ESP8266 Community Forum

- Mon Jul 04, 2016 8:57 am #50166 Hallo, my name is Stefano from Italy.
I'm creating a domotic project with arduino Nano+CAN bus: serveral nano-periphals to move up/down the shade in my home and check anti-thief sensors at window. Now I'm about at the end of project but for the central unit I'd like to use esp8266 instead of arduino Nano so I've built the schema in attach.
My first doubt is the correct manage of different level voltage: 5v for can bus module, 3.3 for esp and 2.8 for sim800l. Plus I don't know esp8266 (it's new hardware for me) so maybe you can help me to find errors or omissions
Any suggestion is welcome!
In my project I added i2c: onboard a RTC with ds1307 and 32k flash to store data about nano-periphals and by external connector 4x20 lcd and keypad.


Thanks, Stefano

P.S.: I hope you will understand my english

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- Sat Aug 13, 2016 8:08 am #52837 Hi,

Although this post is a little old, I will try to give you my feeling about this setting !

ESP8266 is a 3.3V ttl device. It seems to be very tolerant to overvoltage (but not tested and rated up to 3.6V)
SIM800L is 3.4 to 4.4 an not so overvoltage tolerant (5V will destroy it)
its ttl logic seems to be 2.8V (not sure of this) and seems to work safely at 3.3V

So in your schema you are using LM7805 to power the :
ESP8266 breadboard via (I assume) its own 3.3V reg --> safe
SIM800L via a diode which drops 0.6V and gives 4.4V to the SIM800L VCC pin --> safe

be sure to have enough current from your 7805 as it seems that power pick can rize to 2A

I don't understand the resistor divider that you put on the Tx pin of your SIM800L --> could you explain please ?

Finally, as you have probably already tried your set up; could you tell me if it works safely ?
Regards
JP