buy a 2 sheild or add direct to mega

Using Arduino General Electronics
#1

I am possibly looking for some advice,

I am hoping to make a touch screen led dimmer, wanting to run leds at various times or to dim at various times for an aquatic lighting.

I have been told on a previous post that i could add a NPN transistor or an N-channel MOSFET, to control the dimming, I have looked through google and can't seem to see how to install this on the board, If there is a post some one can point me to on how to install it it would be appreciated, another thing would be do i need to add 2 if i am wanting to run a 2 channel lighting system?

Also instead of wiring direct to the board i was hoping to add some screw terminal connections again i do not know how to keep it on the board or where to place them.

I have listed below the items i am looking at buying.

There is a 4 channel sheild, would this need any modification to get this to do what i want, npn transisters included etc.

or would it be simple enough for me to just put clips/transisters on the board.

I am hoping to add the rtc to keep the time, and to set off the lighting/dimming when required, however would i need to add anything extra to get it to keep the settings for the light sequence/touch screen controls ect.

Any help is appreciated, I'm hoping to do the code work rather than the hard ware work but am also wanting to learn.

Mega 2560 http://www.ebay.co.uk/itm/100-Arduino-Compatible-Mega-2560-R3-Version-ATmega2560-16AU-USB-Board-Electronc-/221209822255?pt=UK_Computing_Other_Computing_Networking&hash=item338122042f

screen http://www.ebay.co.uk/itm/SainSmart-Mega2560-3-2-TFT-Touch-LCD-SD-Reader-TFT-Shield-For-Arduino-R3-/271285944993?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item3f29e702a1

screw terminal connect http://www.ebay.co.uk/itm/100Pcs-5-08-301-2P-Blue-Connect-Terminal-Screw-Terminal-Connector-E0Xc-/161107825872?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item2582c654d0

4 channel led control sheild http://www.ebay.co.uk/itm/4-Channel-LED-Driver-Shield-for-Arduino-0-35-0-7-1A-/330973324592?pt=LH_DefaultDomain_0&hash=item4d0f8c2530

example lights used http://www.ebay.co.uk/itm/20pcs-5050-SMD-4led-plastic-waterproof-LED-injection-module-/121175533157?pt=UK_Garden_Lighting&var=&hash=item1c369fe665

psu http://www.ebay.co.uk/itm/12V-5A-60W-PSU-UK-Power-Supply-Adapter-for-3528-5050-5630-RGB-LED-Lamp-Strip-/190912378053?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2c7343b4c5

rtc http://www.ebay.co.uk/itm/Tiny-RTC-DS1307-Shield-Module-Kit-V2-0-Arduino-Compatible-/270941621713?pt=LH_DefaultDomain_0&hash=item3f15610dd1

#2

This screw shield board will let you connect wires to the Mega and still use other shields that are designed to sit on the Mega board itself. I just sold 11 of them, cleaned me out, and will have more available in a week or so. http://www.crossroadsfencing.com/BobuinoRev17/

#3

Do you send items to the uk?

Also the screw shield board, would it allow me to dim lights? or does an adjustment need to be done?

also will the example equipment i chose all work together to do the job i am after?

I'm looking to solder as little as possible.

#4

Your LEDs seem to be 12V 80mA LED arrays with built-in current limiting resistors - this means they
need a regulated 12V. The LED driver shield you reference is a constant current driver for bare
LEDs of a higher rating. It specifically cannot be used with 12V LED run from a 12V supply as it
will drop a volt or so and cause poor brightness and possibly uneven illumination depending on
how the LED is arranged internally.

Any simple NPN transistor or logic-level FET switch can be used to control an 80mA load (or are you
paralleling them for larger currents per control pin?) I’m assuming you are happy for low-side
switching (the simplest arrangement)

The diagram here shows how to use an NPN transistor:

And for MOSFET this thread has a circuit:

(Though that one isn’t suitable for high speed PWM, the 1k resistor should be reduced to 150
ohms or perhaps a MOSFET driver chip used for very high power loads)

If you get MOSFET(s) be sure to get logic-level n-channel MOSFETs.

There are shields with a group of MOSFETs for switching use available IIRC.

#5

Thanks for the advice, all of this is completely new to me so i am picking up what i can.

As regards to a Mosfet what sort of one would i need? a specific ampage? ect.

I am hoping to run 2 or 3 channels of these strips, so possibly 3 strips of 20 modules,

Would i need more than 1 mosfet? possible 1 for each channel?

I have ordered some bread boards and various other bits and pieces to learn.

Thanks for your help.

#6

Yes, I do send to the UK. You will still need some external circuitry to handle the higher voltage/current switching as described in reply #3. Those components could be added to a Mega prototyping shield, available from many places.

#7