# How to connect a CT-sensor to an Arduino Giga?

#### Rensieboy223

Joined Feb 3, 2024
37

#### Ian0

Joined Aug 7, 2020
9,489
What it doesn't tell you is that under surge conditions the output of the CT will blow up the input of your Arduino.

If you want to use the circuit in the article, then add a series resistor between the burden resistor and the input of at least 4.7k and put schottky diodes between the input and both supplies.

I would suggest using an AD8418 and calculating the burden resistor to give 50mV output at full power. The AD8418 will withstand a lot of voltage on its inputs, but will not output any more than the Arduino supply voltage.

If you want a better range of current transformers look at
https://www.micro-transformer.com/products.html

#### Rensieboy223

Joined Feb 3, 2024
37
A couple of suggestions.
View attachment 314881The lower the burden resistor the better the accuracy.
So the OP07 circuit in the datasheet is probably the best, but if you don't have positive and negative supplies for the op-amp it's a bit of a pain to use.
Hey man,

I see the circuit but I don't understand it completely:

What is L2 L?
What is V1 V?
I see a ground label but where do i connect my vcc and my analog pin of my arduino?
And is it correct that i need the CT-sensor and the AD8418A is the amplifier who sets the current into voltage?
And what is 500 L1 in this circuit?

#### Ian0

Joined Aug 7, 2020
9,489
Hey man,

I see the circuit but I don't understand it completely:

What is L2 L?
What is V1 V?
I see a ground label but where do i connect my vcc and my analog pin of my arduino?
And is it correct that i need the CT-sensor and the AD8418A is the amplifier who sets the current into voltage?
And what is 500 L1 in this circuit?
The inductors are the secondary windings of your current transformers.
500 is the value of R3
V1 is the Arduino power supply.

#### Rensieboy223

Joined Feb 3, 2024
37
The inductors are the secondary windings of your current transformers.
500 is the value of R3
V1 is the Arduino power supply.
Okay, and where does the output of the amplifier go to the Arduino Analog Pin?

#### Rensieboy223

Joined Feb 3, 2024
37
The inductors are the secondary windings of your current transformers.
500 is the value of R3
V1 is the Arduino power supply.
And what do you suggest as burden resistor by R4?

#### Rensieboy223

Joined Feb 3, 2024
37
A couple of suggestions.
View attachment 314881The lower the burden resistor the better the accuracy.
So the OP07 circuit in the datasheet is probably the best, but if you don't have positive and negative supplies for the op-amp it's a bit of a pain to use.
Okay guys,

Here below my schematic:

Okay so values:
- GND : Ground supply of Arduino Giga
- 3.3V : 3.3V from Arduino Giga
- A1 : Analog Pin 1 from Arduino Giga
- AD841A : The current amplifier chip
- ZMTCT124I: The CT-sensor for 100Amps

Do I need any more resistors, burdens or capacitors i my circuit for improving the accuracy and quality of the sensor?
Or what can i design better on this CT-sensor schematic?

#### Ian0

Joined Aug 7, 2020
9,489
Okay, and where does the output of the amplifier go to the Arduino Analog Pin?
Yes.

#### Ian0

Joined Aug 7, 2020
9,489
Okay guys,

Here below my schematic:
View attachment 314906

Okay so values:
- GND : Ground supply of Arduino Giga
- 3.3V : 3.3V from Arduino Giga
- A1 : Analog Pin 1 from Arduino Giga
- AD841A : The current amplifier chip
- ZMTCT124I: The CT-sensor for 100Amps

Do I need any more resistors, burdens or capacitors i my circuit for improving the accuracy and quality of the sensor?
Or what can i design better on this CT-sensor schematic?
You must have the burden resistor.
Select the burden resistor to give 50mV at your maximum current.
You probably need the diode to keep the common mode voltage within range.

#### Rensieboy223

Joined Feb 3, 2024
37
You must have the burden resistor.
Select the burden resistor to give 50mV at your maximum current.
You probably need the diode to keep the common mode voltage within range.
Okay how do i calculate the burden resistor?
And where exactly do i need a diode?

