Sine wave

leto · Joined: 02 Aug 2005 Posts: 14

Hi,

I have made a sine wave from a PIC16F628 and a DAC0808. My problem is that it is (0-5V) range sine wave and I need an AC sine wave (-2.5v, +2.5v).

Im trying to test the inductive properties on a coil, so I need an AC input. May be using an oamp or something but i dont know how connect it.

I have a simetric power supply +5v -5v.

Thanks for your help.

Leto.

rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

Use a summing configuration and add a -2.5V to your 0-5V sinewave.

Go to the National Semiconductor web site and look at their amplifier application notes. There is one that give basic application circuits.

Also, Google for "op-amp tutorial". This one is very goodhttp://homepage.mac.com/tbitson/weather/TI_OpAmp_Tutorial.pdf and is also available from the TI web site.
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Or you may be able to couple your 0V-5V sinewave through a large capacitor. The capacitor will block the average DC level, letting the AC go to the coil. Use a large electrolytic cap with the + terminal to the DAC and the - terminal to the coil.
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rwyoung · Joined: 12 Nov 2003 Posts: 563 Location: Lawrence, KS USA

Gonna have a hard time driving an inductive load through a capacitor. It will be somewhat difficult through a jellybean op-amp too. If you have much inductance at all you might want to consider the op-amps and buffers from Apex intended for direct drive of small DC motors.
_________________
Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

It all depends on what type of inductor he is measuring and what he wants to measure about it. He will need some series impedance or another way to monitor the current. As long as the capacitive reactance is very small compared to the inductive reactance the capacitor shouldn't add any new difficulties.

Leto, tell us more about the application.
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Eugeneo · Joined: 30 Aug 2005 Posts: 155 Location: Calgary, AB

You may consider using a simple H bridge driver, I've ran into the same problem building a flame detector.