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LM 3914

ebee
Hello,

anyone into electronics to help me (I have some suspects).


I am having trouble with LM 3914/5/6

I get the current program of LEDs by making path to ground 0V from Pin 7.

Pins 7 & 8 give use approx 1.25 volt ref

It`s the pin 6 & pin 4 Rhi and Rlo bits in order to get values of other than the supply lines.

i.e if we put in two resistors R1 & R2 from pin 7 to 0V and calculate the voltage at the junction then we could use this as a hi or low I think but what about the other (to get a hi and a lo) .


Then methinks factor in the internal comparitor divider chain into these figures to see if a significant variation occours .


I initially want to prog my LEDs to say 10 or maybe 15mA current and the hi and low volt comparisons say 1.8v to 4.0v.

Thanks
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  • 0
    Ha two first line suspects answered already, thanks guys.


    Yes Mapj I already know that. It`s just adjusting my head around it is the problem

    Truth is, about 30 years ago I built a gadget for some plumbng heating bods for checking gas valve solenoids but me poor heed has got older and more cluttered and worn out since. I think I`d be ok setting the high by calculating current thru resistors it`s just starting at non zero that`s giving me a headache.


    AJJ, Yes thanks I have the data sheet it`s just following it.


    I will make a sketch to let you know what I`m thinking and you`d probably spot where I`m wrong (or right even) .

    Cheers guys.
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  • 0
    Ha two first line suspects answered already, thanks guys.


    Yes Mapj I already know that. It`s just adjusting my head around it is the problem

    Truth is, about 30 years ago I built a gadget for some plumbng heating bods for checking gas valve solenoids but me poor heed has got older and more cluttered and worn out since. I think I`d be ok setting the high by calculating current thru resistors it`s just starting at non zero that`s giving me a headache.


    AJJ, Yes thanks I have the data sheet it`s just following it.


    I will make a sketch to let you know what I`m thinking and you`d probably spot where I`m wrong (or right even) .

    Cheers guys.
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