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Part 2: electronics Phil Prosser’s Phenomenal Pinball L ast month, we showed the overall configuration of the pinball machine and introduced pretty much all the modules that make it up. Besides the cabinet, controller, score display and deck, pretty much everything else is modular. Those modules fall into two broad categories: electronic and electromechanical. It helps to have the electronic parts working as you build the electromechanical parts, so that you can test and actuate them properly. Therefore, we will present the electronics first, starting with the circuitry and then the PCBs and assembly instructions (we published the parts list last month). Some parts are required, like the Control Board and Power Supply. Most of the others are optional, although you’ll almost certainly want to build most of them. In some cases, like the bumpers, targets and kickers, most good machines will have several. With pinball, more is more! Our Control Board has been designed to have enough inputs and outputs for what most constructors will need. Later, we will eventually present an expansion board, in case someone wants to build a monster pinball game! While not strictly necessary, it’s very helpful to have a computer with a USB port for testing. You also need a serial terminal program such as PuTTY to access the debugging information. Now let’s get stuck into the electronic side of the game. Circuit details Machine The full circuit of the Control Board is shown in Fig.4 overleaf. The sections in dashed boxes are repeated multiple times, as described in the notes at the top of those boxes. We use 74HC595 serial-to-parallel shift registers to drive all the outputs and 74HC165 parallel-to-serial shift registers for monitoring all inputs. This allows us to have hundreds of I/Os with just a few pins used on the Pico 2. These chips are relatively inexpensive, so the board doesn’t cost a huge amount to build despite its size. All this I/O could have been handled in a single very-high-pin-count FPGA or microcontroller, but this would probably cost about the same as the discrete solution and would definitely need to be a surface-mount device. We thought it was best to make this easy to work on. There is also a level of nostalgia in using old-school devices. Australia's electronics magazine siliconchip.com.au This customisable pinball machine has everything you’d expect: a ball launcher, flippers, bumpers, ramps, targets, rollovers, sound effects, flashing lights – the works. You can build it just like ours or design your own using the electronic and mechanical modules we’ve designed and tested. 50 Silicon Chip Adding to the number of parts on the Control Board, there is substantial input and output protection. The inputs can be expected to be subject to some pretty serious EMI. Given that this is a large device and very mechanical, it is also likely that during construction and servicing, the inputs will be subject to abuse. All inputs have 1kW series resistors and clamp diodes limiting the 74HC165 input voltages to safe levels. We also have 1kW pullup resistors to 3.3V on all inputs, making it easy to connect switches between these pins and GND. This means that if you choose not to use a particular input or sensor, it defaults to an inactive state. The 1kW pull-ups provide a relatively low impedance, which makes coupled noise less likely to be a problem. We run a ground line along with each input group from the controller to the pinball deck, which should minimise ground-related noise problems that can occur when switching high currents. There are four 74HC165 devices on the board, providing 32 discrete inputs. This is just enough to make a decent pinball machine. We considered using resistor arrays on the inputs and outputs, but the cost from reputable suppliers was far more than individual parts. We felt the trade-off between parts count and cost to constructors fell well on the side of individual resistors. LED outputs We need a lot of lights to make the machine pretty, meaning we also need a lot of controllable outputs. We chose to use LEDs for most outputs, though you could connect incandescent bulbs with some modifications. The supply current draw could get out of hand unless you are careful, though. There are thirteen 74HC595 chips on the board, providing a total of 104 outputs. 