Having trouble getting power from the 12V


 
J

JoePhan

New member
Hello,

When I plug in the usb into the Raspberry Pi, everything seems to power up just fine (LED, screen turns on). However, when I try to plug in my 12V, 2A power supply, the LED does not turn on, and there doesn't seem to be any signal from anything. Any ideas? Here's a picture of the board, if that might help http://imgur.com/a/cdU5P

Had a question about the P-MOSFET: Does the square portion need to be soldered to the board? Does it matter how flat it is against the board? I'm wondering if the problem may lie there.

Thanks for the help!
 
Well, found the problem. Seems like I put my diodes in reverse! 12V seems to work fine now.

However, looks like my servo doesn't seem to work. Makes a little sound when initially plugging in, but nothing after that. I took off the propeller, and it doesn't seem to make a difference. How much voltage should be going to the servo? I'm not seeing much of a reading when I measure the jack on the heatermeter board.
 
Hey good work on the 12V! The P-MOSFET does not need to have its tab soldered down. It is fine to just float there as the connections are made to the pins as well. If you plan on running a higher current blower (>500mA) then it is advisable to just fill that in with some solder.

The servo is powered from the 5V / GND pins on the output, so check that first to make sure you're getting 5V at the servo. The servo pin normally should have ~0V and jump up to some small voltage when the servo should be moving (and a few seconds after). The value will vary depending on how your multimeter reads it, as it is a ~1.5ms pulse every 20ms. Mine reads about 0.375V. On an oscilloscope you'll see 5V pulses going out.
 
Ok, so I measured the voltage coming out of the output at the servo, seems to be getting 5 V. Also measured the servo connection, and monitored occasional jumps to 0.374-4 V. However, not seeing any movement in the servo. So it appears those connections seem fine? Is the servo possibly broken? Or is something else going on?
 
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