Electionics question

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10-07-2007, 12:46 PM
jmig

Electionics question

Well, I hooked all of the axes and everything actually worked. Yeahhh

I also hooked up the throttles (Suncom dual) buttons. They worked except for the two HAT switches. I suspected that they wouldn't.

Anyway, my question has to do with powering LED's. The IOCockpits Master card or Display cards will power LEDs with 5 volts. I want to be able to test the warning lights/master caution with a separate switch. I had planned on using an independent 5 volt circuit with the spring loaded test switch.

My question is this, will the five volts for this circuit backup in the IOCard possibly destroying the card? If so, how can I do what I want to do?
10-07-2007, 01:48 PM
JBaymore

John,

Without looking at a schematic... the likey answer is YES... you could end up frying something.

If I want to power the SAME LED from two distinct and separate sources, I will install a diode in each of the voltage supply lines to the LED device. A diode, among other thngs, can act like a "one way valve" for current flow.

So when the power is coming to the LED from source A (through diode A) the OTHER line connected to voltage source B is STILL connected to the SAME wiring. So electrical energy could flow back down that wire. But because there is diode B on the source B supply line, no electric current flows "backwards" down the supply B source line with unintended consequences because the diode B is blocking it from "reverse" flow.

It would be REALLY good if both +5 V souerces were coming from the SAME unit. Can you pick up the +5 on the card to route to your test switch? Two separate voltage sources can set up some problems if they are not sharing a common grounding.

Hope this helps.

best,

.................john
10-07-2007, 04:27 PM
jmig

Quote:

Originally Posted by JBaymore

John,

Without looking at a schematic... the likey answer is YES... you could end up frying something.

If I want to power the SAME LED from two distinct and separate sources, I will install a diode in each of the voltage supply lines to the LED device. A diode, among other thngs, can act like a "one way valve" for current flow.

So when the power is coming to the LED from source A (through diode A) the OTHER line connected to voltage source B is STILL connected to the SAME wiring. So electrical energy could flow back down that wire. But because there is diode B on the source B supply line, no electric current flows "backwards" down the supply B source line with unintended consequences because the diode B is blocking it from "reverse" flow.

It would be REALLY good if both +5 V souerces were coming from the SAME unit. Can you pick up the +5 on the card to route to your test switch? Two separate voltage sources can set up some problems if they are not sharing a common grounding.

Hope this helps.

best,

.................john

"Can you pick up the +5 on the card to route to your test switch?"

The number one pin on the output socket provides the 5 vdc. I also have to provide the Master card with 5 vdc from an outside power source.

Another question. The landing gear has three LEDs to represent the three gear trucks. It is better to provide 5 vdc to each in paraell with a resistor or send the 5 vdc to the three LEDs in series without a resistor?
10-07-2007, 06:27 PM
JBaymore

Quote:

Originally Posted by jmig

The landing gear has three LEDs to represent the three gear trucks. It is better to provide 5 vdc to each in paraell with a resistor or send the 5 vdc to the three LEDs in series without a resistor?

John,

In my pit, the landing gear indicators are set up using SIX distinct and separate LED output control lines. Each one is controlled by the timing of the gear deployment / retraction specified in the aircraft.cfg file. The gear do not come down or go up at the same EXACT rate in a real aircraft. So the nose gear, for example, locks and goes green a tiny bit before the the left main, and the right main is the last to lock. Ditto on retraction. Adds nice realism.

Three independent Phidgets LED outputs drive the three green leds for the gear in position indicators. A separate three LED outputs (mounted in the same annumciator housings) drive the red in-transit indicator lights.

You might want to think about that.

The resistor layout depends on the circuit board design. For example, Phidgets does not need any resistor at all. Series LEDs often do not work well.... due to variance in the manufaturing tolerance characteristics of each individual LED. I'd go parallel. If you are driving them from one output, check the current capabilities of that output to make sure that you get the correct current limiting resistor.

best,

.................john
10-07-2007, 08:51 PM
jmig

Quote:

Originally Posted by JBaymore

John,

In my pit, the landing gear indicators are set up using SIX distinct and separate LED output control lines. Each one is controlled by the timing of the gear deployment / retraction specified in the aircraft.cfg file. The gear do not come down or go up at the same EXACT rate in a real aircraft. So the nose gear, for example, locks and goes green a tiny bit before the the left main, and the right main is the last to lock. Ditto on retraction. Adds nice realism.

Three independent Phidgets LED outputs drive the three green leds for the gear in position indicators. A separate three LED outputs (mounted in the same annumciator housings) drive the red in-transit indicator lights.

