Way back in 2021 March-April timeframe I discovered about Owon XDM1041 Digital multimeter (55000 counts) which was low-cost and had RS232 interface (later started coming with USB).
I immediately understood that it could be very useful for various use cases and especially for the test automation projects.
I did a detailed review and shared my finding in the blog as well in two YouTube Videos.
Recently, I thought, It would be good to show engineers what is there inside a programmable multimeter like XDM1041 so here I am with a teardown blog.
Just realized this is my 53rd teardown blog, wow!
Never thought I will do so many teardowns when I started one year back.
The reason I started was, I wanted to understand how consumer electronics or very high-volume design and manufacturing works.
There is no book or video available to share the knowledge. What I have seen is nobody is interested to share. Most people are really scared of sharing the knowledge and experience 🙂
I strongly believe that experience must be shared so that others can take the advantage. Hardware development is quite hard and rarely any book is available which shares the real experience on consumer electronics and high volume manufacturing.
Anyways, let me show you what I saw when I took apart XDM1041 Digital Multimeter. I still use it in my office for automated testing for many projects.
It’s accuracy is good for DC voltage, AC Voltage(not <500mV), you can’t expect too much from a low priced multimeter from precision point of view.
I saw some issues with low AC/DC current measurement, resistance measurement, even high value capacitance also are off. Some noise fixes are discussed here.
For test automation you will mostly use DC voltage and in some cases AC voltage and resistance/continuity in low ohm range.
This is how you see the multimeter from front and back. At the front, you get a large color tft display, buttons for user interface and ports for probes.
on the backside you see the RS232 port (newer version has USB, which is good) and AC power port.
you can easily open the multimeter from the back side, two scews are hidden in the base rubber pad and 3 are exposed on the back plate.
once you open, the first thing you will see is a small PCB, which is for RS232, basically UART connections are coming to this board along with 5V and GND and a MAX232 equivalent IC from SIPEX SP202EEN is there for UART to RS232 level conversion.
Another PCB which is attached to the back panel is for AC Power port. This PCB has AC to DC converter for 230V AC to 5V conversion.
Looks like they forgot to wash the PCB, very dirty.
The circuit is quite common, AV Port has fuse inbuilt, on the PCB AC input goes to MOV protection to a standard EMI filter based on choke and then AC to DC power convertor based on Flyback topology. I checked the Power Chip but they have scratched the IC number.
They have even used pie filter on the secondary side after converting to DC, this helps in removing the noise component.
Especially good for a multimeter like noise sensitive product.
There is one more board in the XDM1041 digital multimeter, which has the core multimeter functionality for high precision measurement.
For measurement, they have used a purpose built multimeter chip from HYCON HY3132 and it is interfaced with MCU over isolated UART, even power is isolated.
For Power isolation, they used DC to DC convertor module from AIPULNION FN1-05S05, a good brand for AC to DC converter modules, they have many UL compliant modules also.
For digital signal isolation, they have used Everlight ELD207 Dual Channel Opto-isolator IC.
This measurement board connects to the MCU board via FFC cable.
There is another board which is the main controller board. This board has GD devices GD32F303 MCU, Buzzer, Color TFT Display connected over SPI and a linear regulator for 3.3V voltage conversion from 5V input.
A small battery is also soldered on the PCB mainly for the RTC I guess.
X1 is the low frequency crystal (32.768khz). High frequency crystal is not populated on U3.
YYS37HV-133-A1 is the TFT Color Display Module used, i could not find a reference online but it is equivalent to any 3.5 inches TFT Color Display .
U6 with marking T202-N looks like a ATTINY202, another MCU?, not sure why they have used. May be to handle serial protocol on RS232.
there is another board used which is connected to the probes, mainly used for analog processing of the sensing signals.
It has voltage dividers, relays for probe/ channel selection.
Relay is from Fujitsu FTR-B3GA4.5Z, 4.5V rating, 2 Form C (DPDT-NO, NC).
An LDO for a clean voltage for the circuit and an isolator NSI8141 from NOVOSENSE
That’s all in this teardown.
I hope you found it interesting. See you in my next blog soon.
I am currently working as an embedded systems design consultant helping companies build custom embedded products and develop test automation solutions for their PCBs.
If you have any feedback about the blog, you can share it in the comments below or contact me directly.