Subject: RE: [stella] Current for Port Output From: "patrick lichty" <voyd@xxxxxxxx> Date: Wed, 29 Sep 2004 17:41:58 -0400 |
All right! Now here's a subject where I'm not lagging the crowd. OK< here we go. First, there are technical concerns, and pragmatic ones. In the 70's most circuits were operating on what's called TTL logic. That's where you get the whole 5v thing. What I see coming out of the port is a logic level (5v) that's enough to drive something like a pin set up as a serial port on a Stamp or a PIC processor. However, in being able to sink 1.6 mA, I don't recommend driving an LED with it. In 1985, I networked 2 Atari 800's though their serial ports, and it worked fine, but to drive anything other than a logic level, I needed to throw it through a transistor driver, a 7406 buffer, or something that could drive more than 5-6 mA. And, considering that the new white LEDs have forward voltages of up to 3V @ 20 MA, that's a hell of a lot of power. (Currentxvoltage=power, therefore the white LED's pulling 60mW, while a red LED[1.7 Forward Voltage, 12ma current would draw 20mW) The Riot's port can only handle about 9 mA. You can probably find an LED to run from there, but you'll probably bake it eventually. Pragmatically, we're talking about 20+year-old electronics! Why stress them out? Slap a buffer on there, and give them a break! It's not tough. Just make sure you have the right resistor on the LED to limit the current. Patrick Lichty Editor-In-Chief Intelligent Agent Magazine http://www.intelligentagent.com 1556 Clough Street, #28 Bowling Green, OH 43402 225 288 5813 voyd@xxxxxxxx "It is better to die on your feet than to live on your knees." -----Original Message----- From: Paul Slocum [mailto:paul@xxxxxxxxxxxx] Sent: Wednesday, September 29, 2004 10:29 AM To: stella@xxxxxxxxxxxxxxxxxx Subject: Re: [stella] Current for Port Output > From the RIOT datasheet: > >Output High Current (Sourcing): -100 uA >Output Low Current (Sinking): 1.6 mA > > >Is that what you mean? I don't think so, but not totally sure what those values mean. My EE knowledge is pretty limited. I'm wondering how much current it can drive. I know they were thinking of using it to operate an LED, so I'm assuming it can drive at least 20mA or so? -paul Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://stella.biglist.com --+---------------------------------------------------------------- You are subscribed as: voyd@xxxxxxxx To unsubscribe, send email to: stella-unsub-152035@xxxxxxxxxxxxxxxxxx Or go to: http://stella.biglist.com/unsub/stella/voyd@xxxxxxxx --+--
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