I was wondering if there are any examples of using PD to take images from a USB camera every 3 seconds or so and saving the image out to individual filenames that includes the time stamp in the filename.

My goal is to create a poor mans DAQ (data acquisition) using PD, a multi-meter, and image recognition.

My thought process:

1. PD plays audio signal that increases over time for a duration of 3 second, then appends the signal value that was played to a text file with a time stamp.
2. Have usb take camera shot every 3 seconds of a digital multi-meter screen and output that to a file with the time stamp in the filename.
3. Use machine learning / OCR on image files and append the decoded OCR numerical data to another text file that includes a time stamped text value from the filename so I can sync up the original signal played and the value that comes from the multi-meter output.
4. Plot the values from text file showing input signal vs output signal

PS I'm using Ubuntu 20.04 Linux.
If anyone has another way of doing this please let me know.

Thanks

@Still What is the multi-meter reading?
If it is an audio level then you could bring the data back into Pd from a microphone and plot the level against the level of output from Pd.
Image capture could be done in Pd with GEM but the data will be huge and OCR is not a Pd function that I know of.
Using a microphone instead would bypass those stages....... and the plot could even be presented in real time.
David.

@Still said:

I was wondering if there are any examples of using PD to take images from a USB camera every 3 seconds or so and saving the image out to individual filenames that includes the time stamp in the filename.

My goal is to create a poor mans DAQ (data acquisition) using PD, a multi-meter, and image recognition.

My thought process:

PD plays audio signal that increases over time for a duration of 3 second, then appends the signal value that was played to a text file with a time stamp.
Have usb take camera shot every 3 seconds of a digital multi-meter screen and output that to a file with the time stamp in the filename.
Use machine learning / OCR on image files and append the decoded OCR numerical data to another text file that includes a time stamped text value from the filename so I can sync up the original signal played and the value that comes from the multi-meter output.
Plot the values from text file showing input signal vs output signal
PS I'm using Ubuntu 20.04 Linux.
If anyone has another way of doing this please let me know.

Thanks

@whale-av said:

@Still What is the multi-meter reading?
If it is an audio level then you could bring the data back into Pd from a microphone and plot the level against the level of output from Pd.
Image capture could be done in Pd with GEM but the data will be huge and OCR is not a Pd function that I know of.
Using a microphone instead would bypass those stages....... and the plot could even be presented in real time.
David.

It's a voltage level around 200+ volts. It's measuring non-linear vortex inductor coils. When you input different audio signals it outputs very high voltages and very low voltages .1 to 200+ volts (very non linear). So I don't think I could bring that data back in easily. I would do the OCR using python or Octave.

@Still [pix_write] in the GEM library will capture the image from [pix_video] and write it.
The zexy library has [time] which you could use to add a timestamp to the file name.
David.

@Still easier would be to just scale and shift the voltage down to line level then run it into an audio input, no OCR, meter or cameras needed. This would likely only require a simple circuit and can possibly be completely passive, hard to know without more circuit details. Worst case a transistor, an opamp and a handfull of passives, maybe $5 in parts.

Thanks I'll have to research the circuit. I'll spend the $5 the issue is designing the circuit so it doesn't fry my computer some of coils have been shown to produce ozone (which is very high voltage).

an example

The circuit is fairly basic and not much beyond ohms law is needed, the high voltage is not an issue, a fuse or diode can be added for protection in a worst case scenario failure. Really you are just designing the input section of a standard meter and you can look at the schematics of any meter that is not auto ranging to see how to do it. There should be some manuals for the old heathkit solid state analog panel meter kits on the web, those should give a good description of the circuitry including the protection circuitry.

If you are more comfortable with software than solder, there likely is an arduino meter kit, would be a simple task to hack the code and transmit the needed data to the computer.

@oid said:

arduino meter kit,

Yes I find programming much easier and it produces less smoking components in my vicinity ;-D

@oid I agree...... plus an opto isolator if there is one with the dynamic range.
And I was going to discuss the same idea, but I was stuck at the dynamic range for a line input (96dB...?) and whether it would be DC coupled.
Also accuracy required...? Bit depth for 0.1 to maybe 1000...?

@Still But looking at the other videos it seems to be an AC signal from 0.1 to 200V (plus?) and so an isolating transformer (not tapped) should be sufficient.
You probably won't find one, but you could make your own.
Simply winding 300 turns of insulated wire onto a ferrite ring for the input and one turn for the output will output less than one volt ac (there will be losses) when the input sees 300V ac.
Larger ferrite rings have lower frequency ranges..... choose a size to match your range. They are very insensitive to external flux.
Then a 600 ohm resistor to current limit before the line input of your computer (I think..... more research necessary as impedance unknown). But I doubt that the core is capable of supplying much current.
David.