Site icon Pallav Aggarwal

Teardown: Selec 3-Phase Multifunction Meter

Here is a teardown of a 3 phase multifunction meter (MFM383A) I purchased a couple of years back when I was developing project for a customer where energy metering was required and I needed a reference meter to check if my board’s measurements are good or not before going for Lab testing.

I was not using the meter since quite a long time now so thought of open it up and see how it was built.

In the front side you see large glass segment LCD and 4 switches for User interface.

and on the back side there are terminal for connecting AC input, pulse output.

They have separated the whole circuit into two parts, in one power section is there and on other part MCU and EEPROM is there, both PCBs are connected together using dual row male, female header connectors.

You can also observe that both crystal grounds are connected to ground for better stability and noise reduction.

To keep the cost low, power board is kept single sided only.

Some high resolution images of the multifunction meter:

Various ICs used in the multifunction meter are :

MSP430F47127: Ultra Low Power MCU. They have implemented Energy meter code and rest of the user interface in the same MCU. No separate energy metering IC is used. You can only see passives to condition AC voltage input and current input(via CT) going directly to MCU’s ADC input.

24C32 : EEPROM for saving calibration data and settings

TNY264PN: AC to DC Converter to generate power supply(isolated) for the whole meter circuit. Line filter is also used before AC-DC section to filter out input noise.


It is always great to see how different companies are designing products, their choice of microcontrollers, ICs and the over all construction.

You learn a lot by looking at someone else design, you get to know their perspective.

Hope you have enjoyed the teardown pictures and learned something new today.

If you have any further question you ask in the comments section, I will try to respond as soon as possible.


I am currently working as an embedded systems design consultant and helping companies build custom embedded products, develop test automation solution for their PCB.

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