Introduction: Current Meter, Network Frequency and Non-invasive Power

About: Hello, my name is Carlos. I have a YouTube channel where I share my projects in

In this post we will see how to measure the current frequency and power with a non-invasive current sensor SCT-13-50, a dual amplifier LM358.

The most interesting thing about this project is that we can measure the current without having to open the circuit, because the sensor sct013-50 is very similar to an ampirometric clamp.

It must be taken into account that only one of the cables must be passed to make the measurement, because if we pass the two conductors we will obtain an erroneous reading.

Step 1: Circuit

The circuit is very simple to assemble, we will assemble it with an arduino nano, we can also use a mega arduino but we must make a slight modification to the code, please observe the comments in the source code, to see which lines should be commented and comment.

Let's use the sh1106 display to visualize the current consumed, the network frequency and the apparent power at all times. The LM358 is an operational amplifier, whose function is the rectification of the alternating wave generated by the sensor sct-013-50, this wave is not suitable for the analog pin A0 of the arduino, because this pin supports voltages ranging from 0 to 5 volts and the voltage that the current sensor can deliver is +/- 1 volt. The negative half cycle can damage our arduino, so we must eliminate it, this could be achieved with rectifier diodes but the silicon diodes cause a voltage drop of 0.7 volts and germanium 0.6 volts, this is too much for the signal that it gives us the current sensor sct0-013-50, so we are going to use an operational amplifier the LM358 in its configuration as a voltage follower. The LM358 is a general purpose dual operational amplifier, does not require dual source, high gain, low power consumption, 0.7 MHz bandwidth.

Step 2: Characteristics:

  • No. of operational amplifiers: 2
  • Does not require dual source (However, with a simple source it is not possible for the output to obtain negative voltages)
  • Supply voltage: 3 V to 32 V single source (± 1.5 V to ± 16 V dual source)
  • Low power consumption
  • Typical bandwidth: 0.7 MHz
  • Frequency compensated internally
  • High gain
  • Compatible with all forms of logic

The other configuration of the second operational amplifier is set as an operational non-inverting amplifier.

Step 3: Look at the Next Circuit

Step 4: Complete Circuit

We will need a resistor of 4.7 Kohm and 1 Mohm, at the output we will have an amplified and square wave suitable to connect a microcontroller to a digital pin.

The frequency of this wave will be directly related to the frequency of the network used in our country, in this example it will be 50 Hz, for the area where I live. Let's take an example taken from experience and captured with an oscilloscope. The wave generated by the current sensor is a wave that goes from -1 volts to 1 volt, it is a sine wave. The voltage value delivered by the sensor will depend on the current consumed by the appliance. The greater the current consumed, the higher the voltage delivered by the sensor. Once the wave has been rectified by the first operational amplifier (remember that the LM358 has two), we will only see the positive half cycle of the wave, which makes it suitable for the analog pins of any microcontroller.

Step 5: PinOut LM358

Step 6:

In this image we can see in the yellow sine wave an alternating signal, which is not suitable for our arduino, lower in the green wave we see a wave with half wave rectification.

It is observed that the frequency is almost 5o Herz, the same as that of the electrical network, which is used is my country, we will use this frequency to obtain information and send it to the arduino for its representation a display oled.

Step 7:

We compare the two waves, and note that the yellow part is the negative half cycle that we will not use.

Step 8:

We compare the two waves, at first glance it seems that both waves have the same amplitude, but if we look closely at the oscilloscope data, we will see that the square wave has 3.7 volts, while the rectified half wave is 132 mV.

Step 9:

If we see the multimeter the reading is almost zero as in the display oled, but in it we can see the intensity consumed, the power and the frequency of the network.

Step 10:

To be able to measure the current with the sensor, we only have to pass one of the cables.

Step 11:

Here we can see the current consumption in both the multimeter and the display, it is almost the same, although we can improve the pressure by modifying some parameters in the source code.

Step 12: Source Code

Step 13:

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Step 14:

The EnD ;-)