LED circuit indicator

Hi CDK, so what. Those LED's as shown on previous photo's lights up enough at 0.5 mA to be bright enough for his application. That photo was even at 0.17 mA (my battery is an old one and I charged it long before I went overseas, thus the battery may only have been 8 Volt. Thus the current was even lower. Have a look at the photo.
If you mean that 18 Kilo Ohm and 56 Kilo Ohm in series together with the LED's may even be too low to glow in the situation after the load is gone faulty, you maybe right. I will check that tonight, when I have time.
Bert

 

If you have two separate LEDs (4 wires), then it becomes very easy. Just put one LED + resistor across the switch and another from the load side of the switch to ground. The first will light when the switch is off, the second will light when the switch is on. Both will light when the switch is open and the load is disconnected (which might be nice to know before you count on the load device working). 18K resistors should be fine - 2K ohms for maximum brightness.

 

Indeed jonr and it is confirmed that even by both having 56 Kilo Ohm, that both LED's are bright enough to show up at 12 Volt, should the load fail. In view that Red is only 12.000 mcd, I recommend a 18 Kilo Ohm for the red and a 56 kilo Ohm for the green LED. There will be not a better circuit, as far I can see, even if he would be using LED lights in future.
Bert

 

The OP want to use 3-wire leds, with a common cathode and current requirement 4-25 mA.

 

Yes we know, but it is the wrong item for his application. 5 mcd is often the standard for dual color LED's and that for back lighting is not enough. Bert

 

Hi bcervelo, If you can wait till the Friday of 4th of October, I will be driving through Somerset West and after I come down from the pass in the direction of Cape Town, I think, after the Shell Petrol station, the first or the second robot, I will turn left and then left again. There is a petrol station who sells Diesel at the best price in the area. I will fill up my car and leave an envelope with an example 2 LED's glued together after I have grind them + a couple of different resistors and 2 more LED's. Also with some instructions on how to glue them. You probably could use super glue, but I use special stuff, what melts the two LED's together. After lunch time you can pick it up from the little one man office. I will put the code name on the envelope in your private mailbox, thus your identity will stay confidential. This is an offer you cannot refuse, except if you are in the hurry.
Bert

p.s. those 10 x 2 Led's + resistors will cost you approx Rand 60 from Mantech Electronics, while you pay for nine wrong types over the thousand Rands. But that is my personal opinion.

 

Well bcervelo, here it is. Take it or leave it.

I used 18 Kilo Ohm for the red led and 22 Kilo Ohm for the green LED.
You may want to use 12 Kilo Ohm and 22 Kilo Ohm, or if it is not bright enough,
you can use 5,6 Kilo Ohm and 10 Kilo Ohm.
It took me about an half hour to make it, but if I would do a second one, it will probably a quarter of an hour.
I first with a plyer hold both LED's against the side of the bench grinder disk, that took not more than 3 minutes, then I run into trouble as my special stuff to glue was vaporised due to broken top, thus I used super glue and nearly glued my fingers together, Then the soldering, cutting and placing a piece of shrink sleeve over the bare wires was a piece of cake. It is 8 mm and should fit into your hole. The shrink wire can be shorter and is available from Builders warehouse, any electrical wholesalers in various colours and in 1 meter length.


Now if your LOAD fails, open circuit, blown bulb, the green and red lights come on.
If you are in "off" switch position, the red LED comes on via the lower inductance or resistance of the load.
If you are in "on" switch position, your load is on, the red LED with resistor is off, as it is short circuit and the green light is on.
Now you can experiment and see whether it is bright enough at the Gordon bay in bright sunlight or too bright, use lower or higher resistors, grind a little more away or not and the bonus is that it will cost you only 5% of what you wanted to do with those Farnell high current, low mcd LED's. Good luck. Let me know whether you like to find an envelope at that diesel petrol station in Somerset West on the 4th of October.
Bert

 

In my opinion, lights that are bright enough for outdoor daytime use are irritating at night.

I recently paid $20 for a microcontroller board and small touch screen display. That's getting to the point where I would consider a "glass cockpit" without physical switches and indicators.

 

Fair comment, All what he has to do is to increase the resistor value and drop the intensity which he will lose in anyway when potting the LED's. He has his mind set on LED's , if he decide for an uP solution, it depends how complex it is for him to mastermind the outputs. Bert

 

You know jonr and CDK, if readers are putting their cards straight on the table, then it is much easier to assist them.
I overlooked that he mentioned later on that it is for night use. He mentioned that he only has very little space volume and a hole of < 10 mm, I would have recommend a 3 mm RED LED and a 3 mm GREEN LED, with 2 resistors, medium intensity and 180 degrees angle. For him to start soldering a transistor, when he has limited knowledge of electronics, may become a nightmare for him. To solder a resistor to the anode or cathode of an LED is not a problem, as it does not matter on which side it is soldered. I have here some 3000 LED's, some of them produced 40 years ago by Siemens, those one's, you need an atomic power station to lighten them up, they may have been good for this application. Most of them leftover from jobs.
But to solder a resistor to any side of a LED, is possible for anybody.
In anyway, I hope he gets his problem sorted out.
Bert

 

Hi bcverlo,

It is probably too late in anyway, but if it was for myself, I would have made it as per below drawing. A double throw switch which short circuit two zener diodes, which gives you the advantage to switch it to night mode or to daylight mode.
If the switch is closed, the zener diodes are short circuited and then the full voltage is over all the LED's . In night mode, the zener diodes are in series with all the resistors which are switched on, by any of the 9 load switches, i.e. lights, radio, whatever. thus the led is no longer bright and affect our vision at night. One may has to experiment, whether it should be a 3.9 or a 5,1 or a 6,8 Volt zener diode, too see what is a good result at night, but that is a minor experiment . Bert

 

That's a nice design.

 

Hi Bert

Sorry i have been offline for a few days, thanks for the offer of the LED,s and resistors at the moment i am looking into ideas to upgrade the panel, unfortunatly i am not in a position to do the work at the moment.
I am sure i can make the 2 LED version work as you say they are small enough to fit into the 10mm hole behid the lable.

Thanks for the circuit diagram that is going to be very helpfull when i start this project, the day night feature is a great idea.

 

Thank you jonr. Not often forum members get a compliment.

One could even make it even more fancier and replace the switches and zener-diode's with 2 Philips photo-resistors. I don't even know whether they still make them. I still have here a handful from 40 years ago. Automatically the brightness is adjusted. However it means that the resistor values will have to be very careful matched with the LED and the photo-resistor, although one can place, a let say, 100 KOhm 1/4 watt resistor parallel over the photo resistor, in view that the dark resistance could be as high as 1 or 2 Mega Ohm. The light resistance is between 20 and 100 Ohm. Also the position where the photo resistor would be mounted has to be taken into account. But yes, one could make it automatically.
Bert

 

Hi bcervelo, I would consider to use 3 mm LED's 2 or 4 in that hole of 8 mm would do fine. Either to place them parallel or in series with a different resistor value. Although the 3 mm led's are better for night vision then the super bright 5 mm type. Whatever happen, whether you have time or not , on the 4th of October the petrol attendant in Somerset West will get an envelope. If it is not collected by you, consider that a massive black gentleman has a couple of LED's to play with when he comes home on that Friday night. Will inform you when there are a plan of change, should I leave earlier or later. However, the boatshow is on in Cape Town on the 5th of October and thus it is quite certain, that I will pass Somerset West next week Friday.
Bert