Timed LED circuit with ATX PSU, help

atxledrelay

I want to make a circuit that turns on and off the light (LED) of a given time (eg. on 9 pm and off 6 am). I also want it to be adjustable.

My idea about the design:
I will be using an ATX computer power supply and 3 w LEDs. Control circuit is connected to +3.3 V or +5 V line for voltage conveniency. This part of the circuit will be responsible of opening the relay (switching on the light) at a given time of day and close it at a different time. It have to be adjustable, so I can change time settings.

The LEDs I'll be using is a cool white LED and a warm one, connected in groups like in drawing (one group being the same LED part).

Since the voltage of the LEDs is varying from 2-3 V I want to put 3-4 LEDs in serial, but I need to lower the voltage somehow (and regulate current?), because +12 V is too much.

(Cooling and heat sinks is no problem, I'll just connect fans to the +12V line and add a resistor.)

Summary:

  1. Since the PSU is a switched-mode PSU, is the linear regulator not needed? How can I connect these LEDs in very safe and efficient way?

  2. I don't think NE555 is the right IC for this project. The best thing would probably be to buy a micro controller (àla Arduino) and program it (I'd have to read up on that). Or do you have an idea of how I can make the timer circuit?

  3. Should I use the Panasonic TX-S reed relay? I've also looked at TI TS5A3157, but I don't think that is what I need (The TI is an analog switch).

Archived: Old, messy design drawing, newest drawing below:

Design drawing

Best Answer

The ATX power supply sounds good. You won't need regulators for the LEDs. The ATX power supply should be good enough. However, you will need current limiting resistors. As for the timing circuit, I believe you have overthought it. I would simply use a plug in timer like that of the local hardware store. For example:

http://www.amazon.com/Best-Sellers-Home-Improvement-Plug-Timers/zgbs/hi/6291363011.

For about $10, you can set the on time and off time. All you have to do is plug the power supply into the timer and the timer into the mains.

Better yet, I would look at getting a 12V wall wart power supply for the lights. The ATX is probably cheaper if you have one lying around, but the wall wart would be much more compact.

Related Topic