40 of these are dedicated to the score and player number displays. The remainder is buffered with open-collector transistors. This allows us to drive LEDs at much higher currents than the 74HC595 supports, siliconchip.com.au which is 50mA total per chip. We run the white LEDs at 25mA, although the transistors will happily sink much more current than that with lower-value current-limiting resistors. The LED outputs use 64 transistors, but these are cheap and any pin-compatible NPN device will do (BC337/8, BC546/7/8/9 etc). If you need to handle more current, that is quite possible; just watch the 5V supply total limit. All the 74HC595 shift register inputs are driven in parallel with the SER (serial data) and SRCLK (serial clock) signals, so data is clocked into all shift registers simultaneously. However, this has no effect on the outputs of any chips until one of the individually driven RCLK pins is driven, allowing us to clock eight bits of data to any of these chips at any time. Every time eight bits (one byte) of data is clocked to a register and latched, the states of the eight connected outputs are updated simultaneously. We are driving these devices way below their maximum rate and can still update all the outputs in a couple of hundred microseconds. From a modern data communications perspective, this is terrible. But since we are interacting with human beings, this allows a solid 1kHz update rate for everything on the pinball table, which is more than fast enough. One concern we had was driving SRCLK and SER to so many devices across such a large board. We have included a 100W series resistor at the driving end. The signal measured across the board is quite clean, showing very safe setup and hold times without undue ringing. Power outputs Pinball machines need to be able to drive solenoids at relatively high voltages and current, as well as things like bells and lamps. This is a job for a power Mosfet. Having only 3.3V to drive the Mosfet gates from the Pico 2 demands the use of logic-level devices. In our machine, we use 12V 1.5/2A solenoids but drive them at 24V. The flippers use two in parallel, which amounts to a short-term demand of 6A, although only for 100ms or so. This is why we have 10,000μF of supply bulk storage on the 24V rail (split between the Control Board and the Power Supply Board). For these Mosfets, we have specified IRLZ44NPBF devices, which are about $1 each if you buy 12. These are rated at 55V and 47A with a maximum 1.8V Vgs (gate-source voltage) threshold. This means we can drive them straight from the 74HC595 outputs, given that the chip is running from a 3.3V supply, for compatibility with the Pico 2. Make sure you use logic-level devices (ideally the ones we’ve specified) or they won’t work properly. Be careful as not all ‘logic-level’ Mosfets are equal; for example, we cheekily used some MTP3055VL devices in development, but these are only “on” enough to allow testing, and should not be used in a permanent installation. Each power output has a normally reverse-biased 1N4004 diode across it to absorb the significant inductive spikes from the solenoids. These are included on the controller as ‘belts and braces’; you will see that we also specify diodes across the solenoids themselves under the pinball deck. Once you see the machine in operation, you will understand our conservative approach here. ...continued on page 54 Photo 6: the Control Board for the Pinball Machine will take a while to build. But since it’s split up into sections, you can tackle it one bit at a time. July 2026  51 Fig.4: the Control Board is large but it’s made of lots of repeated sections, so we’re only showing each one once. There are four instances of the input section inside the dashed red box, giving 32 total inputs. The tables show their default functions. There are five low-current output sections (green box) to drive the Player and Score 7-segment displays and eight medium-current outputs (cyan box) to drive up to 64 LEDs (note the use of different resistor values in some sections). The 12 high-current outputs are inside the purple dashed box, with the default functions of each listed. 52 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine July 2026  53 Sound interface We used a ‘1-bit PWM DAC’ library for sound, which uses the onboard PWM modulator and an interrupt service routine (ISR) to generate an analog 8-bit output at a sampling rate of 11kHz. This is not hifi, but it does the job. The output is from a single digital I/O line at pin 7 (digital output GP5). It goes through a low-pass RC filter before being amplified by an LM384 power amplifier, producing sound from the small connected loudspeaker. Future expansion We’ve considered what might happen if someone more ambitious than us runs out of inputs or outputs, so we’ve provided a four-pin header (CON20) and three two-pin headers (CON35CON37) for future expansion. In a pinch, CON35-CON37 can be used as three extra switch inputs. We plan to describe a board in a future issue that can be connected to these four headers to provide even more inputs and outputs. In