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| Help Validating PCB Design |
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| microcompiler:
I’m new to PBC design and in general the hardware side of electronics is a hobby. I’ve had a couple of collage classes in electronics and that’s it. I have much more experience on the software side of electronic devices. This is my first real PCB that I plan to have Seeed fabricate and assemble using Ublox’s new dead reckoning GPS unit. To save on costs I would like to use as many components as I can from Seeed’s “OPL list”. I’m asking for assistance validating my Raspberry HAT design. This design is pushing my hardware knowledge to the limits but I really want to see a working version of this board running on Windows IoT core. It's now become a personal mission. Therefore, I’m reaching out to this form for help! I have created this project using Altium Circuit Maker and it’s published under the project name Raspberry Pi GPS Dead Reckoning HAT. I included several project screen shots below for review. I think I’m getting close to a final design but not confident enough to send for fabrication. The down side to this project is the NEO-M8U modules are $40 a piece in small quantities. Therefore I can’t afford screwing it up. Any advice you are willing to provide would be great! Here are the specific areas that I would like to get feedback around: * Am I using right capacitors and resistors values on the NEO-M8U, BNO005, ADS1115 chips? * Is the overall circuit design solid? * Power will be supplied in two ways. From the Raspberry directly with the usb port or using this battery module. What is the simplest/cleanest IC to prevent an issue if both power sources are connected at the same time? Both are clean power sources but I want to prevent smoking the device if power is connected both ways at the same time. * Do I have the battery correctly designed to charge the rechargeable battery properly once power is restored to the device? I think it’s laid out correctly from a design perspective but I’m not confident it’s correct on the PCB. * Do you see any issues with the PCB traces or layout? * What other items do you I need to change/fix to increase my chances for a working HAT the first time? * I’m actively developing code for a breadboard versions of the NEO-M8U, BNO005, ADS1115 chips therefore at this point I would be stepping backwards if I used other chips. However, I’m open to changing other components. Would you change any of the other components and why? |
| sokoloff:
The GPIO connector needs to come off the bottom of the board, not the top. (The 3D model shows it coming off the top.) I don't like how the pads for that connector are laying out. (It could just be my unfamiliarity with CircuitMaker. What does the top layer of the board look like without the components? Just the top copper, soldermask, and silkscreen.) I don't see any fiducials to aid in pick-n-place. (Doesn't matter for hand-assembly.) If you're doing one-off prototyping, all of that could be reasonably hand-soldered, reducing the risk of wasting the $40 modules. Once you know it works and (ideally) there's a market, then you can have it made by a contract manufacturer. I'd plan on a hand-assembled test run of a couple boards (maybe more than one spin at that, recycling the module if you need to) before calling the design "done". |
| theatrus:
--- Quote from: microcompiler on May 02, 2017, 01:08:14 am ---I’m new to PBC design and in general the hardware side of electronics is a hobby. I’ve had a couple of collage classes in electronics and that’s it. I have much more experience on the software side of electronic devices. This is my first real PCB that I plan to have Seeed fabricate and assemble using Ublox’s new dead reckoning GPS unit. To save on costs I would like to use as many components as I can from Seeed’s “OPL list”. I’m asking for assistance validating my Raspberry HAT design. This design is pushing my hardware knowledge to the limits but I really want to see a working version of this board running on Windows IoT core. It's now become a personal mission. Therefore, I’m reaching out to this form for help! I have created this project using Altium Circuit Maker and it’s published under the project name Raspberry Pi GPS Dead Reckoning HAT. I included several project screen shots below for review. I think I’m getting close to a final design but not confident enough to send for fabrication. The down side to this project is the NEO-M8U modules are $40 a piece in small quantities. Therefore I can’t afford screwing it up. Any advice you are willing to provide would be great! Here are the specific areas that I would like to get feedback around: * Am I using right capacitors and resistors values on the NEO-M8U, BNO005, ADS1115 chips? * Is the overall circuit design solid? * Power will be supplied in two ways. From the Raspberry directly with the usb port or using this battery module. What is the simplest/cleanest IC to prevent an issue if both power sources are connected at the same time? Both are clean power sources but I want to prevent smoking the device if power is connected both ways at the same time. * Do I have the battery correctly designed to charge the rechargeable battery properly once power is restored to the device? I think it’s laid out correctly from a design perspective but I’m not confident it’s correct on the PCB. * Do you see any issues with the PCB traces or layout? * What other items do you I need to change/fix to increase my chances for a working HAT the first time? * I’m actively developing code for a breadboard versions of the NEO-M8U, BNO005, ADS1115 chips therefore at this point I would be stepping backwards if I used other chips. However, I’m open to changing other components. Would you change any of the other components and why? --- End quote --- First off, congrats on a well labeled schematic with an easy to follow design. 