LEDMatrix and RTC shield incompatibility


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I have a stack with the following shields:
1. TinyDuino (attached to battery)
2. TinyShield RTC
3. TinyShield LED Matrix

I'm using the LoLShield library (with Tiny Circuit's changes) to control the LED Matrix. When I init the library it causes 7 of the leds in the matrix to light up at about 1/2 power. See the attached image.

I've looked at the Tiny Circuits shield compatibility chart, but it doesn't list the LED Matrix at all. I don't see the RTC being incompatible with anything (expect itself).

I've tried two different LED Matrix shields. One red and one green. They both have the same problem and the exact same 7 leds light up.

If I remove the RTC from the stack, I don't have the problem. Without the RTC in the stack the LED matrix performs just fine.

Here's the code that makes this happen with the given stack:

#include "Charliplexing.h"

void setup() {

void loop() {

Any ideas?

Tony Batey

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The Maxim chip on the RTC uses has pins 2 and 3 used as interrupt pins for the output. If you don't need interrupts you can remove the R4 and R5 resistors that are tie pins 2 and 3 to VCC on the RTC board. This should let you use both boards together.


« Last Edit: May 20, 2015, 04:14:39 PM by Tony Batey »


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