Solar Powered Bluetooth Headphone From Old Wired Headphone

Hi fried!

Recently, I converted my old wired headphone to solar powered Bluetooth headphone and today I will share it to you. Most of the components for my Bluetooth headphone are collected from various old electronic devices which are not in working condition. I always try to reuse & recycle old electronic components to reduce e-waste. Reducing e-waste will make our planet earth safer for now and future.

This instructable is a start towards recycling old electronic & reduction in production of e-waste.

1. Old Wired Headphone

Common problem of a wired headphone is breaking the cord. Another common problem is found on volume control knob for storing dust. Most of the cases both speakers remain in good condition when we through the headphone on trash. I have selected my old unused headphone which had problem on volume control knob and cord.

2. Old Power bank

When we through a power bank on trash, 95% cases it is for damaged battery. Every rechargeable battery has a limited charging cycle e.g. Li-ion battery has 300 to 500 discharge/charge cycles. After the specific charging cycles the performance of the battery falls dramatically and we through it to the trash. But, do you know there is more than 95% chance to find the control circuit in good condition and you can easily use the circuit in other devices? I found the control circuit of my old & unused power bank in very good condition.

Control circuit of every power bank has two sections. One is charging circuit for charging the internal Li-ion battery of power bank and another section is boost converter circuit. Li-ion battery use in power bank can not charge another Li-ion battery directly. Boost converter step up the voltage of Li-ion battery from 3.7V to 5V so that it can charge smart phone, tablet etc.

3. Old portable DVD Player

I collected a nice button pad from a damaged portable DVD player. I used the button pad for controlling the music and audio for my Bluetooth wireless headphone.

4. Li-ion Battery from old Mobile Phone or MP3 player

Bluetooth headphone use little power to operate and I found that an old but working battery from mobile phone or MP3 player can power the headphone for several hours. I collected a battery from my damaged MP4 player and I found the battery in working condition. I used that battery for my headphone. If you want to get longer backup you may buy a new battery but I think for wireless headphone a old battery is enough.

5. IDE Ribbon Cable from Old Computer

IDE cables are used in computer for connecting HDD or DVD drive with motherboard and very good for using as jumper wire. I used IDE ribbon cables for different connections because they are thin, durable and highly conductive.

6. 2 LEDs (one red, one green) from Old FM Receiver

Two LEDs can be used to indicate the Bluetooth module’s connection status. I got two nice LEDs (one red, one green) from a old AM/FM receiver.

1. RN-52 Bluetooth Audio Module (sparkfun.com)

This bluetooth audio module is a FCC Certified high quality stereo audio in a small form factor.The RN-52 module combines a class 2 Bluetooth radio with an embedded digital signal processor (DSP). The module is programmed and controlled with a simple ASCII command language. It provides a UART interface, several user programmable I/O pins, stereo speaker outputs, microphone inputs, and a USB port.

The module operates from 3.0 to 3.6 V power source and is bluetooth v3.0 compatible.

2. 2V 1W Thin-film Flexible Solar Panel (seeedstudio.com) or Thin Film 1W 6V (amazon.com) or 3.6V (flexsolarcells.com)

This thin-film flexible solar panel from SeeedStudio is built on an ultra-thin backsheet. It can be installed in a curve of up to 30 degrees. In addition to its unique flexibility. It packaging with durable, high light transmittance ETFE film and fast curing EVA film.

3. LT1763 - 3.3V Regulator

This regulator provide a constant 3.3V output for minimum input voltage 3.7V.

First, you need to separate the control circuit from the power bank. The control circuit contains one micro USB port and one standard USB port. Micro USB port is connected to the input of internal Li-ion charging circuit. Standard USB port is connected to the output of internal boost converter. Li-ion battery is connected to the input of the boost converter and output of the battery charging circuit. The standard USB port is actually the charging port for charging your device from power bank. It is connected to a 5V boost converter because 3.7V Li-ion battery is not capable to charge another Li-ion battery.

Remove micro USB port & standard USB port from the circuit using hot air. Be careful when removing the ports, I set the temperature of the air gun around 200 C and it took around 5 minutes to remove both ports.

For charging a Li-ion battery with 2V solar cell we need a boost converter and a charge controller circuit. Li-ion battery should charge with constant 4.2 V. So, 2V solar cell is not capable to charge a 3.7 V Li-ion battery and for that we need a boost converter. Boost converter will step up 2 V to 5 V. The output of the boost converter will be fed to the input of a Li-ion charging circuit. Charging circuit provides constant 4.2 V output to charge a Li-ion battery. If you use 6V solar cell instead of 2 V you can directly connect solar cell to the input of the charging circuit through a diode without using the boost converter. Diode will reduce 6V to 5.3V to make the voltage acceptable for the charging circuit.

