Photo organ LM324
Electronic

We often hear electronic organs played on different occasions, but have you ever heard of a "photo organ"?

That's what we're going to build in this project. It's an original musical instrument that can produce different tunes according to the amount of light received by the CdS cell, and has a wide coverage of about three octaves.

The schematic lets you see that the DC current amplified by U1:A is carried to the U1:B, the integrating circuit, and U1:C oscillates a square wave according to the input voltage.

This output from U1:C is amplified by Q5 and activates the speaker. Q1 and Q3 are used to prevent the speaker from emitting a sound when the organ is not being played.

When you finish assembling the circuit, turn power ON and set the control volume in a position where the sound dies away when the CdS cell is exposed to the light.

Now shut off the light coming to the CdS cell with your finger, and the organ starts playing and changes its tune as you move your finger. Try playing your favorite tune by adjusting your finger position over the CdS cell.

Bill Of Materials For Photo organ
23 Resistors
	Quantity:		References		Value
	2		R1, R19		33k
	4		R2, R4, R14, R16		10k
	5		R3, R6, R11, R17, R23		100k
	2		R5, R20		220k
	5		R7-R10, R15		47k
	1		R12		4K7
	2		R13, R21		22k
	1		R18		100
	1		R22		470k
3 Capacitors
	Quantity:		References		Value
	1		C1		10uF
	1		C2		0.01uF
	1		C3		3.3uF
1 Integrated Circuits
	Quantity:		References		Value
	1		U1		LM324
5 Transistors
	Quantity:		References		Value
	4		Q1, Q2, Q4, Q5		2SC945
	1		Q3		2N5401
2 Diodes
	Quantity:		References		Value
	2		D1, D2		1N4148
7 Miscellaneous
	Quantity:		References		Value
	1		-		4.5V
	1		AUDIO		800 ohms : 8 ohms
	1		BAT1		3V
	1		CDS		LDR
	1		LS1		SPEAKER
	1		ON		OFF
	1		RV1		50k