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U O R OW Y D L I N U B GIANNI PALOTTI’S JACKPOT A slot machine is a game where you insert a coin, and the machine randomly chooses a combination of symbols. Depending on what symbols turn up, you might get a payout; rare combinations could net you many times what you put in. They can be fun to play but it gets expensive if you’re using real money. Why not build this machine with colour graphics and sound; it’s just as fun to play, but you can’t lose your shirt! T his slot machine displays four virtual wheels, each with 17 symbols drawn from a set of six: cherries, a bell, a bar, the number seven, a lemon and a bonus starburst (see Fig.1). It is based on a Micromite Plus LCD BackPack, producing colour graphics and sound. To keep things simple, this Slot Machine differs a little from a real slot machine that has the symbols in a fixed order on the wheels. Instead, it randomly selects one of the six symbols for each wheel over the 17 ‘runs’ or ‘loops’. Each symbol showing at the end of each cycle therefore has six possibilities. Still, as this is updated over 17 cycles, the possibility of repeating the same symbol too often is avoided. The design includes a 5c coin input slot; this gives the player a more realistic ‘casino’ feeling when compared to a typical downloadable slot machine game. The standalone cabinet also makes it more interesting than any old app. I made the coin input from a funnel with a reflective photosensor. Every time a coin passes through, a highto-low signal transition is sent to the Micromite Plus LCD BackPack around which the game is based, and it adds one credit in response. It has a limit Fig.1: the six possible symbols that randomly appear on the four ‘wheels’ during play. The payout varies depending on what combination is shown in Fig.2. of three credits (coins) per spin, and wins are calculated accordingly, based on the chart shown in Fig.2. You could use a pushbutton instead of a coin slot, but that would remove some of the fun. An add-on module offers the possibility of a solenoid-operated ‘kicker’ to eject any coins collected into the coin tray. This can be done by operating a tilting table, or the coins can be ejected into a thin tube (with an internal diameter slightly bigger than the 5c coins) located under the coin input funnel. However, the details of those options are not described here and will be left as an exercise for the reader. Some changes to the overall case dimensions would be necessary to implement either option. Operation Once power is switched on, the program starts an initialisation routine which sets up the sound module and loads images from an SD card using the BLIT READ command available on the Micromite Plus. Once the initialisation is complete, the gamer can insert coins into the slot. The first coin will activate the “PlayReady” LED, and the “Play 1 Coin” button becomes active. You can choose the number of coins you would like to play by continuing to push this button or hold it down until no more coins are transferred from the “CREDITS” box into the “COINS IN” box. The maximum number of coins you can play for each spin is three. When “Spin Wheel” is pushed, it changes the symbols displayed on the screen using the “BLIT WRITE” command, based on random numbers generated by the RND(TIMER) function, which tells the computer to use its internal clock value as a random seed. This number is then further processed Slot Machine Payouts ● ● ● 1 ● ● ● 2 ● ● 3 ● 5 ● 5 ● 8 Values above the red line are multipled by the amount of coins inserted (up to three coins). 10 ● 18 20 ● 25 30 ● 50 JACKPOT Fig.2: the payouts that are given depend on the result of the spin. For example, if you get “7 cherry lemon cherry”, that’s two cherries, so you get a payout of three if one coin was inserted, six if two were inserted or nine if three were inserted. siliconchip.com.au Australia's electronics magazine May 2022  77 Fig.3: the circuit of the Slot Machine is simple as most of the work is done by the Micromite. It triggers audio playback by sending commands to the DFPlayer Mini module, which connects to the loudspeaker via CON1. The rest of the circuit is mostly a power supply and a way to interface to the pushbuttons, LED and coin sensor. to achieve an almost-random value from 1 to 6. The process is then repeated 17 