and battery indicator, and changed a resistor value to give 12.5V DC output. 6) Custom P-Channel MOSFET switch - I connected the DC-DC converter through this switch direct to the batteries, and use the 3.3V output on the 4S battery board to turn the power on and off to the DC-DC converter and the front panel battery indicator. The maximum current draw when off is around 10uA, which is a couple orders of magnitude less than the self discharge rate of these particular LiIon cells. 7) Speakers are 2" 53mm Full Range (150Hz - 18kHz, as measured, 135Hz - 20Khz as advertised) 10W rated, 15W Peak and thats accurate. Since this is WIP, I will post a schematic for the next revision and hope to find some PCB assemblies that do not require modification along with better assembly instructions. I printed the speaker housing as one unit, pausing just before the last side prints to add some polyfill stuffing. I left two ports below the speakers to route wires to the front panel / electronics assembly, which need to be sealed. This is printed on a large format FDM i3 clone using PLA filament and was printed on its side. ** I will note the stl files posted result in a speaker port that is about 1 mm too small and I had to use a rotary tool to make the speaker fit ** The result is a speaker that has good response down to 125Hz and easily outperforms the commercial version on volume and distortion. With a 12Ah battery pack, it will run for about 8 - 10 hours while charging a phone on moderate volumes. Definitely larger than the commercial version, but came in around $32 including filament. With this particular speaker, very flat response down to 150Hz, and a bump in the response around 100Hz - due to the quarter wave design being a little too long. Stay tuned for a 3" version with improvements Speakers: Aiyima 53mm Full Range 10W/15W 4 Ohms (Aliexpress) Battery Gauge: 1/2/3/4/5/6/7/8S Lithium Battery Capacity Indicator (Aliexpress) Amplifier: 10W/15W/20W Stereo Bluetooth Power Amplifier Board 12V/24V XY-P15W 40W (Aliexpress 40W) Battery 4P pack: 18650 Battery Shield V8 V9 4P (Aliexpress) DC-DC Converter: Single Cell Lithium Battery Boost Power Module Board 3.7V 4.2V 5V 9V 12V USB Mobile Phone fast charge TPS61088