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• Doing the BOM

  Benchoff • 01/12/2016 at 02:04 • 0 comments

  A few more revisions until I'm away from Eagle for a few weeks. I've updated the schematic, fixed a few major issues, and added an audio amplifier. Yes, it's a fantastically stupid idea, but I can see the value in having an optional 2 Watt class D audio amp on this board.

  With that addition, I've run out of room on the board. Therefore, it's time for the BOM.

  Part	Value	Device	Digikey Part No.	Unit Price 1k
  C1	10uF	CAP_POL1206
  C2	10uF	CAP_POL1206
  C3	0.1uF	0.1UF-25V(+80/-20%)(0603)
  C4	0.1uF	0.1UF-25V(+80/-20%)(0603)
  C5	10uF	CAP_POL1206
  C6	10uF	CAP0603-CAP
  C7	10uF	CAP0603-CAP
  C8	0.1uF	CAP0603-CAP
  C10	10uF	CAP0603-CAP
  C11	10uF	CAP0603-CAP
  C14	33nF	CAP0603-CAP
  C15	33nF	CAP0603-CAP
  F1	PTCSMD	PTCSMD	F2110CT-ND	0.22
  F2	PTCSMD	PTCSMD	F2110CT-ND	0.22
  JP1	POWER_JACKPTH_BREAD	POWER_JACKPTH_BREAD	Adafruit 373	0.76
  JP2	3.5mm Audio Jack SMD	AUDIO-JACKSMD2	CP-43515TSSJCT-ND	0.59
  Q1	12MHz	CRYSTALCTS406	CTX855CT-ND	0.75
  R1	2.7k	RESISTOR0603
  R4	270R	RESISTOR0603-RES
  R5	270R	RESISTOR0603-RES
  R7	150R	RESISTOR0603-RES
  R9	150R	RESISTOR0603-RES
  S1	SWITCH-MOMENTARY-2SMD-1101NE	SWITCH-MOMENTARY-2SMD-1101NE	CKN10388CT-ND	0.33
  USB1	USB_TYPE_A_FEMALE_TH	USB_TYPE_A_FEMALE_TH	A31726-ND	0.797
  USB2	USB_TYPE_A_FEMALE_TH	USB_TYPE_A_FEMALE_TH	A31726-ND	0.797
  D3	PRTR5VV0U2X	PRTR5VV0U2X	568-4140-1-ND	0.202
  Power	IC buck regulator	TPS62143RGTR	296-39448-1-ND	0.99
  D1	PRTR5VV0U2X	ESD Protection Diodes	568-4140-1-ND	0.202
  D2	PRTR5VV0U2X	ESD Protection Diodes	568-4140-1-ND	0.202
  R10	CRCW0402100KFKED	100k Ohm 0402	541-100KLCT-ND	0.02
  L1	IHLP1212BZER2R2M11	IHLP1212BZER2R2M11	541-1322-1-ND	0.75
  C18	TMK316BJ106KL-T	10uF cap 1206	587-1337-1-ND	0.07
  C17	TMK316BJ106KL-T	10uF cap 1206	587-1337-1-ND	0.07
  C16	TMK316BJ106KL-T	10uF cap 1206	587-1337-1-ND	0.07
  IC3	TPA2016D2RTJR	TPA2016D2RTJR	296-25430-2-ND	1.46
  USB	FE1.1S	FE1.1S	N/A	0.66

  capacitors and resistors aren't free, but they're free enough. I did the math for 1k units on this, just to demonstrate how fantastically stupid manufacturing this would be.

  In 1k quantities, the BOM for this board is $9.16. With the resistors and caps and board, it's going to be $10. If this were a product, it would sell for $20-25 without the Raspberry Pi Zero, or just a tiny bit less than a proper Raspberry Pi.

  Nevertheless, there's a value in making stuff small, so I'll be making a few of these for personal projects. The github for this project has the updated schematic.

  The next task, before sending this out for a real fabrication, is a refactor of the entire project. Looking over the BOM, there are some fantastically stupid choices here.

  Here's a digikey cart

• First Design Revision

  Benchoff • 01/09/2016 at 15:14 • 0 comments

  The boards are already off to OSHPark. Here's what I'm looking at:

  This is probably the smallest and most compact PCB I've ever designed. It's composed of three sections: the USB hub, the Audio output, and Power supply.

  The USB hub

  Everyone needs to build their own USB hub! It's the zeitgeist of the Raspberry Pi Zero. This hub is built around the FE1.1s 4-port USB 2.0 hub controller. This chip doesn't require pullups, pulldowns, extra power regulators, and operates at full speed (12MHz). I have 10 chips coming to me via eBay and China.

  I broke out two USB ports in this four-port hub. Because I envision this project being used in a few projects where space is at a premium, I've also added solder pads for the power, ground, D+ and D- of a third USB port. An Edimax WiFi module can easily be added with some wire, solder, and hot glue.

  The upstream port connects to the Pi through solder pads. The D+ and D- pins of the OTG port are available on the back of the Pi Zero, labeled as PP22 and PP23. This is more solder and hot glue; this board is intended to stack tightly against the Pi Zero - there shouldn't be any issue of the wires pulling out.

  Protection of the USB ports is done through ESD diodes and a polyfuse. This isn't a completely protected port, but it's better than nothing.

  Audio Output

  The Pi Zero doesn't come with audio output. Because the Pi can play audio through it's PWM peripherals, adding audio doesn't take up that much space. The instructions are given by lady ada, and implemented with standard value parts.

  The same part number for ESD diodes as used in the USB ports is used here in the audio port. Output is though a 3.5 mm jack, or if this project will find its way into something that requires even less space, solder pads for left, right, and ground.

  Power Supply

  Although it takes up the smallest area on the board, the power supply has had the largest consideration of anything in this project. Instead of a microUSB port, I'll be powering this project through a wall wart, delivering 12VDC. This 12VDC is also broken out to solder pads, as a lot of cheap TFT displays exclusively use 12VDC

  The design for the power supply is able to accept anything between 9 and 14V, delivering 2A at 5V. This is a high performance power regulator, and for this project I'm using TI's TPS62141. Design was generated by TI's WEBENCH software. This power supply is overkill, and there are other parts in the family that would be better suited for less powerful builds.

  Actually Building it
  

  the boards are off at OSH park, and in two weeks I'll be gone for a month. This is going to take a while to put together. If the first one works, I'll make about three or five of these things. I can see this being useful for a few projects, at least.

  Files are available in the github, improvements in layout and design will be made.

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