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[...] I have a reed relay that is 12V. The coil resistance is 1050. That would pass a current of about 12mA. If that relay is using an external 12V supply do I need a resistor to run this relay?
Is the reason that I need a transistor is because the stamp cant generate the 12v for the relay even though the relay is connected to an external 12V battery?
So, in a nutshell, i could hook the relay up with an external 12v supply, add a resistor to a pin, set the pin to high and i should not have any problem with it frying the stamp?
GearMotion,Thanks for the reply. I know that the diagram that you referred to would work. I guess I am just trying to understand why/when you would need a transistor. Isn't it true that the relay at 12V and the stamp at 5V are seperate. I have a stamp that is on a seperate power supply than the relay. So at 5V regulated the stamp can put out 20mA. So, knowing that, WHY would I need a transistor when the relay only needs ~11mA across the coil? Again 5V/1050= ~11mA.
My base question is with the info that I gave about the relay, 12V, 1050 resistance coil, WHY would I need a transistor?
Electronics is an engineering discipline and we use mathematical "tools" for most of the work. Statements like "a transistor is a switch" is a great proof that the one answering you haven't even got the basics down on the simplest active component in existence, so you might not wanna take everything from that direction as Gospel...My "religion" is exact knowledge and what follows from that, but you decide which "religion" you will follow of course.Btw. If you need my background for evaluating my posts: I'm not a 12 year old kid who thinks building 2-wheeled mini-'bots of others design gives me street cred, but a seasoned electronics engineer who actually designs 'bots (and other stuff).
Thank you for the information. Don't fear that I won't understand it. I did. I actually got that information the other day. Also, I am not a 12 year old kid. i am a programmer that wanted to venture into other areas. So, again, thanks for your help.