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I've got a small device that I have not yet opened. It sends some unknown sequence of voltage and current through a medium for a few seconds thereby calulating and then displaying a result value on a display. During the measuring time it also displays some small waiting animation on the screen. I guess that one small chip will be handling all these activities.

Now I'm wondering how I could grap the result and import them into a smartphone through the audio jack. I want to loose the integrated display of the device and only use the smartphone screen. What would be the smartest way to go?

Grabing the display signal doesn't seem to be feasable because it are multiple digitally coded lines and not one signal with ampiltude. Could I maybe listen to the measuring signal through the audio line and then try to do my own reference measurements, or might this disport the actual measurement? Is there maybe some other way to grab this information to provide means of interoperability?

What voltage (& current?) can be measured my a mic in line and how must the signal be modulated? Some fixed frequency or can microphone electronics also analyse frequency?

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closed as unclear what you're asking by Dave Tweed, Chetan Bhargava, Leon Heller, Daniel Grillo, Nick Alexeev Feb 27 '14 at 19:22

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ You're going to have to be a lot more specific about what the device is and what it's measuring. \$\endgroup\$ – Dave Tweed Feb 27 '14 at 16:40
  • \$\begingroup\$ picture for example? \$\endgroup\$ – Codebeat Jan 25 '17 at 5:25
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Grabbing the display signal doesn't seem to be feasible because it are multiple digitally coded lines and not one signal with amplitude.

LCD waveforms can be translated into data, but it requires some time and effort. Generally the display is static, so you can use an ADC and a system of multiplexors to check each segment and common in turn and it can be relatively easy and fast once you understand how simple segmented LCDs work. As a beginner, though, it can seem daunting.

Could I maybe listen to the measuring signal through the audio line and then try to do my own reference measurements, or might this disport the actual measurement?

It completely depends on the medium and the measurement process, but most likely you will alter the reading by tapping into those lines.

Is there maybe some other way to grab this information to provide means of interoperability?

You should probe around the board with an oscilloscope during and after a measurement to see if the designers left a serial stream or other data stream coming from the device for debugging and development purposes. If you can identify the chip or circuit, you may be able to find enough information about it to make some intelligent guesses as to how it might send data out other than the LCD, if it does at all.

What voltage (& current?) can be measured my a mic in line and how must the signal be modulated? Some fixed frequency or can microphone electronics also analyze frequency?

I wouldn't put more than 250mV voltage swings into the microphone of a device I cared about. Additional testing will help you find an appropriate input level, but I'd start off small at around 10mV, fed through a 470nF capacitor into the microphone input, then go from there to find the dynamic range of the microphone input of a given device.

You might find more help if you told us what the device is and does, and showed pictures of the internal circuitry and measuring apparatus.

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