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Adrian  wrote:
> In message <6pru5l-oju1.ln1@q957.zbmc.eu>, Chris Green 
> writes
> >Adrian  wrote:
> >> I'm looking for a USB controlled mains switch (230V AC) that I can
> >> connect to a PI to turn a mains power supply on and off.
> >>
> >> I've done a bit of digging around on the net, and the options seem to
> >> fall into two categories, either a relay device which means having to
> >> rewire the device (which I'd rather avoid), priced around 30Euros or one
> >> that sits in line (between the device and the supply).  The latter
> >> appears to be in excess of 100Euros, which is considerably more than I
> >> want to pay.
> >>
> >I don't understand the difference. Surely anything that's going to
> >turn something on/off needs to be "one that sits in line (between the
> >device and the supply)" doesn't it?
> >
>
> The cheaper option involves cutting the plug off the item, and hard
> wiring it into the board.  I've got two problems with that.  Firstly, it
> means that I can't readily reuse that item elsewhere as I'd have to
> replace the plug (a bit of a faff if it is temporary move), and secondly
> if I'm trying to control something fed via a wall wart then it gets
> messy unless I leave the wall wart powered all the time (which I'd
> rather not do), and switch between it and the device.

You could just chop up a mains extension cable and insert your relay in the
middle.

> No, but USB seemed to be the most likely solution as it works equally as
> well for Non-Pi situations.  Power may also be an issue.  My initial
> requirement is for a low power device, which (without checking the
> numbers) might be within the capability of running directly from the Pi,
> but I can foresee needs where that won't be the case, so a standard
> solution has its attractions.

The advantage of wireless is you get isolation for free, so you don't need
to worry about mains backfeeding into the Pi, which makes construction
cheaper.  It doesn't need to be wifi, there are also options using 433MHz
'remote control' frequency, which is point to point and longer range:

https://energenie4u.co.uk/catalogue/product/ENER002-2PI
https://www.ebay.co.uk/itm/396124241128

also with power measurement:
https://energenie4u.co.uk/catalogue/product/ENER002-2PI-RT

The transmitter speaks GPIO and there's Python code to control them from the
Pi.

Theo

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