|Created||July 20, 2013|
|Last modified||July 20, 2013|
Crude linear or log signal amplitude to LED brightness conversion.
Assuming Audio outputs are low impedance (< 1k) then if audio signal is at approx 0V with zero signal then V(base) = Q2 Vbe above 0V i.e. approx 0.6V.
Hence Q2 wired as diode cancels Q1 Vbe drop.
Therefore even small signal swings above ground that are << Q1 Vbe, start to turn Q1 on.
Q1 acts as voltage to current converter with: iLED = V(base)/R2
Remembering that V(base) is V(in) + Vbe then V(emitter) is approximately equal to V(in).
Thus LED brightness is approximately linearly related to audio amplitude.
For linear amplitude to brightness conversion, R3 = 0R (i.e. it's a piece of wire!).
Note that perceived brightness is on a roughly log scale so linear actual brightness may not be the best way to represent the signal amplitude.
For a very crude log scale conversion, set R2 = 0 and R3 = 100R.
Simulate > DC Sweep > Run DC Sweep
Simulate > Time Domain > Run Time-Domain Simulation
No comments yet. Be the first!
Only the circuit's creator can access stored revision history.