I thought it could be pretty cool to try switch adapting the Hungry Hungry Hippos game. In researching what had already been done I found this product from Enabling devices which is a mechanical adaptation utilizing a paddle to make pressing the lever easier. I also found this project from the UConn Biomedical Engineering program which used motors and was switch adapted.
Below is a video of my version in action. It’s a little more compact (just a servo, arm and paper clip) but also for now just focusing on the eating lever of each hippo.
Below are pictures of the control board. The servos could be simply driven from an Arduino directly, but I decided to solder together a more robust board with a few extra features. The essential components are the microcontroller, switch jacks, servo pin headers, and power jack.
Since the servos I was using exhibited a motor whine even when just holding position I needed a way to idle them. Unlike analog servos, digital servos keep trying to hold their position for as long as they have power even if you stop sending them a control signal. So for this I added a transistor for each servo acting as a low side switch, cutting off power when the servo is not in use. Also, these servos draw a huge amount of current when moving quickly out of a full stop. Though powering them from 4 D batteries worked fine, most of my power supplies would temporarily shut down when detecting the sudden huge current draw. To rectify this I added a very large capacitor that was able to supply the initial surge current needed. Again, using battery power instead, different servos, or moving them more slowly would have also worked.
I opted to hot glue the control board under the center of the game board to better conceal and protect some of the wiring and electrical components. I got some Duplos from my daughter to act as risers for the game board.