Beginning a new Project!!

These days came back to me the idea of making a multimeter PCB, in the past I came to this idea looking at some voltmeters and ohmmeter diagrams but I didn't have many of the components to test those ideas, until a few days ago, when I received plenty of electronics stuff, analog switches, precision OPamps, display… So, these days I can test my designs on a breadboard first, and be more confident about the final design of the PCB.

The idea is to make a simple multimeter, which can meet the needs of my projects and easy to expand in the future, so I will look for these features:

  • Voltmeter with a ± 20V range with an error of 2%:

This range covers like 80% of my projects, so for me is enough.

  • Ohmmeter which be able to test resistor from 10 Ohm to 1 MOhm:

Like the voltmeter most of the time I don't need to test resistors out of this range.

  • Powering from a Nine-volt battery:

All the multimeters I have used before were powering with this battery and I don't want to spend much time on that.

  • PCB max size of 100x100 mm:

This is the limits of the PCB manufacture I but probably the dimensions will be small to keep a pocket and portable size.

  • Calibration available:

For me it is an important feature to enlarge the life of the product and to make accuracy measurements.

Knowing what I want to do is time to show the ideas I have about the different parts of the design, right now I am going to explain the big picture of the project and in next posts I will explain the different parts more in deep.

The central block of my design will be a STM32 MCU, the simple explanation to this is that my manufacture ensembles many of these uC with no extra charge and in addition I already have a STM32 development board where I can test before making the PCB, also the manufacture of these IC has a lot of resources and good documentation, these things help a lot.

Next one is the major block of the design, the instrumentation circuit, this is where the things get interesting, the job of this block is simply getting the voltage or impedance at the input and transform it to a voltage the ADC can read.

After this headache we get to the simple blocks, one OLED I2C screen easy to use with (I already use it in early projects) and some GPIO inputs like buttons, potentiometers (?) to control the whole thing.

Finally, a potentially nightmare, the power supply block, it needs to power the MCU, the ADC, the screen, the instrumentation circuit, parallel voltages for the OPamps, etc. I hope to pass through with not many issues and noise.

This is all for today, in the next posts I am going to explain in more detail the blocks and design some good schematics in KiCAD.

Ata outra! (See you soon in Galician)