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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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 17 Nov 2006 15:54 amplitude comparator |
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I don't know if the name is right but here is my where I rush.
I got 2 sinusoidal signal, on the fisrt one (yellow) it is my oscillator. see TEK008
The seconde one is my antenna (blue). At is normal fonction the signal goes like the (TEK009)picture when somthing is approching the antenna the signal change and appeir like the (TEK010)picture. I want to compare the two ( amplitude ) of these signal
Last edited by sec on 17 Nov 2006 16:15; edited 1 time in total |
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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17 Nov 2006 15:57 Re: amplitude comparator |
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maybe firstly demodulate the blue signal. so I'll got a clear sinusodal signal.
this is the circuit. does anybody got link for analog divider ?
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ionp
Joined: 26 May 2006
Posts: 39
Helped: 4
Location: USA
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17 Nov 2006 23:10 Re: amplitude comparator |
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The blue waveform looks to me like 60Hz pickup on the antenna is adding to the oscillator signal.
You may not need the oscillator running at all to pick up 60Hz when someone gets close to your antenna, as they may be coupling this in from house wiring.
You can keep the antenna at a high impedance for 60Hz, band pass filter for 60 Hz, and then diode detect to get a varying level as someone gets close. Then, a standard comparator or opamp can switch when a threshold is exceeded.
Is this supposed to be a people detector?
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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18 Nov 2006 4:12 Re: amplitude comparator |
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yes it is a 60 Hz freqency, and yes, it suppose to be a "pedal" and detect the proximity of a foot. With a foot action the output voltage should change!
Added after 3 minutes:
the filter should be passive to not affect the antenna or it dosen't matter ?
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ionp
Joined: 26 May 2006
Posts: 39
Helped: 4
Location: USA
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18 Nov 2006 16:53 Re: amplitude comparator |
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It doesn't matter if the filter is active or passive.
The 60Hz coupled into your antenna will be very weak, so it is important that you keep your connection high impedace, so as to not load it down.
Perhaps an opamp buffer stage at the antenna, and a 10 meg ohm resistor to keep the averave DC on the antenna within tha opamp power supply rails.
You could probably get it to work without much filtering, except to keep your oscillator signal out of the opamp.
Is the oscillator performing some other purpose, or do you perhaps not need it any longer?
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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19 Nov 2006 3:31 Re: amplitude comparator |
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no, I don't need the oscillator anymore. but it was a proximity detector that I find on the internet, and I see that it is not what I needed. here a view of my new circuit. what modification should I do, I want a better gain ? The output is about 2V pk-pk when it is at is "highest point". Ok I got from my scope a picture, hope this will help you tu understand my probleme. I think tthe transistor act as a diode rectifier, this cause the wave form of the 60Hz signal.
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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19 Nov 2006 3:57 Re: amplitude comparator |
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| oops I forgot to show you the signal when there nothing around ... well I'm sure that you can see it in your head, it is just ripple, like when the signal=0v on my scope capture. The ripple is mostly create by my scope. Does anybody know about analog latch, I would like to latch a the peak of the frequency
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19 Nov 2006 3:57 Ads |
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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19 Nov 2006 16:14 Re: amplitude comparator |
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I'm approching the end of my project, here some news. the signal is clearer and more linear, only the pusle width change .... and I don't need anymore an analog latch, I need a converter from pulse width to voltage. I need some idea or link to internet site.
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ionp
Joined: 26 May 2006
Posts: 39
Helped: 4
Location: USA
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19 Nov 2006 21:45 Re: amplitude comparator |
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How about a series diode followed by a shunt RC?
This peak detector should help smooth your output, and you can juggle the R and C values to get it to hold to your liking. Perhaps start with a time constant of 1/10 second, using a 100K resistor and a 1uF capacitor.
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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19 Nov 2006 22:10 Re: amplitude comparator |
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| can you show me, I don't see what you mean ??
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ionp
Joined: 26 May 2006
Posts: 39
Helped: 4
Location: USA
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20 Nov 2006 2:14 Re: amplitude comparator |
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Something like this.
The diode takes your pulse train into the pulse input on the left, and removes the flutter of pulses yielding one long pulse on the output, to the right. When the pulse train stops, the output will drop a short time later.
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sec
Joined: 08 Aug 2006
Posts: 98
Location: Canada,QC
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06 Feb 2007 2:53 Re: amplitude comparator |
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For those who are interest in proximity detector here a brand new version. The antenna act as a capacitor, with change the frequency. The older version was attenuate is the person was in contact with a ground, not this one ! R and C can be change !
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