Version 2.0 of my other project, Network Amplifier. This time around, I'll be hosting all the components including the amplifier and power supply within the cavity of a centre speaker from a surround system. Decided to go ahead with just mono as I didn't want to add new or modify the crossovers in the existing speaker and it will serve well as yet another prototype for self-contained WiFi speakers. Reducing the footprint is also a strong motivator for this project, as at the moment version 1 takes up the room of the original amplifier (that I retro-fitted) and the two 'bookshelf' speakers that are the back left and right surround speakers of the same system that the centre speaker is from. Fitting a touch screen and upgrading to RPi2 are nice to have items as the original version 1 does everything that we need. I'm going to be testing another FM radio module in this model as the current one's receiver is quite weak.
Raspberry Pi B+
Linux based computer
Generic USB hub
Powered hub for the WiFi and Bluetooth dongles
4 inch WaveShare SpotPear LCD touch screen
Comes with an sdcard image compatible with an RPi B+
After the PT2314 was exhibiting the same quirks as I'd seen before in rev 1.0, I reluctantly accepted that a RPi2 was not going to be part of this build... You see, the RPi2 does not have the P5 header that the older Pis have and thus does not have an extra i2c port (accessible at least) that I have used in the past to make the PT2314 work. For some insane reason, the on-board i2c pull-up resistors on the RPi prevent the PT2314 from working. Since the P5 header does not have pull-up resistors on the extra i2c port presented there, it just works. Sure, I could've removed the smd pull-ups from the RPi2 but then would have had trouble with the TEA radio module since it also communicates via i2c. In the end, it didn't turn out too badly as the sdcard image that came with the WaveShare SpotPeat 4inch LCD touch screen doesn't work with the newer RPi2 which meant that I would've had to fiddle around a lot more to get the screen going. A few more cuts into the original speaker were required to fit it all in there and overall I'm quite happy with the result not to mention that it has a very high WAF rating. :)
One of the main components of this build is the PT2314. This not only routes the up to 4 channels of stereo input into a single stereo output, it also has built in bass / treble, volume and mute control, all over i2c. With the original network amplifier, it was the discovery of this IC within that spurred on a much more ambitious goal than was first envisioned. Well, It seems that although the functions of the PT2314 are quite powerful, there isn't much competition in this 'space', which isn't the greatest thing as although I did manage to find a ready to use module on eBay, the PT2314 has once again proved to be a little elusive to get going via i2c communication. I already knew that I would have to use a logic-level converter to compensate for the 3.3v <--> 5v differences in IO voltages between the RPi2 and the PT2314 module. The voltage conversions were working just fine, as the i2c signals that I was sending from the RPi2 were clearly seen by my oscilliscope. This however did not seem to make a difference in it's operation as the PT2314 module was from an i2c perspective - dead. I double checked everything, the VCC to the PT2314 is recommended to be 9v, so the logic levels were shifting from that voltage... Hmmm, maybe there is something here, I'm sure that the logic levels from the i2c from the original amplifier hack weren't 5v. Perhaps the VCC and the logic IO VCC aren't the same voltage, just like the RPi2. This could prevent the '0' logic signal from sinking low enough to register and is something that is worth testing. In the meantime I've ordered another couple of PT2314 modules as I can't rule out that I either damaged the device (static / etc) or that it really was just faulty. I knew that there would be a period of 'down time' between v1.0 and v2.0 amplifiers but this was just not acceptable. I made the decision to retro fit another one of the speakers from the surround sound package. A rear speaker would do nicely with a powered amp retro fit w/ Bluetooth audio (A2DP)...
As luck would have it just after creating this project, I received the TEA5767 FM Radio module that I am keen to test out. Instead of buying the raw FM module, I bought it incorporated with a TDA1308 Class AB stereo headphone amplifier on the same module. There are two 3.5mm sockets, one is the headphone amp output, the other is a 3.5mm --> antenna input.