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triise
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I came across this problem when I was throwing together a caution light panel and I failed miserably, but, I got up, dusted off and went straight back into it. I tried a single circuit, with a resistor at the back of each LED, it worked fine until I pressed the caution light test switch, that put them on all at once, and hey presto, a melt down, rethinking this with with an open mind, I thought it would be simple but it shat on me, physics was never my strong point at school. I was using 12 volt by the way tore :music_whistling:

Windows 7 64 Home Premium, i5 3570K (3.4 @ 4.4GHz), Asus P8Z77-V LX, 16GB dual channel 1600 ram, EVGA Nvidia GTX980ti, 240 GB OCZ SSD, 3 TB Raptor, Thrustmaster Warthog Hotas and Throttle, Saitek Pro Combat Rudder pedals.

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For driving low current LEDs, BJTs are better than FETs. A FET is more expensive, standard TO-220 package may require a heat sink, at least one resistor is required on the gate or drain and each discrete component must be soldered separately. That can make for a waste of time and space on a board. An IC of MOSFETs would be good but the ULN2003 is standard and very easy to source.

 

BJTs in the form of Darlington arrays solve all the problems. You only have to solder a single IC and they contain base resistors.

 

For the LED current limiting resistors, he ULN2003 is not a current limiting device so a resistor will be needed for each LED. Connecting a single resistor to the supply line will definitely burn it out. With a 12V supply and 2V LEDs, you will be using about 10W when all are lit and a power resistor that large gets hot. Also some LEDs would draw more than others and produce uneven results. Use one resistor per LED, connected after the Darlington array.

 

Like Warhog mentioned earlier, your other option is to use a Max7219 and a matrix. Or you could even use one Darlington array for the "rows" of a matrix and use higher current NPNs for the "columns." There are so many different ways :)

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As Mike says, the 2n7000 is very handy, I generally have a few on hand in the parts box, but for the amount of leds for the caution panel the uln2xxx makes things a little easier I think. My point is that if you are using 2 volt leds with a 12 volt power supply, 2 volts are consumed by the led and 10 volts by the resistor. If the current through the led is 20ma then the power that the resistor dissipates is 10v multiplied by 20ma, which is 200mw. Multiply that by however many leds you need and that is a lot of wasted power that the resistors convert to heat. Also the resistor used would need to be able to handle that amount of power dissipation, at a minimum a 250mw or 1/4 watt resistor would be needed, but recommended would be a 500mw or 1/2 Watt resistor. A better alternative would be to reduce the input voltage, either using a fixed power supply such as 5 volts or an adjustable one, there are plenty of adjustable switch mode power supplies available. Boltz said in his post to connect the resistor after the darlington array, the darlington array switches each circuit to ground so you do not connect anything after the darlington array, you cant anway, just thought that might have caused some confusion, no offense to Boltz, he seems a lot more knowledgeable than me, also I was wrong about the Arduinos current handling capability so take anything that I say with a pinch of salt and do your own research.

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Here is the layout of my curcuit. I've drawn in the transistors separate, but they are in the Darlington array. Also after I switched to 5V supply and added a 1 ohm 10W resistor things seem to work. Also I measured the total Amperes drawn by 1 LED, and it was 13 mA. So things seems to work, but I don't get my calculations to match it. But, if it works, don't fix it :)

BTW, I'm using the ULN2803A (6 in total for my caution panel).

1297355757_Screenshot2015-04-0518_35_28.jpg.70c9c5259c07a3bbefc1cc6eda560cc5.jpg


Edited by triise

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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You need a separate resistor for each LED.

 

The single resistor in your schematic sets the current for all LEDs combined, but you want that current to be different depending on the amount of LEDs that are on at the same time. It also won't be distributed evenly between LEDs due to manufacturing tolerances.

 

Assuming a forward voltage of 2.4 V, with a 1 ohm resistor you should get a current of 2.6 ampere (2600 mA). Either something is already broken, or your circuit does not match your schematic.

 

To get the 13 mA you are measuring with a single LED, you'd need a 200 ohm resistor (again assuming a forward voltage of 2.4 V).

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Ian;2368277']You need a separate resistor for each LED.

