2pcs ACS712 Hall Effect Current Sensor Module 30A Range ACS712 Module + 2pcs Voltage Sensor Module DC0-25V Voltage Tester Terminal Sensor for Arduino

Nice units that are exactly what I needed! The construction is well done and each unit was separately wrapped.

These work OK and will do the basic job. Don't expect the precision of an expensive multimeter or data acquisition system, though. Sampling with the Analog pins of (most) Arduinos, you'll get 10 bits of resolution (1024 levels).On the current sensor: the chip on mine responds at about 66 mV per Ampere sensed (that's about .066 V - same number, expressed differently, for the noobs). It's important to know this because much of the online information says you'll have from .170 V to .2 V per Ampere. The difference is the particular chip on the board. Mine is an ACS712T ELC-30A (optimized for a 30 Amp range). The data sheet mentions a -5B (185mV/A) and a -20A (100mV/A) version. If you're getting crazy results, look into which chip is on your supplied board. Needed my microscope to read the top of this chip, but found "30A" in the part number, which fixed a lot that was wrong about my readings. Safety-wise, Arduino is isolated from the metered current by the Hall-effect sensor chip.The voltage sensor is just a simple voltage divider. Sure, the screw terminals are really nice, but if you've got to make a quick measurement, then take the circuit apart, you can build this out of precision resistors from your junk box. (If you're going to install something permanent-ish, this board may be worthwhile). As far as I can tell, there's no circuit isolation here, so your Arduino is exposed directly to a circuit that could be pumping out _any_ voltage, if you're not watching out for it. I don't think it's even fused. Maximum sense-able voltage with this device is 25vdc. Not sure what the safe max is, but that probably depends on your Arduino: this voltage divider will knock the input voltage down by a factor of 5 or so.Finally, getting a good measurement out of these requires that you measure and take into account your Arduino's Vcc voltage. If the Arduino thinks its supply voltage is 4.726 vdc, and your example code uses 5vdc, and a center voltage of 2.5v (5vdc/2), your measurements won't make sense. Your sketch needs to use the measured Vcc and Vcc/2 for the center to make the measurements match reality. Also, the Arduino has an internal Vcc measurement (_most_ boards do, anyway), which may differ from an external measurement (with a meter) of Vcc. I'd go with the internal value, if pressed to choose. Getting Vcc and center point right affect your math greatly.The price is right, and I'd buy these again, for simple hobby uses.

Was iffy about this but it turns out pretty well