theory, we (or you) could add any number of both, but most likely we will add one bank of 8 inputs, two to four banks of 8 LED outputs and one bank of 4-8 high-current Mosfet-based outputs. That should be enough for a very complex Pinball Machine indeed! Keep in mind that the existing Photo 7: the Power Supply Board provides 3.3V and 5V DC rails to power the Pico 2, LEDs and so on from the 24V supply. It also passes the 24V supply through to power the solenoids and audio amplifier. design already has several spare inputs and outputs, so it’s possible to build a somewhat more complex machine than ours without needing any expansion. It depends on how ambitious you are! The software will need to be modified to handle the extra I/Os but that should not be difficult. Power Supply Board Old-school pinball machines ran their solenoids at quite high voltages, in many cases exceeding what are currently considered ‘safe’ levels. We want to make our pinball machine something that anyone can fiddle with, without fear of a significant shock. So the whole thing operates from a 24V DC 5A plugpack or power brick. A rating higher than 5A won’t hurt. We have used several different supplies while working on this project, including a 20V 6A laptop docking station supply. This is a touch short of our target of 24V, but works well enough and it was free. We succeeded in achieving excellent performance from the flippers with a 24V rail, but had to use dual solenoids per flipper and overdrive the 12V DC rated solenoids at 24V. This gives us the oomph we need without the use of hazardous voltages. To ensure the power supply rail handles the high current pulses, we have 6600μF of storage on the Power Supply Board and another 4400μF on the Control Board. Our lighting in the game is all LED-based, so the power supply has Fig.5: the power supply is mercifully simple. The incoming 24V DC (or thereabouts) is fed straight through with some capacitors to help handle current spikes. That supply is also converted efficiently to 3.3V and 5V rails to power digital logic and LEDs by a pair of integrated buck (step-down) regulators, REG1 & REG2. 54 Silicon Chip Australia's electronics magazine siliconchip.com.au high-efficiency buck (step-down) conversion of the 24V DC to 3.3V DC and 5V DC rails for logic and lighting. The current draw on these rails can exceed 1A, so linear regulators are not a sensible option. The Power Supply circuit is shown in Fig.5. It’s intended to be mounted reasonably close to the Control Board, as there are some quite high current spikes that will be drawn when solenoids are actuated. We won’t linger on the power supply design, as it is quite conventional, with the two stepdown converter sections basically being lifted straight from the LM2576 data sheet. The only difference between the two buck regulator sections is in the feedback divider resistor ratios. The LM2576T-ADJ uses negative feedback to regulate its feedback pin to 1.23V. So with a feedback ratio of 2.6 (1 + 1kW ÷ 1.6kW), that results in an output of 3.198V (1.23V × 2.6; close enough to 3.3V). Similarly, 1 + 3kW ÷ 1kW = 4 and 1.23V × 4 = 4.92V. All rails are fused, as we have a creeping suspicion that there will be quite some ‘poking around under the deck’ for a machine that is well used. The 3.3V and 5V converters are pretty efficient (typically about 80%), so their normal draw from the 24V rail will be a couple of hundred milliamperes in the worst case. For example, a 1A draw from the 5V rail is a load power of 5W. At 80% efficiency, that’s 6.25W drawn from the input, which is just over 250mA for a 24V supply. We have used rather chunky pluggable terminal connectors for the outputs on this board, and in many other places in this project, such as for solenoids. The current will see 3A pulses when each flipper is operated, with brief pulses to 6A. So we cannot use lightweight plugs and wiring. These connectors are rated at 10A and allow you to unplug parts of the machine during construction and service. Photo 8: the finished Pinball Machine (legs not shown). Note that the backboard has a strip of white LEDs run around the inside of the bezel that flash when certain events are triggered. Remaining circuits The Control Board and Power Supply contain about 95% of the electronics in the Pinball Machine, but there are another 10 simple circuits/boards used, mostly to keep the wiring manageable: 1. Player Number Board: this is a simple 7-segment display on a small carrier board wired to a 10-pin IDC siliconchip.com.au Fig.6: these helper circuits (starting with the Player Number Board) mostly serve to simplify wiring the various LEDs, switches, sensors and solenoids up to the Control Board without the wiring becoming a mess. They all connect back to the Control Board with some combination of 10-way ribbon cables and figure-8 cables for the solenoids. Australia's electronics magazine July 2026  55 Fig.7: the circuit diagram and PCB overlay for the Score Board, which uses six 7-segment LED displays. These displays must have commonanode wiring. Don’t trick yourself and accidentally install common-cathode parts, they look identical but don’t work. header (Fig.6). Connecting it to one of the low-current output headers on the Control Board allows the current player number to be displayed. 