The PowerBoost and amplifier circuits would need some soldering before I could use them with my breadboard. I purchased a soldering iron in a starter kit from Amazon, which included a soldering iron stand and some helping hands to hold the component while it is being soldered. The kit also included pliers, solder and some tweezers. Everything I needed to get started.
I soldered the headers and jumpers into the amplifier, and the terminal blocks for the speakers.
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| MAX98306 Amplifier with soldered headers |
I also soldered the headers onto the PowerBoost and some wires onto the power output to power the amplifier.
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| PowerBoost 500c with soldered headers and power wires |
I also needed to solder some lengths of wire onto the speakers.
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| Speakers with soldered wires |
I've not soldered since school, but it didn't take me long to get back into it. Some of the headers weren't perfectly straight, but the connection seemed solid enough.
With an the soldering complete, I assembled the prototype on the breadboard. I aligned a switch with the BAT, EN and GND pins of the PowerBoost on the breadboard, so I could turn the whole circuit on and off more easily. I connected the battery to the PowerBoost using the JST connector and tested that it powered on and off with the switch.
I then added the amplifier to the breadboard and connected the speakers. I temporarily connected the red, black and ground wires from the audio pigtail cable to some male-female breadboard wires, and plugged the red into the R+ pin on the amp and the black into the L+ pin. The ground needed connecting to both the R- and L- pins, so to achieve this I connected the ground from the pigtail to L- and bridged the L- and R- connections with another breadboard wire.
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| Completed amplifier prototype circuit |
It worked!
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| Prototype circuit playing amplified music from phone |
The sound quality was impressive and at a reasonable volume. It sounded like it should be loud enough to work as a small music player in the corner of a room, like a small radio. It wouldn't replace a full HiFi system, but that wasn't my intention.
I then tested the circuit powering the Raspberry Pi as well as the as amp, by connecting a wire from the 5V pin on the PowerBoost to GPIO pin 2 on the Pi and from the GND pin on the PowerBoost to GPIO pin 6.
I also plugged the audio cable into the Pi, though I'm not testing the Pi audio here, just the power.
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| Raspberry Pi and amp powered from the PowerBoost and battery |
I also connected the Pi to a monitor to check it was working. Turning the circuit on, the Pi booted normally, and displayed the Desktop on the monitor.
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| Raspberry Pi fully booted running on battery |
Overall this was a successful test of all the parts required. I'd tested that the PowerBoost worked well running on battery, that the PowerBoost could power the amp and the Raspberry Pi, and that the amp played audio at a reasonable volume through the speakers.
The next stage is to make the wiring a little more permanent, removing the need for the breadboard. I'd still like to keep the circuit relatively modular, in case I decide to swap out any parts. I'm going to investigate a number of different options for semi-permanent connections, something like the battery's JST connector or the speaker terminal blocks would be good, but I'll see what I can find.
I'm also keeping in mind that I'd like to make the shutdown friendlier. Currently turning the circuit on is fine, but when it comes to turning off, the Pi ideally needs to be shutdown first, otherwise I'd risk corrupting the SD card. I'm not planning on storing any music on the SD card, so it would only be the OS I'd risk corrupting, which could easily be restored, but still it's not ideal.
So, some sort of method for safely shutting down the Pi before turning off the power would be ideal. If I could also detect a low battery and shutdown the Pi safely that would be even better.
I'll investigate these options and write about my findings in a future post.