#LED driver board issues

1 messages · Page 1 of 1 (latest)

ornate kraken
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Hi all,
I spent a few hours with trying to light up my MF LED driver board.
First some learnings, then my questions.
0) Check the docs on the website and on github !

  1. I have version 1.1 as it turned out this one cannot be powered purely from the Arduino.
    Even if power need would allow (test Arduino + 1 one led output).
    I think v1.3 has this feature.
  2. Led output legs are not numbered. Logically left is 1 = cathode (-), right is 2 = anode (+). (But during the failed attempts I also questioned this 😞 )
  3. On the LED outputs 5V can be measured therefore resistence is needed before the led.
    Please share your comments for the above mentioned points and here comes my questions.
  4. How many leds can I connect to one output?
    100 ohm - orange (2V) - orange (2V) could work?
    Or if I take a blue (3V) with 200 ohm can I connect 2 in parallel?
  5. Can I share one of the lines among all the leds? And wire only one wire from the LED output to each led?
hard spoke
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Just to comment on item 3, a current limiting resistor can be installed on either leg of a led. It makes no difference before or after the led.

hard spoke
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For item 4, I would suggest you stay within the shift register specs. A 74HC595 shift register is limited to 70mA total current. So you should probably target 10 to 15mA per segment.
Maybe one of our electronics expert could give a better explanation.

mental kestrel
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The LED driver regulates the current until Voltage flows through your LED

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You dont need any resistors at all

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that's one of the key benefits of the LED driver.

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The comments from @hard spoke apply to a 74HC595 but not the chip which is used on our LED drivers.

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  1. no. you can't.
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  1. it follows the convention of all breakout boards. 1st pin is always GND
hard spoke
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OK. Sorry. I stand corrected.
It would be good if the technical specs were available. I checked the product page and did not find any link to technical details.

ornate kraken
# mental kestrel 4) no. you can't.

Thanks a lot Sebastian for clarifying. Indeed this part of the docs (connecting leds) would need some clarification. With 3 yrs of MF past it took half a day with trying to figure out 🙁
Back to my questions:
4) no resistor needed, clear. At one stage I connected 2 orange leds in parallel. It worked. Any reason not doing this ?
Normally in the annunciator boxes there are place for 2 leds. I would like to drive 32 annunciator from the driver board.
5) Can I share the GND line? Or should I send double wire to all Leds?

mental kestrel
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the chip drives the led by raising the voltage until the predefined target current is reached.

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if you connect two leds in parallel then the total current is the sum of current running through each LED.

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a single LED of the same column will be noticeably brighter than if you connect two LEDs

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@twilit lichen, the chip is a current sink driver. So i guess one would have a common VCC and connect individual cathodes.

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yeah. thats correct - i just checked the schematic

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...

ornate kraken
ornate kraken
# mental kestrel <@818484383606243342>, the chip is a current sink driver. So i guess one would h...

Sharing VCC could be also justified by what I measured with a multimeter. Right (+) pins seems shorted to each other. Left not. This was also strange for my limited electronics knowledge 😀
The only issue I think with this is that 32 led's total current would go higher, so thicker wire would need. AWG24 can not handle this. AWG22 or less would be needed, or much better to wire 2-3 shared VCC lines.

twilit lichen
# ornate kraken Thank you again. If I don't kill the board with it, then this could be a solutio...

Don't connect LED's (without a R like this driver board) in parallel. They must always be connected in series if driven by a LED driver. Two orange LED's with 2V forward voltage could work on 5V power supply, but I havn't the data sheet in mind.

Even LED's of the same type, each LED has a slightly different forward voltage. If connected in parallel one LED is slightly brighter than the other one. First you will not see it. But over the time the forward voltage will change differently due to different aging of each LED (different current). This goes faster and faster over time. It can't be said when, but after some time the different brightness might be seen.

mental kestrel
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Thanks @twilit lichen for clarifying

ornate kraken
ornate kraken
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Hi guys, If you are not tired, yet. What happens if the EXT PWR is 12V. Q6: Can the system handle?
Q7: Can I connect more (up to 3) high voltage (3V) leds in this case?

twilit lichen
ornate kraken
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Thanks again for your support. I think I make some promotion again to this fantastic board. 😉
I successfully connected:
23 x 2 orange leds in series each +
9 single blue leds.
Here are current needs:
Uno+Driver board = 30mA
All potis MIN => +130 mA
All potis MED => +240 mA
Therefore these configurations can safely powered from the board.
However setting all potis to MAX would go up to 1000 mA ! (I tried this only channel by channel).
So be careful - as the documentation highlights - without external power you can go only up to 400 mA.

mental kestrel
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🚀

fast veldt
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I just finished my built. After speaking to Roberto, I came here to see what breakout boards MF has and also checked out the website. Unfortunately my built is currently using all Arduinos max and powering them up from a powered USB hub. Everything seems to be working fine including the 10 servos and 5 segment displays. I spread them out over the 6 Arduinos. So far I am not smelling any burning. LOL!

Front_of_OVHD.jpg Back_of_OVHD.jpg
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Here is a mod I did for the safety cover for the switches. I used a limit switch placed on a 3D printed holder that sits over the back of the switch and connected a wire that engage and disengage the limit switch. Worked flawlessly. I have done 1 so far.

mental kestrel
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Cool! I like that it works! THat's really a nice detail. I never got to it, my plan was to use reed-switches installed in the panel and a small magnet attached to the cover.

fast veldt
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Magnet would be cleaner though I guess. I am planning to put a piece of 3D printed plastic which will hold the wire and glue that to the back of the cover so it won't be easily visible.