Thursday, April 10, 2014

Ground Reinforcement


  • My LED and servo system encountered a voltage-drop problem due to large current. 
  • Installing "big ground" greatly lessened the problem.
  • The ground is a junk aluminium bar. I am happy with using no money. 
  • And my cheap USB oscilloscope ($70) saved my day again. 
Anodized aluminium is not conductive.

I attached an aluminium flat bar to the device's frame to reinforce GND. The frame is made of polycarbonate. The flat bar is connected to the GND of the third module and of the controller.


The surface of the flat bar is anodized, so basically it is not conducting electric current. I made a hole and connected a wire through the crimped connector.


Anodized aluminium is good to avoid occasional short circuit during wiring. The back of the device is narrow after installing light modules.

重要なのはピーク電圧で、これが高過ぎると誤作動する。大体 600mV あたりで誤作動を起こす。

Test condition: 12 servos and 72 LEDs were controlled so that those consumed as much power as possible. The important statistic is the peak voltage of the IC's ground compared to the controller's ground.


The following figures show how the aluminium flat bar affected the ground voltage.
GND 強化前
GND 強化後
強化前、700mV 以上だったが、125mVまで減った。どうしてもPWMのタイミングで大量の電流が流れるので、こいつを抑えるにはもっと太くしないとだめなのかもしれない。(インピーダンスは指数関数的に増加する)

The voltage drops reduced from 700mV to 125mV. This is OK, but considering that I am going to put more modules and energy consumption will increase, the ground should be more stable. Maybe I need more thick flat bar or copper flat bar would lessen the problem.