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mathertel / DMXSerial

An Arduino library for sending and receiving DMX packets.
BSD 3-Clause "New" or "Revised" License
336 stars 79 forks source link

Is there a bug in the shield design? #3

Closed alexkamp closed 8 years ago

alexkamp commented 8 years ago

hey,

I had a look at http://www.mathertel.de/Arduino/DMXShield/DMXShieldSchema.png

What makes me wonder is how OK1 and OK2 are connected. It looks to me like the arduino-side (left in the schema) is just turning a led on and off (even if the LED is inside the optocouplers). However, vanilla-led wiring (as in the simple example: https://www.arduino.cc/en/Tutorial/Blink) says:

D2 -> Resistor -> LED -> GND your design does D2 -> Resistor -> LED -> 5V

Given that D2 provides 5V, connecting it to another 5V looks fishy. Is this a bug in your design?

maehem commented 8 years ago

He is essentially driving the LED using Open Collector. See this explanation and comparison here: http://electronics.stackexchange.com/questions/44923/driving-a-led-with-an-open-drain-digital-input

You would write a zero to turn the LED on and 1 to turn it off. So it is the inverse of the other method.

mathertel commented 8 years ago

Thanks maehem for the comment and reference. ... and YES, it works as designed.

campino commented 8 years ago

So I learned something. Thanks.