Hi... I am testing out a 5x7 LED matrix, being driven by an MCP23018 I/O extender. Everything is working great, scrolling text and all.
The problem is... The LED's are much brighter when only one light is on in a column, and much dimmer when all seven are on.
I'm probably missing some basic electronics thing, I suppose. Any ideas?
Schematic is here, or click through for bigger:
- 1 604-TA12-11YWA Kingbright YELLOW DIFFUSED 5X7 DOT MATRIX LED Display $2.22 Datasheet
- 1 579-MCP23018-E/SP I/O Expanders, Repeaters & Hubs 16B I/O Expander I2C interface $1.58 Datasheet
- 1 652-4116R-1LF-100 Resistor Networks & Arrays 16pin 100ohms Isolated Low Profile $0.60 [url=http://www.bourns.com/data/global/pdfs/4100r.pdf[/url]Datasheet[/url]
- 5 512-2N3904BU Bipolar Small Signal NPN Transistor General Purpose $0.10 Datasheet