2. Score Board: this board has six 7-segment displays, four 10-pin IDC headers and a small amount of drive circuitry (Fig.7). It’s driven by four low-current output sets to show the score as four digits plus two zeroonly digits (so the score is always a multiple of 100). That means you can 56 Silicon Chip get a score approaching one million – much more impressive than mere thousands! The onboard resistors and transistors allow the zero digits to be switched on or off using pin 8 of CON101, meaning there’s no connection to the decimal point segment of DISP1. 3. General LED Board: this connects up to eight separate LEDs to a 10-way ribbon cable (Fig.8). The LEDs connect to this board via two-pin polarised Australia's electronics magazine headers. It’s driven from one of the medium-power outputs on the Control Board and is used for general lighting and effects. 4. Bumper LED Board: this has eight LEDs in a circle and fits around the outside of bumpers (Fig.9). Like the General LED Board, it connects to a medium-power output set on the Control Board. The Bumper LEDs use one 8-bit output port each from the Controller and siliconchip.com.au Fig.8: the General LED Board, which connects up to eight separate LEDs. generate patterns triggered by time and when the ball hits the bumper hard enough. We used the brightest reasonably-priced LEDs we could find. The resistors on the Control PCB set their drive current to 20mA. Our deck had drilled holes into which we inserted 3D-printed clear LED bezels, to be described in a future article. The PCB is mounted with the LEDs pushed into the bezels, and we glue a couple of the LEDs to the bezels to secure the assembly. As shown in Photo 4 last month (and reproduced on page 62), this board is sized to fit around the bumper mechanisms. 5. Cascade LED Board: this has 15 LEDs in a triangle pattern (Fig.10). The extra LEDs let us flash some interesting patterns. It’s typically placed in the middle of the deck and is driven by two medium-­ power output sets on the Control Board. Note that there is no LED16 due to the triangular layout. 6. Switch Input Board: this connects up to six regular switches and two inductive sensors to an 8-way input port on the Control Board (Fig.14). The inductive sensors differ by needing a 24V supply voltage, hence the 3-way connectors for them. These should connect to CON2-CON4 on the Control Board as those are the input headers with a connection to 24V (CON1 supplies 3.3V). 7. General Input Board: this connects up to eight regular switches to an 8-way input port on the Control Board (Fig.15). 8. High-Current Interface: this adds four back-EMF clamp diodes across the wires to up to four solenoids (Fig.11). It’s important that these are close to the solenoids. It can also simplify the wiring by keeping the four figure-8 cables from the Control Board siliconchip.com.au Fig.9: the circuit diagram and PCB overlay for the Bumper LED Board is shown above and to the left. Depending on how you plan your Pinball Machine, you might need several of these. Fig.10(a): the PCB overlay for the Cascade LED Board. The circuit diagram for this board is shown overleaf. Australia's electronics magazine July 2026  57 Fig.11: the HighCurrent Interface Board. This board should be kept close to the solenoids. Fig.10(b): the circuit overlay for the Cascade LED Board. Note that it only has 15 LEDs instead of 16 due to the layout. together up to this board. This board is used for the flippers and reload mechanisms or other things you want to control. 9. Rollover Board: this connects up to eight inductive sensors to an 8-way input port on the Control Board (Fig.12). 