ESP8266 Community Forum

- Sat Aug 15, 2015 2:46 pm #26095

If you were using 2 MOSFET circuits mentioned above tied together (only 1 pullup needed on the 3V side), you will end up with an AND configuration, so no needs for inverter ...

Martin

I still don't think you have appreciated what I am doing. My logic needs two separate NAND gates. I have the logic and the one transistor needed. I am not going to buy even one MOSFET, let alone two when I can achieve the same without. You seem to have got 'hung up' on the inverter issue. The topic, and my original query, was just about the input requirements of the ESP Rx pin. It had nothing to do with 'inverters' or level shifting. It is relevant however to anyone wanting to drive the Rx pin from any external circuitry.

Mike B

- Sat Aug 15, 2015 3:54 pm #26098 Hi Mike,
If I understood, you simply wish to multiplexing 2 serial 5V inputs into the single 3V input of the ESP, right ?
That is what my circuit suggestion is doing, as simple as possible.

- Sun Aug 16, 2015 7:23 am #26150 Martin

I am multiplexing in both directions with the ability to choose the source in each case and also, optionally, adding the Tx and Rx so I can see what is happening between the PIC and ESP in both directions on a single RS232 stream. It is not quite so simple as you might think. Anyway, problem solved.

The Rx input is not just a CMOS input with clamp diodes. It has an active pullup of unknown strength. This was my original, and only issue. It needs to be driven with something more than just 4000 series logic. My only query was just what is the input characteristic of this Rx input. Seems no-one knows.

Unless someone from the ESP team can give this info. then we can consider this thread closed. Just let it be a warning to other designers of ESP interfaces.

Regards

Mike B

- Sun Aug 16, 2015 10:15 am #26164 If you want actual technical data, you might have more success asking on the Espressif "bbs" bbs.espressif.com.