OUTPUTS (J3): These outputs are programmed as active low output. They are held at 13V and fall to 0Vwhen active, it can source or sink 10mA.These outputs would normally be connected directly to the input channels of wire in type communicators.Alternatively each output can be used to drive a relay (coil resistance > 1200 Ohms) connected between theoutput terminal and the 13V supply terminal. The relay will energise when the output port operates. It isrecommended that a back EMF protection diode is used in parallel with the relay coil.
Looking at the optocouplers datasheet http://www.fairchildsemi.com/ds/MO/MOCD207M.pdf a forward voltage of around 1.4v @ 30mA is suggested. Should I use a 390R resistor to drop from 13v? The alarm manual says the outputs can source or sink 10mA so would 30mA flowing into them overload them? Or should I try and limit the current to 10mA and hope it is enough for the optocouplers - I can't see the minimum current in the MOCD207M datasheet?Thanks!
So that's 13V -1,25V = 11,75 / 0,03 = 391So yes, 390 Ohms are perfect ;-)// Per.
Hi, thanks for the reply's.Thanks for the detailed advice Lefty! I will try that Should I use resistors on the arduino digital pins also? If it is written HIGH via the internal pull ups and I ground the pins, how much current would flow? I know the pins supply about 30mA but how much would it sink?No need for any external resistors for the digital input pins. The internal pullups are like 40K to 50K ohms, so very little current flows when the output transistor of the opto conducts to ground.Output pins can sink current to an external circuit when they are commanded to a LOW state and can source current to an external circuit when commanded to a HIGH state. But an input pin is just a very high (many megohm) input sensing pin that draws no current to speak of from what ever is supplying voltage to the pin.So lesson here is that output pins and input pins are two totally different animals on a arduino board. Most of the rules and limits for output pins are different then the rules for input pins, but both do have rules and limits of course.Apparently the 13V output from the alarm can supply up to 200mA so I plan to run the arduino & ethernet shield from that. Would you simply run 13V into the Vin or step it down first?I suspect not as ethernet boards are somewhat current hungry as I recall, but don't know directly. The basic Uno type arduino board draws about 50ma, so add that to whatever the ethernet shield requires plus anything else you are wiring to the arduino board like leds, etc and see what the total works out to. Thanks!
Quote from: Zapro on Jan 06, 2013, 02:43 amSo that's 13V -1,25V = 11,75 / 0,03 = 391So yes, 390 Ohms are perfect ;-)// Per. No it's not, it will burn up the output pin of the alarm module that has a 10ma maximum rating.