times to simulate the wheels spinning, after which the result is analysed and any payout is processed, as per Fig.2. The addition of sound effects makes this unit more fun and adds to the 78 Silicon Chip reality of the game. After all, the point of playing slots is to have fun! Circuit details The main circuit is shown in Fig.3. It’s based around the Micromite Plus LCD BackPack (November 2016 issue; siliconchip.com.au/Article/10415). Australia's electronics magazine This has a powerful onboard PIC32MX470F512H 32-bit 120MHz processor plus a 320x240 pixel colour touchscreen that’s used as the display and for user input. The touchscreen has a 3.2-inch (8cm) diagonal measurement compared to the 2.8-inch (7cm) screen siliconchip.com.au Parts List – Slot Machine 1 Micromite Plus LCD BackPack (without touchscreen) loaded with SlotMachine V10.bas [Silicon Chip Cat SC6211] 2 microSD cards loaded with sounds & images 1 3.2-inch LCD touchscreen with ILI9341 controller 1 4-pin female header (to mount the touchscreen to the BackPack) 1 double-sided PCB coded 08105221, 76 x 53mm 1 DFPlayer Mini audio player module [Silicon Chip Cat SC4789] 1 5V DC coil SPDT relay (RLY1) [Omron G5LE-5V or CIT J107F1CS125VDC] ● 7 2-pin headers, 2.54mm pitch (CON1, CON3, CON9-CON13) 1 4-pin header, 2.54mm pitch (CON2) 1 PCB-mount DC barrel socket (CON4) 1 2-pin polarised header and matching plug, 2.54mm pitch (CON5) 2 8-way female headers, 2.54mm pitch (CON6, CON7) 1 18-way male or female header, 2.54mm pitch (CON8) 1 9V battery clip to barrel plug (optional) 1 3W 4W miniature loudspeaker 1 grille to suit the loudspeaker 1 panel-mount slide or toggle switch (power on/off) 3 square miniature panel-mount pushbuttons (Collect, Spin & Play Coin buttons) [Jaycar SP0716 or Altronics S1080] ▲ 1 red panel-mount LED in a square housing [eBay item #353825669342] 1 PS126EL1 paper sensor (optional, for coin sensing) various jumper wires various M3 machine screws, nuts, washers and spacers (for mounting the PCBs, coin sensor etc) Hardware 1 300 x 350mm sheet of 7mm plywood 1 136 x 95mm sheet of 14mm plywood 1 150 x 130mm sheet of 3mm black perspex/acrylic ■ 3 65 x 52mm sheets of 3mm black perspex/acrylic ■ 1 100mm length of 20 x 12mm aluminium angle 2 M5 x 15mm hex socket cap head machine screws 4 No.4 x 10mm self-tapping black screws for mounting the front panel 4 M4 x 10mm panhead machine screws & nuts 3 M4 x 6-7mm panhead machine screws 2 M3 x 20mm panhead machine screws & nuts 14 No.4 x 15mm wood screws Semiconductors 1 7805 5V 1A linear regulator (REG1) 1 2N2222A 40V 600mA NPN transistor (Q1) ● 1 1N4004 400V 1A diode (D1) ● Capacitors 2 100μF 10V electrolytic 2 100nF multi-layer ceramic Resistors (all 1/4W 5%, small body types if possible) 2 10kW 1 2.4kW ● 6 1kW 2 1kW ● 1 120W ▲ add one more button if a coin sensor is not being fitted ■ or purchase laser-cut pieces from the Silicon Chip Online Shop (Cat SC6181) ● these components are only needed for the optional ‘coin kicker’ normally used for this BackPack. That larger size makes it better suited to the Slot Machine. Since it has the same number of pixels as the 2.8-inch screen and a compatible controller chip, it’s a direct swap; the only consideration is that the mounting holes no longer line up with the BackPack PCB. siliconchip.com.au Because of this, I glued a 4-pin female header to the outer side of CON4 on the BackPack to provide extra anchorage for the screen. The components besides the BackPack and LCD are hosted on another PCB that adds just a few things to the BackPack: Australia's electronics magazine • • • • a simple linear power supply some buttons and LEDs the coin sensor a DFPlayer Mini digital audio player, described in the December 2018 issue (siliconchip.com. au/Article/11341). This PCB concentrates all the extra connections into two sets of wires, one 9-way and one 3-way, that emanate only from one side of the BackPack. The DFPlayer Mini is responsible for producing all the sounds. It is wired to a miniature 73 x 51mm 4W 3W speaker mounted in the back of the Slot Machine. Power comes from a 9-12V DC plugpack or battery through a DC barrel jack or direct USB input to the BackPack. Micromite control Programming the Micromite Plus LCD BackPack is easy as it is done in BASIC. The software configures the COM port required to control the DFPlayer Mini music player module (COM2), sets the correct music files source (micro SD slot) and sets the volume to the required value (20). The BASIC code can be downloaded from the Silicon Chip website and loaded into the BackPack in the usual manner, eg, using TeraTerm or MMEdit to load the software into the BackPack over its USB virtual serial port. Once running, the coin input generates an INTH command which runs a routine where the number of coins inserted is registered without affecting other operations or music playback. The rest of the code is based on which button is pressed and how much credit is available at the time. In addition to loading this software, you must load each audio file on the micro SD card in the correct order. The sound effects are also part of the download package, although the ‘background music’ is not included as it depends on your taste. Select a music track and convert it to a 44.1kHz 16-bit stereo WAV file. The files must then be copied into a folder named “mp3” on the micro SD card in the following order: 1. Background music track 2. Coinin.wav 3. Play1Coin.wav 4. RunArm.wav 5. SpinWheel.wav 6. NoWin.wav 7. Jackpot.wav May 2022  79 The main screen for the Slot Machine indicates your total winnings (or losses!) To get the files in the correct order, it’s best to copy them one at a time. However, you can prefix the files with a four-digit number, to guarantee the correct playback order. We have done this for the supplied files. For example, the first file would be prefixed with 0001, the second file with 0002 etc. This is because the DFPlayer only plays a file based on its order in the file system and does not look at the actual file name, unless it has a numeric prefix as mentioned above. The image files must be loaded on a separate micro SD card in the BackPack slot. These files are named “SlotScreen1.bmp”, “SlotScreen2. bmp” and “PayOutChart.bmp” and are included in the download package. Most of the parameters in the code can be easily modified to suit your preferences. This includes the ‘rewards’. Note that any code changes to PAUSE(delay) commands can alter Fig.4: assembly of this add-on PCB is straightforward; start by soldering the lowestprofile components and then work your way up to the taller types. As most of the headers connect elsewhere via jumper wires, you could substitute male for female headers or vice versa, depending on what jumper wires you have. * only for the coin kicker the coordination between the sound and program sequence. Electronic assembly Build the Micromite Plus LCD BackPack as per the instructions in the November 2016 issue (link above) and, once it’s up and running, load the BASIC code (“SlotMachine V10.bas”) onto it as explained earlier. Next, build the extra circuitry on the PCB coded 08105221 (76 x 53mm). Follow the overlay diagram, Fig.4. There isn’t much to it – solder the resistors as shown (use small body resistors or bend the leads close to the bodies), followed by diode D1 orientated as shown, then transistor Q1 and the two 100nF non-polarised capacitors. Then fit the headers, including the two 8-way female headers CON6 and CON7 (not visible in Fig.4 as they are under the DFPlayer Mini module). Note that you can use a male or female header for CON8 depending on what type of header you have fitted to the BackPack, and what sort of jumper wires you intend to use to join the two boards. Follow with the DC socket, then the electrolytic capacitors with their positive (longer) leads towards the bottom or right side of the PCB, as shown. Then mount REG1 with its tab towards the edge of the PCB, followed by RLY1 if you are using the coin kicker option. Finally, plug the DFPlayer into its socket with the micro SD card socket entry towards the nearest board edge. Note that if you’re using the coin sensor, the 120W and 1kW resistors specified may be suitable, or they might need to be changed, with either possibly being a higher value. For this reason, extra 1kW and 2.4kW resistors are specified in the parts list. You can swap them out later if you find the coin sensor doesn’t work well with the initial resistor values. The wiring is relatively straightforward, with most connections running between the two main boards. Coins are ejected via the underside of the Slot machine, so you might want to put a small tray underneath it to catch them. