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Author Topic: N00b needing help with 12V LED strips  (Read 2227 times)
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Hi,

I’m new to Arduino and I’m working on a wearable 12V LED strip project. I'm a mechanical engineer/designer and so have some experience of electronics but my knowledge is more than a bit rusty.


Background to Project:

A wearable battery powered light-up costume for professional theatrical use by someone else.

I'm hoping to use between seven and ten sections of LED strip, each around 1metre long. It is single-color 12V SMD3528 LED strip (non-addressable). It has 60 x 0.08W LEDs per metre. i.e 4.8W, 0.4A per metre.

I just want each full 1m section to switch on and off in sequence (or a chasing pattern) at an absolute max of maybe 5 or 10 Hz. I don't think I need to do any PWM initially- the sections don't need to be on at the same time and I'm assuming I can find a battery that can provide 0.5-1A at 12V. It would be good to be able to have it all light up together at some points in the sequence but it looks like this would be difficult in terms of the current draw so I'm happy if this is not doable.

It only needs to run for around 10-20 minutes per battery charge.

The electronics and battery need to be as small as possible. I'll probably design a custom housing for the whole system.


The Problem:

It needs to be durable and safe. I'm slightly concerned about excessive heating and/or electric shocks. I like the idea of a small self contained arduino shield that doesn’t require me to design/build a handmade PCB with mosfets. I would be more comfortable with an off-the-shelf solution initially.

Some options I've found, both from Sparkfun:

1. Power Driver Shield Kit
https://www.sparkfun.com/products/10618
This looks like a simple MOSFET kit but it only has 6 outputs which is not enough for this application. It also uses the non SMD mosfets which are very tall. I don't know if these outputs could be easily multiplexed (?)to give me more?


2. 4x4 Driver Shield
https://www.sparkfun.com/products/10256?

- "The 4x4 Driver Shield is designed to enable users to switch DC loads up to 5A at up to 30V."
- "Uses only digital pins 7, 8, 11, and 13, leaving all serial, PWM, and analog input lines free"

This sounds great, and its a good size but it's seems more designed for motors and solenoids etc. I'm wondering if I would have problems trying to run the LED strips from these outputs at the frequencies I'm hoping for?

What I'm trying to do seems to be a very common use for arduino so I'm suprised that I can't find more options for readymade high power shields. I can't see any references to people using motor-type shields for powering LEDs.

Both of the options above work with larger sized Arduino boards, but anything suitable that might work with a smaller mini pro /lillypad type board would be even better.

Apologies for the rambling question, but I have been trying to research this and am really unsure. Any help, thoughts or other options would be very much appreciated.

Many thanks,

Barry.
p.s For power source I'm currently looking at high capacity LiPo R/C batteries, but this might be a topic for another day...
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Your project is calling for custom made boards to be quite honest.  As you discovered, both products use large, through hole components, which will ultimately end up in a bulky setup.  You can get mosfets capable of switching 1A that aren't that big in an SMD package, but you may have to design the circuitry yourself.  Not that hard to do.  And at that point, you may as well build a custom board that has a 328P Atmel on it, with the various signals needed for your project, including the mosfets.  From your description it doesn't sound like you need a whole lot from the Atmel, so you can eliminate quite a bit from a stock Arduino board when designing your own custom one.  The only issue now is that you don't want to have to design your own ... that's a hurdle for you to jump over.
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Hi,

Many thanks for the advice. It's not that I don't want to design a custom board, I just don't think I'd be confident enough to do it as my first Arduino project...

I think I might buy the 4x4 driver shield and have a play with it to see if it does what I need, and then see if I can gain some confidence to go further.

Thanks again,

Barry.
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You could put those MOSFETs and 2-pin connectors on a protoshield and plug the shield onto an Uno. Or use a seperate standalone board.
The gates get driven by IO pin thru 150 ohm resistor, one leg goes to common ground, the other leg goes a screw terminal for LED-, the other screw terminal gets 12V for the LED+.
Connect +12 & Gnd to your source. Connect the 12V source ground to the Arduino ground.
Can drive 6 MOSFETs from 6 PWM pins.
Need more PWMs?  Can do software PWM as well.
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Many thanks for the advice. It's not that I don't want to design a custom board, I just don't think I'd be confident enough to do it as my first Arduino project...

