I'm a complete noob when it comes to electronic so if you feel the need to call me stupid for not figuring this out on my on, I wont be offended.

I have searched Stack Exchange without finding an answer, or not understanding the answer.

I have a small solution to control the radiators in my cabin. It's ugly as.... I use a Raspberry Pi(old version) to control a key-fob. Since I read, somewhere that the key-fob might use more power than the RPI can deliver it could potentially fry the RPI. My solution is to use one cellphone charger to power the RPI and one to power the circuit with the key-fob. I have put a relay between the two.

Below is a simplified fritzed version of the current solution.

Current solution

What I want is to change to use a single cellphone charger.

Below is my version on how to solve this.

enter image description here

The problem for me is that I am to much of a noob to figure out if this will fry my RPI. Any suggestion and/or help on how to solve this is much appreciated.

@Elliot Alderson want's more information. Which I totally understand. As I stated before, this is a VERY ugly solution.

This is an image of my "electronics" box, it's the device that want's 2A. In reality it doesn't at the moment but in the future, when I want to control the world it might use much more than 2A.

enter image description here

The green card is a simple remote to control lights over 433Mhz. It's sold by a Swedish company called Clas Ohlson. This item looks the same as the one I have, but I'm not sure, Remote to control lights. The remote control uses a 3v button battery. I use a voltage regulator to get 3.3v Spec for voltage regulator to replace the battery.

The electronics box is connected to the RPI enter image description here

I'm not sure which version of pi it is but I know it's first generation.

The RPI communicates with a server in my closet. The server holds and controls state for the radiators. I have written the server software. The hardware of the electronics box is a ugly hack. The server software is worse. The RPI polls info from the server.

The 2 buttons on the electronics box is so I can "manually" turn on and off the radiators in the cabin. The buttons actually sends a state-change to the server and then change state of the radiator.

I use the same charger for both RPI and the electronics box. I bought them from Kjell.com. Linocell usb charger.

According to the sticker on the charger

  • Wall charger
  • Art No: 95717
  • Input: AC 100-240V 50-60Hz 0.3A
  • Output: DC5v 2.4A Max

I am aware that the more functionality(components and so on) I add to the electronics box the more power it will need. The Wall charger I use today might not cut it, and I have to upgrade.

The question remains. To day I use two power sources and a relay between RPI and the remote control(green card) since I don't want to accidentally fry my RPI.

Is it safe to share one power source for both RPI and my remote control circuit, regardless if I add more power hungry crap on the non-RPI side of the relay?

I'm sure that some of you are rofl - happy I can contribute to some happiness. I am a noob that are willing to learn. Any tips,pointers, suggestions and so on are very welcome.

If anyone needs more info, I'll do my best to supply it.

  • 2
    \$\begingroup\$ Hello and welcome to electronics stackexchange. Your idea is fine, anyway you have to be careful with voltage fluctuations. This would happen if your charger is on the limits of what it can provide. Check if it can provide 2A for your device (the one driven through relay) plus anything what is needed for Raspberry. Also, be sure that you don't loose too much on the wires between charger and the rest of the setup. \$\endgroup\$
    – smajli
    Jun 24, 2019 at 12:34
  • 1
    \$\begingroup\$ I guess you can't read circuit diagrams yet because you are posting Fritzing cartoons - those cartoons may tell you something very basic but they are full of superfluous crap (for an EE) and you should try and move away from them. You probably don't appreciate the subtlety of a proper schematic diagram but believe me, they are much more superior to cartoons. \$\endgroup\$
    – Andy aka
    Jun 24, 2019 at 12:42
  • \$\begingroup\$ Thank you both very much for the comments. @smajli: If I can guarantee that the "phone charger" can deliver enough A for both sides of the relay, will the solution work? \$\endgroup\$ Jun 24, 2019 at 12:48
  • 1
    \$\begingroup\$ Thank you both very much for the comments. @Andy: Fritzing is working fine at the moment, I use it to figure stuff out before testing on a real board. As I move away from noob status I will check out alternatives. \$\endgroup\$ Jun 24, 2019 at 12:49
  • 1
    \$\begingroup\$ @BeachBumBob The problem is that you have left out so much information that no one can help you. At the very least we need to see a link to the manufacturer's datasheet for the USB charger and for your "device that needs 2A". The little cartoons don't really tell us anything. \$\endgroup\$ Jun 24, 2019 at 12:56

1 Answer 1


To day I use two power sources and a relay between RPI and the remote control(green card) since I don't want to accidentally fry my RPI.

That's a good policy. Most cell-phone 'chargers' can't actually deliver their rated current reliably - if at all. Using a dedicated supply for the Pi makes it much less likely to suffer from brownouts or surges caused by an overloaded power supply.

Is it safe to share one power source for both RPI and my remote control circuit, regardless if I add more power hungry crap on the non-RPI side of the relay?

IMO, no. The advantage of your current setup is that it maintains galvanic isolation between the Pi and all the 'power hungry crap' that might damage it. Using a common supply will make the system less safe.

  • \$\begingroup\$ Not the answer that this noob was hoping for. After reading the galvanic isolation link I understand more about the problem and understand it is the safest. Thank you for your time. \$\endgroup\$ Jun 25, 2019 at 9:47

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