I'm designing a small USB radio transceiver with 3 main components:

  1. Sparkfun's RFM69HCW 915 MHz Transceiver. [Datasheet]
  2. Microchip's MCP2210 USB-SPI Bridge. [Datasheet]
  3. A simple USB port from Digikey.

However, even with just these three components, there are a huge number of things I'm uncertain about even after scouring the datasheets! I hesitate to ask them separately, since they are all closely related and it would be a waste of space to do so. Any and all help/answers is greatly appreciated.

Here is my current working schematic: J3 is the USB port, U2 in the middle is the MCP2210, and U1 on the right is the RFM69HCW.

USB Radio Transceiver Schematic

MCP2210 Questions:

  1. Page 6 of the datasheet states that VUSB should be bypassed with a .22uF to .47uF capacitor. Will any value from that range work? What design considerations are there? (C8 in the schematic)
  2. Page 6: What value bypass capacitors should I use for VDD? (C3 in the schematic)
  3. Page 6: How do I know if I meet inrush requirements before building any of this?
  4. Page 6: Do I really need to implement a Low-Power Suspend mode? Is it possible to just turn off the option so I don't need to worry about it? If I do need to implement it, what does that entail?
  5. Page 8: What is the logical high voltage of the reset pin? 3.3V or 5V? I'm not sure which rail I need to connect the pullup to.
  6. Page 9: Section 1.9 Oscillator, Note 1 states: "A series resistor may be required for quartz crystals with high drive level." This is the one I'm planning on using: ECS-120-20-5PX-TR. Does it have a "high drive level"? If so, what resistance should I use?

RFM69HCW Questions:

  1. I can't tell whether or not the SPI lines on the radio are OK with being 5V rather than 3.3V (since the MCP2210 datasheet states on page 6 that VDD sets the logic levels for SPI). How would I figure that out since I can't find it in the datasheet?
  2. Is there anything special I need to do signal- or ground-plane-wise, since I have a radio/antenna on board? I've only done digital logic boards before.
  3. Since the radio chip is the only slave, can I just tie its SS pin low so that it's always active? What pulldown value should I use? (R3 in the schematic)
  4. The radio has three ground pins, but only one 3.3V input. Do I need decoupling caps between only the 3.3V and the closest ground pin, or between the 3.3V and each ground?

USB Questions:

  1. What do I attach the USB case to?
  2. Do I need to do any decoupling/bypass at the USB power pins?
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    \$\begingroup\$ Too many disparate questions. Voting to close. Have you thought how long some unpaid volunteer to this site would have to spend researching this lot? Plus, it seems you are not very good at recognizing decent answers to previous questions (I see two in your portfolio). Think about this dude. \$\endgroup\$ – Andy aka Jun 22 '17 at 7:28
  • \$\begingroup\$ @Andyaka I know it's disparate questions, but there's no way I could ask them all separately. And yes, I have. Trust me, I do my research many times over before coming here for help. And I'm not quite sure what you mean by your last statement. If an answer is good, I upvote it, and if it works successfully for me, I mark it as an answer. What else is there to do? \$\endgroup\$ – Jashaszun Jun 22 '17 at 13:28
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    \$\begingroup\$ Well you have accepted one answer since I posted my comment so maybe you did secretly know what I meant! \$\endgroup\$ – Andy aka Jun 22 '17 at 14:11
  • \$\begingroup\$ @Andyaka Yes, I did review them to make sure, and I'm not sure why I didn't accept that one. One mistake, from a while ago. The rest are still accurate. \$\endgroup\$ – Jashaszun Jun 22 '17 at 14:14
  • \$\begingroup\$ From the set of question, it is apparent that you have no foggiest clue what you are doing. You are 18 as your profile states, you need to go to a school and learn some basic engineering first, then study USB standard (mandatory modes of operations), then research demo boards offered by all chip manufacturers, understand the function of resets as example. You need to learn to read specifications carefully, and understand that in this particular case the Vusb from 2210 is for internal consumption only, and the radio can take up to 130 mA, etc. You have a long way to learn. \$\endgroup\$ – Ale..chenski Jun 22 '17 at 18:14

My advice: start with reference demo board, MCP2210 Breakout Module. Follow their BOM and layout to the letter, including RESET area, since your "design consideration" questions would require several pages of explanations.

Then add the radio module, again in full accord with manufacturer's application advises and demo boards. This should take care of use of GND pins etc.

Then apply the main architectural idea for an embedded design: (1) power-on HOST (master) first (in your case it is SPI bridge); (2) hold all slave peripherals inactive until the SPI host is activated (from USB side). (3) Use GPIO to enable the slave(s), which might include power gating and definitely RESETs of proper polariy; (4) activate the slave(s) across the USB-SPI-bridge as software/firmware is ready.

This approach should take care of all slave RESETs, and avoid excessive inrush, etc. Push-buttons should be placed only on development boards.

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  • \$\begingroup\$ Thank you for your help. I will certainly look into the demo board. I didn't know until today that such things existed! \$\endgroup\$ – Jashaszun Jun 22 '17 at 19:57

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