Question 1

It it possible to change the address of the lcd to have multiple lcd on the same bus?

Accepted Answer

To further expand on Wes' answer (which is excellent!), you can have up to eight (8) on the same bus, per the chip datasheets. The chips have a portion of the address hard-code (which cannot be changed) and the three remaining address lines (A0, A1, and A2) can be jumpered to ground to set seven (7) other addresses - the 8th being no jumpers. IF you happen to get one with an 8574 chip and another with 8574A or 8574T, then you could potentially have up to 16 modules on the same bus as the A and T versions use a different hard-coded address than the 8574.

Question 2

Has anyone run this display on 3.3 volts successfully? I'd like to use it on an 8266-12E to display the ip address.

Accepted Answer

It works on 3.3V, but just barely: it's unusably dim. I changed the supply voltage to 5V and was able to successfully drive it with 3.3V-level I2C signals, although the PCF8574 data sheet says that the minimum Vih level is 0.7 * Vcc = 3.5V. My scope says that the signals are rising to about 3.8V, so there must be some kind of pull-up to 5V on the I2C backpack board. I don't want to rely on that, so for my final design I'll use a PCA9306 I2C level shifter.

Question 3

Do these come with an I2C backpack?  I just ordered some of these and they came with no backpack in the package.

Accepted Answer

There are several product options on the page, some have I2C, some don't. If you chose one that has I2C, it should come with an I2C backpack.

Question 4

Does this work for the old raspberry pis that have a 26 pin gpio?

Accepted Answer

This module uses an i2c serial interface rather than discrete gpio pins.  If your rpi has an i2c, it should work.

Display Size	3 Inches
Total Usb Ports	4
Batteries Included	No
Batteries Required	No
Brand	SUNFOUNDER
Item Model Number	8541582407
Product Dimensions	19.05 x 12.7 x 0.51 cm; 86.4 g
Item Weight	86.4 Grams

[SunFounder]SunFounder IIC I2C TWI Serial 2004 20x4 LCD Module Shield for Arduino Uno Mega2560 I2C LCD [並行輸入品]

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