PT2314 audio processor PCB

[kjetilei]

Hi,

I'm planning to build a RDS FM based radio/alarm clock with multiple audio sources, remote, LCD screen and various "weather sensors".

Most of the parts have been bought/received but I soon discovered that it was hard/impossible to find a premade Arduino friendly audio processor module with multiple inputs and I2C.

Hence I set out to make my own module based on the PTC PT2314 audio processor.





I have no prior PCB designing experience and my electronics knowledge is basic. I have made a PCB with Fritzing and I would really appreciate it if you could help me with a "sanity check" of my design and component selection.

I have opted for 0603 resistors and ceramic capacitors and a couple of 0805 ceramic capacitors.

The design is based on the MOSA MS6714 (PT2314 compatible) application example since the component count is smaller than for the PT2314 example. This is mainly to be able to create an even more compact module but it means that I have left out the input surge protection resistors in the PT2314 example.

I hope the choices I have made does not degrade the audio quality noticeably and is still "safe" enough. The radio/alarm clock is in no way meant to be hi-fi grade with it's tiny 2x3w speakers but it doesn't hurt to make it decent if possible

I have attached photos of the PCB and the Fritzing file that I hope you can give me feedback on. Notice that I struggle a bit with the Fritzing file, where not all of the nets and connectors are marked as routed in the PCB view (but the PCB in itself should be ok) - I don't understand why, but it could be due to my inexperience with Fritzing/electronics or due to a bug or something in Fritzing (I have experienced a couple but truly appreciate the application).

PT2314 datasheet
MS6714 datasheet

A couple of screen captures from the datasheet:




I have also included a few photos of commercial implementations of the PT2314 for reference:






Some homemade uses of the PT2314:
andrewzuku's Arduino car stereo

BikerMatys non-Arduino PreAmp:
http://www.youtube.com/watch?v=uQHkPZ5bRPI

[VaidasZ]

Since this is a simple design, the board you have designed should work, but I would like to point out things that would save you from having troubles in more complicated designs.

From electrical point of view:

• For every power input pin of the IC (especially digital IC's) you must place a bypass capacitor (a capacitor from Vcc,Vdd,... pin to the ground). This capacitor must be as close as possible to the Vcc and GND pins of the IC. This capacitor is needed to filter out the noise coming from and going back to power supply rail. Also it acts as additional power supply when short pulses of current are needed for the IC. In this design please add the ceramic 100nF capacitor close to pins 1&2.


• Keep signal tracks as short as possible. Long tracks can pickup noise a lot easier. This might lead to noisy analog signal and even parasitic oscillations. For this reason I would suggest placing components in different way. As in the pictures you have attached, all capacitors should be close to the pins of IC.


• Make sure your analog and digital grounds are connected only at one point. Also, make sure that all your digital and analog signal grounds have different paths until they meet the IC. Otherwise you will have a digital noise in your analog circuitry, it can even cause parasitic oscillations. You definitely don't want that.

Some additional guidelines for a good PCB design:

• Vias must be apart from component pads. There must be at least some solder mask between them. Otherwise when soldering in the oven, the solder will be sucked by via. This will lead to less solder for the pad and probably unreliable connection;


• To save space, you can place the components closer to each other and/or place them on the other side of the board.


• Try to keep track widths and corners consistent - this makes the board look better;


• Avoid 90 degrees corners on the PCB tracks. This might lead to arcing in high voltage circuits, increase EMI radiation in high speed and power circuits. Also, in my opinion board looks nicer without them


• In a high frequency/high power design you don't want to have unconnected copper islands.They might lead to EMI problems. Also it will affect the impedance of transmission lines.

Hope this helps 

[kjetilei]

Thanks for the great feedback VaidasZ!

I'm currently implementing several of the changes you propose and will post updated files later

[kjetilei]

I finalized the updates and tried to implement as many of the suggestions as possible without total rerouting. Most of the audio paths are short, exept for the two audio channels that needs to cross the IC due to the IC's pinout.







The schematic is not my proudest moment I focused my attention on the PCB...

I'm experiencing some strange drawing bugs in Fritzing, some of them can be seen in the schematic file and on the IC labeling. Luckily these are only minor problems.

[upnxwood16]

Not sure of the speakers you are intending to use but I just found a all in one solution from PTC,  it has the same features as the PT2314 and has a speaker amplifier in one foot print. http://www.princeton.com.tw/en-us/products/multimediaaudioic/multiplefunctionaudioamplifier.aspx The PT2830 and PT2335 are the ones that I am working with.

[kjetilei]

I bought a pair of 3w 4ohm USB speakers that I intend to gut and use.

I noticed the nice combined ICs after I had ordered 10pcs of PT2314

Have you created PCBs for the PT2830 and PT2335 or are you using a breadboard setup or similar? Please let us know your experiences with these ICs.