I am a solar power enthusiast but with almost zero knowledge in electronics. However, I have asked here and there and I managed to build a simple circuit board that should suppose to deliver me 5V in order to charge a phone through a USB port.

So I have the following system: enter image description here

I read 12V from the solar panel and I can read the voltage along the red line between difference components, but once I connect the multimeter to the green terminal, I have 0V.

This is the part where knowledge kills me and I don't even know how to search for it, but shouldn't I read a voltage closer to 12V rather than 0V? Am I doing something wrong or do I need a resistance or a device that would close the system? But I was thinking that the multimeter has that inside, and that's why one can ready the voltage.

Bottom line, can anyone help me to understand why do I have 0V at the USB inlet? Is the circuit wrong?

EDIT: Here is a circuit scheme (it's the first time I built something like this, so please let me know if I need to add more info):


simulate this circuit – Schematic created using CircuitLab

EDIT 2: As requested, please see the back of the board enter image description here

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    \$\begingroup\$ Post a proper and accurate schematic. Without that you are floating a leaf in the water. \$\endgroup\$ Jan 2, 2017 at 20:37
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    \$\begingroup\$ What voltages do you measure at each step along the way? There are few components, so, the most likely problems are going to be "bad solder joints" (check especially, the ground connection to the 7805) or perhaps during your construction you caused the diode to fail-open. \$\endgroup\$ Jan 2, 2017 at 20:46
  • \$\begingroup\$ Lawrence, I have added a diagram. Will this help? And thank you for the ideas. I didn't think about it. I checked for short-circuits using the "beep" thingy on the multimeter. I read 12V at the inlet, then if I connect one terminal to the inlet and another one after the voltage regulator, I get like 11.5V \$\endgroup\$
    – Physther
    Jan 2, 2017 at 20:53
  • \$\begingroup\$ Double check the connections and the datasheet for the 7805. I've seen variants (78M05?) with different connections... \$\endgroup\$
    – user16324
    Jan 2, 2017 at 21:01
  • \$\begingroup\$ I have this written on the regulator (L7805CV), and I found this on Google sparkfun.com/datasheets/Components/LM7805.pdf By analyzing the scheme, it looks okay. Or is it? And how can I test this particular one? If I read the voltage before and after, I get a very small drop. Is that a good sign? \$\endgroup\$
    – Physther
    Jan 2, 2017 at 21:09

1 Answer 1


I know this does not solve this specific problem, but this cheap thing will do the job perfectly, and you can also add this charger module and a booster module (I do not have the right to put the link to it because of the "reputation rules" out there) to charge a single-cell Li-Ion battery at day, and use it at night. Happy hacking!

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    \$\begingroup\$ Thank you. I will surely consider those (or similar) parts for the next step. \$\endgroup\$
    – Physther
    Jan 2, 2017 at 20:54
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    \$\begingroup\$ With solar or any other eco energy source efficiency is always an issue. The 7805 circuit you have put together while a great learning exercise is only about 40% efficient. The switching regulator in this answer is 80-90% efficient. \$\endgroup\$
    – RoyC
    Jan 2, 2017 at 21:35
  • \$\begingroup\$ Now that I managed to fix the thing, I am checking the link you recommended. So let me get it straight. With the "cheap thing" can one connect the solar panel to "In" and "Out" and an extra battery on "Bat+" and "Bat-" terminal? So I can charge a battery and when there is no sun, the battery would charge the phone through the USB? And is that a replacement for what I am trying to build? Thank you \$\endgroup\$
    – Physther
    Jan 3, 2017 at 14:09
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    \$\begingroup\$ the 'cheap thing' is a step-down, switch-mode buck converter. in other words, it will take any voltage from the solar panel between 6 and 24v and turn it into 5v, with a maximum current of 3 amps. With that current you can charge a USB device and a battery at the same time, using a charger module. \$\endgroup\$
    – uiguig
    Jan 3, 2017 at 14:14
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    \$\begingroup\$ The charger module will ensure that the battery (Li-xx - Li-ion or Li-Po) does not overcharge and it will handle the charge safely. \$\endgroup\$
    – uiguig
    Jan 3, 2017 at 14:16

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