Bluetooth Audio Receiver

This is a Bluetooth audio receiver using the MH-18M module.

I didn't know until recently such a one-chip Bluetooth audio module is available.

As audio signal handling via Bluetooth requires several processing functionalities such as communication, Analog/Digital converting, and amplifier interfacing, I doubt such a single-chip break-out board can support all the complex functionalities.

But to my surprise, it can receive an audio data stream from a smartphone and directly interface with an audio amplifier.

Also, the small breakout board can support automatic connection with a smartphone via Bluetooth protocol at the initial pairing stage.

Luckily I found this module from some web pages while surfing the Internet to search Bluetooth receiver devices.

Usually, many receivers are available from high-end ones that cost several hundred dollars to less than 10 dollars of low-end and entry-level receiver modules.

Firstly, I didn't believe this cheap 3 dollars receiver module can do such complex jobs interfacing between a smartphone and audio amplifier.

But the result is quite surprising and interesting.

Let's look at more details of this Bluetooth audio receiver module.

Let's look at the circuit diagram of the MH-18M receiver module to interface with LM380 audio amplifier.

The break-out board can be powered up by a common 5V smartphone charger.

When 3.7V lithium battery power is used, modifying the circuit on the board by replacing the diode with a 0ohm resistor is required. (Red box on the MH-18M board shows the diode)

As I don't want to temper the circuit board and make some mistakes, I'm using a common smartphone charger for powering it up.

To connect the MH-18M board with a smartphone charger, a female USB Type-A connector is used at the power supplying side.

For interfacing with LM380 audio amplifier, a 3.5mm stereo female connector is attached to the audio out pins. (L and R pins of MH-18M)

That's it and everything is ready for playing music from a smartphone to an audio amplifier.

Connecting MH-18M with a smartphone is also very easy.

When power up the MH-18M, the blue LED on the board start to blink.

And it is supposed to start advertising itself to other Bluetooth devices for pairing and connection.

As you can see in the picture above, MH-18M is automatically discovered by the smartphone.

You can pair and connect with MH-18M by registering it in the Bluetooth menu of the smartphone.

When you connect MH-18M to the smartphone, you can hear a pre-programmed signaling sound from the audio amplifier.

That's it!

Any required settings and configurations are finished and everything is ready for playing music.

The following parts are required to connect MH-18M to the audio amplifier.

- USB female Type-A connector

- 3.5mm stereo female connector

- Smartphone charger and USB Type-A male cable (Both ends are Type-A male connectors)

- Audio cable (Both ends are 3.5mm stereo jacks)

The LM380 audio IC is quite an old 14 pin amplifier package that can support 2.5W output.

I thought it was already obsolete but some Internet web stores are selling this chip still.

I'm using this small power amplifier for only testing purposes.

Before hooking up any new audio source devices to my power amplifier, I'm testing the device with this small power (About 2Watt) amplifier.

The sound quality from this amplifier is not much impressive.

It is just used for checking an audio output is correctly produced by the amplifier when connected with the newly made audio devices.

As the LM380 amplifier is mentioned in this story, let's look at a few details of the amplifier circuit.

I will not explain quite the details of the amplifier circuit as the main subject of this story is the Bluetooth audio receiver module.

Nowadays LM386 IC is more popular than the LM380 chip as the overall circuit of LM386 is simpler and requires minimal external parts for proper operation.

I don't know why I had bought this chip, somehow I have 3 of these old amplifier chips in my inventory.

When compared with the LM386 amplifier circuit, the LM380 (14 pins) circuit is almost similar.

But LM380 can produce about 2W output with 16V power supply instead of humble less than 700mW output supported by LM386.

Although LM380 can produce high audio output, audio quality is not much impressive for casual music listening.

Therefore, this audio chip is mainly used for toys that produce interesting sounds for children or amateur electronic DIY hobbyists.

As the LM380 circuit is similar to the well-known LM386 circuit, I will not explain further about this small amplifier circuit.

Finally, I'm testing the MH-18M Bluetooth audio receiver module with my power amplifier.

The power amplifier uses the TDA2050 (Maximum 35W output) chip and the making of this amplifier is similar to the one I had introduced in other instructable below.

https://www.instructables.com/Audio-Amplifier-Using-TDA2030A/

The previous audio amplifier uses the TDA2030 (Maximum 20Watt).

But the overall circuit configuration and the operating scheme are almost similar.

Personally, I like the sound quality of TDA2050 more as it produces less noise and supports more dynamic sound output.  

Likewise, to connect the LM380 amplifier, this power amplifier is connected with MH-18M module via stereo cable.

The power amplifier can produce more powerful sound than LM380.

But the overall sound quality seems a little bit flat without details of dynamic features contrary to the case of I listening sound directly connecting audio source such as PC. 

I can play music from mp3 files stored in the smatphone without any problem.

Anyway, with just 3 dollars of Bluetooth audio receiver chip, the general outcome is quite satisfying and even somewhat surprising.

Thanks for reading……