#### Ian0

Joined Aug 7, 2020
9,489
What is the maximum current you want to measure? (rms)
Divide it by the current transformer ratio. That gives the output current from the current transformer.
That current needs to produce 50mV at the input of the amplifier.
Use Ohm's law to calculate the burden resistor.

The amplifier has a gain of 20. That will give 1V rms at your microprocessor pin. For a 3.3V processor, 1V rms is a convenient 2.82V peak-to-peak. If you have a 5V microprocessor you can use a larger signal.

Don't forget to connect the reference pins of the AD8418.
The diode is D3 on my diagram. It prevents the AD8418 inputs from going too negative.
The TSC2010 is an equivalent to the AD8418, and it will withstand more negative voltage at the inputs.

#### Rensieboy223

Joined Feb 3, 2024
37
What is the maximum current you want to measure? (rms)
Divide it by the current transformer ratio. That gives the output current from the current transformer.
That current needs to produce 50mV at the input of the amplifier.
Use Ohm's law to calculate the burden resistor.

The amplifier has a gain of 20. That will give 1V rms at your microprocessor pin. For a 3.3V processor, 1V rms is a convenient 2.82V peak-to-peak. If you have a 5V microprocessor you can use a larger signal.

Don't forget to connect the reference pins of the AD8418.
The diode is D3 on my diagram. It prevents the AD8418 inputs from going too negative.
The TSC2010 is an equivalent to the AD8418, and it will withstand more negative voltage at the inputs.
The maximum current is 100Amps

#### Rensieboy223

Joined Feb 3, 2024
37
What is the maximum current you want to measure? (rms)
Divide it by the current transformer ratio. That gives the output current from the current transformer.
That current needs to produce 50mV at the input of the amplifier.
Use Ohm's law to calculate the burden resistor.

The amplifier has a gain of 20. That will give 1V rms at your microprocessor pin. For a 3.3V processor, 1V rms is a convenient 2.82V peak-to-peak. If you have a 5V microprocessor you can use a larger signal.

Don't forget to connect the reference pins of the AD8418.
The diode is D3 on my diagram. It prevents the AD8418 inputs from going too negative.
The TSC2010 is an equivalent to the AD8418, and it will withstand more negative voltage at the inputs.
What do i need to connect the VREF1 and VREF2 and NC to?

#### Ian0

Joined Aug 7, 2020
9,489
What do i need to connect the VREF1 and VREF2 and NC to?
See diagram in Post #6.
NC normally stands for "not connected", and this instance is no exception.

#### Rensieboy223

Joined Feb 3, 2024
37
So, is this better?

What extra do I now need?

Calculation for my burden Resistor=

AREF= (3,3V/2)
Peak Current = Root2 * 100amp = 141,1Amp
Amount of turns= 2500

Secondary Peak current = 141,1amp/2500 = 0,05644Amp
Burden resistor = (3,3V/2) / 0,05644Amp = 29,23ohm

Good?

#### Ian0

Joined Aug 7, 2020
9,489
So, is this better?
View attachment 314917

What extra do I now need?

Calculation for my burden Resistor=

AREF= (3,3V/2)
Peak Current = Root2 * 100amp = 141,1Amp
Amount of turns= 2500

Secondary Peak current = 141,1amp/2500 = 0,05644Amp
Burden resistor = (3,3V/2) / 0,05644Amp = 29,23ohm

Good?
Almost there:
1. If you calculate for 100A rms you can never measure more than 100A rms, which you may wish to do in cases of overload.
If 100A rms is the maximum you could ever need to measure, even in overload conditions you are OK.
2. The AD8418 has a gain of 20. So you need to scale the reference voltage by 20.
3. The burden resistor is the load on the transformer secondary, so it goes across the transformer terminals.

I always aim for 1V rms on the processor pin, at my reference current. That gives 16% headroom for overloads, and makes the maths simple for the burden resistor calculations. It also lets me reuse all my software that I have written for AC current inputs, as I just have to scale the result to the reference current.