Help with WiFi web server analog input code

Hi Michele

A very nice project!

The issue may be with your use of the dtostrf function, although I admit I am not familiar with it, but I've googled around and had a look.

In the original example that you worked from, I observe that the code is:

   char temp[10];

   dtostrf(temperature, 2, 1, temp);

so the char array temp is declared as 10 chars long, and the minimum width of the converted string is expected to be 2 chars (2nd Parameter)

In your code you have used:

1. char weight[4];
2. dtostrf(loadGrams, 5, 0, weight);

Thus your minimum converted string width is actually 1 character MORE than your char array weight.

Whether or not this relevant, I don't know, but it looks suspicious. How about a couple of prints to serial monitor to show the values of loadGrams and string weight after the call to dtostr  and also to confirm that the value of loadGrams really is 0 when the cell is unloaded.

"If in doubt, print it out"

Best wishes

Neil

Hi Neil,

Thank you for responding, I really appreciate it. Great point about my use of dtostrf. I'm very new to Arduino and programming, so I'm not surprised I made that mistake.

Here are the changes I made to the code to print weight and loadGrams to the Serial Monitor:

http://pastebin.com/embed_js.php?i=yy1nxj8j

Here is what the Serial Monitor shows as the values of loadGrams and weight:

http://pastebin.com/embed_js.php?i=hqZGcv4z

As you can see, loadGrams is -500.00 before and after dtostrf is called and weight is -500, all when the scale is unloaded. (Note that I did not include the complete output from the Serial Monitor sine I don't want my network name and IP address shown.) So, this suggests that something is going wrong with the load cell code, correct?

Thanks again for helping out, Neil.

I have a tutorial that reads from the analog inputs and presents them on a web page

look here for the series Fast Track to Arduino Programming  there are not too many yet, there is a list to help find what you need.

I am using an Ethernet port but the principle is exactly the same when using the WIFI

Regards

Peter

Hi,

What is the value of 'loadAdjustment'? In github, it's set to 0. is it same in your case also?

And one more point. You could print analogSamplesAverage and do a manual calculation of map function just to ensure that it is working fine.

This is the formula for manual calculation :

     float loadGrams = map(analogSamplesAverage, analogLow, analogHigh, loadLow, loadHigh);

wil become

     loadGrams = ( analogSamplesAverage - analogLow ) * ( loadHigh - loadLow) / ( analogHigh - analogLow ) + loadLow

formula from here.

Hi Vishnu,

Thanks for the suggestion about checking out analogSamplesAverage to see if something is going wrong with that calculation. I will look into that later today when I get home.

loadAdjustment is essentially a way to zero the scale if there is a container on the scale that you don't want to weigh (e.g. if I have a container that weighs 5 grams that holds items weighing 40 grams, and I just want to record the weight of the items, I would set loadAdjustment equal to 5 so loadGrams would be 40 and not 45). Since I'm not using a container of any kind, loadAdjustment should be set to 0.

Hi Michele

It's a pleasure to be of assistance. Have you changed the code as I suggested you need to and checked the printed values again?

If the print still shows -500.00 then I guess there is a problem with the load cell code - in the averaging perhaps. Maybe there is a hitch when the load cell reading is zero - an untrapped exception.

Good luck

Neil

Hi Neil,

I just tried changing the code to the following:

char weight[10];

dtostrf(loadGrams, 5, 0, weight);

Unfortunately, the prints still show -500. I also tried char weight[20], but that didn't change the print. So, I believe there is something wrong with the load cell code, likely caused by the way I have combined the two sets of code.

Hi Vishnu,

As shown below, I printed out analogSamplesAverage twice to see what its value is in the Serial Monitor:

http://pastebin.com/embed_js.php?i=1sGEeTY3

Both times, analogSamplesAverage prints as 0. I also tried replacing the map function that I used with the formula manual calculation, as shown below, but analogSamplesAverage still prints as 0 both times:

http://pastebin.com/embed_js.php?i=MHqGQpJz

So, it seems that something is going wrong with the running average/smoothing functionality of the code. 

Hi Michele

Well that's one thing that isn't the problem then .

At least by printing things out, you are eliminating potential errors.

Good luck with digging deeper into the load cell code - maybe by printing out each value and the running average as you collect a series of samples.....

Neil

Thanks, Neil.

I've definitely learned a lot about how one diagnoses a coding problem. Very helpful.

Michele