ESP8266 Community Forum

- Fri Dec 30, 2016 11:16 am #60157

No, I don't have any pullups. For what? In other proyect with pca9685 nevwer use that.

The PCA9685 have 5 pines, VCC, GND, conected to external power (5v) and SDA, SCL, connected to nodemcu module. And the aditional power v+ and gnd to external 5v power.
Here example, connected to a UNO:
http://www.naylampmechatronics.com/modu ... efault.jpg

Pull-ups are probably included on the PCA9685 board. If that is the case then that is why you probably have not needed them. But most of the time a 4k7 - 10k resistor is included. That is adequate for most situations. I typically use 2k2 in order to make sure that capacitance will not have much effect on the rise time of the I2C signals.

Pull ups are required. Maybe they are on the board you are using. If not then they must be added. I2C relies on the pull-ups to produce a high. The chips will produce a low only. This allows more than one device to be connected to the same lines.

- Fri Dec 30, 2016 12:31 pm #60161 Right, PullUps are mandatory if the board doesn't provide them.
And, as rudy said, if the PCA9685 is on 5V rail instead of 3V, your need bi-directional level shifters on both SDA/SCL.

- Fri Dec 30, 2016 7:41 pm #60178 If your PCA9685 board looks like this, you probably does not need pull up resistors. This board can run with VCC=3.3V so logic level converters are not needed. There are many clones of the Adafruit board and the ones I have used are true hardware clones so the Adafruit drivers and tutorials work.

The board can be used with 3.3V systems as shown in this tutorial. Note Vcc=3.3V, no pull up resistors, and no logic level converters.