Problem achieving display brightness

[Higgsfield]

Running on your breakout board, the 64x48 display CFAL6448A-066BW, runs perfectly. In our circuit, is running dimly, and seems to be putting a lot of noise onto the SDA and SCL lines. They show a square wave and fall short of the VCC rail. If we drop the value of the pull up resisters the display brightens a small bit. With the display out of the circuit these lines are fine and communication with other I2C devices works just fine. This must I sure be a symptom of something else not working or connected correctly. Any thoughts on what we are doing wrong would be appreciated.

Here is the circuit diagram. I notice on our implementation CS is connected to ground, while on the breakout board it is left floating?

We fold the the flexible printed circuit over so the pin direction is reversed!

Looks like I might have BS1 and BS0 swapped around?

Crystalfontz LCD Blog

Looking for additional LCD resources? Check out our LCD blog for the latest developments in LCD technology.

 

[CF Kelsey]

I don't see anything that stands out to me that would cause the issues you're describing.

We leave CS as floating to allow it to be controllable, tying it to ground should not cause any issues. I also don't think you have the BS0 and BS1 swapped. BS1 is pin 8, BS0 is pin 9, so in your reversed numbering BS0 should be 4 and BS1 5. BS0 should be low, BS1 high. Which looks correct.

You might try adding additional decoupling caps. Our design uses both a high and low on each of VDD and VBAT.

Have you checked the voltages at the display when it is included in your circuit?