pull switch with timed "off"

[sm_jamieson]

I need a 2-pole bathroom pull switch with the following behaviour: a. Quick pull/release causes toggle between ON and OFF of "pole 1" b. A normally on "pole 2" with timed OFF (say 30 mins)

A quick pull/release should always cancel the timed OFF. I wish to use this to disable my humidistat fan for a certain period of time, in order to stop it triggering due to a hot bath, etc. It needs to always revert to normal auto function, else the family will leave it switched off !

Any ideas without using an PIC / Rasperry PI, etc ?

Simon.

[Tim Watts]

The easiest way (IMO) would be to get a small enclosure, with a bit of DIN rail and use a DIN timer module and, if necessary, a DIN relay to achieve the required logic. Use a "Disabled alarm" pull cored switch, these are SPST momentary action. Include a 2 pole (fused if required) isolator feeding the whole lot.

Sometimes, trying to get "clever" with a Pi and mains is non trivial - and DIN module relays and timers exists at Farnell and RS - and merely need enclosing and wiring.

I am thinking of:

Feed fan through relay's "NC" contacts.

Feed relay coil from DIN timer.

Trigger DIN timer with pull cord.

That would be *very* simple to wire up in a box - and the timers are dead common as they would be the sort used for delayed-on landing lights in blocks of flats (assuming they go up to 30 mins).

[sm_jamieson]

time, in order to stop it triggering due to a hot bath, etc. It needs to a lways revert to normal auto function, else the family will leave it switche d off !

I'll look at the DIN modules. I forgot to say, I was thinking of triggering the timed off from the same pullswitch, the trigger being a "long" pull, i .e. hold the momentary action in "make" position for say 5 seconds.

So, default mode is humidistat acting as normal - i.e. the new pull-switch doing nothing. Quick pull to override the humidistat into fan permanently O N. Another quick pull to cancel override. A long pull to disable fan for 30 minutes. Any time during the 30 minute disable period, a quick pull to put it back into normal mode. A bonus might be that the override to ON is timed ... You get the idea.

Simon.

[PeterC]

I did see one by MK(?) and it might have been a variation on the timed stair lights - or not, can't recall now. Somewhere I've a little timer and a diagram for just such a purpose. The switch is an ordinary 2-way pull and the timer breaks the circuit and also removes voltage from itself, then the changeover repeats the process. Can't remember where it is now!

[Mike Humphrey]

Are you using the pull switch just because it's a bathroom? If you make the control side SELV (under 50V) you could use several push-buttons which would make the logic simpler. If it's too complex for relay logic i'd be looking at 555 timers and

74-series or 4000-series logic gates.

Mike

[tabbypurr]

You could use a time delay relay. Or power the fan via a PIR detector, just reversing its switching function. A computer seems bizarre overcomplication.

NT