NG Current specs, out pins, and transistor/relays

Hey Arduino Heads. So I, a noob Arduino user, have just a few quick questions about the NG:

  1. How much current does the Arduino use? I’d guess it might be around 1W worth of power, so at 5v that means about 200mAh. Does anyone know its exact amperage at 5v?

  2. How good/reliable is the built-in voltage regulator? If I’m running an otherwise 12v circuit, do I need to regulate down to 5v before I go into the Arduino to be safe? I’d imagine that I do.

  3. Without involving duplicators or any other outboard chips, there’s 11 usable output pins, correct? This assumes that 0 and 1 are dedicated serial pins; is this right? Can 0 and 1 be used as 2 thru 13 are, or are they only ever for serial? What does AREF do?

  4. Does anyone know what RadioShack part I need if I’m looking for a transistor to toggle a 12v circuit from the NG’s output pins? I pretty much just need to get from the PWM pins to 12v-rated and -regulated LEDs, and I’d prefer a transistor to a relay (less contacts to deal with). This brings up another question:

  5. If my LEDs are rated at 12v and have built-in voltage regulators, will PWM even work, or at least work properly? Wouldn’t these regulators just convert the pseudo-lower voltage signal back to the 12v they like? Is there a simple way for me to get these LEDs to fade via PWM without removing their regulators? I’m married to these particular LEDs as they are 1Watt-powerful and I’ve already bought a whole bunch (had to for budgetary reasons).

Thanks in advance for taking the time to reply. I’m working on a undergraduate music thesis project and am fairly new to this world of hacking and circuit-bending, so I apologize for the basic questions. I can best be reached at jklewis@wesleyan.edu, but I’ll be checking this thread too.

Take care,

Jake

hi

Hey Arduino Heads. So I, a noob Arduino user, have just a few quick questions about the NG:

  1. How much current does the Arduino use?

Very roughly: about 20ma for the chip without driving anything, and lots more (60?) for the FTDI chip. You can look in the datasheets for the exact value.

  1. How good/reliable is the built-in voltage regulator? If I’m running an otherwise 12v circuit, do I need to regulate down to 5v before I go into the Arduino to be safe? I’d imagine that I do.

The regulator is a standard 78M05. You can give it anything between about 7 to 25V DC and it will be fine. 7V is the bare minimum.

  1. Without involving duplicators or any other outboard chips, there’s 11 usable output pins, correct? This assumes that 0 and 1 are dedicated serial pins; is this right? Can 0 and 1 be used as 2 thru 13 are, or are they only ever for serial? What does AREF do?

0 and 1 default to digital operation, like the other digital pins, until you use the Serial.begin command.
Analog reference is just that, for case where you would like to alter tha range of the analog pins. You need to change the Sketch code to do so.

  1. Does anyone know what RadioShack part I need if I’m looking for a transistor to toggle a 12v circuit from the NG’s output pins? I pretty much just need to get from the PWM pins to 12v-rated and -regulated LEDs, and I’d prefer a transistor to a relay (less contacts to deal with). This brings up another question:

A relay won’t do what you want. Instead, look on the net for transistor driver. See the diagram later in this post. A part like a 2n3904 or a 2N2222 is good for small loads. Don’t buy from Radio Shack, they will charge you $1.99 for a part that costs .10 from an electronics supplier!

  1. If my LEDs are rated at 12v and have built-in voltage regulators, will PWM even work, or at least work properly? Wouldn’t these regulators just convert the pseudo-lower voltage signal back to the 12v they like? Is there a simple way for me to get these LEDs to fade via PWM without removing their regulators? I’m married to these particular LEDs as they are 1Watt-powerful and I’ve already bought a whole bunch (had to for budgetary reasons).

Most LEDs have a voltage drop of 2 to 3 V. If you have 12V LEDs then you probably just have standard LEDs with a resistor that optimizes them for operation at 12V. Solution: save money and learn more by buying raw LEDs and 330R resistors, and then learning ohm’s law!
(R=V/I; R= 10V drop/.02A = 500 Ohms) Resistors are 2cents, leds are $.05 to $1.00 each.

If you absolutely have to use your 12V LED’s, then you just need to replace the leds and resistors in this diagram with your LED strips. A 2N2222 or similar will drive 500ma safely. They’ll also need their own power supply.

Hope this helps

D