A thought occurred to me. So far I've been using the Arduino to supply power to the Z80 and other ICs (Integrated Circuits aka chips). This can't be the case in the long run. I either need to use a battery or a some mains power adapter.
Now a battery would be good, but what to use. I need 5 volts. If I use 3 AA or AAA batteries, they are 1.5 volts each and thats only 4.5 volts altogether. Add a fourth and I get 6 volts. Too much. So I search the web and find I need something called a Voltage Regulator, but which one? Further reading says I could use a 7805. This will convert much higher voltages to 5v the (the 05 in the 7805 gives us a clue here it seems). Reading further tells me ideally a voltage 2-3 volts higher on the input would be preferable so an 8 volt battery? Hmm, lets go with a 9 volt PPV battery.
The 7805 comes in a few flavours, such as 78L05, 78M05 and 78S05. The L model give 0.1 Amps of current output, the M 0.5 Amps and the S 2.0 Amps. There are others, but its important to choose one that has enough power to drive the circuitry. At this stage I'm not sure. I need to look at the datasheets for ICs I already have to see what range current is expected. I expect it will be either L or M. Anything higher and I think higher and I think I'd fry the circuits.
There is also the implementation of the Voltage Regulator in the circuit that need some thought. It seems we need to put capacitors either side of the voltage regulator to stop it fluctuating too much and for safety a diode to stop us from blowing things up by connecting the battery up the wrong way. This article has a diagram on how to connect it up: http://stuff.nekhbet.ro/2006/06/18/how-to-build-a-5v-regulator-using-78l05-7805.html
I need some more components!