Victory multimeter vc921 adds rs232 computer host computer communication function

 The vc921 I have has been used for more than 4 years. In my memory, I have only changed the battery once. It is still an ordinary dry battery, which is very energy-saving. Although it does not have energy current, there is no current setting, so the meter will basically not be damaged. (The first multimeter I bought was scrapped by a friend who used the current setting to measure the voltage.) I saw someone modifying the 9999 display online a long time ago, but I haven’t done anything about it. I recently wanted to buy a second home meter, so I gave it a try and turned on rs232. Communication needs to modify the FA byte in at24c02 to CE.
1. The USB to serial port uses WCH's CH340E, which does not require a crystal oscillator. It is small and requires no peripheral parts, making it easy to place. When the multimeter switches the rs232 output, you need to press and hold the rel button on the left for 3 seconds. After switching, it cannot automatically shut down. If it cannot automatically switch the unit, you need to manually press the range button. In addition, the rs232 status screen displays the word max.
2. Because there is still space to place a select button, because after the vc921 automatically shuts down, you have to twist the disk to off and back again. I heard that it will damage the PCB copper. As a result, there is no suitable button for the proofing return. It may be more convenient to use the tip of a test pen to press it. The entire board size is not quite right and I don’t have calipers at home. It's best to adjust it yourself if necessary. I used a knife and diagonal pliers to repair it for a while before I could put it into the two screw jacks.

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eeprom modification location:

The host computer displays, and the device selects PeakTech 3415: