We are building a Raspberry Pi with 2 servo motors connected to one power supply. But whenever the servo motors are provided with a signal to power and then move, the raspberry pi's green light turns off, and then when the servo motors stop moving, the green light comes back on. We assumed that this is a loss in power but when we measured the voltage throughout the circuit, we found it to be a consistent 5 volts. Is there something else going on here? Does the raspberry pi's green light not necessarily mean it has power?
\$\begingroup\$
\$\endgroup\$
2
-
1\$\begingroup\$ Did you measure the power source output? Is that constant? \$\endgroup\$– Willy WonkaCommented Oct 15, 2018 at 6:29
-
\$\begingroup\$ Preferably you should not use the same power supply for servos and a computer with delicate storage state such as a raspberry pi. \$\endgroup\$– Chris StrattonCommented Oct 15, 2018 at 14:56
Add a comment
|
3 Answers
\$\begingroup\$
\$\endgroup\$
1
If the power drops very quickly (which is the case when the servos start to move and you did not provide enough capacitance), you are not able to measure this (short) power drop with a standard multimeter. (according to this site, green LED is SDCARD access and does not monitor power).
Solution: You need to provide (a lot) of capacitance (like e.g. 2x 470uF) to the servos.
Best would be to have a seperate power supply for the servo and the pi.
answered Oct 15, 2018 at 10:45
-
1\$\begingroup\$ Capacitors won't be enough in the case of a servo mechanical stall, that would probably cause the pi to brown out and brings a risk of file system corruption. \$\endgroup\$ Commented Oct 15, 2018 at 14:57
\$\begingroup\$
\$\endgroup\$
The green light is Read/Write activity from your storage device (sd card, hhd etc) it has no reference to any GPIO activity. As for your 5V power, its is as good as what you bought to power the PI, so current capacity are really limited to the USB3 power port, the pcb lands up to the header. I wold say at the most power it could handle without board damage would be around 10A but I would de-rate this rating for temperature and safety margins down to 6.5 A.
Your "green light off" just means the computer finished loading your program, and its doing nothing but executing your code in memory.
\$\begingroup\$
\$\endgroup\$
The green light on the Raspberry Pi that you are talking about has nothing to do with power warnings. If the light is constantly lit, then it means that the connection between the SD card and the Pi was successful. If it is consistently blinking, it shows that the Pi is either reading or writing from the SD card.
Now if you are suspecting loss of power, you might want to consider using a more heavier power supply. Or you could also use a DC-to-DC boost converter. They step up the input voltage to a higher output voltage. Hope this gives some idea!
