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Topic: Basic info about a LED PWM "dimmer" circuit at ~3amps (Read 4 times) previous topic - next topic

ironspider

Greetings all,

I am working on what (I hope at least) I think will be a pretty basic setup.  But, since I am pretty new to Arduinos (about a month) I wanted to ask a question about this specific project.  Basically I want to be able to PWM a large number of LEDs and I'm not sure how it interacts with the Arduino chip.

My ultimate project goal is to program an ATtiny85 to read a Pot and then set the LED level accordingly.  I am predicting the project could use up to 100 LEDs which draw about 33mA each at 5v (resistors are alrady embedded in these LED Lamps).  So, since it is possible to have all the lights on at the same time, doesn't that mean that I'd need way more Amperage (100x33mA = 3300mA = 3.3Amps) than the Arduino can handle?

I eventually want to move the ATTiny85 onto its own PCB and then use a PoT for the "dimming" (via PWM).  So what I'm asking here is what kind of technology do I need to research to allow more amperage into my project?  I bough a cheap 5v 4a wall wart style PSU from ebay that I was planning on using to power the project.  So do I need to use something like a transistor to allow the higher amperage to draw off the 5v on the PCB (from the wall wart) and avoid the ATtiny85?

I guess I'm asking what will I need to prepare for to turn what is one of the most basic beginner-level tutorials (PWM LED dimming with a PoT) to work at a much higher draw from the LEDs.

My completely inexperienced thought process was that I would need some kind of 5v voltage regulator capable of handling like 4Amps (since I imagine the $4 wall-wart PSu from ebay is not regulated), some caps to smooth that, a PoT, the ATtiny85, the LEDs and something (transistor? relay? MOSFET?) that can handle controlling these LEDs other than the ATTiny85?

Am I on the right track here?

Thanks!

PeterH


So do I need to use something like a transistor to allow the higher amperage to draw off the 5v on the PCB (from the wall wart) and avoid the ATtiny85?


Sounds right to me. Depending how well behaved the wall wart is you may not need to regulate its output.

In case you're interested, I would have thought you could achieve the same PWM result using a 555 timer plus a couple of external components, but I don't anything wrong with the approach you're taking if you prefer to use a microcontroller.
I only provide help via the forum - please do not contact me for private consultancy.

terryking228

Hi, Maybe look at the Arduino Power control page on the ArduinoInfo.Info WIKI:

http://arduino-info.wikispaces.com/ArduinoPower
scroll down a ways to here:
http://arduino-info.wikispaces.com/ArduinoPower#DC

and you will see an example of controlling/dimming multiple Amps of lights (could be LEDs).  Example code there too.
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

Chagrin

My completely inexperienced thought process was that I would need some kind of 5v voltage regulator capable of handling like 4Amps (since I imagine the $4 wall-wart PSu from ebay is not regulated)...


FWIW, nowadays you can safely assume that all power supplies are "regulated".

PeterH


FWIW, nowadays you can safely assume that all power supplies are "regulated".


Maybe it's a valid assumption where you are, but it's not an assumption I'd want to make.
I only provide help via the forum - please do not contact me for private consultancy.

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