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Nov
06
2011
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Posted 193 days ago ago by Derek Backus  0 Comments
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One of our good customers came to us with an idea for a trade show booth scene that included various Las Vegas gaming items. These included a Black Jack table, a roulette table and a slot machine. Because this was for a trade show booth, the requirement was for movement and animation including spinning the roulette wheel and animating the slot machine (with sound).
Sounds fairly straight forward right? It is not!
Slot machines are very well designed both mechanically and electronically. The machine is designed not only to detect when someone is trying to cheat but will also constantly check for faults in the circuitry, coin return, buttons, etc. Everything is constant ally checked by the electronics to make sure everything happens as it was intended.
To automate this machine, we selected the Parallax Propeller board.Parallax has designed a great platform for us to create software that talks to the outside world via input sensors and output pins. The software is very simple to grasp and allows us to easily setup (in the case of this project) five relay outputs, a switch input, a relay input and a servo output.
Problems we had to overcome:
- When the machine is opened, the machine faults.
- If a coin is pulled the wrong way through the coin chute, it will fault. This prevents people from tying strings to the coin and pulling it back out.
- The coin mechanism seems to somehow sense coins. I could swipe my finger and get it to sense a coin -- sometimes. Other objects would not register a coin.
- There was a coin reject mechanism before the coin sensing "eyes". If a coin was passed in front of these sensors while the reject mechanism was engaged, the machine would fault.
- A total of 5 buttons had to be pressed... in order, some multiple times. One of these was mechanical and the other 4 were optical sensors.
- The machine counts coins as they are ejected from the machine when a jackpot is hit. If there are no coins, the machine faults.
So, as you can see above, there are multiple items we had to solve to get the machine to continually play throughout the CES show. I will detail below the steps we took to eliminate each of these problems and make the wheels turn.
When the Machine is Opened, the Machine Faults
Simple... we shorted the switch so the machine always thought it was closed.
Feeding Coins & Sensing when Coins are Required
There are many error checks on the machine, but in the end, it was a matter of running coins across the light sensors -- only when required -- to get the credits to register on the machine.
The way this works:
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Determine if the machine will allow coins to be inserted. This means detecting if the coin reject mechanism is in a position to allow a coin to be passed by two optical sensors. If there coin reject is engaged and a coin passes the sensor, the machine will tilt. This machine works by energizing a solenoid when a coin is allowed to move past the sensors. If this solenoid is not engaged, the coin will drop down to the reject slot.
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There are two sensors to detect coin movement. The coin has to move in the proper direction and at a fast enough speed so the system doesn't tilt. The forward movement required is so someone cannot tie a string to the coin and pull it back out. This is solved by simply placing the sensors in the proper order on our platform.
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The light sensors seem to know it is a coin being passed and not another object. I could sometimes get my finger to register and sometimes other objects. Usually, though, other objects wouldn't register.
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We used a constant rotation servo to move the coins around. Using a servo this way, however, didn't allow us to set the position of the servo. We used a simple Radio Shack roller switch to sense when the coin has moved past the sensors.
Pressing Buttons
The machine is designed so that all functions required to play the machine are tactile. To make the wheels turn and coins shoot out, a series of steps needs to happen, in order.
- Add money to the machine, if necessary. This machine requires 3 credits to play.
- Place a bet.
- Pull the lever.
- Press each of the three wheel buttons.
So, we're pressing a total of 5 buttons to get this machine to cycle through one session of play.
Coin sensing and adding money are detailed above.
The first button we press is the bet button. This is the only mechanical button we found on the entire machine. We use one of the outputs of Propeller to drive a transistor circuit that engages a 5V relay. Using the connection of the relay, we short the switch (press the button). This button is pressed three times because it takes three coins to pull the handle.
The handle is actually tied to an optical switch. This took some effort to figure out how this particular switch worked. After looking up the part number on the internet, it was determined this switch was a transistor that caused a current to flow when the optics were interrupted. Simple, then... we just short the proper two contacts (there were four) because that is essentially what the transistor would have done. We used the same transistor/relay combination we used for the bet button.
The next three buttons -- the ones that stop each wheel from turning -- were next. These worked exactly the same way as the handle so no trial and error involved.
Once the above five buttons are pressed, we repeat the entire cycle.
Coin Payout Mechanism
This slot machine, and I'd imagine all slot machines include a hopper that can collect hundreds of coins to payout when requested. The way this typically works is that a coin is inserted into the machine, it is checked for proper size and direction and then is dropped into the hopper.
When a jackpot is hit or a payout is requested by the player a coin payout mechanism is activated that throws coins out of the hopper, counting each one to make sure the number of coins paid is correct.
You can see with the mechanism in this machine, we could not automate the machine unless we figured out some complicated electronics or made a coin return mechanism. We chose to make a mechanism that returned the coins back into the hopper instead of shooting them back to the player. You can see in the video that it is just a simple slide that grabs the coins and directs them back into the hopper. It looks simple but took some time and effort to achieve a reliable mechanism.
To get the plastic to bend to the proper shape for the slide, we cut the shape we wanted on our laser cutter (an Epliog 36EXT), and put it in the oven to soften it a little. Then we took styrene strips and wrapped them around the outside of the bent acrylic slide to hold the coins in place. This video does not show the cover, which is required to keep the coins from popping out of the slide when the payout mechanism gets a little too aggressive.
Download the Propeller Code
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