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Author Topic: Read A/D avr values in noisy enviroments  (Read 4116 times)
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Vineyards
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« Reply #25 on: June 04, 2015, 02:24:17 02:24 »

Are you talking about snubber diodes? A LP filter does averaging anyway. In my opinion, there is not a magical solution that answers all the questions. As I wrote before, it depends on signal characteristics environment etc.

For example, diodes are leaky components. They will effectively short a High Z signal if they are used as clamp etc. You need a buffer but then how will you protect the buffer. If it is an opamp you could put resistors on the input and if it is a voltage follower you could place a resistor between  non-inverting input and output rather than shorting these two. This way you could prevent excessive current flow through that component.

Posted on: June 04, 2015, 09:22:31 09:22 - Automerged

If problems persist, you need to galvanically isolate input from the rest of the circuit and the known methods for that are optical, inductive, capacitive isolation (ic's) as well as V/F, F/V converters.
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Vineyards
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« Reply #26 on: June 04, 2015, 06:23:09 06:23 »

Check out this link. There you can choose an opamp and see if it will work within desired voltage levels: http://analogplayground.com/diamond/
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2N5109
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« Reply #27 on: October 26, 2015, 08:24:38 20:24 »

Put 100uF capacitor across ntc 4.7k resistor. The noise is driving the ADC nonlinear so DSP filtering is not effective. Also need to determine if magnetic or electric field of AC 60 Hz is being pickupped. Could try metal shield around resistor+avr.
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kreutz
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« Reply #28 on: October 27, 2015, 09:11:58 09:11 »

The complete DSP book (2nd Edition), mentioned early in the thread,  is in here:
 
http://ft-sipil.unila.ac.id/dbooks/The%20Scientist%20and%20Engineer's%20Guide%20to%20Digital%20Signal%20Process.pdf
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2N5109
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« Reply #29 on: December 01, 2015, 08:21:57 20:21 »

Current in 220v AC circuit is probably relatively high and coupling voltage into ADC input via its magnetic field and flux, v=-d(phi)/dt.  We need to know more about circuit arrangement. At low frequencies of 50 Hz, conductive shielding is not effective against magnetic fields, and probably interferes with whatever temperature measurement you make.

You could try to reduce  flux (INT(B*dA)) by considering the area that magnetic field is operating on and reducing it by putting wires close together.  Twisting them so there is cancellation in net integral will help also. It is difficult to know unless there is more detail description of problem.  

Attacking the problem at the source is important in this case since large induced voltage from 220VAC line could cause nonlinear response in the ADC which cannot be filtered by linear means described above.

--2N5109    
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witsanukai
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« Reply #30 on: January 06, 2016, 02:02:19 02:02 »

Can refer to below document too.

http://www.st.com/web/en/resource/technical/document/application_note/CD00211314.pdf

but almost on power line noise induce just apply 0.1uF capacitor at AVCC and ADC input and also implement moving average problem must disappear base on my experince.
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Vineyards
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« Reply #31 on: January 09, 2016, 06:05:41 18:05 »

Could you possibly use a diode and cap and take average samples? We deal with this all the time in motor control boards as the back emf plays havok with the surrounding sensitive parts!
Are you talking about snubber diodes? I think a simple LP filter would be a better choice for analog measurement circuits. However as mentioned earlier everything depends on what you want to measure. The difficulty here being, as input resistance and capacitance increase it becomes more and more difficult to put anything between the signal and the input. Because most components are tremendously leaky when high Z is involved. Even the high input capacitance or low input resistance of an opamp makes it unfeasable for use in high Z applications. For example, a typical pH probe produces 414mV which is not a very low level signal however as the current from the pH probe is usually in the femtoampere range, you can not measure it correctly if you use an opamp having too high a Input bias current, or capacitance or too low resistance as much or all of the energy that is output will be leaked to the ground (or wherever) causing faulty measurements. Under such conditions it will take ages for the measurement stabilize if it ever can.

As a result leakage rate of a component will become very important. Diodes are particularly notorious for being leaky components so are electrolyte condensers.
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