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reprap radio

Posted by Tom_Neverwinter 
reprap radio
August 12, 2013 07:45PM
I am not sure if I am hearing things or if I createda radio curcuit, but I can swear I heard the radio playing on my stepper motor.
I had just started to fine tune my z axis pot.
following the wiki article
being anxious to fine tune my printer;
I first set it high (max)
the lowered it.
then I went to check the reading on the multimeter, however
I did not turn the multimeter on, and had only touched the pot
this is when I could have sworn the radio was playing.
after I removed the red probe never touching the black probe it stopped,
I measured and it said .32##

is this even possible? or am I spending too much tiem on my printer
Re: reprap radio
August 12, 2013 09:04PM
Technically, if you live near a large radio source (most likely an AM radio station or someone with an amateur radio) then it's possible.

With only one lead connected to your electronics, the multimeter and leads acted like a piece of wire antenna. You can probably reproduce it using just a long piece of wire.

As the pot adjusts the current on the stepper driver (and hence the current flowing through the stepper), a small variance in voltage on the pot (created by the antenna) will change that current. Particularly at low step rates, stepper motors can audibly hum when "held" in position, so noise is easily produced if the current is adjusted enough.

FWIW: If you're near such a large radio source, then I'd suggest shielding your electronics and cabling, particularly the cables to the end stops, to cut down on the possibility of interference during prints. Noise issues can be hard to track down if you're having intermittent problems.

Note: AM radio changes the amplitude of the signal in time with the audio signal, which is why this sort of thing happens - the audio signal is induced in the antenna and gets fed to the pot. Unlike AM, FM keeps the amplitude steady and changes the frequency in time with the audio signal, which won't give any real difference in voltage when you touch the pot. If you're further interested in radio and how this all works, do some googling on radio principles, as there's way too much to explain here.
Re: reprap radio
August 12, 2013 10:17PM
Thanks for the information I will definitely shield my electronics around here
Re: reprap radio
August 13, 2013 10:44AM
Any chance of a video/recording? That would be really cool to hear!
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