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.5: cut the plywood shapes as shown. Note the dotted outlines that show how the various parts fit together. Don’t forget that the ‘floor’ is made from thicker (14mm) plywood. You could use other materials such as MDF or even acrylic. Chassis assembly Now we move on to building the cabinet. It’s mostly made from plywood and perspex, with a couple of metal brackets. The plywood cutting details are shown in Fig.5, while the perspex and metal pieces are shown in Fig.6. To save some effort, we can supply laser-cut perspex pieces made from 3mm-thick black acrylic (see the parts list); or download the templates from siliconchip.com.au/Shop/11/6443 Fig.5 also shows how some of the siliconchip.com.au other pieces mount to the side panel. So once you’ve made all these pieces and cut and drilled the holes, assemble them as per Fig.5 and the photos. The 3mm black perspex front panel is where the coin slot, LED screen, three pushbuttons and LED are mounted. This panel can be made of two separate components or formed from a larger piece, by bending it at the required point to a 110° angle after heating it (eg, with a hot air gun). If bending it, make the cut-outs after the panel is formed to avoid them distorting. Australia's electronics magazine Our laser-cut front panels are supplied as two separate pieces. You could fill the joint with black silicone after assembly if you want to. The 5¢ coin input unit is made from the same material as the front panel. Our laser-cut set includes these four pieces, which are assembled as shown on the right side of Fig.6. The correct location of the sensor opening must be worked out according to the final sensor or microswitch selected. Once all the pieces are ready, ...continued on page 84 May 2022  81 Fig.6: the front panels (upper left) can be made from two flat pieces or one bent piece, as depicted at right. Making the metal brackets is simply a matter of cutting the aluminium angle to length and drilling some holes. The four remaining acrylic pieces shown opposite are assembled to form the coin chute as depicted at lower right. The Micromite Plus LCD BackPack that controls the whole Slot Machine is based on Geoff Graham's Explore 64 (shown at actual size). 82 Silicon Chip Australia's electronics magazine siliconchip.com.au We will be supplying a double-sided PCB for the add-on module of the Slot Machine from our Online Shop. This is the 3W speaker I used. It works well and I recommend it, but there are plenty of other options. siliconchip.com.au Australia's electronics magazine May 2022  83 Fig.7: here is how to wire it all up. Switch S4 is not needed if you’re using the coin sensor and vice versa (although you could have both if you want). The power switch can be any type that can handle the current. Take extra care with the wiring between the add-on board and the BackPack, especially the GND, 5V & 3V3 cables or you could fry something! If using the optional switch (S4) for Coin In instead of the coin sensor then you will need an additional cut-out for another pushbutton on the lower front panel. The dimensions of this will be provided in the download for the front panels on the Silicon Chip website. assemble the cabinet using small 3mm wood screws, ensuring that each holding hole is fully pre-drilled so that the plywood does not split. Once complete, the box can be primed and painted as required. To allow coins to slide out of the base, glue a thin section of material (preferably perspex) to the top face of the floor. You can use any metal or plastic lid from any suitable container for the 84 Silicon Chip coin catching tray. I was fortunate to find one of exact size that only needed to be cut around the edges to make a suitable shape. Use the small black self-tapping screws to attach the front panel on either side. Wiring After the chassis has been assembled, you’re ready to mount the BackPack, control board and other Australia's electronics magazine electronic components and wire it up. See the photos, which show where the various parts go. Those photos should also help you figure out the wiring, but for clarity, we’ve also provided a full wiring diagram in Fig.7. Double-check the wiring between the control board and the BackPack before powering the Slot Machine up since a mistake there could cause damage to either or both boards. SC siliconchip.com.au