Still some problems

Yesterday we found out that the I2C expanders (PCF8574) could not source the LEDs of the LED matrix. We did some measurements and apparently the output ports of the PCF8574 IC's gave only 70µA as output current which is to low of the LEDs to light up. The LEDs need 20mA. As a solution we drew another PCB to place on top of our original PCB. This new PCB has an LED driver circuit with a transistor for each LED. Below you can see the new PCB.

We also have a problem with our program for the arduino, it seems that using the NFC card reader with SPI and the I/O expanders with I2C work perfect separately but if we combine the 2 programs, only the SPI works and the I2C doesn't work anymore then. We are still trying to find what causes this problem, maybe the arduino is not able to use SPI and I2C at the same time or maybe it's something else, we don't know but we hope we'll find it soon.

finally some progress

Our PCB is made by the LPKF machine, this week we are going to solder all the components on the PCB. The I2C finally works, I found the error, I used B01000000 (8 bit) as address for the I2C but apparently arduino uses the 7 bit address so B0100000 and adds a '0' or '1' (for write or read) by itself. I also noticed that I made a little mistake in the last schematic of the test setup (the LED was reversed). I changed it in the schematic, below you can see the right one.

here you can see the program code I used for this schematic:

Today we are going to finish the pcb gerber files so that our print is made and we can finally start with soldering. Our program in arduino is still not 100% this is probably within the i²c part of the code. To test our program we are using a test setup with 1 i²c, 2 pullup resistors of 4K7 and a led. The schematics of the test setup you can see in a former blog.