Minimatt1100
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Location: Sydney, Australia

FM Transmitter with Python - Is it safe?

Tue May 28, 2013 12:22 pm

Hey guys!

So I'm still pretty new to the Raspberry Pi community and I've only been playing around with small things, using other people's scripts and guides. One of the more recent projects I tried out was using the GPIO Pin 4 as an FM transmitter. I know there are many other posts about this, but I can't find any about whether the process is safe.

I am running the standard Raspbian Wheezy and the script I am following is from: http://www.icrobotics.co.uk/wiki/index. ... ransmitter

My concern is that when I first tested out the script, transmitting at 100MHz, my Pi started overheating for the first time. It would have been about 5 minutes of transmitting before I realised that my Pi was too hot and needed to be shut down. I repeated the progress, this time with a temp monitor but couldn't recreate the overheating (thankfully).

I'm now curious to know whether 100MHz is too high of a frequency for the CPU to handle? I read on a GPIO sheet (https://www.modmypi.com/blog/raspberry- ... heat-sheet) that the max frequency for Pin 4 is approximately 75MHz, however I have seen many other Pi users tinkering with theirs at 100MHz and higher - so I am unsure on whether this is safe or not. Can anyone confirm or deny my queries?

Cheers!
Matt

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redhawk
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Re: FM Transmitter with Python - Is it safe?

Tue May 28, 2013 12:54 pm

I'm not sure why your Pi is getting hot, are you sure you're not confusing this with the LAN chip (opposite the USB ports)??

I've use the transmitter on many occasions so it's safe for the Pi, however the power of the transmission (which varies with the length of wire) could get you in trouble with the radio police. :)

Richard S.

Minimatt1100
Posts: 9
Joined: Sun May 19, 2013 3:06 am
Location: Sydney, Australia

Re: FM Transmitter with Python - Is it safe?

Tue May 28, 2013 1:03 pm

Hi Richard,

In all honesty, I'm not sure what was overheating as I wasn't expecting it to and I wasn't running any diagnostics. If I have the guts to play around with the script again, hopefully nothing will overheat. If it were the LAN chip, would you know why that would be overheating? I wouldn't have been abusing my Ethernet at the time of the FM transmission - and also, considering chips do heat up, they won't be damaged so long as the temperature doesn't exceed their maximum recommended temp right?

Cheers

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malakai
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Re: FM Transmitter with Python - Is it safe?

Tue May 28, 2013 1:13 pm

I think without knowing how hot or where it was getting hot it is hard to tell. the chips can get to 80ish C. Off the top around 75c for Lan and 85c for the GPU typically the GPU is reported around 60c or so from various apps like XBMC. With that I think you probably touched it and got worried but the temps are normal and can operate just fine.

This command will give the temp of the Processor

Code: Select all

/opt/vc/bin/vcgencmd measure_temp
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Minimatt1100
Posts: 9
Joined: Sun May 19, 2013 3:06 am
Location: Sydney, Australia

Re: FM Transmitter with Python - Is it safe?

Tue May 28, 2013 1:24 pm

Hi malakai,

I reckon you're probably right and my nerves are just getting to me. I will definitely keep this script in mind when I next play around with the transmitter. Thank you very much!

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