I want to display the True RMS of the main voltage by Arduino and Max7219. At first, I used of circuit #1 (the following circuit) and True RMS library ([This link](https://github.com/MartinStokroos/TrueRMS  "this link")). The circuit could successfully return the True RMS and print it on "Serial Monitor" of Arduino every 0.5 sec. The accuracy was acceptable. This circuit was supplied from PC.
[![Circuit #1][1]][1]


At the next step, I decided to use of Max7219 (LedControl library) to display the True RMS voltage on 7-segment display. For this, I used of circuit #2. I don't know what happened. The displayed voltage had variations. In circuit #1, the maximum error was 1 volt (checked by a True RMS Multimeter - for example, the voltage was 210 volts and the printed voltage was 209 or 211 volts). But in circuit #2, the error was up to 10 volts with a fast variation. For example, the voltage was about 210 volts (using multimeter) for a minute, but the displayed voltage by Arduino was 203, then 209, then 217, then 205, then 200, then 215, .... 
I also used of another True RMS multimeter to check the first multimeter. The voltage was the same value that the first one showed. The problem was that the voltage approximately remained constant, but Arduino reflected a variable voltage. I checked the supplied voltage from PC. It doesn't have effective changes.
I also used of circuit #3. But I still had the same problem. It seems that the used of Max7219 is causing the problem. What is the solution?

[![Circuit #2][2]][2]


[![enter image description here][3]][3]

Thanks

  [1]: https://i.sstatic.net/8ys1m.jpg
  [2]: https://i.sstatic.net/VdzUA.jpg
  [3]: https://i.sstatic.net/bjgva.jpg