DualS0ImpCounter - Hardware

Arduino based hardware for capturing impulses from S0 impulse meters.

based on Arduino Pro Mini (or clone, with ATmega 328p MCU)
power supply using a 12VDC wall plug
big buffer capacitor only for the MCU itself, right before it´s diode decoupled 5VDC regulator,
resistor network from 12VDC supply to ADC input to detect power loss early enough
2 S0 impulse inputs using optocouplers, active LOW (compatible with S0 outputs, which are usually open collector outputs)
connection to host over RS232, so NOT USING USB POWER SUPPLY
RS232 connection without DTS signal, so that the MCU cannot be surprise-reset by the host on (re-)connect
reset circuit (connection from a GPIO out to /RES input)