 

The single resistor in your schematic sets the current for all LEDs combined, but you want that current to be different depending on the amount of LEDs that are on at the same time. It also won't be distributed evenly between LEDs due to manufacturing tolerances.

 

Assuming a forward voltage of 2.4 V, with a 1 ohm resistor you should get a current of 2.6 ampere (2600 mA). Either something is already broken, or your circuit does not match your schematic.

 

To get the 13 mA you are measuring with a single LED, you'd need a 200 ohm resistor (again assuming a forward voltage of 2.4 V).

 

Thanks Ian and Tore, I was going to ask someone to share a wiring diagram because I am so way out of my depth here. My occupation path during my life did not involve designing electronic circuits so I am learning as I blow things up. :music_whistling: You know something, I thought the caution panel would be the easiest one to build, and boy, did I find out the hard way, I'm still flummoxed with the whole thing, nearly made me give up with the whole pit build, but I gave myself a slap, all the money I have spent so far ain't going to waste. I think it is really difficult when, say!, you were good at your profession, and you come into this and hit walls, and it's way out of your comfort zone. Sorry Tore didn't mean to hijack thread just felt it was important to let people not to give up when the chips are down.


Edited by weeb

Windows 7 64 Home Premium, i5 3570K (3.4 @ 4.4GHz), Asus P8Z77-V LX, 16GB dual channel 1600 ram, EVGA Nvidia GTX980ti, 240 GB OCZ SSD, 3 TB Raptor, Thrustmaster Warthog Hotas and Throttle, Saitek Pro Combat Rudder pedals.

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Thanks Mike for the references. Only thing I don't like about them is soldering each. I guess it is not really much work but a neater approach would be nice.

 

I have attached an example circuit diagram for using the ULN2803A for a caution panel. I apologise for the very bad work. Many wire connections are missing since I don't have much time. Many cross but it is just a repeating pattern for each chip. Should at least show the basics of what you need to create.

 

In my caution panel, I used 74HC595 shift registers so that is another way.

 

The MAX7219 has a max voltage of only 5V and max current is 40mA. If your LEDs are within this then that is the best way to go. It has the lowest component count.

Caution Panel with ULN2803_schem.pdf

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Thanks Calum, that gives me another pointer. Appreciated m8. :thumbup:

Windows 7 64 Home Premium, i5 3570K (3.4 @ 4.4GHz), Asus P8Z77-V LX, 16GB dual channel 1600 ram, EVGA Nvidia GTX980ti, 240 GB OCZ SSD, 3 TB Raptor, Thrustmaster Warthog Hotas and Throttle, Saitek Pro Combat Rudder pedals.

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Ian;2368277']You need a separate resistor for each LED.

 

The single resistor in your schematic sets the current for all LEDs combined, but you want that current to be different depending on the amount of LEDs that are on at the same time. It also won't be distributed evenly between LEDs due to manufacturing tolerances.

 

Assuming a forward voltage of 2.4 V, with a 1 ohm resistor you should get a current of 2.6 ampere (2600 mA). Either something is already broken, or your circuit does not match your schematic.

 

To get the 13 mA you are measuring with a single LED, you'd need a 200 ohm resistor (again assuming a forward voltage of 2.4 V).

 

Thanks for the input.

 

Look what it looks like with one resistor:

${1}

 

Now I'm using one (1) 10W 10Ohm resistor for all the LEDs. I think I've read that the ULN2803APG does have some internal resistors. Maybe thats why it's working? Also I use 5V supply voltage now, not 12V.

 

for some reason my youtube links doesn't seem to work... link:


Edited by triise

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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Using a single resistor may work for a certain period of time, bit as Ian has said, due to manufacturing tolerances all leds are not equal, and you will find that the most conductive led will conduct more than the rest and burn out sooner, then the next and so on. Boltz, I suddenly had a eureka moment and understood what you were saying, funny how everything is clearer once the meds have kicked in.


Edited by cefs
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Triise, can I ask you which 8" LCDs you got for your MFDs, and have you hooked them up/tested them yet?

 

Sure, here is the link: http://www.ebay.com/itm/111340471971?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

Haven't hooked them up yet, but they fit perfectly behind the MFDs.

