OK, good. I think the 12v line can deliver 200-300 ma max. It's actually coming from an A/V switcher that is controlled by the computer. I can't find the exact specs so I'll call the factory on Mon.
How much current would be needed to drive 16 of those circuits? The 12v 4pdt relay coils I looked at each take 75 ma and I would need 4.
hi,
Regarding the current loading for the displays.
Assume 15mA to 20mA per segment, including the decimal point its: 8 * 0.015 = 120mA or 8 * 0.02 = 160mA.
Taking the lower figure of [15mA/seg], 120mA for 8 LED's in Group 'A' gives, 8 LED's *120mA = 960mA, say 1Amp
So when all segments of Group 'A' and 'B' are lit it gives a worst case current requirement for the LED's of 2Amps.
The transistor switching requires just a few tens of mA's, say 25mA.
Regarding the 4 relays, 4 * 0.075 = 300mA when all energised.
If you decide to power the LED's and relays from one 12V psu, I would suggest a 2.5A to 3A rated psu.
IMHO the ON/OFF switching selection for Group 'A' and 'B' would be best suited to a relay,
no voltage losses across a series transistor and it would cheaper/simpler.
Perhaps if you posted details of the full project, I could make some suggestions that may help.
It appears to me that the computer/circuit is over complex and inefficient for what you are trying to do with the displays.
At the moment I am just seeing a 'bit' of the project which makes it very difficult for me to hit the target.