Some users of the Handyboard with the expansion board have reported a jitter in their servos that occurs when one or more servos are turned on AND one or more DC motors are also being run by the Handyboard. In some cases this jitter is hardly noticable and in some cases it can cause ther servos to move all the way against their stops. This problem seems to be affected by the individual Handyboard, the individual servos and the battery level at the time.
If your robot suffers from a servo jitter problem, this page will explain the steps you can take to eliminate the problem. If you have not experienced the problem, or do not use servos, you may still implement this fix -- it should not hurt anything else. Or you may simply wish to bookmark this page should the problem ever come up. All Handyboards sold by KISS Institute after 7/1/04 will have this fix implemented before they are sold.
KIPR wishes to thank Terry Grant of NASA Ames Research Center and his Summer students Elton Kong, Christian Rayburn & William Davison for isolating the problem and suggesting this fix.
You need to remove the Expansion board from your Handyboard. First, TURN OFF the Handyboard and remove any sensors, servos or other items that are attached to the Expansion board. Then remove the display, grasping it carefully and pulling straight upwards:
Next, you need to remove the expansion board. This is a little trickier since there are several sets of connectors that hold it to the main board. You may wish to loosen it a at each corner before pulling straight up.
The Handyboard has an inductive element that isloates the battery ground from the logic ground. We need to bypass the inductive element to remove the jitter. The best way we've found to do this is to first remove the battery ground supply. This is done by removing the two right most pins from a group of 4 pins at the front-left (near the servo ports) of the Handyboard. You may either clip these pins off, or simply bend them forward so they no longer go into their socket. Note: the left two pins need to stay intact.
The last thing you need to do is to jumper the servo ground directly to the logic ground, before any of thisolation circuitry. This step requires you to solder a short piece of wire. Use insulated wire (gauge 22 to 26). Solid core or stranded will both work fine. Use a piece of wire about 3/4 inch in length. Strip and 1/8 inch from each end and tin the ends with solder. Place the wire in the holes shown below, and solder them in place from the other side.
That's it!! Now you just need to put the expansion board back onto the Handyboard and then put the display in place.
