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I have a project in mind where I put a Pi into an old radio along a small amp (e.g.), or similar. The only problem is I'd like to only have one power lead to the whole thing.

The amp takes a 12V input lead, and while I see it's possible to power the Pi with 12V, is it advisable in this case to power both from the same source? Even if it is, would it have a significant effect on audio quality if I did? Is all of this a terrible idea and should I be doing it another way?

  • I this board becomes a reality, I might not even have the problem any more! – Tom Medley Jul 28 '14 at 8:16
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You will need to either use a Voltage Regulator to drop the 12v to 5v or modify a car charger. I used an old Tom Tom car charger to drop the voltage. See here

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    A voltage regulator is pretty wasteful, as more than 58% of the energy is converted into heat. Which comes to 5Watt of heat when the Pi is using 700mA. You'd need a very large heat-sink for that. A Buck-converter (what's inside a car charger) would be a lot better. – Gerben Jun 10 '14 at 15:43
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    @Gerben - I agree but it can be done. I prefer a 12v to 5 car charger. – PhillyNJ Jun 10 '14 at 15:46
  • Car charger is a good idea, especially those ones with USB port on it :) The problem is that the OP supplied a 2Amp "input lead" - when the amp goes into overdrive it may cause the Pi to brownout and reset. – Piotr Kula Jul 9 '14 at 17:00
  • @ppumkin I am not sure I understand. Are you saying if the radio starts to pull more that 2 amps, the Pi will shutdown? If that is the case, what about an inline fuse for protection? – PhillyNJ Jul 9 '14 at 17:08
  • Amps is power. If the amp is low is only draws low power but when you turn it up and bass kicks in it needs peak power. Since its rated 2A its possible the amp takes about 1.5amp peak. So the Pi is left with 0.5amp. Unfortunate these power supplies you have are notorious for being crap and usually 2A only provides ~1.5A at constant peak. So the Pi will reboot. The only way to stop that is getting a bigger PSU. Best option is a switching power supply ,3A,4A or even 5A. Some have 12v and 5v outputs. Fuses only protect from over voltage. – Piotr Kula Jul 9 '14 at 18:34
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You would need a buck converter like LM2596. It can drive upto 3A at high efficiency. In contrast, 7805 heats up pretty quickly. If you want to connect many modules to the pi, please go for buck converter option. You can find more info here

LM2596 based voltage regulator

Needless to say, high efficiency => More power left for your radio application

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I would suggest getting a better power supply. If you try and run an Amp and the Pi off that crappy, cheap power supply you are going to have issues, especially with WiFi on the Pi because of the incredible noise generated on them. Also, you might run out of power when your crank up the volume causing the Pi to reset (brown out)

I usually suggest switching power supplies, like the ones used in computer. They provide high quality, clean power and are very efficient.

You can find them on dx.com and ebay12 volt ($10-$15) for 5Amp, but then you still need 5volt right? Many people suggest an ubec dc-dc

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You can also try and find a universal power supply with a USB port. So the lead will supply 12volt and you can power a HUB with various things and the Pi.

enter image description here

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I recently became aware of PiPower, which looks like it could do the job too:

Pi Power is a switching power supply for the Raspberry Pi. It plugs into the GPIO header, and has an extra tall stacking header to keep the board out of the way of the display connector and facilitate plugging something else into the GPIO connector as well.

It has a 2.1mm barrel connector that will accept 6-15 VDC. It supplies up to 2 amps of 5 volts. At supply voltages over 9 volts, it has a ripple of 25 mV P-P. At lower supply voltages, the ripple goes up to 45 mV.

enter image description here

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You could use an power adapter AC-DC with dual DC output of 12V 2A and 5V 2A which should be enough for RPi and AMP. But You should use some kind of power switch so the unit doesn't take electricity when the radio isn't turned ON. It will also prolong life cycle of power adapter. Link: https://www.banggood.com/12V-5V-Black-Plastic-AC-DC-Adapter-For-HARD-DISK-Drive-Power-Supply-10x4x3cm-p-1170143.html?rmmds=search

Peace and all good! JoS

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