ESP8266 Community Forum

- Mon Jul 10, 2017 10:01 am #68119 While checking on some signals I discovered I was getting 4.2V TX signal from my CP2102 based USB serial adapter.

I couldn't understand this at first because the CP2102 has an internal 3.3V regulator and the output signals are referenced to this.

I then found this discussion on silabs forum http://community.silabs.com/t5/Interfac ... m-p/194104 where it seems quite a lot of modules (including the 2 I had) are badly wired up. The CP2102 RST signal is incorrectly wired to the USB 5V supply effectively bypassing the internal regulator and running the CP2102 chip itself out of spec.

No direct harm seems to be done by this and the higher TX voltage does not seem to cause the ESP8266 any problem.

Nevertheless I have corrected my development interfaces by cutting the track to the RST pin on the CP2102 module.

- Mon Jul 10, 2017 2:30 pm #68133 Almost all 3.3V USB-TTL adapters I came across actually weren't 3.3V. They just had a 3.3V supply line but still 5V TTL levels.
If you design your own board, just make sure the TTL chip never sees 5V - they all work fine with 3.3V only. Put the voltage regulator in front of them.
If you use available modules... maybe still put the voltage regulator directly in the supply line:
https://www.thingiverse.com/thing:768406
I use this USB 3.3V adapter on all my 5V serial adapters. Works just fine... And there is no chance that any TTL level will ever exceed 3.3V.

- Mon Jul 10, 2017 3:14 pm #68135 Any usb serial using the CP2102/9 family interface should be putting out 3.3V levels. The core of the chip runs at 3.3V and the outputs are referenced to this.

I have 4 adapters. 2 worked correctly like this. The other 2 had the badly wired RST line and were putting out 4.2V until I corrected them and then they put out 3.3V as per the chip spec.

- Mon Jul 10, 2017 6:15 pm #68142 I use these. Both 5 and 3.3 levels via jumper header. No regulator for the 3.3 volts. It has two diodes in series to drop the voltage. Crude but it works.

CORRECTION - These do have a 3.3 volt regulator and do not use diodes to drop the voltage as I said above. I saw the diodes and I thought it was the same as a different USB to serial converter I also use. U2 in the picture is the 3.3 volt regulator. I was looking more closely at the board as I now need both RTS and DTR. DTR is available on the chip but not brought out on a pad.



CH340 module instead of PL2303 https://www.aliexpress.com/item/1PCS-CH ... 81570.html

Less than $1 USD.

Last edited by rudy on Wed Jul 12, 2017 3:25 pm, edited 2 times in total.