Pages: [1]   Go Down
Author Topic: Controlling Multiple LED Drivers with single PWM Output  (Read 3063 times)
0 Members and 1 Guest are viewing this topic.
Australia
Offline Offline
Newbie
*
Karma: 0
Posts: 5
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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

Logged

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 626
Posts: 34143
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Australia
Offline Offline
Newbie
*
Karma: 0
Posts: 5
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
Logged

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 626
Posts: 34143
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 146
Posts: 5503
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.



Logged

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

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Australia
Offline Offline
Newbie
*
Karma: 0
Posts: 5
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
Logged

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17294
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
Logged

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 146
Posts: 5503
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.

Logged

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

Valencia, Spain
Offline Offline
Faraday Member
**
Karma: 146
Posts: 5503
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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...

Logged

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

Australia
Offline Offline
Newbie
*
Karma: 0
Posts: 5
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
Logged

Offline Offline
Edison Member
*
Karma: 116
Posts: 2205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
1 or 2 ohm resistor

Really?
Logged

Australia
Offline Offline
Newbie
*
Karma: 0
Posts: 5
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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
Logged

Manchester (England England)
Offline Offline
Brattain Member
*****
Karma: 626
Posts: 34143
Solder is electric glue
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Pages: [1]   Go Up
Jump to: