got a timer circuit...now I want it to power a LED strip - HELP

[Trefle10]

Hi, I recently purchase a circuitcreation.com K109 kits to use in my project but I need some help to get it completed.
This project will act as a night lamp for my kids, when they press the button it goes ON for let say 15 minutes (configurable) and then turn the lights off.

I was able to assemble and test it, it all works fine.
the red led goes on when I press the switch and stops after the programmed time.

schematics and technical info here:
http://www.circuitcreations.com/uploads/K109_Timer_Manual.doc

now the documentation indicates that I have 3 output on this... I was sure I had one where I can connect my LED strip to get it powered ON when the circuit was active...

OUTPUT   OUTPUT DESCRIPTION
LED      The LED output illuminates the red ACTIVE LED while the delay timer is activated.  This signal can also be used as a timer ON output.
LCH      The LCH output is initially low when the circuit is powered up and will be set to a high of 2.5V when the timer delay interval has completed.  The LCH output will remain high until it is reset by either removing power from J1 or changing any of the S1 switch settings as long as a new timer interval has not been started.
OC_OUT   The OC_OUT output is an open collector output that is open when the timer delay interval has not completed and is pulled low when the timer delay interval has completed.  The OC_OUT output can be used to connect to higher power circuits such as a relay.

The fun part where I need help. I want to light-up a strip of LED lights (12volts and max 3A)
with this. Basically when the switch is ok the strip of LED should go ON.

Now where should I connect these LED strips to?
I see there is a note indicating an output on the open collector that could be used for relay...
do I have to use that? if so how to use and what relay to get?  I never used a relay so any help will be appreciated to select the right one.

If there is another way to power these LEDs let me know.


Thanks for your help.

[Zero999]

You need to connect the relay between OC_OUT  and +V.

The 2N3904 is not designed to switch any more than 200mA.
http://www.ece.rice.edu/~jdw/data_sheets/2N3904.pdf

Another way to do this is to use a PNP transistor which is rated to 5A or more (it's wise to leave a fair headroom). Connect the emitter to +V, the collector to the load and the base to OC_OUT, via a 2W 120R resistor.