This is a quick knock up circuit I did on http://circuits.io/
The AT-Tiny uses three wires RX, TX & GND to communicate with the controller. The protocol will say which pump 1-4 and how many mL and the At-Tiny will take care of the rest. Just keep the Enable lines up, no need to for anything else as we're not changing direction or anything. I've left off the possible 4th pump as I haven't got one.
Because of varying head heights of the water storage, return from recycling, etc. issues I have chosen to use a flow meter to regulate water input. The idea being that all water input pumps can be pumping together and shut off once the required amount has been delivered. The flow meter introduces an additional complexity because the flow meter instructions say that the water speed should rise gradually and that air should be prevented from enterting the system. My pumps will be submersed so I'm not sure that will be an issue. For this discussuion that's not really an issue because that is a software problem likely to be quite simple by just modualting the control line.
The flow meter produces 1120 pulses per litre and takes a TTL supply voltage.
This circuit activates either pump, watches the flow pulses and then kills all pumps when the required flow is complete.
The NXP code is pretty basic
#include "mbed.h"
DigitalOut led(LED1);
DigitalIn DATA(p23);
int main() {
while(1) {
led.write(0);
while(DATA);
led.write(1);
while(!DATA);
}
}
The AVR code was a bit trickier as it uses the timer interrupt. Took me a while to get my head round it
.include "TN13DEF.INC" .org 0000 ; reset interrupt vector rjmp on_reset .org 0012 ; timer0 overflow interrupt vector rjmp tim0_overflow on_reset: ser r16 out ddrb, r16 ; set the pin I/O ldi r16, 0b_0000_0101 ; set the clock multiplier out tccr0b, r16 ldi r16, 0b_0000_010 ; turn the timer on out timsk0, r16 sei ; turn on interrupts main: nop ; I walk and walk, do nothing rjmp main tim0_overflow: ; negate portb in r17, portb com r17 out portb, r17 reti