# How to detect signal from microwave sensor?

Started by June 20, 2010
Dear Friends

My application should detect signal that come from MicroWave cavity (the
one used in house alarm).
When people walk in front a MW, a little signal of few mV and frequency
between 10-50Hz is generated (beat signal). I should detect this!

I'm developing on ATTiny micro family. Now:
Since AtTiny have 20x amplifier buit in, which is better:

a) add 3 new bit by Oversampling and Decimation
b) amplify the signal and use the basic 10 bit ADC

The scope is understand if someone walked if front sensor. Now how I SHOULD
PROCEED??

c) Filter the signal with FIR like sen(x)/x with cut frequency = 50 Hz? If
yes, which are the minimum point I must acquire (M coefficient
http://www.dspguide.com/ch16/2.htm)

d) Calculate a FFT?

I need to understand which are the step to follow and few other detail
suggested by experience that I not have
Thanks

On 06/20/2010 02:53 PM, gpezzella wrote:
> Dear Friends > > My application should detect signal that come from MicroWave cavity (the > one used in house alarm). > When people walk in front a MW, a little signal of few mV and frequency > between 10-50Hz is generated (beat signal). I should detect this! > > I'm developing on ATTiny micro family. Now: > Since AtTiny have 20x amplifier buit in, which is better: > > a) add 3 new bit by Oversampling and Decimation > b) amplify the signal and use the basic 10 bit ADC > > The scope is understand if someone walked if front sensor. Now how I SHOULD > PROCEED?? > > c) Filter the signal with FIR like sen(x)/x with cut frequency = 50 Hz? If > yes, which are the minimum point I must acquire (M coefficient > http://www.dspguide.com/ch16/2.htm) > > d) Calculate a FFT? > > Please try to be coincise in reply because in previous thread the reply > have only add confusion.... > I need to understand which are the step to follow and few other detail > suggested by experience that I not have

gpezzella wrote:
> Dear Friends > > My application should detect signal that come from MicroWave cavity (the > one used in house alarm). > When people walk in front a MW, a little signal of few mV and frequency > between 10-50Hz is generated (beat signal). I should detect this! > I'm developing on ATTiny micro family.
All you have to do is a basic bandpass filter, rectifier and adaptive threshold. ~20 lines of C code. Or you can drop ATTiny and do the work with LM358 and few analog parts.
> Now: > Since AtTiny have 20x amplifier buit in, which is better: > > a) add 3 new bit by Oversampling and Decimation > b) amplify the signal and use the basic 10 bit ADC > > The scope is understand if someone walked if front sensor. Now how I SHOULD > PROCEED??
There are two ways to proceed: do it yourself or hire a consultant. The whole job should take a couple of hours.
> c) Filter the signal with FIR like sen(x)/x with cut frequency = 50 Hz? If > yes, which are the minimum point I must acquire (M coefficient > http://www.dspguide.com/ch16/2.htm) > d) Calculate a FFT?
General rule: don't mess with the methods that you don't understand. It is not going to help.