I hear ya.  On the other hand, there's no time like the present.  Everyone starts somewhere. smiley  This is exactly where I started, by building a custom controlled for an LED project.

It might be worth it for you to try and prototype this first.  Whether you use a stock Arduino board, or you prototype that as well.  You don't need much, the Atmel, a crystal with caps (or resonator) and a 3.3V - 5V source.  Once you burn a bootloader to it (using a stock Arduino), you've got yourself an Arduino clone that you can program the same way you would any stock Arduino.  Pull the necessary lines for an FTDI, at a regulator if you're going to feed the whole thing 12V (for the LEDs) so that you can drop the voltage down to 5V.

After that, just add the MOSFETs where you need them, connect them to the Atmel pins, add the headers for your LED strings and power supply and you're done.
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Thank you both for further advice. I'm not getting notified of new posts for some reason and just checked back in to see.

I''m getting the driver board delivered today, and will see how the digital output looks.

If it's not great, the next step would be the proto-shield with mosfets and PWM, but size-wise this will be similar to the uno+driver board so I might have to start looking at the fully custom version...

Many thanks,

Barry.
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Does it have to be that specific size?  The reason I ask is because there's a good chance if you custom make it, it'll be much smaller which might help.  But you do want to prototype it first, have all the bits and pieces in place that you will end up using on the final design.  There are many parts for which you can get both a through hole as well as a smaller SMD version.  So make a prototype with the through hole parts and when you know everything works for sure, then recreate it in a SMD form factor.

Going back to your original post, do you have a link or datasheet for the LED strips you plan on using?
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Yes indeed, I think prototyping would be the first step before a SMD version...if I do end up doing that.

The LED strip will be something like this one:
http://www.amazon.co.uk/Lighting-EVER-Flexible-Waterproof-Strips/dp/B004JRK35W/ref=sr_1_8?ie=UTF8&qid=1352245506&sr=8-8

The sections (i.e individual arduino outputs) will be around 1m each (0.4A) but there may be one that is around 2m or slightly longer.

I''ve now got the driver shield so will do some intial tests with that. The size doesn't look too bad, I may be able to use a right-angle 25 pin connector to keep it lower profile.


Thanks,

Barry.
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This one with a Promini would be really small

https://www.sparkfun.com/products/9627

http://www.gravitech.us/arpromi5v.html
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The LED strip will be something like this one:
http://www.amazon.co.uk/Lighting-EVER-Flexible-Waterproof-Strips/dp/B004JRK35W/ref=sr_1_8?ie=UTF8&qid=1352245506&sr=8-8

The sections (i.e individual arduino outputs) will be around 1m each (0.4A) but there may be one that is around 2m or slightly longer.

Yeah, so each 1 meter will need 400mA.  You can get dual mosfets that can drive 1.5A (each), or even 1A ones, in a package no larger than 3mm x 2mm.  Just saying. smiley

Since you said you won't be lighting all the strings up at the same time, battery consumption will be whatever you are pulling for the strings, so 400mA per string, plus a bit of overhead for the Arduino (clone or not.)  Regular AA batteries can handle roughly 2A per hour.  So flipping 400mA through various strings will get you approximately 5 hours worth on 3-4 AA batteries.  It gets better with a LiPo, however you will need to build a regulator circuit so the LiPo's voltage can be brought down for the Atmel.  I'm willing to bet you can run those strings with a 3S cell battery.  The only thing is, 11.7V is a long way to drop to 5V for the Atmel and you will develop some heat doing that.  Might be worth running the strings off of the Lipo, and the Arduino clone off of 4x AA batteries.  Sure it's two packs, but you won't be dealing with a whole lot of heat doing that.

I have been known to attach a custom PCB right onto the 4x AA battery pack, with three wires going to a string of LEDs (DATA, CLK, GND) and a heavier battery pack elsewhere supplying the strings (the GND from the Arduino clone ties in with the big battery pack's GND.)
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Hi Lillii

I'm working on a similar project (but need wireless control). What did you end up doing?

Regards

mark
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