You might want to think about that.

The resistor layout depends on the circuit board design. For example, Phidgets does not need any resistor at all. Series LEDs often do not work well.... due to variance in the manufaturing tolerance characteristics of each individual LED. I'd go parallel. If you are driving them from one output, check the current capabilities of that output to make sure that you get the correct current limiting resistor.

best,

.................john

Thanks for the info. I will look into the current rating of the IO Master Card
10-07-2007, 11:58 PM
sas550

Hi! I might have missed something but as I understand it you wan't to use one separate switch for testing the lights, correct?

If so, why not make a variable for that switch that will light them all. Saves you the extra wiring aswell.

If I didn't understand you right (it's early in the morning here) just disregard. :)
10-08-2007, 07:39 AM
jmig

Quote:

Originally Posted by sas550

Hi! I might have missed something but as I understand it you wan't to use one separate switch for testing the lights, correct?

If so, why not make a variable for that switch that will light them all. Saves you the extra wiring aswell.

If I didn't understand you right (it's early in the morning here) just disregard. :)

If by variable you are talking programming, I rather run wires. LOL I find Opencockpits to have wonderful boards. They are doing a great service for the sim community. However, I have enough trouble understanding how to wire the things up. much less program them.

Programming will have to wait for phase two. right now I want to get it working and flying. Then, I will start making the "OH, Wow" stuff.

Thanks for the idea. I am interested in figuring out what can be done via programing. First, I want to get it working doing the basics.
11-11-2007, 07:17 PM
washburn_it

I'm using IOCards and to drive a LED safely you have to use a limiter resistor connected to the positive pin of the LED.
Typically a red LED (3.5 mm diameter) absorbs 15/20 milliAmpere, this is a simple formula to calculate the limiter resistor value (if you don't know it already):

R= (Vcc-Vled) / Iled

where

Vcc --> source voltage applied to the LED
Vled --> threshold voltage of the LED (it can vary from led to led, ask the vendor)
Iled --> LED current (it can vary from led to led, ask to the vendor)

Usually you can consider that a value of 15/20 mA and an average threshold voltage of 2.5 Volt is a safe value for most of the LED .
In my case,for backlighting, I'm using white superbright LED (5 mm diameter) and the limiter resistor is 270 ohm 1/4 Watt.
If you want to use an independent switch, as JBaymore clearly explaned, you must also consider 0.6 Volt that is the (typical) threshold voltage of the diode used to protect the Master Card output from "reverse" voltage (when you switch the "independent" switch and the output is turned off).
So the final formula will be:

R= (Vcc-Vled-0.6) / Iled

Hope this helps.

Regards
11-11-2007, 09:13 PM
jmig

Quote:

Originally Posted by washburn_it

I'm using IOCards and to drive a LED safely you have to use a limiter resistor connected to the positive pin of the LED.
Typically a red LED (3.5 mm diameter) absorbs 15/20 milliAmpere, this is a simple formula to calculate the limiter resistor value (if you don't know it already):

R= (Vcc-Vled) / Iled

where

Vcc --> source voltage applied to the LED
Vled --> threshold voltage of the LED (it can vary from led to led, ask the vendor)
Iled --> LED current (it can vary from led to led, ask to the vendor)

Usually you can consider that a value of 15/20 mA and an average threshold voltage of 2.5 Volt is a safe value for most of the LED .
In my case,for backlighting, I'm using white superbright LED (5 mm diameter) and the limiter resistor is 270 ohm 1/4 Watt.
If you want to use an independent switch, as JBaymore clearly explaned, you must also consider 0.6 Volt that is the (typical) threshold voltage of the diode used to protect the Master Card output from "reverse" voltage (when you switch the "independent" switch and the output is turned off).
So the final formula will be:

R= (Vcc-Vled-0.6) / Iled

Hope this helps.

Regards

Thanks Washburn. Welcome to My Cockpits.
11-12-2007, 09:28 AM
pdpo

Hi,

one nice thing also about opencockpit outputs is that the chips used for the outputs have an
internal resistor which limits also some of the current. And when you connect 2 leds in series on one output there is no need to add an additional external resistor. THIS DOES NOT APPLY when using only one led for an output.
You can calculate the internal resistor value by experimenting an measuring the current and voltages on several places. Done this a while ago and I think there was about 80 ohms of internal resistor.

Anyway I have several indicators where I put two normal bright leds in series in order to avoid the resistor and have more light in stead of using a superbright one and a limiting resistor.

Greetz Peter