[sdiy] Digital Input Circuit

Stewart Pye stewpye at optusnet.com.au
Sun Jun 16 03:51:22 CEST 2013


I'm designing a sequncer based around an AVR XMEGA microcontroller 
powered by 3.3V. It has some trigger inputs that accept nominal 5V 
trigger signals, though it should be able to handle any voltage between 
-15V and +15V as it is part of a modular synth.

There are 8 inputs. The circuit I have drawn is a series input resistor 
to the base of an NPN transistor. The emitter goes to ground and 
collector goes to the input pin of the microcontroller (with internal 
pullups turned on). There is a reverse diode across the B=E junction. Is 
there a more elegant solution than this? An IC that will handle the 
input voltage range required with just a series resistor?


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