> For the complete documentation index, see [llms.txt](https://mujoseph.gitbook.io/mujoseph-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mujoseph.gitbook.io/mujoseph-docs/emma-mk1-drsstc/hardware-overview/mechanical-design/feedback-current-transformers.md).

# Feedback Current Transformers

## Hand-made Cascaded CT

The Eastern Voltage Research [guide](https://www.easternvoltageresearch.com/tesla-coil-workshop/how-to-build-cascaded-current-transformers-for-tesla-coils/) was followed to construct the cascaded current transformers used to provide zero-crossing detection ([ZCD](/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design/current-sense.md#zero-crossing-detection-zcd)) and over-current-detection ([OCD](/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design/current-sense.md#over-current-detection-ocd)) feedback to the [*Current Sense PCB*](/mujoseph-docs/emma-mk1-drsstc/hardware-overview/electrical-design/pcb-design/current-sense.md).

The hand-made CTs have a 1024:1 turns ratio. The top two CTs are used for generating the ZCD and OCD signals. The bottom CT is terminated with a 22 $$\Omega$$ (1 W) resistor. Voltage across the resistor can be measured via the pin headers using a differential probe or single-ended probe with the oscilloscope ground floating. 

<div data-with-frame="true"><figure><img src="https://2297250131-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FzNHSl7dsTOS0XjlMXnIe%2Fuploads%2FThIhaaBed7ufBzDqUIgG%2Fcustom-made-ct_1.png?alt=media&amp;token=08098389-b557-43f4-8d72-4897dada6ee8" alt="" width="563"><figcaption><p><em>Emma Mk1</em> feedback current transformers</p></figcaption></figure></div>