Roulette Wheel Sensor
This device was designed to monitor the rotational speed and direction of a roulette wheel and detect on which number the ball landed.
Jamtech designed and manufactured this device, used in the gaming industry.
One of the greatest challenges of this project was the satisfactory function of the optical sensors in high ambient light conditions with large mains-born flicker. We solved this through a detailed programme of research and development.
How does it work?
The roulette wheel sensor uses an optical method to collect ball in track speed, wheel speed, wheel direction and ball land position information.
The unit has a total of four optical sensors, two for wheel direction and speed, one for ball land position and one for ball in track monitoring. Optical data in the form of reflected light is converted to real time a digital stream and then processed by a 32-bit ARM core CPU.
The internals of the wheel sensor are shown below.
Use was made of PCB mounted electrochemically etched parts for the optical adjustment mechanism to reduce manufacturing costs.
How is wheel speed measured?
The use of a red light source is made to exploit the red, black and green colours found on the number ring of the roulette wheel, as the red numbers reflect more light than those on a black or green background.
Consider a single sensor collecting reflected light for numbers either side of ‘0’ illustrated below
From the above, the zero position (numbers 26 & 0) of the wheel is determined when the period of least flection is approximately twice that of a red number. Once this has been detected, the wheel RPM can be determined from the time interval between successive zero passes.
What about wheel direction?
To find the direction of the wheel a second sensor is added which is positioned a half number angle (approx. 5o) from the first sensor. Thus a classical quadrature signal illustrated below is produced, from which direction can be determined.
The above looks at wheel movement detection only and perhaps belies the design hurdles that had to be overcome before a stable design was realised. However, the roulette wheel reader was successfully implemented into the clients gaming system.