I power my board with external 5v, and have serial input as well. The serial line is also high at 5v when no data is present. If I then shut the 5v to switch the device off, I still see that SOME of serial line is leaking through the 328p chip, and pin 7 & 20 (VCC) are then seeing about 3.5v.It's causing some issues.Suggestions?
Would a 20k be even better or do I start to affect my serial data at some point?
This 10k idea seems to work pretty well. Without the resistor, I get 4.1v on the RX pin when the MPU isn't powered.With the resistor I get 1.1 on the RX pin when the MPU isn't powered.That's a big improvement.Can you elaborate as to what is happening on the RX inputs that makes this work?Would a 20k be even better or do I start to affect my serial data at some point?
the 10k resistor is limiting the current that can flow into the cpu. V=I*R where V=(5v-1.1v), R=10000 so I=3.9/10000 or i= 0.39mA the resistor is dropping 3.9volts. Chuck.
I'm still curious what happens inside that pin that is so different when the chip is powered and not, that this 10k affects this voltage so much.