[HH] cheapest/simplest way to control a relay from a PC

[Greg London]

>
>> Powerswitch Tail - $25
>> https://www.adafruit.com/products/268
>> ...did anyone mention this already?
>
> No, it didn't come up.
>
> The device is basically an enclosed solid state relay with a couple of
> 120 V pigtail cords - one plug, one socket. Screw terminals to supply
> the 3 to 12 VDC control signal. It doesn't include a computer interface.
>
> That's nicely done for $26. Not useful for this project, but could be
> handy in the future.

My concern would be that it's actually an SCR internally,
which doesn't work with DC. SCR's are (were?) commonly
used for switching AC stuff (dimmers and motors and so on),
but they won't work with a DC load.


Fuzzy SCR lesson follows for those interested:

SCR => Silicon-controlled rectifier

One might think of an SCR as a "latch". When you turn it "on",
it latches on, even if you remove the on signal, and it stays
on until the voltage you're controlling goes negative. 120v AC
goes negative at a 60hertz rate, so when you turn it off, it
goes off when the 60hertz AC goes negative. So SCR's are OK
to use with AC to design things like light dimmers and
"relays" for 120v AC devices.

They're a relatively cheap way to switch on AC.
I think true solid state relays are more expensive.
This is old school information I'm going off of,
it's been a while since I worked with SCRs and similar.
So, it might be that solid state relays have gotten cheaper
than when I worked with them.


If that thingy really is a solid state relay, then it'll work
to turn on a DC load. But that would mean that prices for solid
state relays working at 120v and 10amps or so have dropped
considerably since I did anything with them.

If it is a true solid state relay, then the only other concern
might be if it has issues when working with 5 volts at something
like 5 milliamps for the LED. That's a lot lower voltage than 120,
and a lot smaller current than most 120v AC devices.


Greg