10. Bumper Driver Board: this is like a combination of the General Input Board and High-Current Interface (Fig.13). Having them together means one less board to mount, as they are both required for bumpers and kickers. It also provides one extra high-­ current channel, allowing for the three bumpers and two kickers to be connected via a single board, plus three extra headers and current-­ limiting resistors for high-power LEDs (mounted on top of the bumpers) to be wired in parallel with the bumper solenoids. Control Board assembly First, make sure you have a good couple of hours spare and are armed with a cup of your favourite beverage. Construction is not hard, but it is a proper task. Get all the parts together and ready. Follow the plan, and if you stop, make sure you stop somewhere sensible so you can pick up in an orderly manner. The Control Board PCB overlay is shown in Fig.16 (at actual size, but split across two pages). Start by fitting all the resistors. There are only a few values, which is a mercy, but there are a lot of the 1kW, 220W, 150W and 82W parts (plus just a few of the 100W, 2.2W and 2.7W). We mounted them all in the marked sections on the PCB, one value at a time. An old trick when loading a lot of parts is to get a sheet of packing foam or similar. Once you have bent the leads of the parts and inserted them through the pads, put this on top of the board, then holding the foam to the PCB, you can flip it over knowing all your parts won’t fall out. Another cheeky trick if you find yourself stuck is to solder some parts from the top of the board. Next, install the diodes. Start with the 1N4148s, which are the most numerous (64), and watch their polarities as they don’t all face the same way. After that, solder the larger 1N4004s, again paying attention to their orientation (don’t forget D1, all by itself next to the Pico mounting position). Fig.14: the Switch Input Board. This connects up to six regular switches and two inductive sensors. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.12: the Rollover Board (left and below) connects up to eight inductive sensors. Fig.13: the Bumper Driver Board PCB overlay is shown directly above, and its respective circuit diagram directly below. It provides an extra high-current channel allowing for three bumpers and two kickers to be connected via a single board. Now is a good time to solder all the ICs to the board. There are a few things to watch out for here. First, don’t get the 74HC165 and 74HC595 chips mixed up, as they come in the same package but have different functions. Second, double-check the orientation of each part before soldering it! It’s really annoying to fix a rotated chip and usually involves destroying it to get it off the board safely. Third, we suggest you solder chips directly to the board rather than use sockets, as sockets can oxidise and become a source of unreliability. Also, since these are fairly sturdy logic chips with lots of protection, they are unlikely to fail, and sockets are an additional cost. Still, if you want to use sockets, you certainly can. Fig.15: the General Input Board connects up to eight switches to the Control Board. siliconchip.com.au Australia's electronics magazine July 2026  59 Next, load all the 100nF capacitors. We used (and suggest you use) ceramic capacitors as they are better for bypassing digital ICs. However, if you have a box full of 100nF greencaps or MKTs, you certainly could use them. Now mount all the terminal block sockets and headers, including the box headers. All connectors are keyed; be careful to get them in the right way around, as we rely on the ribbon cables to simplify a lot of wiring and you don’t want them back to front. The notch is marked on the silkscreen. We have specified boxed connectors for the 10-way cables so that as long as you mount the headers the right way around, it should be almost impossible to break anything no matter where you plug things in. Loading the transistors is easiest if you mount them close to the board and solder all the outside legs from the top of the board. This gives you plenty of room to get your soldering iron in, then flip the board, solder the outside pins on the bottom, then snip off the outside legs before soldering the middle pin. Now you can install the pushbutton switch and LED next to it, followed by all remaining capacitors. Mount all the Mosfets, making sure you do not short any of the tabs together; heatsinks are not required. Follow with the volume potentiometer. Now fit two SIL header strips to the Raspberry Pi Pico 2. These can be cut or snapped from a longer header (eg, snap a 40-pin header in half to get two 20-pin headers). While you could solder the Pico 2 directly to the board for reliability (making sure you get it the right way around!), we recommend that you instead solder header sockets to the board, allowing it to be unplugged if necessary. Phew, you are finished. Sit back and behold that Control Board, straight from the 1970s, except for the Raspberry Pi board, of course! You will need a power supply before you can test it, though... Power Supply The locations of all the components on the Power Supply Board are shown in Fig.17 overleaf. Fit the resistors, then the diodes (watch the orientations), followed