# Sq Wave Unipolar to Bi-Polar

#### evolive

Joined Jun 1, 2004
2
Hello,

I am looking for a way or IC that will take my Square Wave that has only positive amplitude and convert it so that it'll have a negative and positive amplitdue.

Is there a chip taht does that for me?

Thank you.

here's a picture of what i like to do...

#### beenthere

Joined Apr 20, 2004
15,819
Hi Evolive,

Yep, it's an op amp. If your square wave isn't too fast or of too great an amplitude (we really need parameters for a good answer), the the attached circuit will do the trick.

Any old op amp will probably do, from 741 up. It has to have + and - voltage supplies, though. The circuit is an inverter with an offset adjustment. It will work with a square wave input of up to about 10 volts. If the offset is not enough to equalize excursions, then make R3 smaller for more offset.

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#### evolive

Joined Jun 1, 2004
2
Originally posted by beenthere@Jun 1 2004, 09:19 PM
Hi Evolive,

Yep, it's an op amp. If your square wave isn't too fast or of too great an amplitude (we really need parameters for a good answer), the the attached circuit will do the trick.

Any old op amp will probably do, from 741 up. It has to have + and - voltage supplies, though. The circuit is an inverter with an offset adjustment. It will work with a square wave input of up to about 10 volts. If the offset is not enough to equalize excursions, then make R3 smaller for more offset.
Hello,

THANK YOU for the ckt... i'll give it a try...

well.. as for specs...

we ran the motor and it went up to 5000rpm... so... umm.. that would be.. 4000hz (it has 48 teeth)

we also saw an amplitude of +7V

===============
Frequency: at least up to 4400Hz (~5500RPM)
Amplitude: ~ +7V
Wave: Digital Squarewave
===============

I think that's all the spec you need...

but here's a link to the hall-effect sensor and also the f-v converter chip in case ur wondering

Hall-Effect Sensor - Geartooth Sensor (note the output signal, it only has a postive amplitude and has an d/a converter built-in)

NTE995 - Frequency-to-Voltage Converter (equivalent to lm2917)
http://www.nteinc.com/specs/900to999/pdf/nte995.pdf

#### bipin

Joined Mar 21, 2004
80
Hi,
The circuit given by beenthere is a good one.
At the same time the easiest way is to connect a 1uF capacitor in series and take the O/p. You will get a bi-polar square wave from your uni-polar square wave. if there comes a distoriton just increase the value of the capacitor.
best of luck
bipin

#### beenthere

Joined Apr 20, 2004
15,819
Hi Evolive,

There's another way out. Your Hall effect sensor probably has one leg to ground, and another to a +12 VDC source. You can keep the relative voltage difference and get the bipolar output if you can arrange to have the sensor tie to +/- 6VDC.

For that matter, your F -> V converter will probably be happy if you just pass the unipolar square wave through a capacitor at its input. I think the spec is that the signal has to cross zero, but does not have to be symmetrical in the excursion. At 4800 Hz, something between 1uF and .1uF should do the trick. Check the national Semi site for some application data.