Improve Keweisi USB Meter Resolution

The Keweisi KWS-10VA USB meter is a nice gadget for your garage, but it has its drawbacks.

It has a resolution of only 10 mA and even worse, it skips the first 40 mA. I.e. if the current is 50 mA, it shows a 1 for 10 mA and if it is 100 mA it shows a 6 for 60 mA. (It even shows 96 for 1 A.) This can be very annoying if you want to rely on the values.

So now, how you can increase resolution to 1 mA and compensate for the negative offset of 4 digits?

You need a soldering iron, a knife and 4 resistors.

1. 2 x 1 Ohm resistor or one 0.5 Ohm resistor
2. 1 x 2.2 MOhm resistor (or 2.0 MOhm resistor, see text)
3. 1 x 1.5 kOhm resistor

Open the case by inserting a USP connector at one side and then use a
big screwdriver to gently spread the two case parts. Use e.g. your fingernails to completely separate the two parts.

First, you desolder the big flat 050 resistor (0.005 Ohm) and replace it with two parallel 1 Ohm resistors resulting in a 0.5 Ohm resistor. This increases the resolution by 10 but also limits the maximum current to 1 A.

Second, you break the tiny track from the upper side of the new 0.5 Ohm resistor to the capacitor C1, right below the chip, with a knife. Be careful not to break the adjacent track.

Third, you gap the break with a 1.5 kOhm resistor.

Forth, you solder the 2.2 MOhm resistor between the 3 Volt supply (connected to R3 and C5 and R4) and the chip side of our 1.5 kOhm resistor. This introduce a positive offset which compensates the internal negative one of the chip, so that we will get a reading of 1 for 1 mA.

To fine adjust the readout you can change the value of the latter two resistors. I.E. to get a higher readout, you can use a 2 MOhm resistor and eventually tune it by connecting e.g. a 50 to 100 kOhm one in series.
To get a lower readout, you can connect a series resistor to the 2.2 MOhm one or try connecting a 100 to 220 kOhm resistor parallel to the 1.5 kOhm one.

At last, you can try to cut the pin for the decimal point of the upper current display. It is the middle pin in the second row from the bottom, the one which has a black mark on the photo. But it is not easy. I used a tiny screwdriver and a hammer, but maybe it is easier to just paint it black on the display side :-)

Now attach the case and thats it.

Good Luck