Trouble getting a push-button to trigger a transistor (as a switch)


I have an Adafruit 8x8 Neomatrix ( that I'm trying to control (on/off) using a push-button connected to a TIP120 transistor, all hooked up to an ATTiny85.

The Neomatrix is an LED board that has Din, 5V, and Ground pins, and you control all the LED's through a software library. The board uses 3.5mA at it's peak (all LED's lit on White).

I have an ATTiny85 where I'm reading the state of a push-button (using the Arduino sample debounce code), and my intention was to control the power going to the Neomatrix board, as a sort of on / off switch.

I've connected the VCC of the Neomatrix board directly to the 5V of the DC Barrel jack, and one of the output pins of the ATTiny (through a resistor) to the base pin of the transistor, the collector going to the Ground pin of the Neomatrix, and the collector of the transistor going to the DC Barrel Jack ground.

The code and hookup are working fine when I am simply toggling an LED on and off using the button, but when I hook up the transistor and the Neomatrix board, the toggling works once, and then stops working (when I run the same "trigger wire" (connected to the transistor base) back to my LED, it also doesn't work anymore, but if I reset the ATTiny, it works again, it's like it's getting frozen somehow).

Here's a screenshot of my setup (designed in Fritzing):

If anyone can give me some advice on what I might be doing wrong, and how to properly use a TIP120 as a switch in this instance, it would be much appreciated.


Do you have a pinout for that big thing on the right (with all the leds on).

There's only 3 pins (labeled in the diagram referenced in original post): VCC, GND, and Digital In.

OK I've traced all the lines and (bar any mistakes I may have made) It looks like you are using d3 of the ATtiny85 to enable the LED thing. and D1 to send digital to it. In the meantime you're using D4 to sense the button press.

If this is what you intended, I'd have been inclined to put the tip120 between 5V and the LED things 5v pin, To be honest I don't really know anything about these gizmos but this may help others understand how you have it wired.