Good news is that, power bank circuit contains both boost converter and Li-ion battery charging circuit in a single board (very useful!!!). Boost converter of some power bank circuit is not capable to step up 2 V and in that case you have to use 6V solar cell or an external boost converter circuit like this. I am lucky enough mine is capable to convert 2V to 5V. To know more about power bank circuit you may visit the link.

Let's slightly modify the control circuit of the power bank to make it suitable to connect with solar cell and battery. In the power bank output of the charging circuit and the input of the boost converter circuit is connected to same Li-ion battery. We need to detach the boost converter input from battery. We will connect it to the output of the solar cell as shown in the above image. After detaching the boost converter from the battery connect positive output of the boost converter to the positive input of the charging circuit and ground of the boost converter to the ground of the charging circuit. With this connection output of the solar cell will be feed to the input of the charging circuit after stepping up to 5V with boost converter. Follow the attached photo to make the thing clear.

In this step, I will show you how I got a 800mAh Li-ion battery from my old mp4 player. I got it in very good condition. You can also get an old Li-ion battery battery from an old mobile phone or laptop.

After desoldering the battery from the circuit board I tested it with multimeter. Then I connected it to a power supply adjusted in 4.2V to check either the battery is charging or not and I was happy to see that it was charging. I added a photo when it was charging.

If you found a battery is taking enough charge you can sure that the battery is in good condition. When you first connect a battery with 4.2V supply it will draw around 1 A at starting and gradually fall to zero. It should take enough time depending on the capacity to reduce the current around zero A for a good battery. After completely charging the battery you will get around 4.2V if you check it with multimeter.

I collected this nice button pad from my old & damaged portable DVD player. The pad contains 17 buttons. For my bluetooth headphone I need only 5. So, I used round part containing 5 buttons from the pad. For the purpose I divided the pad into three parts and used only middle part for this project. I stored another two parts for my next work. I didn't find pcb board as maker friendly. So, I modified the pcb board as my requirement. I connected ground pin of all buttons together. Then I soldered 15 cm long thin insulated wire collected from the IDE cable to connect the buttons to bluetooth module. In the next step I will explain modification of PCB in details.

After cutting the PCB board into three parts I took middle part which contains five buttons in a round shape for controlling purpose of the Bluetooth module. There was no soldering pad available for connecting the buttons pad with the module. So, I used a knife to remove solder musk from the trace of every button. After removing the solder musk I soldered HDD ribbon cable to all five buttons. Then I connected grounds of all the buttons together and connect another wire to it.

In this step I will show the connections between all the power elements like battery, charging & boost converter circuit, solar panel and voltage regulator. In previous step I have showed you how I modified the control circuit of power bank to make it usable for my project. Here, I connected the battery to the output of the charger circuit. Then, I connected the regulator circuit to the battery. Finally, I connected the solar panel to the input of the boost converter integrated with the charger circuit PCB.

This step was one of the hard step for my project. In this step I will show you how I connected all the separate circuits to the bluetooth module (hart of the system). The RN52 Bluetooth Audio Module is a tiny module and if your not good in soldering you will get it hard to solder connecting wires to the bluetooth module. First, I soldered the button pad to the Bluetooth module. Then I made a separate tiny module with two LEDs collected from FM receiver and one button switch. I soldered this module with the Bluetooth module according to the schematic attached. Then, I connected the output from the 3.3V regulator to the VDD and Ground pin of the Bluetooth Audio Module. Finally, I tested all the connection and powered up the circuit to make sure that all elements are working as expectation.

Before connecting all the circuits to the wired headphone I required some modification for the headphone. First I cut the wire and separated it from the headphone. Then uncovered the speaker to connect the jumper wires to both of the speaker. I soldered HDD ribbon cable to both of the speakers to connect with the Bluetooth module.

This was the final step of my work. I attached button pad with my right speaker with hot glue. Then, I attached the Bluetooth module with the base of the headphone using duct tape. With the left speaker I attached the battery with a on/off switch using hot glue. I attached charging circuit and regulator to the bottom of the solar panel. Finally, I fixed the solar panel at the top of the headphone base. I used duct tape and hot glue to tightly attached all the things to the headphone.

After completing all the steps I turned on my creation an I felt very happy to see everything was working parfectly.