Piezospeaker Amplifier & Volume Control

MichelB

Hi, how do I connect 4 of LM358 with -9V if I use a Parallax wall-mount supply 9V? I suppose that 8 is connected with Vin of Board of Education. Thank you in advance. MichelB

Mike Green

There is no negative supply voltage available. The LM358 can be operated with only a positive supply. Connect pin 8 to Vin and pin 4 to ground (Vss). The datasheet (from National Semiconductor) has several examples of "single-ended" use (with only a positive supply). Remember that your 9V wall wart may be noisy and you may need some extra filtering for the LM358. Try it first. You can always add a 220uF to 470uF 16V electrolytic across the 9V supply near the LM358 if you need it. Don't forget a 0.1uF ceramic capacitor close to the LM358 across the supply leads.

MichelB

Thank you very much Mike (it's the 3d time you reply for me), I'll try what you wrote. Best regards. MichelB

Chris Savage

The LM358 can be used with a dual-supply system…the part from National up to +/- 16V, but I think the OP is referring to Andy’s article on the subject at the following link. The answer to your question is that using a wall-adapter you really can’t generate the -9V. You would need a dual-supply referencing the same ground for this to work.

http://forums.parallax.com/showthread.php?p=517152

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Chris Savage
Parallax Engineering