[chbot] Knob shafts / extensions and insulation

Volker Kuhlmann list0570 at paradise.net.nz
Wed Aug 31 09:09:16 BST 2016

On Wed 31 Aug 2016 17:44:11 NZST +1200, Mark Beckett wrote:

> If the mains and the other parts are seperated, then it is
> permissable ... however.

Thanks Mark, much appreciated. In this case the connection between mains
and arduino is one of a) >4mm air/FR-4, b) approved switchmode 5V
AC/DC supply, c) approved relay.

For b) I was thinking of butchering an unused USB charger.
Alternatives: Element14 is getting in PCB mounted SMPSUs, Vigortronix
e.g. VTX-214-005-0503, 5W, $9.41+GST.

If all components connecting the ULV-side with mains are approved, and
it's OK to have a metal-case+shaft encoder screwed into the box, the
problem would be solved very easily. Fixing components so nothing is
loose shouldn't be too much of an issue. This helps me with other
projects too.

I've gone off capacitive power supplies a bit since I realised that their
power draw is constant - if it isn't used in the load, it's wasted in a
zener. However, to learn something:

> Plastic extension or a plastic knob will work, but the issue is
> whether these have any sort of voltage rating.

Well they won't have. All that stuff is made for audio. So using an
encoder with a plastic shaft isn't actually sufficient, if the encoder
pins are connected to 240Vac? Only the plastic shaft is protruding
through the case. The fact it's plastic isn't good enough?

> I've seen the use of a Hall effect switch used to retain the
> waterproofing, so maybe this could solve the problem.

Yes, I'm planning on using a hall effect for sensing the on/off state of
a 25A 240Vac load. Preferably on the outside of a TPS cable. I hope it's
good for zero-crossing detection too.


Volker Kuhlmann
http://volker.top.geek.nz/	Please do not CC list postings to me.

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