1 2 Previous Next 15 Replies Latest reply on May 14, 2015 3:27 AM by doorleyr

    Galileo (gen 2) not receiving power?


      I'd been tinkering for a few days with a new, fully operational Galileo gen 2 and tonight, had made a simple circuit as pictured (photographed after the problem arrived).



      It worked; the voltage divider receives from the 3.3v, is connected to GND and outputs to an LED connected to GND.
      (I sloppily disregard circuit convention).


      After a few minutes (with the divider set so as to make the LED quite dim), everything seemed to 'turn off', including the lights on the Galileo itself.

      Even after disconnecting and reconnecting the power several times and moving to different power points, the device seems to be completely dead (or otherwise the power able has somehow failed, though with no observable damage).


      I haven't made some horribly destructive circuit, have I? Has my unit simply malfunctioned?

      I am currently investigating the use of the device in a classroom which has pooled another 15 devices, and it concerns me that if I may so easily break it, how might the students possibly fare?!


      Is there any test I can perform to resuscitate the device?

      Is this a common problem?

      Is this in violation of any terms of the warranty?


      Tyson Jones (PootPooter)

        • 1. Re: Galileo (gen 2) not receiving power?

          Hi PootPooter,


          How did you exactly connect your circuit? I mean, what is the pin order of the pot you used? If you could be very specific it would be great.


          According to the picture I understand the following:

          Pin 1 -> 3.3V

          Pin 2 (center) -> GND

          Pin 3 -> LED -> GND


          Is my interpretation correct?




          • 2. Re: Galileo (gen 2) not receiving power?

            Yep, your interpretation is correct.

            (I'd formerly checked the voltage was not too high for the LED and so hadn't used a resistor).


            Could any circuit design from Vin to GND ever cause the Galileo to fail?!


            • 3. Re: Galileo (gen 2) not receiving power?

              Hi PootPooter,


              Usually the pinout of a pot is similar to the picture below. The center pin is the pin 2. You should connect it to an input of another device, for example a LED. The pin 1 and pin 3 usually are connected to VCC and GND so the center pin can be set between those limits: VCC and GND.


              Potentiometer Pin Out.jpg

              According to your circuit, and you already confirm it, the center pin was connected to GND. This means that when you moved the knob towards the pin 1 (connected VCC) you did a connection between VCC and GND (a short circuit). That probably was the cause of the issue.




              • 4. Re: Galileo (gen 2) not receiving power?

                I think I see my misunderstanding of the voltage divider now, thanks.
                So you're suggesting my setup would have been equivalent to connecting 5v to GND directly?
                Does this damage the device?



                • 5. Re: Galileo (gen 2) not receiving power?

                  Hi PootPooter,


                  Yes, that is what I'm suggesting. And yes, that kind of connections will damage the board. The correct way to connect a pot as a voltage divider is like in the picture below:




                  • 6. Re: Galileo (gen 2) not receiving power?

                    How exactly is such a setup different?
                    If I turn the divider knob all the otherway, this will still cause a short-circuit between Vin and GND, won't it?


                    Also, are you claiming the Galileo has no inbuilt protection against short-circuiting from Vin to GND?
                    Isn't that kind of dumb? I've read other boards have it (Short 5v to ground)



                    • 7. Re: Galileo (gen 2) not receiving power?

                      Hi PootPooter,


                      Check the pictures below. The picture on the left is the voltage divider circuit composed of two resistors. The resistor R1 is connected to VCC (point 1), the resistor R2 is connected to GND (point 3). The middle point between each resistor is the output voltage (point 2). That output is connected to your device, in this case a LED. The picture on the right is the same voltage divider circuit but using a pot instead of two resistors individually. The principle is the same: point 1 to VCC, point 3 to GND, and point 2 is the output voltage. In a voltage divider, the input voltage (VCC, point 1) will never be connected directly to GND (point 3) because there always will be a resistor value between them (R1+R2), so there won't be a short circuit between VCC and GND.


                      Voltage Divider using two resistorsVoltage Divider using a pot


                      What you did was to connect the point 1 to VCC (3.3V), the point 2 to GND, and the point 3 was taken as the output voltage, so it was connected to the LED. When you moved the knob towards the point 1 (3.3V), the R1 value went to zero making a short circuit between VCC (3.3V) and GND. Summarizing, the point 2 and the point 3 were wrongly connected. Let me know if this answered your first question.



                      Regarding the protection against short-circuiting, there is no protection against short circuit between Vin and GND, however you weren't using the Vin pin. You used the 3.3V output.


                      Galileo Gen 2 pinout.jpg

                      The Vin input in the Galileo is connected to the same point that the barrel jack used for powering the board. Check the picture below; it is part of the schematic of the Galileo Gen2 where the barrel jack connection is:



                      The Galileo has two voltage outputs. One for 5V and another one for 3.3V. Those voltage levels are generated internally by two voltage regulators. The voltage regulator used to generate the 5V is the TPS62130 (datasheet: http://www.ti.com/lit/ds/symlink/tps62130.pdf). Check the schematic section of the voltage regulator to generate the 5V output:



                      The TPS62130 has short circuit protection. You can check the datasheet on page 16 to see a more detailed description. On the other hand, the 3.3V output signal is generated by the voltage regulator TPS652510 (datasheet: http://www.ti.com/lit/ds/symlink/tps652510.pdf). Check below the schematic section of this voltage regulator:



                      Notice that this 3.3V level is generated from the 5V generated by the first voltage regulator described before. The TPS652510 doesn't have short circuit protection, it has only a limit current but there is no protection. Since you were using the 3.3V output, and it was connected directly to GND, there wasn't any protection against that short circuit and the board got damaged. Let me know if this explanation answered your second question.



