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16  Using Arduino / Microcontrollers / Re: ATtiny my night light, can't find the bug. on: October 01, 2014, 08:02:50 am
A big Thank You to fungus and hiduino, everything is working now !

I managed to stuff everything in a Kinder Surprise.

That's a good idea.

It would be cool if you put in an RGB led and a shake sensor.

Shake it to get 10 minutes of RGB patterns, gradually fading.

(I might have to do that...)

Dunno what the battery life would be. I guess it depends mostly on LED brightness.
17  Using Arduino / Microcontrollers / Re: ATtiny my night light, can't find the bug. on: September 30, 2014, 01:24:49 pm
Code:
analogWrite(LEDO,HIGH);

"HIGH" is defined as "1".

18  Using Arduino / LEDs and Multiplexing / Re: Twister - Driving multiply high powered RGB-LEDs on: September 30, 2014, 12:41:30 pm
Im not settled on the 3W leds, I just thought it would be cheaper, and easier to build?

(you mean compared to LED strips?)

Cheaper? Depends on how many LEDs you put under each tile.

Easier?     Definitely not. LED strips make everything incredibly easy.

19  Using Arduino / General Electronics / Re: Noob Question about Transistors on: September 30, 2014, 10:35:05 am
If he is asking what I think he is asking, then yes the voltages must "match".

If you have 50 V on the collector and 20 V on the emitter, you must have about 20.7 V on the base to turn it on. You cannot apply just 0.7 V to the base.

Yes, of course. All voltages at the base should relative to the emitter, not relative to GND.

20  Using Arduino / General Electronics / Re: Help! Get a signal from Arduino Uno into the computer on: September 30, 2014, 09:58:17 am
And if it's for being able to read several buttons on a computer. if you're not obligated to use an arduino, scrap an old gamepad/joystick, and wire what you want to switch to the contacts of its buttons, and then you've got a little usb device which will be easily readable (it should be easy to find how to write a program that can read joystick buttons).

This, too.

If it's just a switch that pretends to be a keypress then get a $5 keyboard and hack it open.

21  Using Arduino / General Electronics / Re: Noob Question about Transistors on: September 30, 2014, 09:07:57 am
I don't think they do . You just give some current (has a minimum) to the base and collector => emitter is open and you give no voltage (or very low) and the collector => emitter is closed .

It's very non-linear, like a diode.



Below a certain voltage, no current will flow.

When you reach a certain level, massive amounts of current will flow and the voltage doesn't really go up any more.
22  Using Arduino / General Electronics / Re: Warm water on: September 30, 2014, 08:14:44 am
http://www.ebay.com/sch/i.html?_nkw=immersion+heater+coffee

23  Using Arduino / General Electronics / Re: Noob Question about Transistors on: September 30, 2014, 07:59:22 am
Vbe for a transistor is usually fairly constant (like voltage drop across a diode).

So long as your base voltage is higher than Vbe then you're good as far as volts go.

You do have to worry about how much current is going to pass through the base - a resistor is usually needed for this.

24  Using Arduino / General Electronics / Re: Selecting a Transistor on: September 30, 2014, 07:53:27 am
Incidentally the statement "Give it as much current as possible." isn't useful.  There are
other issues to consider such as turn off time will gets slower if over-saturated.

He's using a mechanical relay...


Even if he wasn't, you seem to have deleted the part where I said "When you're using a transistor as a switch". When you're using it purely as a switch then it's usually best to err on the safe side.

25  Using Arduino / General Electronics / Re: Resistor required for PN2222A transistor base? Diode also? on: September 30, 2014, 07:51:05 am
I'm having a bit of an issue with the statement:
Quote
only there to stop too many amps coming out of the Arduino pin

That is not the *only* reason that you need to place a resistor at the base of a transistor when using it as a driver.  Please try and control your urge to oversimplify your advice.  This is how *bad* Instructables pages get started.

If only instructables would follow even simplified advice....

I have no issue with the statement that the value of the resistor is not critical, as long as it is between say 680 ohms and 4.7K ohms.  I consider those to be extremes and as you might see in many many examples... a 1K resistor is just about right as a "generic" value.

??  1k can't garantee saturation on most transistors, let alone 4.7k ohms.

eg. Here's the graph for a 2N2222, a 1k resistor won't go anywhere near the 800mA it's capable of.

Below that, the BC327. It's a similar story, the gain rapidly drops below 100 as you go towards higher currents. 1k isn't enough (unless you don't care about voltage drop/heat).

The only harm is choosing a value that's "too low" is a bit more power consumption but that's hardly applicable here.

26  Using Arduino / General Electronics / Re: Selecting a Transistor on: September 30, 2014, 06:23:59 am
Are you saying that, provided the transistor is entirely saturated, it really doesn't matter which specific NPN transistor I use, assuming that the gain is within spec?

Yep.

If so, why are there so many different (very similar) transistors available on the market?

Mostly historical reasons...

Many transistor have been around for a looooong time. Every time somebody invents a slightly better transistor they can't simply stop making the old one because people have been designing stuff using it. It just gets added to the list.

Could they reduce things to half a dozen different types? Probably. Will they ever do it? Nope.

The datasheet usually has a single line description telling you what it's best suited for:
BC549: "Low noise stages in audio frequency equipment"
BC337: "Switching and Amplifier Applications"

You're doing "switching"...

27  Using Arduino / General Electronics / Re: Selecting a Transistor on: September 30, 2014, 06:00:52 am
You don't need all that.

When you're using a transistor as a switch you should completely saturate it. Give it as much current as possible.

An Arduino pin is happy at 20mA so that means something around 220 Ohms (assuming a 5V Arduino).

Quote
So is the 549 suitable for this application?

It doesn't have a very high maximum current (only 100mA). Maybe a BC337 is better.
28  Using Arduino / General Electronics / Re: Help! Get a signal from Arduino Uno into the computer on: September 30, 2014, 04:59:27 am
Is there any possibility to do this with Uno by connecting extra stuff to it?

The Uno acts like a serial port on the PC. If you can make your stuff work with a serial port you can use an Uno, yes.

29  Using Arduino / General Electronics / Re: Resistor required for PN2222A transistor base? Diode also? on: September 30, 2014, 04:39:57 am
I've added a PN2222A NPN transistor

However, I've been told that I should add a resistor on the base connection. How do I work out what value of resistor to add?

No fancy calculations are necessary, it's only there to stop too many amps coming out of the Arduino pin. Something in the 220 to 330 Ohms range is good.

30  Using Arduino / General Electronics / Re: Help! Get a signal from Arduino Uno into the computer on: September 30, 2014, 04:25:03 am
Hi,
I'm working on a project for an exhibition were I need to make a switch to act as a key (keyboard) in the computer. I'm a total newbie and have no idea what I'm doing right now with the electronics.

The Arduino Leonardo is designed for exactly this.

http://arduino.cc/en/Reference/MouseKeyboard

All you need is a Leonardo and a switch, nothing more.
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