[Coco] Coco interfacing, running a coco from 12 volts and more.
Bruce W. Calkins
brucewcalkins at charter.net
Tue Feb 7 22:25:31 EST 2012
I don't have a CoCo 2/3 at hand to refresh my memory ATM. However as I
remember it, there are three pins feeding from the transformer to center and
both sides of a full wave rectifier on the main board. Feeding DC in on
either side with ground to the center is enough to run the CoCo. IIRC it
does not matter which side gets the DC. The ONLY part of a CoCo 2 or 2
needing negative voltage is the RS-232 serial (printer) port.
So, your 12 volt battery gets connected; battery negative to CoCo ground and
battery positive to either high AC input. To get the negative voltage for
your RS-232 port you need another battery which needs very little capacity
compared to the main battery with it's positive hooked to the ground and
it's negative connected somewhere internal to the rectifier with isolation
from the main battery. Since the second battery complicated things with so
little gain I never bothered figuring it out.
FWIW; the transformer is what they call center tapped. I don't recall the
voltage, but the center tap to either outside tap is half the voltage of the
outside to outside taps. 12 volts DC to either side of the CoCo's AC input
is enough to run the CoCo. The center tap on the CoCo side is where the
battery negative goes. The battery positive goes to either outside tap on
the CoCo side.
I used a CB to cigarette lighter plug with the CB plug end split to plug
into the CoCo main board. It still floats about in my stuff, but that CoCo
got it's transformer reinstalled. The way I did it nothing on the CoCo
needs to be changed. You can lower the power losses by removing rectifier
diodes and figuring out needed power routing, but I never bothered.
----- Original Message -----
Subject: Re: [Coco] Coco interfacing, running a coco from 12 volts and more.
> Bruce, can I just check with a multitestor to see which lines are getting
> fed 12 volts while its plugged into the wall?
> A battery has -12 volts too... I'm not sure but I think running +12
> and -12 would be better...
> -----Original Message-----
> From: Bruce W. Calkins
> I ran 12 volts (Truck 12 volts = 11-14.3 give or take a bit.) to two of
> three terminals where the transformer plugged into the main board. There
> was no negative voltage that way, but that is only needed for the "RS-232"
> serial port. The disk drive was not much different, but I soldered the
> wires on that unit.
> Bruce W.
>> I'm not very knowledgeable regarding electronics, but it seems to me that
>> running a Coco 3 from 12 volts wouldn't be much different from running a
>> Coco 2 from 12 volts.
>>> I also need info on running a coco3 from 12 volts. Right now I'm using a
>>> voltage inverter and its terribly inefficient. I'm sure running direct
>>> from the
>>> 12 volt gell cell would add tons of run time. Right now the battery
>>> drained pretty quick!
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