PCB Review: 2 layer ESP8266 Huzzah breakout board with SPDT switches.

[tylerssims]

Hi all,

I'm looking for feedback on my board and design in general. It is the controller board for another PCB with 14-segment displays. The traces are 0.5mm with 0.5mm vias.

It is a breakout board for an Adafruit ESP8266 Huzzah module.  My board takes the Huzzah module, breaks the pins out to headers, adds an LDO regulator to the VBAT, and adds 4 push button switches to enable various pins. It's far from an ideal design, but I'm too deep into my project to layout a full custom board from discrete components.

Here’s the context to what’s going on. I’m powering a board with a bunch of 14-segments displays with this pcb. It’ll draw about 320mA. The Huzzah has about 250mA available to its 3.3V output, which is a little less than my requirement. To get around this I've added another regulator. That’s why I have it going to a separate power rail, for the displays.

I have also included two potentiometers configured as variable resistors. One is a variable pull up resistor, and the other is a variable pull down. They are each connected to an empty pin header and have no other input. I included them in case I need more resistance for my I2C bus or if my internal pull up/downs for certain pins are insufficient. I know it's not very practical but I thought it would make for quick troubleshooting and would be fun to build. Please let me know what you think.

My design and layout: https://imgur.com/a/JtZtVVb

*just noticed my pin labels for RV1 and RV2 are backwards.

Adafruit Huzzah ESP8266 schematic:  https://learn.adafruit.com/assets/96603


Thanks!

[Doctorandus_P]

I still see at least one ratsnest line. (See picture below).
Run DRC and fix all issues that pop up.

Also, an ESP8266 module implies WiFi, and WiFi antenna's don't work well with GND planes.

It looks like IC1 is a voltage regulator (probably 1117 type) These have stability issues, and the decoupling seems inadequate. The "tab" is also supposed to be connected to some adequate sized piece of copper to act as a heatsink.

Where is the power coming from? Do you have a connector to apply power to this PCB?

I see I2C, which always needs pullup resistors. I don't know if the huzzah has pullup resistors, but you should at least add an option to add pullup resistors to your PCB.
Sometimes such PCB's have quite weak pullup resistors (for example 22kOhm) and it's expected to add additional "pullup strength" as the I1C bus gets longer and more capacitance is added.

For "Test points" I prefer to use THT holes. You can stick a probe into them so it won't slide off while you are for example adjusting knobs on a measurement device with your other hand. If you put test points on a 2.54mm grid, you can also solder in a single row header and use dupont wiring to have both hands free during test probing.

Also, doing a review from some pictures is annoying. You can't see much from screenshots.
It's even worse by uploading the pictures to some external site. This often makes it impossible for others to learn from your mistakes and the review if for example the pictures on that other site get (re) moved or the links break.
So at least upload the pictures here, or even much better, zip up the project and post the project itself.

[tylerssims]

Thank you so much for the feedback! It makes the learning process a lot easier.

I took your advice- Reran DRC, added a copper pour around the LDO output tab, and added DNP footprints on the I2C traces just in case I need to add stronger pull ups later (the Huzzah has onboard pull ups already).

Power is coming from a JST connector on top of the module which connects to a Li-ion cell.. The input to my LDO comes from the BAT pin of the Huzzah module which connects directly to the JST connector. The Li-ion is charged through the USB port.

The test points are really just solder pads for the wires which will connect my two parts (I didn't now what symbol to use for them when i started) - but I will certainly take your advice about the THT holes for any real test point in the future.

Here's an updated imgur album (https://imgur.com/a/QtQ6vnx), but I've gone ahead and shared images alongside a ZIP in this post too.

[mariush]

Is there a reason why you can't put those two buttons / switches (RESET and WAKEUP) close to the other two?
The regulator could go to the left to make room for the buttons.  You can easily route those traces to the buttons on the top around the other buttons.

I'm also not a fan of 1117 regulators, the one you chose is probably stable with ceramic capacitors but who knows which person looks at your design and tries to make one with a regular 1117 and  then wonders why all is unstable.

For example, there's 500k pieces of NCP176 in stock at Digikey : https://www.digikey.com/en/products/detail/onsemi/NCP176AMX330TCG/5761739
Has 80-120mV voltage drop at 500mA, so it will work even with very discharged batteries...

Another example ... 200k pieces of AP7366 (adjustable regulator, 600mA max, around 200-300mV dropout voltage) : https://www.digikey.com/en/products/detail/diodes-incorporated/AP7366-W5-7/9867323

[tylerssims]

I could move the buttons again but I the location of them isn’t that important and I don’t think it would make the traces any shorter. I’m just trying to order this board asap. Do you think there is any functional probables with where they are at?

The data sheet specifically calls for ceramic caps so it should be ok (it’s says the output cap MUST be ceramic). These are the proper 1uF low ESR  ones too. I didn’t know this was a finicky regulator, this is the first one I’ve used in a design, so thanks for the info!