Can We Hack It? A Candy Grabber

In the 1980s the arcades were where all the action was. The latest games would forcibly remove 10p coins from our pockets as we went for the highest scores. But one game was a little different; it involved a metal claw controlled by the player as they hunted for a teddy bear, watch, or some novelty toy.

The claw game was great fun, but those claws were weak, and most times the teddy bear dropped back into the pile. So when we found a cheap version on eBay that offered the same fun game, but without the need for 10ps, we had to take one apart!

Made of a solid plastic frame, the chassis is robust and can be worked with hand tools and, with care, small power tools. The red and black plastics are the most robust, while the clear plastic used as windows to prizes in the candy grabber is strong but will crack if not handled gently. The unit is held together with cross-head machine screws which bite into mounting pillars in the plastic.

ELECTRONICS

Powered by 3 × D cell batteries, the candy grabber runs at 4.5 V throughout. This was tested at the motors and joystick controls. Rather than use batteries, the game can be modified to run from a 5 V power source – either a USB battery or a USB adapter.

It should work just as well with a 5 V supply, but a DC buck converter can be used to drop the voltage down to 4.5 V with no loss of functionality.

The grabber unit moves along a gantry system via two DC motors giving us two directions of movement, and there are limit switches along these axes, enabling the unit to stop the motors before the end is reached.

To control the height of the grabber, another DC motor is used to wind a chain with the grabber hand at the bottom. When we press the joystick down, the grabber opens, and when we press up, it closes.

The controls are simple switch inputs connected to a custom single-sided board. They operate at 4.5 V, which means that they can be directly used with 5 V boards such as Arduino. But for Raspberry Pi and other 3.3 V boards, a converter board will be required.

To start the game, a token is inserted into the slot which has a small microswitch which will trigger the game to start – signalling power to the motors, and playing a rather 'vociferous' version of carnival music. Music is provided by the same circuit board and is contained in a chip-on-board (COB) which is covered in epoxy and not available to hack.

A small speaker secured to the bottom of the chassis is easy to work with and can be used with add-on boards for the Raspberry Pi to play real music.

When a player drops their prize into the chute, there is a light sensor and LED. When the prize blocks the light from the LED to the sensor, a winning jingle is played.