Erica’s original system was based around the TLC5940 LED driver chip which was controlled directly by one of the raspberry pis in Erica with an ATtiny45 on the pi daughter board to provide the clock signals.

Erica old LED setup

For anyone who saw Erica in person you will have noted that the LEDs were not always working. Although we haven’t been able to work out the exact cause of the issue we believe it may be due to the chips either overheating (ambient temperatures inside Erica got up to 58C when in the Marlands), or due to large voltages being inducted onto the signal wires linking the drivers.

To resolve these issues we have created a new LED controller design for Erica. The following are the major improvements over the previous version:

• As we wanted to avoid replacing or altering the leds we had already installed the new controller is designed to connect up to the connectors on the existing LEDs.
• The new board uses the same driver chip (TLC5940) as the previous version but is instead controlled by an atmega168 (used on some arduinos) located next to the led driver.
• In order to improve the signalling between the boards the new design uses the DMX512 protocol, this is often used in event or architectural lighting setups
• Cat5 cables will be used to connect the boards together as they are easily available and easier to work with than the original ribbon cable connections
• Internal debugging LEDs to help with diagnosing issues we may encounter.
• Socketed chips to allow replacement if things go wrong

Below you can see the new controller design being tested. The controller itself is on the white breadboard, the blue breadboard is the transmitter that will put on the mech pi daughter-board. The cat5 cable connecting the two boards for this test is over 30m long so it shouldn’t have any trouble with the distances inside Erica

Erica new LED controler test

Rather than build these controllers on strip-board we have designed a custom PCB (Printed Circuit Board)

Design For Erica’s new LED controler