by the fuse clips and fuses, then the capacitors. Next, 60 Silicon Chip Australia's electronics magazine siliconchip.com.au solder the output socket in place, double checking that you have it the right way around. The regulators do not need heatsinks the way we use them. If yours came with five pins side-by-side, use fine-nose pliers to crank them out to match the PCB pad pattern, then solder them in place with the tabs orientated as shown in the overlay diagram. Power supply testing Check that all the components are on the Power Supply Board, including the fuses; then you are ready for testing. Your power supply doesn’t need to be rated at exactly 24V DC, but lower voltages will result in less ‘oomph’ for the electromechanical parts. It does need to be able to deliver at least 5A. We have not tried voltages above 24V, but it should work up to about 30V, with 19V being about the lowest we would bother with. We encourage you to look in your drawer of outdated laptop and docking station power supplies, as these are usually 19-21V at a very high current. To test the board, apply 24V DC or thereabouts to either of the input connectors. There is no reverse polarity protection, so take care with your wiring! Check the 3.3V output; it should be between 3.1V and 3.4V. Similarly, check the 5V DC output; it should be between 4.7V and 5.1V. If either voltage is too high, our prototypes regulated fine with no load, but it’s possible yours needs a load on it, so add a 100W resistor across that output and check again. If it’s still too high (or too low), there’s something wrong with the board, so switch off the power and check it carefully for dry joints, short circuits, incorrectly orientated or wrong-value components. Check the orientations of the diodes and verify that the LM2576s are -ADJ versions. Also check that your power supply is working properly and that the input voltage is as expected with the board powered up. Fig.16: the Control Board is substantial, in part because it completely avoids the use of surfacemount parts. A lot of the work is simply in fitting the many resistors and diodes, but once you’ve done that, the rest is not too bad. siliconchip.com.au July 2026  61 At this point, you should have a functional power supply and are almost ready to test the Control Board. However, it will be much easier to test it once you’ve built some of the various LED and breakout boards. Remaining board construction Photo 4: this photo (from last month) gives an idea of what the wiring is like on the underside of the Pinball Machine. 62 Silicon Chip Australia's electronics magazine These boards are all pretty simple to build, so we will just give some brief notes for each. Use the overlay and circuit diagrams, Figs.6 to 15, as a guide to assemble them. Importantly, it will also help to have an idea at this stage of how many of each board you will need, which depends on your intended deck layout (if it’s similar to ours, you can stick to our suggestions). Even if you don’t know, it’s pretty safe to build one of each for now. You will almost certainly need more than one Bumper LED Board, as bumpers are a staple of a good pinball game. Most of the smaller boards have all the components on one side. The exceptions are the Bumper and Cascade LED Boards, which have the connectors on the back, and the Player and Score LED Boards, which have the displays on the front and everything else on the back. When building the High-Current Interface Board, watch the orientations of the pluggable headers. These need to accommodate the screw terminals, as shown on the overlay, and be in the same orientation as on the Control Board, or the diode will short out the controller output and most likely blow a fuse. For the Player and Score Boards, make sure you use common-anode 7-segment displays; common-­cathode types will not work. Also, get the header the right way around. For those boards with LEDs or transistors, be careful to orientate them as shown in the diagrams. That also goes for all the connectors, including the pluggable terminal blocks. For those boards with LEDs, you may need to solder them on extended leads to fit the deck; if you’re unsure, solder them with maximum lead length. Once these are installed under the deck, some extra lead length is not a problem, and makes installation easier. Keep the heights consistent regardless. Also consider that you may want to use different colour LEDs in some places. We used a mix of red and white; there’s nothing stopping you siliconchip.com.au Fig.17: the power supply layout. You will note that the output connectors are in a different position than shown in the photos, so that a 6-way connector can be used to match the Control Board. from using other colours