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Reading data to PC from a cheap multimeter – 1

I was fascinated of getting data to PC to conditionally control other things, or making graphs to make the thing more understandable.

There are RS232 capable, even bluetooth capable multimeter are available but those costs a fortune for hobbyists. Let’s assume, every hobbyists have enough time (to tinker with things) than money.

I have researched on the internet, and found a couple of ways to add RS232 to a non RS232 capable multimeter. There is no magic, but hope, use a microcontroller or other powerful processor to capture data. The ways to capture data to PC are:

  • Using a microcontroller to read the analog voltage of the signal before getting into the processor of multimeter because everything is analog at the first place.
  • Using a camera with raspberry pi to detect the segments thus capturing the data.
  • Every android phone has camera, making an app that recognizes the digits.
  • Using a microcontroller to analyze the data that is sent to the LCD of the multimeter by its processor.

Every ways have its own advantages and disadvantages. For the first option, if we want to read a voltage, we need to place an adc/voltmeter etc. This method is universal, will work on every meter. It is explained here. This will draw current no mater how small. This will cause loading effect, and change the original reading a bit. I’ve measured the analog voltage of a DT830D multimeter and it is nearly 200mV. And there are some other factors such as the ADC resolution of the microcontroller. the minimum and maximum determinable by the ADC etc. I have tried this way as explained in that instructable but in my case the multimeter reading deviates from original reading too much. So i stopped the project there.

Using a camera and raspberry pi or smartphone is universal but a bit overkill for this project. These are already internet enabled, phone has battery backup and illumination with camera but i am not an android developer. The raspberry pi method is easy and successfully have been implemented by other peoples on the internet.

I am searching for a very low cost, fast performing, lightweight, low power solution so that if the thing is destroyed by accident while using, it would not cost a fortune.

The final and hardest way is capturing data from decoding the signals of the LCD.

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