Inverting LED

Is it possible to get an ordinary red LED with a built-in inverter so that the signal to turn it on turns it off, and vice-versa?

I have a media player whose panel LED is on when the device is switched off. Dunno why - it probably conforms to "Eastern Logic". It drives my wife nuts .... she has Alzheimers and reports it a hundred times a day .... which drives me nuts.

Edited By Peter Greene 🇨🇦 on 11/10/2022 01:20:15

Guessing that the item in question is not actually turned off - it being on ‘standby’. That item may be consuming a considerable amount of power in this mode. Switching off at the wall would solve the problem and save energy usage. However, turning off completely may well lose some setting on restarting.

My sympathy, Peter

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My Google-Fu inspired me to put approximately the right words in approximately the right order and find plenty of advice out there:

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There are even people explaining why devices have the inverse logic in the first place.

Pick something that fits with the physical design of your gadget and you should be sorted.

MichaelG.

Many appliances that are controlled remotely have a LED that remains on. It would not have "an inverter" to operate it but is directly connected to the control board. Only option is to turn off the unit completely at the mains switch.

Or put a sticker over the LED so it can't be seen.

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With respect, Paul … I think there may be some confusion over the word “inverter”

This is the logic that Peter needs to implement: **LINK**

https://en.wikipedia.org/wiki/Inverter_(logic_gate)

MichaelG.

Paul beat me to it with the sticker ! I have a similar audio unit, the light is off when the unit is on, it's off when it is off but illuminated when the unit is on standby ! The problem with the most obvious solution is the unit will loose its's memory if turned off - as a radio it will loose all the stations tuned in and it's a pain to retune. Noel.

Not easily. A LED is an On/Off device like a light bulb, and the Laws of Thermodynamics forbid light-bulbs that shine when the power is turned off!

So inversion needs an extra circuit, with power, that switches the LED on when the signal is off (logic Low), and off the signal is on (logic High).

Easiest to do with a logic chip like the 4049, but a transistor circuit like this should work too:

When signal is Low, transistor T1 turns off allowing T2 to be turned on by R1 and lighting the LED via R2.

When signal is High, T1 turns on, shorting R1 to ground and turning T2 off.

So the modification needs a circuit connected to a source of power. The LED shows the unit has power but isn't doing anything because it's in standby. As this isn't mission critical, the easy answer is to disconnect the LED so it never comes on!

Sorry to hear about Mrs Peter's illness - same thing happened to my dad. Very stressful.

Dave

You are correct Michael, I was not thinking of a logic inverter.

I am also assuming (should never do that), that the LED is also turned on when the media player is working. If a logic inverter was used, the LED would be off. Therefore why not just dis-connect it ? (or cover it as suggested). If required to show when the player is working only in the on position, it just needs to be connected to the working power supply in the unit. (If you follow my logic)

Edited By Paul Lousick on 11/10/2022 10:13:03

Thanks, Paul

I agree with the suggestions to cover or disconnect the LED … those are the expedient solutions

[ on the other hand; I was just trying to answer the opening question ]

MichaelG.

Originally things had Red LED for off and green or other for on, Then the 'on' state seemed rather pointless as it was obviously on when making a noise. Also not having the green LED saved money. I had to fight to get each button on our products 'cos they cost 20p each. If less than 5 years old it will, by EU regulation Lot23', consume less than 0.5W when in standby.

The standby power regulations were brought in originally decades ago to stop coffee machines sitting there with a heater under the pot. Then they kept adding to the list of devices regulated and dropping the allowed power. Although it seems petty, now with loads of devices in every house it probably saves £30 a year in electricity. I think I calculated once that the standby LED in all our company products deployed amounted to 1MW.

Having been through that experience I can totally sympathise. A small square of black electical tape over the LED could be a quick fix.

Distraction works well too. Maybe something like a vase or pile of books etc etc in front of the appliance as well as the tape would help divert attention from it.

And giving her something to do, like sorting through piles of old photos and putting them in albums,or sorting our her jewellery box can provide hours of distraction -- even if the results are not what we would call "sorted"! But the important thing is they liked doing it.

All the best with the huge job ahead of you. It is challenging, but can also be very rewarding. And there is a lot of help available from Alzheimers associations and groups, but no idea of exactly who in the UK as I am in Oz.

Edited By Hopper on 11/10/2022 11:24:35

Edited By Hopper on 11/10/2022 11:25:45

That is actually what they do, dependent on the drive. If you have an active drive (one which can supply or sink current) then connecting the diode to either a positive rail or alternatively a ground will reverse the action.

ragards Martin

Really? thats abt 50M plus devices....

Always the way. You never quite know how to phrase it till people start to answer. I should have been clearer:

The LED is not simply an ON-OFF indicator connected across the supply; it also functions as an activity indicator which is useful (and I don't mind inverting that) and means it's driven by something. In any event, the tape solution is not an option for me.

Michael, thanks for the usual excellent searching (believe it or not I did search some time back without helpful result).

Hopper, the Alz situation is not anything new: I've been at it for the last 3 years, all through CV19 ... and hasn't that been fun.

Edited By Who? on 11/10/2022 22:03:49

Whoops! Sorry about that .^^^^^^... wrong login (didn't know that one existed).

Is 'Who' Peter?

Last post at 22:02:38 has confused me (I've not been drinking but it is getting late).

Anyway, if covering the indicator is an acceptable option then the only solution is to alter the circuitry driving the LED.

Technically fairly simple and might only need a transistor or some other very cheap components, from a practical point of view though it might get very complicated! Whilst the indicator might be on the front panel it is (in 90% of modern electronic equipment) likely to be surface mount LED and possibly coupled to the front panel by a 'Light Guide'. Sometimes even just accessing the circuit board can be difficult so unless you are familiar the product so I suggest searching on YouTube for ' Teardown.

Ian P

Edit, All clear now Peter beat me to it.

Edited By Ian P on 11/10/2022 22:53:38