Step 7: Variations 3
With a small sacrifice in sensitivity, we can substitute an NPN transistor for the LM431. Use the same process as above to calcuate LEDs supported.
Choose an audio-frequency transistor with a high beta (gain) of 150 or more. 2N4401, BC337 are good choices. Also acceptable are 2N2222 and 2N3906. Otherwise, check the datasheet for a device that:
is NPN
has a gain (beta) of 150-500
can handle 500mW or more
can handle 150mA or more
Voltage 50% higher than the Supply
R1 = 50-100ohm (Bright)
R2 = 100k - 390k (Sensitivity)
C = 0.1 to 1 uF. Negative side to music output.
Choose an audio-frequency transistor with a high beta (gain) of 150 or more. 2N4401, BC337 are good choices. Also acceptable are 2N2222 and 2N3906. Otherwise, check the datasheet for a device that:
is NPN
has a gain (beta) of 150-500
can handle 500mW or more
can handle 150mA or more
Voltage 50% higher than the Supply
R1 = 50-100ohm (Bright)
R2 = 100k - 390k (Sensitivity)
C = 0.1 to 1 uF. Negative side to music output.
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