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Forum Index : Microcontroller and PC projects : Why does this "diode mixing" on usb/serial not work
| Author | Message | ||||
| lizby Guru  Joined: 17/05/2016 Location: United StatesPosts: 3378 |
I'm trying to monitor Tx and Rx on an ESP-01 to see why it's not doing what I want. If I "T" off either Tx on the ESP-01 to Rx on a ch340 usb/serial module at 115200 or Rx on the ESP-01 to Rx on the ch340, I can see what is transmitted in a Teraterm session connected to the ch340. But if I try to diode-mix them with Bat85 diodes, black strip to the ch340 side, I get nothing, and if I do them one-at-a-time through the diode, I get nothing. 0V connected in each case. F4 ESP-01 Tx ---o---Rx | `--|>||--o -- Rx CH340 | Rx ---o--|>||--' | `---Tx How do I accomplish what I'm trying to do? (In the meanwhile, I'll just add another CH340 and have one monitor Tx and the other Rx, but it seems like I should be able to mix them with diodes.) PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5089 |
What are the levels at tx and rx when no data is transferred? 3.3v or 0v? If 0v then you have the diodes polarity correct, but need to add a 3k3 resistor to ground at the rx pin of the ch340 to make sure the level gets low. If 3.3v then reverse the diodes and add a 3.3k pullup to 3.3v at the rx pin of the ch34o. Please note that this only works for half duplex. In full duplex transmit an receive can happen at the same time, and your data will get corrupted. Edited 2021-03-21 03:26 by Volhout PicomiteVGA PETSCII ROBOTS |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3378 |
Right, idle high. Thank you. That worked. PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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