[PLUG] powering relays with usb-serial adaptor

[Eric Wilhelm]

# from Larry Brigman
# on Saturday 30 June 2007 11:35 am:

>It could be it doesn't turn the signals on until it sees (senses) the
>other end of the RS-232 signal lines.

Sure enough, if I short RXD to GND it shows about 3.5V open-circuit 
between GND and TXD/RTS/DTR.  It's only enough power to flip these 
little reed relays without an led.

>> If I'm only using it as a relay controller, is there anything wrong
>> with soldering pin5 to the usb ground?
>
>It could be totally isolated (opto-coupler) such that it doesn't
> create ground loops.  Connecting the shield ground to the 232 ground
> could break the isolation.

I'm not seeing any adverse affects, so maybe the isolation is optional 
in this case?  I'm sure ground loops could impact the signal integrity 
at high data speeds, but this is a very primitive device.

I'll look at a non-jumpered setup.  A transistor and solid state relay?

Thanks,
Eric
-- 
Anyone who has the power to make you believe absurdities has the power
to make you commit injustices.
--Voltaire
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