 

Regards,

T

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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Ok, found out why its working and how I get the current readings that I get. And I learned something new about Darlington arrays, in this case the ULN2803APG.

 

There is a voltage drop of about 1 - 1.2V in the transistor (depending on the saturation current on the collector), the supply voltage is 5V. Then using ledcalc, I should use a 28 ohm resistor, but I do in fact have a 10 ohm 10W at the moment. This should mean that the Darlington indeed works as a resistor, and my mA measurements are correct.

My LED's have a forward voltage of 3.2-3.4 V (Ultra bright green).

You can read for yourselves: http://pdf1.alldatasheet.com/datasheet-pdf/view/182611/TOSHIBA/ULN2803APG.html

Check VCE (sat) on the 4th page.

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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Ian;2368277']You need a separate resistor for each LED.

 

The single resistor in your schematic sets the current for all LEDs combined, but you want that current to be different depending on the amount of LEDs that are on at the same time. It also won't be distributed evenly between LEDs due to manufacturing tolerances.

 

Assuming a forward voltage of 2.4 V, with a 1 ohm resistor you should get a current of 2.6 ampere (2600 mA). Either something is already broken, or your circuit does not match your schematic.

 

To get the 13 mA you are measuring with a single LED, you'd need a 200 ohm resistor (again assuming a forward voltage of 2.4 V).

 

The forward voltage is 3.4 V, and as far as I can see the ULN2803 also have a voltage drop of 1-1.1 V. That would explain the 13 mA... i think... :joystick:

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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Ok, did some reasearch on my CNC now. Looks like the bearings for the X-axis is of poor quality. I have a lot of bachlash on both X and Y. That would explain the quality issues of my text and engraving.

 

 

Once again, link doesn't work (at least for me):


Edited by triise

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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Fastened the bolt on the end a bit. It made the turning a bit more heavy, but almost no backlash. Tried to engrave a new panel with very pleasing results compared to the last one.

7ef068e6efcc48e5a11e1c34e18ec81e.jpg

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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It does indeed look better, but while still very acceptable the text is a bit thinner then it should be. Or at least looks that way to me.

 

As for the. "+" sign, perhaps try to remove the inner material with hobby knife so it is solid white? Not critical and Perhaps I'm neatpicking , but that little detail is for some reason an eyesore for me :)

 

And Keep those pics coming :thumbup:

Anton.

 

My pit build thread .

Simple and cheap UFC project

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Quick question:

How do I interface my ON-OFF-(ON) switches on the CMSP panel with DCS BIOS? It looks like I should have gotten some OFF-ON-(ON) switches instead, but the ones I've found were expensive and hard to get. Is there some changes that can be made to make this work? I know that it could be done in HELIOS. So it should be possible in DCS BIOS as well to my understanding.

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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The DcsBios::Switch3Pos class in the Arduino library assumes ON-OFF-ON switches, because they are the most common type. Pin A goes to the "zero" position (down or left), pin B goes to the "two" position (right or up).

 

If your switch is not ON-OFF-ON, you can make it work with the more general DcsBios::SwitchMultiPos.

 

Where did you get the impression you needed OFF-ON-ON switches? Sounds like an opportunity to remove a possible source of confusion from the User Guide.

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Is there no font tinting/CNC contour control in your workflow?

 

 

I'm not sure I understood your question. Are you referring to the fact that my letters don't look the same in the different panels?

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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Ian;2371604']The DcsBios::Switch3Pos class in the Arduino library assumes ON-OFF-ON switches, because they are the most common type. Pin A goes to the "zero" position (down or left), pin B goes to the "two" position (right or up).

 

If your switch is not ON-OFF-ON, you can make it work with the more general DcsBios::SwitchMultiPos.

 

Where did you get the impression you needed OFF-ON-ON switches? Sounds like an opportunity to remove a possible source of confusion from the User Guide.

 

Sorry, it's more due to the fact that I read this late yesterday evening. When I look now it's a bit clearer to understand.

 

Thanks for the feedback :thumbup:

Regards,

Tore

 

- Newbie simpit builder and electronics geek -

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