ADC Median Filter

William Meade · Guest

I have a program that measures wheatstone bridge loadcells with a 16 Bit A/D. I would like to average 10 to 20 readings to smooth out the result and have seen several references to median filters in the list. I have spent the last 40 minutes searching for any kind of code snippets to get me coding in the right direction, but to no avail. I have receintly switched from a basic compiler to PCWH and am new to the C language. Does anyone have a code snippet for the median filter or a link on how to implement such a filter. The reading that I am getting from the ADC is stored in a int32 variable called value. Thanks in advance....
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This message was ported from CCS's old forum
Original Post ID: 14043

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

:=I have a program that measures wheatstone bridge loadcells with a 16 Bit A/D. I would like to average 10 to 20 readings to smooth out the result and have seen several references to median filters in the list. I have spent the last 40 minutes searching for any kind of code snippets to get me coding in the right direction, but to no avail.
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There's code in the archives. Here's the link.
<a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank"> <a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/13211.html</a></a>

But here's how to use the Search engine of this forum.
Go to the Search page, here:
<a href="http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL" TARGET="_blank"> <a href="http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL" TARGET="_blank">http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL</a></a>

1. Type in your keywords in the top box.
2. Click the box for Search in message body.
3. Set the date range in the bottom boxes, so it says
Search from 300 to 0 days.
4. Leave all other boxes in their default state.

If you do those four things, you will get good results.
Sometimes, you might want to increase the search range
to 600 days. (This new forum started on August 24, 2001).

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This message was ported from CCS's old forum
Original Post ID: 14055

William Meade · Guest

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Thanks for the quick reply and info on how to use the search
engine... I always try searching the list first so I don't
ask the same questions that have been asked before.

:=:=I have a program that
measures wheatstone bridge loadcells with a 16 Bit A/D. I
would like to average 10 to 20 readings to smooth out the
result and have seen several references to median filters in
the list. I have spent the last 40 minutes searching for any
kind of code snippets to get me coding in the right direction,
but to no avail.
:=---------------------------------------------------------
:=
:=There's code in the archives. Here's the link.
:= <a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank"> <a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank"> <a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/13211.html</a></a></a>
:=
:=But here's how to use the Search engine of this forum.
:=Go to the Search page, here:
:= <a href="http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL" TARGET="_blank"> <a href="http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL" TARGET="_blank"> <a href="http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL" TARGET="_blank">http://www.pic-c.com/cgi-bin/anyboard.cgi?fvp=/general&cmd=qL</a></a></a>
:=
:=1. Type in your keywords in the top box.
:=2. Click the box for Search in message body.
:=3. Set the date range in the bottom boxes, so it says
:= Search from 300 to 0 days.
:=4. Leave all other boxes in their default state.
:=
:=If you do those four things, you will get good results.
:=Sometimes, you might want to increase the search range
:=to 600 days. (This new forum started on August 24, 2001).
:=
:=
:=
:=
:=--
:=
:=

</html>
</body>
</pre>
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This message was ported from CCS's old forum
Original Post ID: 14057

chas · Guest

:=I have a program that measures wheatstone bridge loadcells with a 16 Bit A/D. I would like to average 10 to 20 readings to smooth out the result and have seen several references to median filters in the list. I have spent the last 40 minutes searching for any kind of code snippets to get me coding in the right direction, but to no avail. I have receintly switched from a basic compiler to PCWH and am new to the C language. Does anyone have a code snippet for the median filter or a link on how to implement such a filter. The reading that I am getting from the ADC is stored in a int32 variable called value. Thanks in advance....

In a recent application I needed to have several running averages of a number of pressure transducers. I created a stucture that holds the data in an array, the index into the data array, the running sum, and the average.

// declare the structure type
struct avg_pres
{
long pressure_reading[16];
int index;
long running_sum;
signed long int average;
};

// declare and initialize the 2 pressure structures
struct avg_pres pressure1 ={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
struct avg_pres pressure2 ={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

Then I use a function to update the data and the average:

void update_running_average (struct avg_pres *sptr, int external_adc_channel)
{
// subtract the oldest reading from the running sum
sptr->running_sum = sptr->running_sum - sptr->pressure_reading[sptr->index];
// read the adc channel for this transducer and store in array
// this is the latest reading
sptr->pressure_reading[sptr->index] = read_ext_adc(external_adc_channel);
// add the latest reading to the running sum
sptr->running_sum = sptr->running_sum + sptr->pressure_reading[sptr->index];
// calculate the average and cast to a signed long int
sptr->average = (signed long int)((sptr->running_sum)/16);

// update the index - points to the next element to update
if(++(sptr->index) > 15)
{
sptr->index = 0;
}
return;
}

The average is a signed long int because it is required in other calculations.

Then in the code I just call the function with the appropriate structure pointer:

update_running_average (&pressure1, PRESSURE1_ADC);
update_running_average (&pressure2, PRESSURE2_ADC);

Hope this helps.
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This message was ported from CCS's old forum
Original Post ID: 14060

Neutone · Joined: 08 Sep 2003 Posts: 839 Location: Houston

:=I have a program that measures wheatstone bridge loadcells with a 16 Bit A/D. I would like to average 10 to 20 readings to smooth out the result and have seen several references to median filters in the list. I have spent the last 40 minutes searching for any kind of code snippets to get me coding in the right direction, but to no avail. I have receintly switched from a basic compiler to PCWH and am new to the C language. Does anyone have a code snippet for the median filter or a link on how to implement such a filter. The reading that I am getting from the ADC is stored in a int32 variable called value. Thanks in advance....

This one is fast and small but not a median filter. It's more like an RC filter but it's great for noise rejection.
Current_reading = Read_ADC;
Filtered_reading = (Current_reading + (Filtered_reading * 15)) /16;
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This message was ported from CCS's old forum
Original Post ID: 14131