# Capacitor on USB cable?

I was messing around with a USB camera. I wanted to change the cable because is trimmed but as I was cutting it I saw a small thing (image below). As I was trying to cut the casing and see what it has inside I saw a spark. I tried to connect it with another cable but I don't know if I'm gonna damage the camera or the USB port.

What is it and can I connect the camera without it?

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First of all try to learn how to use the camera and taking good picture! – GR Tech May 22 '14 at 17:09
I don't see how you would have seen a spark. Especially when your vision is so blurry. Wait, did you have it plugged in when you were cutting it? – Samuel May 23 '14 at 2:30
I bet a dremel grinding wheel would throw sparks when it touched the ferrite. Never tried that myself, though. – RBerteig May 23 '14 at 18:57
This is ferrite bead. Manufacturers use it mostly to pass EMI certification. – user51041 Aug 9 '14 at 23:01

Its purpose is to prevent interference at high frequencies signals.

It may also work without it and with a cable as short as possible.

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From the wiki it seems like a simple component. Its it possible to make one? 'A conductive cable acts as an antenna – Meletis Flevarakis May 22 '14 at 13:21
@MeletisFlevarakis You can't "make" the ferrite core yourself. But you can buy one. – Cornelius May 22 '14 at 13:22
I have many broken electronics. I might be able to find one. Thanks for the help :) – Meletis Flevarakis May 22 '14 at 13:24
addendum: the cable will work fine without it, only data transfer rate might change. – Vladimir Cravero May 22 '14 at 13:40
@VladimirCravero - You could also get noise that corrupts the signal if it's not on there. Granted, this probably isn't going to happen in most environments. Sensitive electronics sometimes need these to isolate themselves from noise on the power lines or received from long lengths of cable, though. – reirab May 22 '14 at 16:06

It is a ferrite bead and acting as a choke, or very small valued inductor. It is acting on all the conductors of the cable together, so it is blocking common-mode noise from entering or exiting the connected device.

The USB connection will absolutely work fine without the ferrite bead present. USB cables are normally sold without it.

It was likely packaged with your device because the device was found to be emitting EMI, and the cable was determined to be the source of the emission. It was cheaper to add a choke to the cable than to do any additional work on the design of the camera itself.

A single ferrite bead acts as a low-pass filter, but it rolls off at frequencies well above the highest frequency used by USB. Furthermore, the effect is applied only to common-mode signals. The USB data is on a differential pair, and both conductors are passing through the same core, along with the power conductors. So the USB data will see very little effect from the bead, while EMI will be blocked by the bead.

Lots more than you want to know can be found by reading data sheets. Here is some documentation from one maker. Discussion of common mode starts around page 8 in that PDF.

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Its a ferrite bead, designed to suppress high frequency noise on the cable.

You can use it without it, but you might get issues with USB data transfer.

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It's a ferrite bead choke, which is used to suppress unbalanced high-frequency signals, typically caused by EM interference. It is essentially a form of passive low-pass filter.

Imaging devices such as scanners and cameras often have such filters on their USB cables because otherwise the EM interference from the cable may introduce noise in the sensor and, thus, the stored image. CCD sensors are often quite susceptible to noise.

Bottom line is that, while the USB connection will probably work fine even without the filter, any pictures that you take while connected to the PC may suffer a degree of degradation in quality.

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