Beginner question
#1
Posted 20 December 2012 - 04:49 PM
#2
Posted 20 December 2012 - 06:41 PM
#3
Posted 21 December 2012 - 01:16 AM
Thanks. I was assuming 200mA for vdd/vss but wasn't entirely sure. Still making my way through the basics.yes you can use that from pin21.
i use: random pin -> resistor (2kohm) -> transistor (bc 547/557) -> stuff.
so nothing will burn and the led or whatever gets all the current it needs
#4
Posted 21 December 2012 - 06:42 AM
#5
Posted 21 December 2012 - 07:27 AM
Welcome to the forums!
There is a wiki page by CW2 giving current limits for the family.
He has a figure of 800mA for the DC output. This is a lot, and you should note this is a maximum, and that the regulator on the board will get hot (especially it you have a higher suply voltage).
Again refering to CW2's page, there are infact two pins on the mini that can drive up to 16mA. You could use these without a transistor, but will still require a resistor.
Asuming the LED has aforward voltage of say 2V:
R = V / I = (3.3 - 2) / 0.015 = 86 ohms
Since resistors come in "preferred values", go for the next highest value - 91ohms.
I was going to post a link to a table of resistor values, but Android has decided to drop my cut and paste ability mid post.
Do a google search for "resistor prefered values"
Hope this all helps - Paul
#6
Posted 01 January 2013 - 08:12 PM
Just for passing noobies,
"i use: random pin -> resistor (2kohm) -> transistor (bc 547/557) -> stuff."
works great, but will logically invert the signal.
ie
myStuff.Write(1) will give 0V
and
myStuff.Write(0) will give 3.3/5V
bear it in mind!
#7
Posted 01 January 2013 - 09:39 PM
i do it the same way, good thing of not blowing something up
theoretically you can connect the transistors different so its no more inverted, but i also go the standard way. (inverting)
#8
Posted 05 January 2013 - 03:45 PM
Thanks for the info. I'm avoiding the vdd/vss/io pins altogether now and simply using a direct connection to the battery. I wound up using all the i/o ports anyways.
#9
Posted 20 March 2013 - 02:04 AM
By the way...
The Basic Stamp 2 (BS2) can source/sink 20/25mA per PIO pin.. but only 40/50mA TOTAL (for 8 I/O pins) (per BS2).
The AT91SAM7X512 can only source 8mA per PIO pin.. but 200mA TOTAL.
Tom
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