Infrared LED array circuit and power supply choice.

[Peteb]

Hello, I'm new here but have many electronics questions to come! Although I'm trying to learn electronics, my knowledge is currently very basic so I am hugely welcome to any help. I'm trying to make a small infrared LED array to support a webcam recording at night. I suffer from insomnia and have done for over 5 months now and it would help hugely to see if something is happening at night, i.e. snoring/ restless leg syndrome etc. It would seem best to either confirm or deny and possibility issues at night so I need to create a way to record myself, preferably cheaply.

I currently have a lot of components to hand, so should be able to make this up with what I've got, but I'm happy to buy anything in if needed. I'm looking to create an infrared LED array with 20 LEDs rated at 1.5-1.6v 60mA. I believe (using this calculator http://led.linear1.org/led.wiz) I can create four rows of five LEDs with an 82 ohm resistor on each line. However, upon testing any 12v power supply (I have three to hand) I get a reading of around 16v. Does this mean that all the power supplies I have are unregulated and if so, what might be a good alternative? Could I use these or make a circuit with some sort of voltage regulation?

I have this circuit for another project, could I use this perhaps? http://www.satisled.com/33w-power-led-driver-mr16-acdc12v-input-dc911v-600ma-output_p1066.html

All the webcam recording will be done on my laptop through USB so it's only the infrared array I'm worried about currently.

Thanks!

[Paul Price]

Yes, it does mean they are unregulated, but you are reading the peak output voltage that will drop dramatically with any load. This is not a problem if you can measure the current across the series resistor to the LEDs and see if ohm's law tells you have the correct current feeding the LEDs. If not, adjust the resistor accordingly, and you are all set.

If you want regulation, a 7812 regulator or a LM317 would allow you to make a simple regulator to fix or adj. the voltage output to fit your fancy.

[Peteb]

Thank you for the reply - I made a quick version of a 20 LED array on breadboard, as per the online schematic. When I used the unregulated power supply it drops to around 11ish volts and around 100mA across the LEDs, plus on the webcam they seem to be hopelessly dim. Although I am aware of voltage regulators, I really wouldn't know where to start. Would you advise looking for a different power source or stick with my 12v 900 mA one and try regulating it? Also, now I've taken a new reading with the power supply under load, would it be expected for the voltage to remain the same 11ish volts that I can now find alternative resistors?