Symptoms:
- The LM317T failed to generate the intended 12V output voltage (it only outputs 1.5V ~ 1.6V). The chip functions normally after it's removed from the board;
- The motor keeps spinning even without PWM input from the timer (according to my design, the motor should not spin without PWM input).
Troubleshooting:
After double checking the schematic and testing the component (LM317T) removed from the board, I thought the problem was with the PCB board itself so I took a new board and soldered the LM317T with 2 resistors and the power cables for testing. As the output of LM317T was still around 1.5V ~ 1.6V, I decided to increase the voltage from 12V to 24V to see if it will change anything. At this moment I noticed there were sparks coming out from the point where the red wire is connected to the board (see below video and photo).
It's when I realize there is a short between the Power and the Ground Plane.
Here is the setting used to generated the ground plane of the board, the clearance (Isolate) is set to 0 (dumb dumb).
Isolate = 0.012".
Isolate = 0.016".
Isolate = 0.024".
Sparkfun recommends setting the value for Isolate to 0.012". I think I will go with 0.016" or even 0.024" (where possible) for extra safety.
Now the cause of the problem is identified, time to get back to Eagle to modify the ground plane clearance and fix some issues found in the board. Life is fun!! :-)
References
Using EAGLE: Board Layout
https://learn.sparkfun.com/tutorials/using-eagle-board-layout/finishing-touches
TUTORIAL on how to add a ground plane to a pcb in the Cadsoft Eagle layout editor.
http://www.pcbway.com/project/share/TUTORIAL_on_how_to_add_a_ground_plane_to_a_pcb_in_the_Cadsoft_Eagle_layout_editor_.html
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