LED (display) question

[Guest PoRrEkE]

Here's the thing.I am currently programming my own Photon software. I have a question though that is probably exactly the same for FSbus and other systems.If you have a look at e.g. NAV1 freq.1**.**This is the "mask" for the value. The 1 in front will ALWAYS be there and the decimal as well.Now I would like to make these light up by default and not control them.The idea is to connect all of them to 1 led output from the print. Then I can turn on/off that "led" (being all the 1's and all the decimal simbols) at once. Is this possible ? And how do I connect those then ? Parallel ? And could it be assumed that this is possible or should I ask Scott from Photon ?

[Guest Erups]

>Now I would like to make these light up by default and not>control them.Ok.>The idea is to connect all of them to 1 led output from the>print.The print?????>Then I can turn on/off that "led" (being all the 1's>and all the decimal simbols) at once. Is this possible ?Weren't you asking for "light them up by default and not control them" ?>how do I connect those then ? Parallel ? And could it be>assumed that this is possible or should I ask Scott from>Photon ?I'm not clear with your questions, but anyway:assuming you have some kind of digital output commanded by your software, you just need a mos and the leds.You use the mos like a switch commanded by your output line:when your soft says OK, the mos closes, and all that's after (your leds) light up.And the reverse.Hope it helps.

[Guest PoRrEkE]

sorry my post confused you maybe a little :)I have mixed 2 ideas.1) is to just power these leds from the segment displays by default and with own power suply .. if possible. then maybe a normal switch built in a panel which turns on/off those2) is to connect all of those leds to 1 output from the Photon print. an output to which you would normaly connect just 1 led. then e.g. as soon as I write a value to the other segment displays i could turn on that "1 led" (being the group of leds in fact).Option 2 would be preferable but I'm not sure if I can just do that.Same thing e.g. for the gear leds. Some poeple mind that those 4 go on at the same time and go off at the same time, which is not realistic. But I don't. So I would prefer to only spend 1 led output for the group of 4 leds ... IF possible.

[Guest petdocvmd]

>sorry my post confused you maybe a little :)>>I have mixed 2 ideas.>>1) is to just power these leds from the segment displays by>default and with own power suply .. if possible. then maybe a>normal switch built in a panel which turns on/off thoseThis would work and makes sense because you are describing static displays.>>2) is to connect all of those leds to 1 output from the Photon>print. an output to which you would normaly connect just 1>led. then e.g. as soon as I write a value to the other>segment displays i could turn on that "1 led" (being the group>of leds in fact).>>Option 2 would be preferable but I'm not sure if I can just do>that.Not directly - you can't sink that current through one channel. However you *could* use the channel to drive a transistor switch that enables an external circuit to complete and power the LEDs.>>>Same thing e.g. for the gear leds. Some poeple mind that>those 4 go on at the same time and go off at the same time,>which is not realistic. But I don't. So I would prefer to>only spend 1 led output for the group of 4 leds ... IF>possible.Yes and you might get away with sharing 4 low power LEDs but again I'd use a transistor to be safe. But ideally you should map them to separate ports if you have enough in your setup.Regards,ScottScott L. Fausel, VMDhttp://www.iflightsystems.com

[Guest PoRrEkE]

Ok, thnx Scott,I'll have 4 cards so first I'll do some counting to see how far I get. If I have enough I'll do it the normal way ;)

[Guest PoRrEkE]

http://www.opencockpits.com/images/esquema2_7s.GIFIs this the way to go if I want to wire them up loos from the card ?And can I use this trick for every 1 and every decimal in my cockpit ? Can I wire as many as I want parallel like these ? Using all the time this value of resistor ?And if I want to put an electric switch (relay ?) between here somewhere which is connected to a LED output from the Photon card so that I can open/close the cirquit here with Photon .. what electric switch would I need ? Or how can I find out which one to use ?

[Guest Erups]

The answer is yes to all your questions.If you wish to control this array, just use a 2n2222 transistor (or compatible if you need more power).It's a NPN.That means that:it works like a "close to ground" switch, the command for closing or opening the switch is a positive on the "gate" if i am not mistaken (i have a problem here because i know the italian names, which are not the exact translation of the relative english ones).But please attention to this:multiplexed IO cards (i'm talking generally) use a progressive scan method.This means that if you put all outputs to 1, they are not really 1 all at the same time.There is a cycle going on in the system, which progressively scans every row, setting the columns on or off, clearing and passing to the next row.That means that your switch would be opening and closing really fast, which in turn means that you need to use lower resistor values.Otherwise intensity difference may occur.I suggest you use another approach if you want to control it:wire for every display array, the 3 leds in parallel but AFTER a small trimmer, one trimmer for all the leds.This will allow you to adjust the luminosity at the same level of the rest of the array.After that, you can wire all the array together, and use a big mos to switch all of them at the same time.

[Guest PoRrEkE]

mos = metal oxide semiconductor ?is that mos you refer to the same as the transistor 2n2222 ?is the 2n2222A also good ?i checked some sites .. how do you know how to wire this thing ?so what trimmer then do you suggest ? a value close to the one on the image ?

[Guest Erups]

>mos = metal oxide semiconductor ?Probably :(MOS really is the technology behind, but by "mos" i call a type of semicon.Let me see if i can find one for you.>is that mos you refer to the same as the transistor 2n2222 ?No a transistor is not the same as a mos, even if in some cases it may work the same.>is the 2n2222A also good ?Sure that was the one i was referring.But do some math on the power drain of the circuit, it may require something "bigger" then the 2n2222a.>i checked some sites .. how do you know how to wire this thing>?They have a layout B C E.Have a look here www.epanorama.netYou can find lots of circuits.Basically every principiant circuit with transistors may be useful to understand how do they work.>so what trimmer then do you suggest ? a value close to the>one on the image ?A 10kohm should do.

[Guest PoRrEkE]

>But do some math on the power drain of the circuitThat's the problem ;) I have elctronix in school but I HATE it and I don't understand any of it :(That's why I ask.If someone could make a scetch of what and how I need to solder and what components I need exactly .. would be well awesome :D

[Guest Erups]

>Let me see if i can find one for you.Look for tip121 (http://www.fairchildsemi.com/ds/TI/TIP121.pdf), it's a workhorse really (80V 5A), you shouldn't need such power, but this it the kind of device you could use and they are cheap too.

[Guest Erups]

>If someone could make a scetch of what and how I need to>solder and what components I need exactly .. would be well>awesome :DUnfortunately only you know what, how many, and where.Look below, i posted a link.That one is cheap and over dimensioned, but would surely do for a LOT of displays :D

[Guest PoRrEkE]

I've counted and what I end up is with 24 leds from the displays that should be lit by default.I'm really sorry but I have never learned anything more than DC networks with resistors and normal lights. Stuff like Kirchov etc. Can't remember much 'bout it :$If it would make things easyer I could opt for a normal manual switch, no problem. But it would be cool if I could make these go on at the same time when the other leds/displays go on.

[Guest Erups]

Go with the tip121.One pin to GND, one pin to your OUTPUT, to the third bin wire all the 24 leds' gnd.

[Guest PoRrEkE]

and for the tip121, does it matter what pin i wire to what thing ?