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Author Topic: Help with Robbe expansion module and LEDs  (Read 354 times)

Akira

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Help with Robbe expansion module and LEDs
« on: December 16, 2018, 05:12:56 PM »

I love the Robbe F-14s that I have, many of them, but one issue frustrates me, and that is this: Trying to switch on/off a LED, singular or multiples, directly from an expansion module.It does not seem to matter which module I use, Switch 16, 4 + 4, 12 + 2, all of them do it.  Every time I try to do it, I find that the LED/s continue to glow, although faintly. even when switched off.  This does not happen using a "normal" switched circuit or using a relay. has anyone else run into this, and if so, what was you fix, short of using the expansion module to switch a relay breaking the LED circuit?ThanksJonathan
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Akira

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Re: Help with Robbe expansion module and LEDs
« Reply #1 on: December 16, 2018, 06:13:29 PM »

UPDATE: Someone on another forum suggested putting a 1000 ohm resistor across the pos/neg feed to the LED. it appears to work. Much less expensive than relays. I need to wait for dark for absolute confirmation and will follow this up. No "apparent' harm to the module.
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bj

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Re: Help with Robbe expansion module and LEDs
« Reply #2 on: December 21, 2018, 09:29:41 AM »

This can happen in a domestic lighting circuit when the switch is AFTER the LED's - when the switch is on the
negative side of the circuit. This condition is known as a "NEGATIVE LOOP" circuit. Domestic solution is to rewire or fit a halogen bulb to "mop up" the very small residual current in the positive wire side of the circuit.
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malcolmfrary

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Re: Help with Robbe expansion module and LEDs
« Reply #3 on: December 21, 2018, 06:34:47 PM »

No familiarity with Robbe electronic bits, but from past experience of electronic bits in general, if a semiconductor switch fails to completely switch an LED off, it is because the semiconductor itself has not gone to a full "disconnected" condition.  How or why in this case is anybody's guess, unless somebody actually knows for sure.  For all I know, Robbe might have put a protection circuit around the output, and that could be leaving a path for enough residual current.
Putting a 1K resistor in parallel with the LED might well redirect enough of the current that is still flowing via the module outlet away from the LED, or at least drop it to a level where you can't see the LED glow.
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