I’ve been searching the internet for a Datasheet for the ESP8266 but have been unsuccessful at this point. If anybody has this could you shoot it my way?
… we’re having trouble with the interface between the master and slave modules. Looking through the schematics and probing voltages, it appears that the slave module’s I/O expander operates on +5V, while the master module generates 3.3V logic signals. It looks like these 3v3-logic signals are at the cusp of being interpreted by the PCA9555 I/O expander on the slave module. Has anyone else found this?
PCA9555 is a I2C device, for I2C device, because the data lines are pulled high by the microcontroller, and the slave devices only pull these data lines to ground, it’s ok to have a 3.3V microcontroller interfacing with a PC9555 powered by 5V. 3.3V is within the high logic range of PCA9555, so this works fine.
Yes, I am aware of the datasheet, but we’ve never had any problem using 3.3V ESP8266 to drive 5V PCA9555. If you believe it’s a problem you can simply add a diode in series between 5V and PCA9555’s VCC pin, so that will drop 0.7V and supply 4.3V to PCA9555. This way 3.3V/4.3V > 75%.