I'm building a project which needs to interface with a computers serial port pin 4 (DTR) pin to trigger the Arduino or attiny (eventually) to start a sketch.
I've found that the 3rd party software has the serial port DTR pin set high by default +6.4V and when the software triggers the event it pulls it to -6.4V. I plan on using a diode to stop the negative voltage and would like to use this 6.4V signal on an input pin on the Arduino or attiny84 so that when the pin goes low it starts a series of events in my sketch.
How would you guys drop the 6.4V to something more safe for the Arduino or attiny84 like 5V?
From my research a voltage regulator is out of the question as it needs at least 7v to drop to 5v. What about wiring two or three diodes in series to drop to 5v or just below?
** forget to mention i'm using a USB to serial adapter that's why i'm getting 6.4v instead of 12v signals if that matters **