# Isolated Balun-Based Variable Current Sensor

A low and high side isolated current sensor with variable gain for side channel attacks

- **Seller:** [Stephan Electronics](https://www.lectronz.com/stores/stephanelec), Lausanne, VD, Switzerland
- **Price:** €45.00 (EUR, before shipping and taxes)
- **Availability:** In stock
- **Categories:** Sensors
- **Product page:** https://www.lectronz.com/products/isolated-balun-based-variable-current-sensor

## Options

**18650 cell holder**

- With 18650 cell holder (89 left)
- No 18650 cell holder (100 left)

## Links

- [Documentation](https://www.limpkin.fr/index.php?post/2023/10/26/Using-a-1%3A8-Balun-for-Current-Based-Side-Channel-Attacks)
- [Code](https://github.com/limpkin/side_channel_amplifier)
- [Schematics](https://github.com/limpkin/side_channel_amplifier)
- [Bom](https://github.com/limpkin/side_channel_amplifier)

## Images

![Isolated Balun-Based Variable Current Sensor](https://lectronz-images.b-cdn.net/lectronz/active_storage/representations/proxy/eyJfcmFpbHMiOnsiZGF0YSI6OTE0NCwicHVyIjoiYmxvYl9pZCJ9fQ==--feb173b01b25f23a006ddc7d38773b30267855fb/eyJfcmFpbHMiOnsiZGF0YSI6eyJmb3JtYXQiOiJKUEciLCJyZXNpemVfdG9fbGltaXQiOls5NjAsNjQwXSwic2F2ZXIiOnsic3RyaXAiOnRydWV9fSwicHVyIjoidmFyaWF0aW9uIn19--a1419a086f227676aca33a49760ac51e58b523e3/sc_ampl_isol_var.JPG)
![Isolated Balun-Based Variable Current Sensor](https://lectronz-images.b-cdn.net/lectronz/active_storage/representations/proxy/eyJfcmFpbHMiOnsiZGF0YSI6OTE0OCwicHVyIjoiYmxvYl9pZCJ9fQ==--c51d82bf785bab944913f0950ae74aede12dd0aa/eyJfcmFpbHMiOnsiZGF0YSI6eyJmb3JtYXQiOiJKUEciLCJyZXNpemVfdG9fbGltaXQiOls5NjAsNjQwXSwic2F2ZXIiOnsic3RyaXAiOnRydWV9fSwicHVyIjoidmFyaWF0aW9uIn19--a1419a086f227676aca33a49760ac51e58b523e3/sc_ampl_isol_var_back%20-%20Copy.JPG)

## Description

Product Overview
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This board has been designed with side channel attack measurements in mind.  
It is meant to be inserted **inline with supply rails**, either on the high or low side.  
A potentiometer allows you to vary the inline resistance, **another one allows you to change the overall gain**.
![](http://www.limpkin.fr/public/mooltipass_mini/10px.png "")

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Frequency Response
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The sensor frequency response for different shunt and gain potentiometers positions can be seen below.  
From DC to 50MHz:  
![](https://www.limpkin.fr/public/sc_ampl_isol/transmission_40db_atten_45r_series_whole_range_1-50M_var.png "")  
From DC to 1GHz:  
![](http://www.limpkin.fr/public/mooltipass_mini/10px.png "")  
![](https://www.limpkin.fr/public/sc_ampl_isol/bode_transf_40dB_atten_0dBm_power_45r_series_through_var.PNG "")   
As you can see, **high frequencies get amplified the most**, which will actually be beneficial in an attack measurement setup as wires will attenuate high frequencies.  
![](http://www.limpkin.fr/public/mooltipass_mini/10px.png "")

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Power Supply Setup
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In side channel attacks, **noise is your enemy**.  
In the center of the board you'll notice 0.1" header holes to solder a quiet 3.7V to 4.1V power supply source (pinout is shown at the back of the board). If you choose to solder a 18650 cell holder, rest assured the board contains a protection circuit against under/over voltage conditions.  
Similarly, the power supply going to your attack target should **also be very quiet**.  
![](http://www.limpkin.fr/public/mooltipass_mini/10px.png "")  

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Measurement Setup Advices
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When performing side channel attacks the following rules should be followed:  
- eliminate any wires you may have, or keep them as short as possible  
- use clean power supplies (batteries, or lab PSU filtered by LDOs)  
- make sure your output isn't saturated (if so, add another resistance in //)  
- keep in mind that any connection may bring noise to your output  
- perform an FFT of your output with the platform off  
- make sure your trigger is repeatable  

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Required power supply
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A clean power supply (between 3.6V and 4.2V) needs to be provided through the two holes in the top of the board. You may add a 18650 holder to your order in order to use a 18650 battery.
Moreover, the board **requires a CR1220 coin cell battery**.

## Shipping policy

All of our devices are shipped from Shenzhen, China. It takes between 2 to 3 weeks to receive your order.
Swiss customers: please contact us directly to arrange a local sale.