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NicMac  
#1 Posted : Friday, June 5, 2009 1:28:58 PM(UTC)
NicMac

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Location: Italy

Hi,
On a hobby basis I'm trying to figure out how electronics worksd'oh!
I'm doing this by buying a lot of kits (a real TPAddict as measured by the hight of boxes I have accumulated!!!), assembling them, and trying to understand how they workThink
I must be very dumb because I cannot even understand what the transistor is doing on the OTTO board.... Somebody please enlighten mePray

Thanks,
Nic

P.S. I hope that Brian's moving is over and that: AC1, Ballsie Lite, Placid will be available soonDrool

Brian Donegan  
#2 Posted : Friday, June 5, 2009 2:34:38 PM(UTC)
Brian Donegan

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To energize the coil on the relay of the OTTO, you need to provide 72.5mA @ 5VDC. The reason the OTTO has the TR input and transistor is to allow a uC or other logic level device to trigger it. Most cannot supply enough current, so we added the transistor to act as a switch to deliver full current from the supply powering the OTTO. The resistor is to limit current delivered to the base of the transistor.
NicMac  
#3 Posted : Friday, June 5, 2009 3:37:55 PM(UTC)
NicMac

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Thanks Brian,

Now I understand (at least I think so....) and look even more forward to AC1!
According to the data sheet the coil resistance of the relay in question is 69R. With 5V this yields 72.5 mA (the figures you indicated......).
If I'm not to stupid this means that I can use this relay with a switch and a 5V source without the need for a current limiting resistor. Correct?
Is this generally true for relays (i.e. that a current limiting resistor is not needed)?
A yes/yes answer would be comforting.

Thanks again,
Nic

P.S. With a retail price in Europe of around 15 euro (about 20$) for the relay alone your OTTO is a real bargain!!

Edited by user Friday, June 5, 2009 3:42:08 PM(UTC)  | Reason: Not specified

Russ White  
#4 Posted : Friday, June 5, 2009 4:16:13 PM(UTC)
Russ White

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Yes. Just connect the supply. :)
Brian Donegan  
#5 Posted : Friday, June 5, 2009 4:17:56 PM(UTC)
Brian Donegan

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Yes, the resistor is only for feeding the base of the transistor, not the relay, so if you are switching 5V directly, you don't need either the resistor or the transistor, but would need to add a little jumper on the board to get the 5V to the relay coil.

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