                      In the Arduino board (Arduino UNO) there are two voltage regulators for the 5V and 3.3V as well. The Arduino UNO uses the voltage regulator NCP1117ST50T3G (datasheet: http://www.onsemi.com/pub/Collateral/NCP1117-D.PDF) to generate the 5V level output, and the voltage regulator LP2985-33DBVR (datasheet: http://www.ti.com/lit/ds/slvs522n/slvs522n.pdf) to generate the 3.3V level output. Check the schematics below for each voltage regulator in the Arduino UNO:


                      5V Voltage Regulator - Arduino UNO3.3V Voltage Regulator - Arduino UNO


                      In this case, both voltage regulators in the Arduino UNO have short circuit protection. But, similar as in the Galileo board, there is no protection for the Vin input pin. The Vin input is connected to the barrel jack in the Arduino UNO, it’s the same point. If you short Vin to GND you will damage the Arduino UNO. Check this site http://www.ruggedcircuits.com/10-ways-to-destroy-an-arduino, the “Method #7: Short Vin to GND” section.


                      I hope you find all this information helpful.




                      • 8. Re: Galileo (gen 2) not receiving power?

                        So the 3.3V has a current limit but no 'short-circuit protection'?

                        Is the limit really so high as to allow a current (from 3.3V) that would break the board anyway?

                        What is the point of a current limit at all if it can't protect against a short circuit?


                        (If I were using the 5V source, the protection would have prevented the board from damage? Seems hardly intuitive; I chose to use 3.3V conservatively )


                        Just to clarify, with a properly connected potentiometer with the middle pin connected to a digital input (but with no external resistors); would turning the knob break the pin?
                        (ie; if I sent the full 5V to the pin, as I did to GND)

                        This example seems a bit scary in that regard Arduino - Potentiometer


                        Thanks extremely for all the help,

                        • 9. Re: Galileo (gen 2) not receiving power?

                          Hi PootPooter,


                          I completely understand your point. I have just said to you the information I got from the Galileo schematics and the datasheet of each regulator used in the Galileo board and in the Arduino UNO.


                          When there is a short circuit the impedance is zero between the two points and the current is theoretically infinite. I haven't found any reference about a short circuit protection in the datasheet of the regulator used to generate the 3.3V in the Galileo, and neither in the Galileo schematics. That is why I said there isn't short circuit protection for the 3.3V output.



                          Regarding your last question. Notice the example you linked is for the analog input, not for the digital input. However in both cases, analog or digital input, the board will work fine and it won't be damaged if you connect a 5V signal. Just make sure to set the IOREF jumper to 5V to make the input pins 5V tolerant. If you set the IOREF jumper to 3.3V and then use 5V in an input pin you will damage the board because the IOREF was set to 3.3V instead of 5V.


                          I will suggest you to check these two examples for the Galileo. One of them uses an analog input and the other uses a digital input. In both examples the inputs are connected to 5V.


                          Let me know if you have further questions.




                          • 10. Re: Galileo (gen 2) not receiving power?


                            What exactly does it mean to "set the IOREF jumper to 5V". Do I just connect the IOREF pin to the 5V pin? (and for how long?)

                            (Sorry for my ignorance, I tried searching this but my google-fu is obviously lacking)


                            Also, do you know exactly what's occurring regarding the potential at a digital PIN when you set it to input mode?
                            I notice that components connected between 5V and the input pin receive very little power (ie; LEDs remain dim).

                            Is the PIN placed at a potential very close to 5V (but slightly less), or does it instead have a significantly large resistance to steal all the power from the other component?
                            (I destroyed my board before I could investigate this further using parallel circuits)


                            Thanks for your patience!

                            • 11. Re: Galileo (gen 2) not receiving power?

                              Hi PootPooter,


                              There is a jumper in the IOREF pin header. Look the picture below. The IOREF means Input Output Reference and it can be set to 5V or 3.3V. If you set the jumper to 5V the IO pins will be 5V tolerant, so you can use signals of 5V level. If you set the IOREF to 3.3V the IO pins will be 3.3V tolerant. The IOREF set the logic level used: 3.3V or 5V. The IOREF is usually set to 5V by default because it is the most common logic level used in many circuits.


                              You don’t have to connect the IOREF pin to the 5V pin; I think you are confused because there is a pin named IOREF. Please check the picture below to see where is the jumper I'm talking about. If you see carefully you will see 3 pins, the left one is labeled as 5V and the right one is labeled as 3.3V, with the jumper you will connect the center pin to 5V or 3.3V. By default it is set to 5V. Please let me know if it is clear now.


                              Galileo Gen 2 IOREF.jpg


                              Regarding the potential of the input pin, when you set the pin as input, the impedance goes high so all the power (almost all) goes to the internal large resistance. It is like you said.


                              Check this site; it might be helpful to you: Why is high input impedance good? - Electrical Engineering Stack Exchange




                              • 12. Re: Galileo (gen 2) not receiving power?

                                I think I understand.

                                You've been remarkably helpful, thanks a tonne!
                                Tyson Jones

                                • 13. Re: Galileo (gen 2) not receiving power?

                                  Hi Diego,


                                  Thanks for this explanation, it's very helpful. I just want to check one thing: if I set the jumper to 3.3V, the IO pins will use 3.3V logic but will the 5V output pin still deliver 5V. The reason I ask is that I'm using the Board to communicate over SPI with a sensor which requires 5V power but uses 3.3V logic.




                                  • 14. Re: Galileo (gen 2) not receiving power?

                                    Hi doorleyr,


                                    Yes. The 5V and the 3.3V output pins will provide 5V and 3.3V regardless of the IO jumper position. The IO jumper only set the voltage level for the IO pins.




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