3 Channel Spectrum Analyzer

This 3 channel 15 LED spectrum analyzer is the perfect addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. The circuit will take line level output from most any audio source, and operates on 12V DC. This means that it can even be run in a car.

Parts
R1                                            (1) 100K 1/4W Resistor
R2                                            (1) 820K 1/4W Resistor
R3, R14, R16, R18                    (4) 2.2 Meg 1/4W Resistor
R4, R5, R6                               (3) 22K Pot
R7,R8,R9,R25,R27 R29            (6)10K 1/4W Resistor
R10, R11, R12                         (3) 680 Ohm 1/4W Resistor
R13. R15, R17                         (3) 580K 1/4W Resistor
R19, R20, R21                         (3) 39K 1/4W Resistor
R22, R23, R24                         (3) 47K 1/4W Resistor
R26, R28, R30                         (3) 33 Ohm 1/4W Resistor
C1, C5, C6                               (3) 0.012uF Polystyrene Capacitor
C2, C9, C10, C11                     (4) 3.3uF Electrolytic Capacitor
C3, C4                                    (2)0.0022uF Polystyrene Capacitor
C7, C8                                    (2)47nF Polystyrene Capacitor
C12, C13, C14                        (3)0.47uF Electrolytic Capacitor
C15, C16, C17                        (3)22uF Electrolytic Capacitor
D1, D2, D3                             (3)1N4002 Silicon Diode
D4, D5, D6, D8, D8                 (5)Green LED
D10,D11,D12,D13,D14            (5)Amber LED
D16,D17,D18,D19,D20            (5)Red LED
U1                                         (1)LM3900 Quad Op Amp
U2, U3, U4                             (3)AN6884 Bar Graph IC
MISC                                     (1)Board, Wires, Sockets For ICs




Notes

1. The circuit expects line level inputs. If you connect it to speaker level, you will have to readjust the circuit every time you change the volume.
2. After the circuit is connected, apply power and signal. Now adjust the pots until the corresponding group of LEDs reacts.
3. Thanks to Alterac for correcting some errors on the schematic that originally appeared on this page. Read all about it in the 3 Channel Spectrum Analyzer Project thread in the forum.

 source