as ttl work on 5v and ESPs on 3v3 you need a bidirectional level shifter :
https://electronics.stackexchange.com/questions/173297/how-does-a-bidirectional-level-shifter-work
@MaBe started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
as ttl work on 5v and ESPs on 3v3 you need a bidirectional level shifter :
https://electronics.stackexchange.com/questions/173297/how-does-a-bidirectional-level-shifter-work