1: Since you're pulling power from the RPi, you may want to add a bulk capacitor (1.0uF-4.7uF) on the board to board connector. A ceramic MLCC X7R would be ideal IMO. This also includes on your power input. 2: Didn't really spend any time here. The reality of getting a full usable 16bits from that ADC may not be possible (just the nature of it). The PGA presumably buffers it so you don't need to buffer further. 3: The simplest is a diode on each input path, though it will drop the voltage to below what the RPi 5V rail expects. There are a number of "ideal diode" controllers, for example: http://www.ti.com/lsds/ti/power-management/oring-and-smart-diodes-overview.page 4: C4/R4 have air wires :) Also, it looks like your ground pour on both layers is more or less randomly connected to components. Think about how this connects to clean it up. Also, is the antenna trace to the recommendation from uBlox? RF traces are critical - they should provide some guidance on width, clearance to the ground planes and bottom plane depending on board thickness. |
| ziggyfish:
--- Quote from: microcompiler on May 02, 2017, 01:08:14 am ---I’m new to PBC design and in general the hardware side of electronics is a hobby. I’ve had a couple of collage classes in electronics and that’s it. I have much more experience on the software side of electronic devices. This is my first real PCB that I plan to have Seeed fabricate and assemble using Ublox’s new dead reckoning GPS unit. To save on costs I would like to use as many components as I can from Seeed’s “OPL list”. I’m asking for assistance validating my Raspberry HAT design. This design is pushing my hardware knowledge to the limits but I really want to see a working version of this board running on Windows IoT core. It's now become a personal mission. Therefore, I’m reaching out to this form for help! I have created this project using Altium Circuit Maker and it’s published under the project name Raspberry Pi GPS Dead Reckoning HAT. I included several project screen shots below for review. I think I’m getting close to a final design but not confident enough to send for fabrication. The down side to this project is the NEO-M8U modules are $40 a piece in small quantities. Therefore I can’t afford screwing it up. Any advice you are willing to provide would be great! Here are the specific areas that I would like to get feedback around: * Am I using right capacitors and resistors values on the NEO-M8U, BNO005, ADS1115 chips? * Is the overall circuit design solid? * Power will be supplied in two ways. From the Raspberry directly with the usb port or using this battery module. What is the simplest/cleanest IC to prevent an issue if both power sources are connected at the same time? Both are clean power sources but I want to prevent smoking the device if power is connected both ways at the same time. * Do I have the battery correctly designed to charge the rechargeable battery properly once power is restored to the device? I think it’s laid out correctly from a design perspective but I’m not confident it’s correct on the PCB. * Do you see any issues with the PCB traces or layout? * What other items do you I need to change/fix to increase my chances for a working HAT the first time? * I’m actively developing code for a breadboard versions of the NEO-M8U, BNO005, ADS1115 chips therefore at this point I would be stepping backwards if I used other chips. However, I’m open to changing other components. Would you change any of the other components and why? --- End quote --- I would make sure you have 50-ohm impedance (this depends on your PCB stack up as well as the width of the trace) on your antenna, also you according to the Hardware Integration Manual (Section 2.4) you will get better sensitivity when it has an external LNA and SAW filter. Also, make sure you have the right antenna. Thanks Brendan |
| microcompiler:
Regarding the connector on the top of the board I'm trying to stick to the HAT standard as close a possible. This type of connector has two parts allowing you to stack boards if you by the long pin header. Yes at this point this is just a prototype and I can try and solder it However, it takes me forever to do right and I normal destroy a few components at the same time. I'm would like to try the Seeed PCBA to do this board if it doesn't cost me an arm and a leg. It looks like it's only a $25 setup fee plus another$10 in components labor. This way I can spend the time working on the Windows IoT drivers. |
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