No COM port detected on Custom PCB  - Page 1
Forum section: electronics / projects

author: rt2gb
author_rank: Newbie
timestamp: April 03, 2022, 05:26:02 am
content: I am using CP2102N-A02-GQFN24 on my custom PCB to program my ESP32 board. I am not able to see any COM port on my Windows 10 PC. I can connect to an off the shelf CP2102N-A02-GQFN28 USB UART bridge board to my computer. So I think that rules out driver issue then I am not really sure what else could be an issue. I was saw numerous people commenting on putting a 1-10uF cap on EN line of ESP32 to fix the timing issue or EN & IO0 line which is connected to RTS and DTR on CP2102 but that didn't help either.I can program my ESP32 if I connect COTS UART bridge board directly to ESP32 EN,IO0,Rx & Tx lines. Most of my schematics is similar to ESP32 Wroom Dev board, except I am using CP2102 24 pin package. You can link for ESP32 wroom below. I am not using buttons for manual programming but I am using NPN transistors (SS8050-G) for automatic bootloading.I have attached screenshot of my schematics. I have also attached timing snapshot from my OScope. In snapshot 'setup_9.png' CH1 is DTR and CH2 is RTS and in another snapshot named 'setup_10.png' has Ch1 as EN and CH2 as IO0.ESP32 Wroom Dev Board link:https://dl.espressif.com/dl/schematics/esp32_devkitc_v4-sch.pdfSS8050-G Datasheet:https://www.comchiptech.com/admin/files/product/SS8050-G%20RevA181526.pdf

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 03, 2022, 08:41:50 am
content: Why there's no 4.7uF on VREGIN / VUSB_BUS?I hope you're not getting the ESP 3.3V from the CP2102 VDD, the CP2102 draws 9-15mA but the LDO is only able to supply 100mA in total.The ESP32 will consume about that when idling and almost three times more when TXing.What's not being detected? The ESP or the COM port?Open the device manager and plug it in, what happens?SUSPEND pins are outputs, can be left floating, so R18 is not required:Quote

author: wraper
author_rank: Unknown
timestamp: April 03, 2022, 08:55:13 am
content: Although not likely to be the root cause of particular issue, yet again that garbage on USB shield.https://www.unit3compliance.co.uk/hdmi-more-like-hdm-why-thoughts-on-cable-shield-grounding/Watch from 31:00

author: rt2gb
author_rank: Newbie
timestamp: April 03, 2022, 04:04:29 pm
content: Quote from: DavidAlfa on April 03, 2022, 08:41:50 amI realized that I am missing decoupling caps on VregIn line so I have a breadboard and I jumped my EN and VregIn line to my breadboard where I have 10uF and 0.1uF caps for individual lines. I think it is more of RC timing problem so that is why I am using breadboard to quickly change the caps if needed. I understand that with breadboard the caps on EN & VregIn are not close the ICs and has added impedance because of jumper cable. Cp2102 24 pin package is too small for me to attach caps to the pins of the IC.Quote from: DavidAlfa on April 03, 2022, 08:41:50 amI am not using CP2102VDD for ESP32. I am using LM27762DSSR for supplying 3.3V to ESP32 from a battery.Quote from: DavidAlfa on April 03, 2022, 08:41:50 amThere is no COM port allocated for my board in my Device Manager. I can use COTS part with CP2012 28 pin package to program my ESP32. I can program ESP32 via COTS USB UART bridge if I remove RX & TX jumper resistors (R15 & R16) on my PCB while RTS & DTR traces are still connected to ESP32 via NPN transistors.Quote from: DavidAlfa on April 03, 2022, 08:41:50 amYup, R18 is optional but I just using it as abundance of caution.

author: rt2gb
author_rank: Newbie
timestamp: April 04, 2022, 06:52:05 pm
content: Got it fixed. I did a mistake while drawing the schematics for D5V0F4U6S-7. It turns out to be 4 CH ESD TVS diodes chip so my USB data traces were not connected to CP2102N chip. I modified the boards and it works after that.