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Topic: Controlling Multiple LED Drivers with single PWM Output (Read 3512 times) previous topic - next topic

Hi Everyone,

I'm very new to this and have a question i can't seem to find an answer on.
I have an LED aquarium project where strings of LED's are controlled by buckpacks / drivers.  My drivers accept a 0-5V pwm input.
Each of these drivers accept an PWM input to control the output current.

My problem is, I have a lot of drivers.

Can i split a single PWM output from my Arduino Mega to drive two or three LED drivers?  Or will this affect the 0-5v signal the pwm output each driver would receive if i was try and run more than one driver off one pwm output?

I hope that makes sense.

All info would be appreciated.

Regards

Dan
Australia


Grumpy_Mike

Yes in theory you can do this. The only thing you have to watch is the current each driver takes. Do not exceed about 30mA in total for the direct connection from any one pin.
At the worst you will need a buffer chip, but you should be OK.

Thanks for that Mike,

I will split them into two first and measure the current draw between the Mega and where i split to the drivers.

You mentioned a buffer chip.  Can you provide me any info or direction where to do some research on buffer chips?

Thanks

Grumpy_Mike

Use a 74HC04, these are inverting buffers and you get 6 in one package. If you use one per output then the signal is upside down so all you need to do is write 255-value to it. However you can use two in line if you want the signal the right way up. One arduino output will drive 20 buffer inputs.

fungus


Hi Everyone,

I'm very new to this and have a question i can't seem to find an answer on.
I have an LED aquarium project where strings of LED's are controlled by buckpacks / drivers.  My drivers accept a 0-5V pwm input.
Each of these drivers accept an PWM input to control the output current.

My problem is, I have a lot of drivers.


How many is "a lot"?

Can i split a single PWM output from my Arduino Mega to drive two or three LED drivers?  Or will this affect the 0-5v signal the pwm output each driver would receive if i was try and run more than one driver off one pwm output?


It depends on the driver but you can almost certainly do more than 1. More than about 10? You might need to use a transistor to amplify the signal.



No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

dhenry

I would follow fungus' sensible questions / suggestions. You will need to know what "drivers" and how many such "drivers" you are dealing with. I would suspect that they don't take much current to drive but it is never wise to assume.

To be save, put a small resistor (1k for example) between the mega's output pin and all the drivers' input pins to see if that will work, if you cannot find the spec for the drivers.

Thanks for the replies everyone.

I'm planning on running a maximum of 2 drivers off one single pwm output.
So will I need a buffer?

I have the spec sheet for the drivers however there's no mention about the current draw on the pwm input.

Regards

Dan
Australia

dhenry

Does it mention something about input resistance to the driver, or requirement of output resistance from the previous device?

If not, try as I suggested: it is likely the input resistance for the driver is very high.

retrolefty


Thanks for the replies everyone.

I'm planning on running a maximum of 2 drivers off one single pwm output.
So will I need a buffer?

As the PWM is a logic level input signal to the drivers I would think you would have no problems driving two such input pins with an arduino output pin, AVR output pins are quite strong compared to standard TTL output drive standards.

I have the spec sheet for the drivers however there's no mention about the current draw on the pwm input.

What you can't be certain of is if two different drivers will track identically over the 0-100% PWM range. That is a 50% PWM output may not give you 50% brightness when using two different driver modules wired to their LEDs. You can only try it and see if that might be a visual problem or not.

Lefty


Regards

Dan
Australia

fungus


Thanks for the replies everyone.

I'm planning on running a maximum of 2 drivers off one single pwm output.
So will I need a buffer?


Only 2? I say go for it. If they're logic level input they probably only need a tiny current so you'll be fine.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

fungus


To be save, put a small resistor (1k for example) between the mega's output pin and all the drivers' input pins to see if that will work, if you cannot find the spec for the drivers.


A Mega? They've got pins to burn...

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Thanks everyone... Might try a 1 or 2 ohm resistor just to be on the safe side... The mega does have a lot of pins however I'll probably be using about 7 or 8 of them...

Thanks again

Dan
Australia


Sorry, sent that message off my phone, meant 1 or 2k ohm resistor.

Will be a few weeks before i get to sorting this one out.

I'll let you guys know how it all goes.

Cheers

Grumpy_Mike

You should not need a resistor, however if you want to be safe then 100R is enough to protect your pin without beeping so much that it would stop it working.

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