From: forgetthismailbox@gmail.com   
      
   Hello, amdx!   
      
   On Mon, 10 Feb 2020 09:39:54 -0600   
   amdx  wrote:   
      
   > >   
   > > Ok, I boobed by putting x2 incorrect resistors. Doh!!!   
   > > I used x2 47k resistors in error and have changed them to the 10k   
   > > resistors.   
   >   
   >   Those are just a voltage divider, setting the voltage on Pin 2. I   
   > suspect you could you could use a resistor value up to 500K and have   
   > little change in the voltage on Pin 2.   
   >    I found the input resistance of a 741 is 2Mohm, so, I did the   
   > calculations, if you use two 10k resistors and the voltage at Pin 2 is   
   > 4.5v, changing them to 500k will only shift that voltage by 0.5v.   
   > It would raise Pin 2 to 5v.   
   >   (Side no, there may be different style 741s, with different input   
   > impedance, I don't know.)   
   >   
      
   It's not a good idea to set huge resistance on high-impedance imput:   
   AMP can receive radio noise on input. 10K is enough normal resistance, I   
   think. With R1 and R2 47K it should work too, but I do not prefer such   
   resistance: too high in high-impedance input. It looks like that there   
   was a problem with badly connected R2, because when leds are off voltage   
   on pin 3 should be below ~6V (voltage on point A), but he had:   
   >> The voltage on pin 3 is 10.2 when Lo, but does fluctuate upto 10.5v   
   >> approx, and when Hi the voltage is 10.6v, and again does fluctuate upto   
   >> 10.9v.   
      
      
      
   ------   
   With Best Regards,   
   Evgeniy Shtrenyov   
      
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