Auto bed leveling servo hookup

[kd7eir]

I have been following Zenmasters instructions for setting up auto bed leveling. I jumpered the two pins on the ramps board as he said to do. Immediately after doing so my lcd dims and I lose the USB connection to the board. Remove the jumper and everything works normally. Any ideas of what may be wrong?

[cperiod]

Your servo is pulling too much power. When I hooked up ABL, everything *worked* but the servo jiggled constantly when printing as power fluctuated to the steppers. I pulled the jumper and ran 5V from my ATX PSU direct to the servo power pin (the middle one in the group you jumpered) and the problem went away.

[quixotic120]

for the servo jiggling during moves you can activate #define PROBE_SERVO_DEACTIVATION_DELAY in config.h - this will disable it unless needed. default is 300 - I found 400 to work best with a tower pro 9g servo. depending on the speed you may have to increase the delay; If the servo doesn't complete it's moves increase it and vice versa

[cperiod]

Defining that improved things, but it didn't go away 100% until I changed the 5V supply to the PSU.

[quixotic120]

interesting. I'm using an LED power supply so I only have +12vdc but I'm sure I have a spare 5vdc supply somewhere around here. I'll give it direct power a shot.

If I use external servo power will deactivation delay will do nothing? I assume it works by cutting +5v to the servo x milliseconds after a command is given.

[Roxy]

If I use external servo power will deactivation delay will do nothing? I assume it works by cutting +5v to the servo x milliseconds after a command is given.

It is a little bit more complicated than that. The power stays connected. After the timeout period, the interrupt routine that feeds pulses to the servo to position it quits sending the pulses. And the Servo goes quiet until it gets a valid pulse train again.

[quixotic120]

interesting. thanks! to be clear my servo works fine but before I enabled deactivation I was getting a lot of jerking. wondering if external 5v power would make things a bit more reliable and consistent

[Roxy]

Another thing you can do is change the angles +/- 1 or 2. Certain positions are more sensitive to twitching than other positions.