Practical experience

The display module with the default screen.
The JOY-iT user guide included with the device provides enough information to get you started, but to learn how to use all the features properly we recommend that you try each of the menu items. Then you can quickly see how they work or what they do.

The measured voltage and current are shown on the display with two digits before the decimal point and two digits after. According to the user guide, the accuracy is ±2% for voltage and ±5% for current. This turns to be reasonably correct in a comparison test with an accurate multimeter, but the display module shows a low voltage even without an input voltage, which is a pity. Although it is within the 2% accuracy spec, it seems a bit strange.

The connector PCB in the measurement module has a jumper with positions marked 2W and 3W. This jumper is not mentioned in the user guide instructions for this module, but a bit of searching revealed that it is used for selection of the external 12 V supply voltage. In the 3W position an external 12 V supply is necessary for operation of the measurement module. In the 2W position the module can derive this voltage from the connected power source, as long as the voltage is between 10 V and 30 V. With my module it worked as low as 8 V.
 
Touching one of the keys brings up a
more extensive screen with a small menu list.

The wireless connection is very convenient for keeping an eye on something from a distance. I powered the display module from a small powerbank, allowing me to walk around the house with the module. You have to be careful with the distance (10 max.), since the range drops quickly if there are a few walls between the display and measurement modules. However, the display module has a signal strength indicator that makes it easy to monitor this.

Conclusion

This set of measurement and display modules is very handy and affordable for measuring voltage and current in all sorts of circuits. Thanks to the large current range (30 A), it is ideally suited to situations with high current levels. The ability to use a wireless connection to the display module and read the data somewhere else is a valuable extra feature that you would scarcely expect at this price. This set is certainly worth the price of around €40/₤35/$45.