Author Topic: Min, Max, Average BM235 BM786  (Read 586 times)

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Offline SzumiTopic starter

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Min, Max, Average BM235 BM786
« on: November 10, 2023, 06:34:33 pm »
I was playing with an esp32 writing code to average an input.  I thought I'd take my EEVBlog BM235 to average the input as a sanity check.

It was immediately apparent that my program had a different time before ittossed old readings than the meter.  Well that made me wonder how many samples does the meter take and over what time?  So I RTFM'd.  I didn't find the information.

Does anyone know?  I also have a BM786 so I'm curious about it also.

Thanks
« Last Edit: November 11, 2023, 12:16:48 am by Szumi »
 

Offline alm

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Re: Min, Max, Average BM235 BM786
« Reply #1 on: November 10, 2023, 07:22:47 pm »
I'd think it keeps collecting until you reset or cancel the average etc. For min and max it's trivial, and for average the meter should just store the sum of all values so far and the number of values, and update both and then calculate avg = sum of all readings / number of readings.

Offline mwb1100

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Re: Min, Max, Average BM235 BM786
« Reply #2 on: November 10, 2023, 07:25:02 pm »
The BM235 has a display update rate of 5 per second (nominal) - so every 200ms give or take.  This might also apply to the updates for min/max/avg.  Also keep in mid that the average is a "rolling average of the previous 16 readings" and the "average reading is flushed if the new reading is greater than +/- 16 counts from the previous average value".

Try doing the same on the ESP and see if you get matching results.
 

Offline mwb1100

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Re: Min, Max, Average BM235 BM786
« Reply #3 on: November 10, 2023, 07:32:13 pm »
The BM786 manual gives a table of the min/max/avg update rates (which differ per mode).  For DCV it says that the update rate is 10/sec (nominal).

It doesn't seem to mention the number of samples used in the averaging or if/when the average is cleared when the reading has a "large" change.
 

Offline SzumiTopic starter

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Re: Min, Max, Average BM235 BM786
« Reply #4 on: November 10, 2023, 10:19:56 pm »
I'm going to have to solder this circuit together.  My solderless breadboard or jumpers are not making a reliable connection.  Thanks for the replies so far.

EDIT

I soldered the connections together and I have stable connections.  It seems at this point that either Brymen meter is averaging over a much longer time.  It is past my bed time.  I'll try to record some data points tomorrow and plot them. 
« Last Edit: November 10, 2023, 11:34:28 pm by Szumi »
 


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