william@pyr1.cs.ucl.ac.uk (07/22/88)
Yep, you can do this. In fact I sucked power from everything coming in including Rx. I had the RS232 inputs all pumping into a bridge rectifier feeding a pretty big capacitor, and this could drive a little CMOS processor and UART. The advantage was that the system could enter a very low power mode to maintain its memory and charge the cap when there was no Rx data, but the processor could be woken up by a change in Rx and could process signals. It also had some control work which required the power in the cap. I imagine that a cap could be used to store a +/-12 volt supply for short transmissions, and all you would need to control it would be a couple of transistors or something. I don't recall the exact spec, but I seem to recall that RS232 levels were defined as valid from (+/-) 3-12V. I think. I remember that I had to decide whether the above circuit should have to be designed around the fact that levels may be as little as 3V. ... Bill ************************************************************************ Bill Witts, CS Dept. * UCL, London, Errrp * Don't believe everything you hear, william@uk.ac.ucl.cs(UK) * or anything you say. william@cs.ucl.ac.uk(US) ***********************************************
wte@ncrcae.Columbia.NCR.COM (Bill Eason) (07/25/88)
In article <44000014@pyr1.cs.ucl.ac.uk> william@pyr1.cs.ucl.ac.uk writes:
=
=Yep, you can do this. In fact I sucked power from everything coming in
=including Rx. I had the RS232 inputs all pumping into a bridge
=rectifier...
<stuff deleted>
=I don't recall the exact spec, but I seem to recall that RS232 levels were
=defined as valid from (+/-) 3-12V. I think. I remember that I had to
=decide whether the above circuit should have to be designed around the fact
=that levels may be as little as 3V.
=
= ... Bill
=
=************************************************************************
=Bill Witts, CS Dept. *
=UCL, London, Errrp * Don't believe everything you hear,
=william@uk.ac.ucl.cs(UK) * or anything you say.
=william@cs.ucl.ac.uk(US) ***********************************************
If you should try this, don't forget the voltage losses you will experience
across the diodes: 0.7V typ? x 2 = 1.4V across a bridge rectifier. This would
only leave a minimum of 1.6V for your circuit.
Just a thought...
... Bill
*************************************************************************
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