## Learning the Art of Electronics, Week 2

[latexpage] 2L1.1 Ok, I form a simple low pass filter using unknown RC values. Then I measure time constant using scope and 500Hz square wave. Time constant is a time it takes for a voltage to reach ~63% of its total value. Measured time constant using RIGOL DS1054z is 0.268ms ( measured using manual cursors: I set Percent for Vert. Units, then Set range of the wave with vertical cursors and then measure time to rise to ~63% (bx-by) ) Measured time constant using Tektronix 2221A is 0.270ms ( I position the wave from 0 to 100% and then using cursors get ▲T for ▲V to reach 63.2% ) t = RC Now I need to find R. And task is to measure R without removing C. We can do that by imagining that RC is just R, but we have to eliminate XC. We can do that by increasing frequency unti we get no phase shift. The higher the frequency the less XC there is. We can see that XC is not effective anymore when we see no more phase shift. I add a known 1K resistor in front of RC filter. Apply sine wave and increase frequency…