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Topic: DC offset (Read 284 times) previous topic - next topic

N-XIGE

I'm working with a sensor and the signals I receive are varying sinusoids. I know the arduino ideally should only work with 0-5V...so here's my problem. How do I put the DC offset?

When working with a signal generator I mostly just do that with the settings. But How do I do it with a sensor? Do I explicitly need to use a battery?

Delta_G

In order to answer that question, one would first need to know the nature of the signals from this yet unnamed sensor. 
If at first you don't succeed, up - home - sudo - enter.

KeithRB

"Sinusoids" does not equal "Half cycle less than zero volts".

N-XIGE

In order to answer that question, one would first need to know the nature of the signals from this yet unnamed sensor. 

It's a HB100 Doppler Sensor

"Sinusoids" does not equal "Half cycle less than zero volts".
Right. Well under the oscilloscope half the cycle does go below zero.

Delta_G

At this point it is up to you what kind of help you get. You can play the short answer game and we will eventually get tired of asking. Or you can decide to lay out all the details so someone can figure out what you need. It is entirely up to you. If you don't want to be verbose and are happy to struggle along then that's just fine. When you decide you really want help with this then come on back with some details. Don't be shy.
If at first you don't succeed, up - home - sudo - enter.

KeithRB

Right. Well under the oscilloscope half the cycle does go below zero.
Is the oscilloscope in DC mode?

KeithRB

The AC nature of the signal is the least of your problems. From the datasheet:

"The magnitude of the Doppler Shift is proportional to reflection of transmitted energy and is in the range of microvolts(μV)."
and
"A high gain low frequency amplifier is usually connected to the IF terminal in order to amplify
the Doppler shift to a processable level (see Annex 1)."

saximus

A very quick Google search revealed plenty of helpful websites. This one in particular goes into detail about the amplifier/filter design. It does look like you will need to offset the output but like KeithRB said, I think the offset may be the least of your problems. Maybe scrap the idea of using the module directly and spend a couple of bucks to get one a breakout board like in the link above.

KeithRB

If he really just wants the Doppler shift and the magnitude is irrelevant, he only needs to get the signal to a logic level, rectify it with a single diode and clip it  to 4.5 V or so. He can then determine the frequency from the pulses.

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