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Forcing a line down

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ericgibbs

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hi,
I think I follow your description of the circuit, but if you show us how you have the res/LED/Transistor connected to the pin, with a simple diagram, that would help us.
 

audioguru

Well-Known Member
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A tiny BCR148 transistor has a built-in 47k resistor in series with its base. For it to saturate with a 0.1V loss then the input to the resistor must be at least 47V or the resistor value must be reduced to 4.3k or less when powered from 5V.
 

Nigel Goodwin

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Most Helpful Member
Scarr said:
Hi all,

Thanks for the help so far

EricGibbs, I have attached a quick circuit (just hope I got it right!)

Nigel, Do you know of a small Ateml part of the top of your head that has a open drain pin? reason I ask is my compiler is for Atmel parts, I probably could port it but if we find the correct transistor might not be worth the hassle. and to trawl throught all the PDF's would take ages.
Sorry, I don't use Atmel processors - but they may well have an open-collector part?, they copied everything else from MicroChip :D

Auido Guru, your suggesting it's the transistor I'm using thats at fault and with my limited knowledge I can see why (however I originally thought it was due to limitations of the transistor) can you sugest a replacment?
Just use a normal NPN transistor, like a BC148, and add an external base feed resistor.
 
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