Some questions:
How many relays-solenoids will the circuit be controlling ?
ans: 1 relay-solenoid for each circuit
What is the purpose of the 4017 multiplexor ?
ans: its the only circuit i am well versed in
and will there be two or more relays on (energized) at the same time ?
ans : yes
pls refer below for a detail explanation
the reason i am using 4017 is its simplicity(i.e. toggle ON and toggle OFF). So, one of the led will switch ON the relay and if i press toggle it will switch off and light the other led.
This is the only ic i am well versed in. The circuit you have seen above, they will be a replica of 7 more-each for one computer port input and separate relay drive. (total 8 circuit)
This is made so that they have individual input and output control. If one of the circuits burn down, i'll probably swap it with a spare without shutting down the other circuit.
For 4017 input voltage would not be a constrain(3 - 12 VDC). If i can use a 7805 to limit the voltage to logic 5VDC for 74LS154. They are 2 reasons i am not using this :-
a) I am not well versed on how to build the complete 74LS154 circuit(like the control i need above). I only know about this chip when you have pointed it out to me. (Thanks)
b) If lets say i am using a 5VDC relay, and it burns out. At hand i have another relay with the same specification but it is a 9VDC relay, till the parts arrive i could temporary used this in the circuit and all i have to do is increase the input voltage and add voltage resistor to the other 5VDC relay to protect them. Its resourceful.
I am building the circuit using ic sockets so any parts on the board can be changed just like inserting an ic.
regards,
naren