Pulling -12VDC from thin air (was Re: MicroVAX II) - test-drb@ccmp.vtda.org

13 Dec 2002

...
 From: "Ethan Dicks"
&lt;erd_6502(a)yahoo.com&gt;

--- Jochen Kunz &lt;jkunz(a)unixag-kl.fh-kl.de&gt; wrote:
  I second that. I know a collector who knows
nothing about hardware and
 how it works.... When I told him that I builded a simple voltage
 inverter (charge pump) to make the RS232 work on the Sun 4/600 MP he
 looked like it was black magic to convert +12V to -12V. (The Sun 4/600
 MP boards needs -12V for the RS232, even -5V are not enough. As I
 mounted this board in a Sun 3/60 case that doesn't provide -12V, I could
 not use a serial console.)  
Interesting to learn about the 4/600 board and the 3/60 case.  Long ago,
I wondered if the two could work together (I _have_ the 3/60 and I almost
had the 4/600 board).

If you'd have known to ask, I could have provided you with a +5VDC to
-12VDC converter module.  It's about 20mm x 30mm x 3mm.  We had to put
them on the Qbus COMBOARD because the original design assumed you could
pull -12VDC off some Qbus pin somewhere, and I suspect that it is not
the case for all Qbus enclosures (don't know where it is available and
where it isn't).  I have several new on the anti-static mat they shipped
in.

-ethan

Hi
 There is another chip in the MAX232 series someplace
that creates +/- 12 V from 5V for serial uses other that
what a 232 chip is normally used for. It just needs
some capacitors for the charge pumps.
Dwight