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Analog reading noise

Posted by nerginer

nerginer

Analog reading noise
July 02, 2010 03:18AM

Registered: 13 years ago
Posts: 22

Hi,
I design a new extruder control PCB. It has AD595A thermocouple ic and a tip122 transistor for driving the heather with PWM.
It works but I saw that when the PWM starts there became a lot of noise with my temperature readings. If it does not active my readings are fine.

Is there a way to solve this issue?

Regards,
Nuri Erginer

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VDX

Re: Analog reading noise
July 02, 2010 03:25AM

Admin
Registered: 16 years ago
Posts: 13,888

... filtering the noise with caps or RC-networks or have a better look on the GND-arrangements ...

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

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nerginer

Re: Analog reading noise
July 02, 2010 04:09AM

Registered: 13 years ago
Posts: 22

I use 100nf cap between analog 0 and GND but it did not solve the problem

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nophead

Re: Analog reading noise
July 02, 2010 04:11AM

Admin
Registered: 17 years ago
Posts: 7,879

I found that the AD595 is very sensitive to supply rail noise, so if you get the 5V from a switch mode PSU you will need to filter it. Details here: [hydraraptor.blogspot.com]

[www.hydraraptor.blogspot.com]

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nerginer

Re: Analog reading noise
July 02, 2010 04:36AM

Registered: 13 years ago
Posts: 22

I will try the same solution to night nophead

I will inform you the results

Thanks alot

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nerginer

Re: Analog reading noise
July 02, 2010 12:17PM

Registered: 13 years ago
Posts: 22

extruder_temp.JPG

Here is the result I use 1 k resistor and 25uf cap. It is still noisy while the PWM is active. As you see when it is not active there is a smooth reading. PID is also working on arduino

Do I need bigger cap?

Regards,
Nuri Erginer

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nophead

Re: Analog reading noise
July 02, 2010 01:29PM

Admin
Registered: 17 years ago
Posts: 7,879

It looks like a ground problem to me. You need to route the ground current from the heater so that it does not generate voltage drops in the ground path between the AD595A and the Arduino ground pin.

[www.hydraraptor.blogspot.com]

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VDX

Re: Analog reading noise
July 02, 2010 03:54PM

Admin
Registered: 16 years ago
Posts: 13,888

... make the Ground-connections shorter and thicker (resolder GND-trays) and use a smaller cap, not bigger ...

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

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nerginer

Re: Analog reading noise
July 02, 2010 05:23PM

Registered: 13 years ago
Posts: 22

extruder_temp2.JPG

Nophead you are the best!!
I just solder a wire from the heater transistor ground to the main ground Above is the result.

Viktor I will try a smaller cap thanks.

Edited 1 time(s). Last edit at 07/02/2010 06:45PM by nerginer.