HELP ! (Please !) - Very basic switch / LED question

Hi,

I am hoping to modify an audio mixing desk so that when a latching pushbutton switch is depressed, a miniature LED will illuminate to indicate activation (as it is currently very difficult to see with black (non indicating) pushbuttons on a black background used in dim lighting conditions !!).

The problem I have is that the switches are DPDT latching, and BOTH poles are currently used to route audio signals. I presume that it is not possible to connect an LED to one of these poles as it will introduce voltage / current where the original design wasn't expecting it....

I had thought about miniature DPDT relays... re-route one 'pole' of the audio signal off the existing switch onto one pole of the relay, use the freed-up pole on the existing switch to drive the relay and use the spare pole on the relay to switch the LED. However, with thirty switches to deal with, this could be expensive and cause quite a power drain.

Is there any easier way (transistor ?) to switch an LED when you only have a DPDT switch (with both poles used for other things !) ??

Many thanks for any help you can give.

Cheers,

Kev.

Reply to
pcmangler2000
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Hi,

How about just replacing the switch with one that...

a) fits in the same hole.

b) is a toggle/handle type that is easy to see which way it thrown.

--
Luhan Monat (luhanis 'at' yahoo 'dot' com)
"The future is not what it used to be..."
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Reply to
Luhan Monat

Does the switch have a bit that sticks out the back when it is in the depressed position? If so, you could use that to operate a microswitch to turn the LED on/off.

Paul Burke

Reply to
Paul Burke

If you're looking for a pure electric/electronic method (i.e. not involving mecanical fixtures around the switches), it will of course depend on the caracteristics of the audio signals that are routed by the switches and the circuit stages before and after.

Can you caracterize them?

For example, if both the preceding and the following stages were AC-coupled (net very probable, I think), you could try to inject a small current on one side of the switch and sense for it on the other side. The disadvantage would be some 'click' during the commutation.

Another, more complex approach would be to inject an sine wave of a given frequency not within the working range of the desk's circuits, and sense for it on the other side of the switch.

-- Andy

Reply to
Andy

c) is a 3PDT switch.

Reply to
Mark Jones

Wow, great suggestion, I'm not the one that needed it, but that is pretty damn brilliant!

Maybe he could even put some switches on that have built in indicator lights.

Way to cut through the crap!

Rocky

Reply to
Rolavine

Have you tried a booklight with doublesided tape? Sometimes easy works well. Otherwise you are looking at replacing all the switches.

--
N
Reply to
NSM

OK, I think I can replace the switches with multi-pole changeover types, now that I've found more suppliers than RS and Maplin !

I'm a bit confused though.. according to this site :

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, near the bottom, there is a pic of the kind of switch I need - labelled "Multi-Pole Switch". However, the text says the pic is of a SIX pole changeover switch. It's got twelve tags... !?? Huh ??

My logic says that if the switch is a 'Changeover' that means it's double-throw, right ?

So if it's laid out like this :-

1 2 3 4 5 6 1 2 3 4 5 6

Then pins 2 and 5 in each row are the common connections and depending on the switch position will connect 2-1 and 5-4 OR 2-3 and 5-6 in each row.

Am I misunderstanding this ? ....or have they just got the wrong picture there and are actually showing a FOUR pole changeover (or possibly a SIX pole 'on-off' type).

Cheers,

Kev.

Reply to
pcmangler2000

I don't see what you're getting at... I know it's a PCB switch - that's what I need. I was questioning my understanding of which pins connect to which when operated. The pic in my url shows a switch with twelve connectors (forget the lugs). If my understanding of how these work is correct then the one shown is a FOUR pole switch - common and two alternate connections per pole = 3 x 4 = 12. OR it's a six pole single throw (i.e. on-off) switch - 2 connections per pole = 2 x 6 = 12.

Reply to
pcmangler2000

Methinks it is a typo. What I see is exactly what you think it is - a FOUR-pole double-throw switch. There are several minor errors like this in the rest of the page.

Bill Jeffrey =============================

snipped-for-privacy@hotmail.com wrote:

Reply to
Bill Jeffrey

Thankyou both for clearing that up ! I thought I was getting senile for a moment then !

Reply to
pcmangler2000

That is the way that sort of switch usually works.

It is indeed a 4 pole double throw latching pushbutton switch

Reply to
Gary J. Tait

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