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16  Using Arduino / General Electronics / Re: Transistor Selection and Wiring to Drive LEDs with PWM control on: August 15, 2014, 05:04:58 pm
MOSFET, better idea. 20mOhm for a good one, at 750mA that is only I^2 x R = 11.25mW, only 15mV dropped across it. No heat sink required. Just make sure it is logic level.

It won't be 11.25mW when you PWM it (which he's planning to).

If he's already got the TIP120s, they'll work. Might as well use them.
17  Using Arduino / General Electronics / Re: Powering Pro Mini and ftdi serial question on: August 15, 2014, 12:09:14 pm
Looks OK to me.
18  Using Arduino / General Electronics / Re: Transistor Selection and Wiring to Drive LEDs with PWM control on: August 15, 2014, 12:08:32 pm
Oh, and the 150 ohm resistor that fungus suggested would work, too.

2.5V/150 ohm = 14.7mA
2V/150 ohm = 13.3mA

I was just erring on the side of "plenty".  smiley

Good point about the heat. I suspect it might be OK (puts finger in air... 750mA x 1.5V... just over a Watt) but a Watt is still going to be plenty hot.  Adding a heatsink is cheap and can't hurt anything.
19  Using Arduino / General Electronics / Re: Transistor Selection and Wiring to Drive LEDs with PWM control on: August 15, 2014, 10:38:03 am
Questions about specs:
Does "collector current" mean the transistor can handle up to a 5 amps load?

Yes.

(With enough heatsinking)

Does "base current" mean that the arduino needs to supply 120 mA to trigger the transistor to "flip the switch?"

No. Numbers under "ABSOLUTE MAXIMUM RATINGS" are the values that will kill the transistor.

The number you're interested in is under "Saturation voltage"

Does "Emitter-base voltage" mean that I need to put 5V on the base to get it to switch?

No.  (see above...)

You need "Base-emitter on voltage" further down.

Questions about wiring:

To wire this up would I do this?

+12v supply -> collector
Arduino PWM pin -> base
+ side of LED wires -> Emitter
- side of LED wires -> ground

No. The transistor has to go after the LEDs, with the emitter connected to ground.

You'll need a resistor between the Arduino pin and the base. Try 150 Ohm.

20  Using Arduino / General Electronics / Re: Switch de-bounce circuit. on: August 15, 2014, 08:55:18 am
I'd prefer to design and build my board with just a single component to do the de-bounce, but I don't want to discover afterwards that I needed one of the more complex options!
I would suggest using a microcontroller such as a Mega328 as the "single component".


The original question was: "Can someone please educate me on the differences between the various circuits (hardware) used to de-bounce input buttons on an arduino?"

To which the correct answer is: None. They're all incorrect.
21  Using Arduino / Microcontrollers / Re: Bootloader problems and can't set fuses (328p) on: August 15, 2014, 07:27:42 am
Maybe it's set so it needs an external clock.
22  Using Arduino / General Electronics / Re: Switch de-bounce circuit. on: August 15, 2014, 07:24:10 am
Software is the most reliable method. Just make sure a minumum time passes between two presses.

23  Using Arduino / Microcontrollers / Re: Bootloader problems and can't set fuses (328p) on: August 15, 2014, 06:25:28 am
The error was: Yikes! Invalid device signature.
It appears that the signature read from the 328p is 0xffffff (Wrong i know).

A signature of 0x000000 or 0xffffff is a wiring error (or bricked/dead chip). You programmer is seeing constant LOW or HIGH on the data line.

I fixed that with adding the -F

No you didn't.

-F can't "fix" a wiring error or bad chip.

24  Using Arduino / General Electronics / Re: Understanding grounds on: August 15, 2014, 05:15:17 am
Let's say I measure voltage between the grounds on the two devices and the one with the 9V power supply is +2V relative to the one on the 12V power supply, for whatever imaginary reason. 

That's not correct. In reality the grounds are "floating", they're not referenced to anything.

(Or they should be if everything is working properly)

25  Using Arduino / General Electronics / Re: Powering Pro Mini and ftdi serial question on: August 15, 2014, 05:12:39 am
Connect all the grounds together, but do not connect the +5V of the power supply to anything except the GSM shield (ie. Do not connect the 5V from the USB and the 5V from the power supply together).

Alternatively,  figure out a way to get the 5V for the GSM from the USB cable that connects to the FTDI.

Or ... get another USB cable and power the GSM from that.
26  Using Arduino / LEDs and Multiplexing / Re: Using 20mA current limiter with 3 color common cathode LED's on: August 15, 2014, 04:06:11 am
Those things are analog. The noise will come from the PWM, not the device.


27  Using Arduino / Microcontrollers / Re: Arduino serial board for sale? (the first arduino board) on: August 15, 2014, 04:01:34 am
Do you mean this?

http://arduino.cc/en/Main/USBSerial


28  Using Arduino / Microcontrollers / Re: No supply if the arduino mega is not connected on: August 14, 2014, 02:27:20 pm
Have you tried measuring the voltages with a multimeter? 

(very radical, I know...)

29  Using Arduino / General Electronics / Re: Guides for soldering? on: August 14, 2014, 01:18:04 pm
So you don't pretin on electronics?

Nope.

(not unless it's a multistrand wire that you have to poke through a PCB hole...)

30  Using Arduino / General Electronics / Re: Guides for soldering? on: August 14, 2014, 12:37:52 pm
So is the soldered I have worth while

There's nothing wrong with it.

should I get a better model?

Of course a full soldering station would be nicer to have, but it won't magically make soldering any easier!.

A bit of practice with the one you have is all you need.

PS: Use the sharpest tip for soldering. Screwdriver (flat) tips are more for desoldering where you have to touch multiple pins IMHO (YMMV - I know people who solder with them but I personally hate them)
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