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76  Using Arduino / Motors, Mechanics, and Power / Re: Transistor/PWM problem on: March 02, 2011, 01:33:33 pm
A 470  base to ground resistor is overkill.  Lets see that the circuit is wired correctly prior to making drastic additions like that.
Say there was an output pin to base resistor already of 470 ohm to limit current into the base to 10mA ( (5-0.7Vbe)/470 = 9mA )
Now the 470 base to ground just cut that in half and likely keeps the transistor from turning on hard enough to fully drive the LED.

How many LEDs are actually in series?

Not true. 470 base to ground only takes 1.4ma max.  .7/470 =1.4ma.
You still have 7.6ma to drive the transistor. That is overkill. The Led is only going handle about 30ma steadily. The transistor is likely to have a gain around 100 or more. You only need .3ma to drive that.
Standard transistor circuit design in the old days.
77  Using Arduino / Motors, Mechanics, and Power / Re: Transistor/PWM problem on: March 02, 2011, 01:28:02 pm
I'm suggesting the 470 because it may be a very leaky transistor. That will show if it is, but only up to a 1.4ma leak.

Also here is a way to drive an led using one resistor instead of two, but only if the supply for the led is the same voltage as the supply for the Arduino.
78  Using Arduino / Motors, Mechanics, and Power / Re: Transistor/PWM problem on: March 02, 2011, 01:15:02 pm
So it's not an Arduino issue then.

If you ground the middle pin of the transistor and the LED stays on, (and assuming you have the rest of unseen circuit correct) then the transistor is bad. (Although it should not change 50 to 100%). Are you sure it's an NPN transistor?

 
79  Using Arduino / Motors, Mechanics, and Power / Re: Transistor/PWM problem on: March 02, 2011, 12:59:14 pm
I see a couple problems.
1) You need to make sure there is a ground connection from the breadboard to the Arduino board or there is no common referece for the circuit. (as MarkT mentioned)
2) For a proper transistor circuit, there should be a leakage drain resistor from the base to ground. Try a 470 ohm (1/4 watt). Usually transistors are good enough these days to do without it, but good circuits are more reliable.

To test whether the transistor is shorted, take the line going to the Arduino and and uplug it. If the LED is still on, then the transistor may be bad or very leaky. Also ground that same line. If the LED is still on, then the transistor is definitely bad.

Or you could just measure the voltage on the line to the arduino. That would tell you if it's an Arduino issue or transistor issue. But definitely connect a ground line, and make sure you have a 1/2 watt 470 ohm resistor for that LED.

One last thing. It looks like you're using a 470 ohm transistor on the base circuit. That means the Arduino will be driving about 10ma at the max. If that's the case, then why not just drive the LED directly with the Arduino (as Crossroads suggested)? You probabbly want more like a 4.7K resistor there (not that this would cause your symptom).
80  Using Arduino / Microcontrollers / Re: Using empty UNO board to program external ATmega328 on: March 01, 2011, 11:14:21 pm
Thanks for the reply.
Well, that is good news.

Also, I should mention in case anyone tries it...

If the UNO is unplugged from the computer, it has no power on it and tends to drag down the reset line, even with a 10k pull up on the Atmega328's reset pin, so I had to disconnect the reset line from the UNO to get the breadboard circuit working when the UNO is powered off.

It may even require powering off the ATmega328's circuit to get the reset to work again... not sure why, just something I noticed.
81  Using Arduino / Microcontrollers / Using empty UNO board to program external ATmega328 on: March 01, 2011, 10:17:02 pm
I wasn't sure if this could be done, but apparently it can.

I pulled the atmega328 out of the UNO board. Put it into a circuit on a breadboard (with crystal and two caps) to drive a stepper motor circuit. Then I jumpered the reset pin on the ATmega328 to the reset pin on the UNO. I also jumpered the RX pin and TX pin similarly. Finally I also jumpered a ground to ground in the same way.

I did not use D0 or D1, so there was no conflict with external circuitry on those pins. The ATmega328 is powered externally at 5v and the UNO board is powered through the USB cable.

I was able to upload sketches just as if the ATmega328 was still in the UNO and it ran great. It never failed to upload new sketches or run them.

My question is, can I rely on this method, or is there a potential conflict between the UNO's crystal clock and the ATmega chip's external crystal clock?  In other words, if the two clocks were to be too far off in frequency, would longer sketches possibly fail to upload correctly?
82  Using Arduino / Programming Questions / Re: For Loop question on: February 26, 2011, 11:40:37 pm
Yup, just found that out.  Thanks.

I was deleting it while you responded.
83  Using Arduino / Programming Questions / For Loop question on: February 26, 2011, 11:32:17 pm
nevermind
84  Using Arduino / Installation & Troubleshooting / Re: Uno does not work with Windows 2000 ? on: February 26, 2011, 11:15:35 pm
Well, it works fine in XP, so I guess it is not compatible with Win2k.
85  Using Arduino / Installation & Troubleshooting / Uno does not work with Windows 2000 ? on: February 23, 2011, 08:47:59 pm
I searched, and the only topic I could find had no resolution to the problem. 
I also went through the troubleshooting guide.
I installed the driver as directed.
My laptop identifies the arduino Uno on Com 5 in the device manager.
The arduino environment shows the Uno is connected to Com 5.
The Uno is the board that is selected.
The upload begins to work.
I get Rx and Tx lights on the Uno.
Then I get a few error messages like:
avrdude: stk500_getparm(): (a) protocol error, expect=0x14, resp = 0x41

Then at the end it says: use -F to override this check.
-F and do what with it?

The Uno's yellow LED stops blinking and stays on solid.

I would have posted in the original thread, but it is now read-only.
Thanks,
Lou
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