I was very shocked when I saw those wireless microphones are selling for $200 and above. And I need one but I can’t afford then an idea comes to my mind. Why not to use an old earbud in microphone mode to get our work done. A small SPY microphone with Bluetooth connectivity and pretty good range with 20hrs of battery backup.
So, now we will now how to setup a connection of this wireless mic with your android mobile. We will discuss the battery backup, IC used and range of this microphone in this tutorial.
This project is sponsored by JLCPCB.com, one of the best PCB manufacturers deals in PCB prototypes, PCBA, SMT assembly, stencil and 3D-printing. Sign-up to JLCPCB using this link and get $54 new user coupons for future orders.
Where to get:
First, I got my hands on old earbuds. These are not in working because the speakers got damaged. After reveling the case and earbud electronics.
I do some measurements of charging procedure. The buds are automatically turned off when they are in charging more. Mine one has a tactile button, so that I can ON/OFF them using that button.
The charging case electronics has a big 3.7volt 400mAH Li-Po battery. Which can be charged using 5volt and then the voltage is controlled by onboard ic.
The earbuds have a same 3.7volt battery of 50mah which can be charged directly with 5volt.
Making a microphone from earbud:
Open the earbud, reveal all the circuitry. Then cut the speaker wires and our spy microphone is ready. It has an PCB antenna which can cover 10 meter of transmission distance.
We can put this small microphone inside diffuser to get rid of external noises.
We are using a 50mAH battery in this microphone which consumes about 19mA when recording and 8ma in ideal on mode.
This microphone has a deep sleep mode which takes less than 0.7mA when not in recording. Calculating the overall time on this battery is around 3hours+ but it can be increased more by connecting a big battery.
It will increase the time duration but then the concept of spy mic is destroyed. The weight of device with 50mAH battery is 15grams, which is able to stick anywhere in small space.
Connection with mobile:
The Bluetooth only turns on the microphone connection while calling, but to hack this function we can download a Bluetooth voice recorder android application.
Which has ability to connect with Bluetooth in microphone mode and to record/playback the files. This can also be used while recording the videos, voice over layer function can be used with editor.
The tactile button on the microphone is able to push it into deep sleep mode and stop the mode.
IC used with datasheet:
But here a small IC with more functions and Bluetooth 5.0 capability is used. You can see download the datasheet and circuit diagram from description.
We can plug an external mic with adjustable gain to cover more distance.
We can also increase the battery backup by using a big Li-Po battery with charging and protection circuit.
Don't forget to sign-up to JLCPCB. Claim the offer of $54 new user coupons now. And get your hands on best SMT, PCB prototyping service. PCB service in just $2 for 5pcs and SMT assembly starting from $8.