ZB1 Reset Circuit Changes
The reset circuit on the ZB1 boards, Rev 1 and Rev 2, consists of a
0.47μF cap in parallel with a 10KΩ resistor. The
recommendation from Atmel (AVR042) is to parallel a diode with a
10KΩ resistor as shown in the Reset Circuit ECO schematic
on the right. This is an easy change to make on the ZB1 board.
Making this change will enable the reset capacitor, C13, to reset the
board when if your USB port is setup to set RTS on close. In the
original circuit, C13 could not pull the RESET line to a low enough
voltage to reset the ATmega microcontroller. Removing 0.47μF of
capacitance from the RESET pin enables C13 to pull the voltage on the
RESET pin below the reset level.
C6 provided noise supression and transient surpression. Since
the RESET pin does not have a protection diode should be added when C6
is removed. Atmel also recommends an optional noise supression
capacitor in from the RESET pin to ground. This should not be
necessary for the ZB1. The only connection to the RESET pin is to the
ICSP header. Since most applications do not permanently wire the ICSP
header the RESET line should not be noisy.