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Topic: I need help selecting a transistor (Read 11806 times) previous topic - next topic

PaulRB


I do have colons and I'm just going to keep them on the entire time. pin 12 to 5V and 4 to 0V.

There are a couple of spare pins on the '328, you could wire them up to one of those. Don't forget you won't be multiplexing the colon that way, so use a higher series resistor, or they will appear too bright.


1) pc6(reset) get's 5v, why is that? What exactly is this pin doing?

That pin, on an Arduino like an Uno, has a pull-up resistor to 5V and the reset switch connects it to 0V.  As your circuit won't have a reset switch, you need to connect it to 5V to allow the '328 to run your sketch.


2)A lot of transistors suggest here all have gain on them and I believe you can buy them without having any gain at all. Would that not be advantageous for me as I don't really need to amplify anything as the BC337's do.

Yes, you do. You need to amplify a small current (~2mA) up to 160mA to drive a whole digit.

Paul__B


I do have colons and I'm just going to keep them on the entire time. pin 12 to 5V and 4 to 0V.

Bad idea.  You certainly would need a resistor, but as you have unused connections on the MAX7219, it makes far more sense to use them as PaulRB has indicated.  No resistor required and you only have to set a bit in the patterns you load to the MAX7219.  And you may change your mind and want to do something with the colon later.  The beauty of software control is that you can change things.


A lot of transistors suggest here all have gain on them and I believe you can buy them without having any gain at all. Would that not be advantageous for me as I don't really need to amplify anything as the BC337's do.

Nonsense!  Transistors are used in order to provide gain; they would be useless otherwise.  Whilst they do not provide voltage gain as emitter followers, the whole purpose is to amplify the current - and as much as possible.


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