Blue Panda

Intro

I was really impressed by how well the Serioux Panda Shaped stereo speakers performed when I received them as a gift. They have a really good sound, there’s a lot of improvement compared to the speakers in my laptop. But this is not what I want to use them for; after all, I’ve got two huge speakers by my laptop. I wanted some portable speakers. With Bluetooth.

 The panda

The Panda speakers are rated at 2x1W (but I suspect they can do more) and contain a TPA6020A2 bridge amplifier. Audio quality is impressively good for their size. This is why I considered them useful for broadcasting music wirelessly in another room.

The energy source is actually very simple: the Panda speakers need either 3 AAA batteries or 5V from a USB port or phone charger or, in my case, a portable battery. So using them with a portable battery makes them portable… except that they are not wireless. I remembered I had a Bluetooth headset bought specially for sending audio from my phone to another room which I don’t need anymore.

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The blue panda

When I initially bought the Bluetooth adapter I did not require or expect good quality so I bought the cheapest I could find, but it turned out that it has very good audio quality. So I decided to pair them together. Luckily the Bluetooth adapter fits perfectly inside the three AAA battery case at the bottom of the panda after removing the contacts and some tiny spacers. The buttons stay flush with the panda so they are not pressed when it is seated on something.

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The Bluetooth module is powered by a lithium battery which I removed. To power it I will be using the 5V from the panda with a 1N4148 diode in series. This, along with a Schottky protection diode inside the Panda, brings the voltage down to about 4V, right what it is expected from a battery. The microphone was removed, but i am thinking of installing it back so that I can use the panda as a call speaker. 

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I did not want to lose the possibility to send audio through the cable to the panda, so I decided to keep its cable. To make it use both audio from the Bluetooth module and cable I summed both signals through 1K resistors before applying them to the original 10K potentiometer (I matched 4 resistors with the potentiometer since I only had 5% tolerance available). This works perfectly as a mixer letting the panda use both sources at the same time, but I can’t seem to find a situation where I could use it like this.

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The finished blue panda looks just like the original one, except the bottom where there are the controls for the Bluetooth. The final audio quality and power are very good and fits great for my need. I believe that if I were to buy same quality Bluetooth speakers I would have to spend a lot more money than these two cost combined.

Here’s the final device sitting on top of my 4×18650 portable USB charger. Given the capacity of the battery i would say I should get at least 20 hours of music at moderate-high levels.

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