if it suits your build, just make sure they are high-brightness LEDs. The parts lists last month includes everything you need to build the boards, but nothing to mount them. We’ll get to that later when we start assembling the Machine. You’ll probably need big bags of M3 machine screws and tapped spacers, although we will also describe the 3D-printed mounts we used in our build. Controller testing The first step is to load the software onto the Pico 2; you can download it from siliconchip.au/Shop/6/3628 Once you have the ZIP, locate the UF2 file within and extract it. With the Pico 2 unplugged from the Control Board, hold the BOOTSEL button on it while plugging the cable into your computer using a USB data cable. BOOTSEL is the small-surface mount button on the Pico 2. It will appear as a removable drive on your computer. Drag-and-drop the UF2 file onto that drive. It will copy and, after a few seconds, the drive should disappear and the Pico 2 will reboot. Before plugging the Pico 2 into the Control Board, make sure the Power Supply Board is producing the right voltages. Wire up the two 6-way pluggable terminal blocks to each other, ensuring the correct voltage is applied to each input on the Control Board siliconchip.com.au with the right polarity. Double-check this before applying power! Apply power and check that all three supply rails are still delivering the correct voltages. If not, check that the electrolytic capacitors on the Control Board are the right way around, and poke around for anything getting hot. Without the Pico 2 plugged in, not much should be happening. Now remove the power, wait a few seconds, plug in the programmed Raspberry Pi (the right way around!) and apply power again. Check that the heartbeat LED next to the Pico 2 is blinking. If it is not, the Pico 2 is either not programmed or is very unhappy. Check the 3.3V and 5V rails; if they are OK and the LED is not blinking, unplug the Pico 2 from the controller board and power it using a USB cable. The LED on the Pico 2 should blink. If not, the Pico 2 is not programmed. If it does not blink, there is a fault on the Control Board (could the LED be reversed?). Assuming it’s ‘alive’, now it’s time to make a few 10-pin ribbon cables with IDC plugs on each end. Make them long enough to be reused in the machine as you build it later. Check that the triangle on each connector indicating pin 1 aligns with the redstriped part of the cable, or at least that it points to the same side of the cable at each end – see Fig.18. It’s important when crimping the IDC connectors that you use enough force to compress the connector so the blades slice fully through the insulation and contact the wires within, but not so much that you break the plastic. It’s a tricky balancing act, but it helps to apply force evenly across the top of the connector during crimping. Now, using five such cables, join the Score and Player displays to the Control Board. Connect CON107 on the Player display to CON5 and CON101104 on the Score Board to CON6CON9, respectively. Apply power and you should see “SC Pin Ball” scroll across the four display segments on the left a couple of times. If that does not happen at all, check the data and control lines, especially SER and SRCLK. These lines run to most of the ICs on the Control Board, so a failure anywhere (like a short circuit) could stop the whole thing from working. Look for solder bridges on the Pico 2 connections. Also check your cables, which are easily overlooked culprits. Check pins 9 and 10 especially carefully if no LEDs work. If only some displays or segments are working, look for the control lines having a problem, including those that go to pin 12 on IC5 through IC9 (L_PLAYER & L_DIGITS0-3). The most likely cause would be in the soldering or an improperly crimped ribbon cable. We use the score display in the SelfTest mode, so you will need to get it working before proceeding. Fig.18: here’s how to crimp the ribbon cables. Most IDC connectors come with strain reliefs like this and are in three pieces. If yours lack that, only having two pieces, the cable can just pass straight through. Pin 1 (red stripe) is usually also marked with a moulded triangle on each connector Australia's electronics magazine July 2026  63 Screen 1: while we used PuTTY, you could use any serial terminal program to monitor the Control Board’s output in SelfTest mode. You will see a scrolling status list in the window. Your COM port will differ; check in Device Manager to see which port you should use. Screen 2: any input that is active (pulled low) is reported by name in this mode. Normally, you make a single input active at a time and check that it was correctly detected. Here, we have intentionally pulled Bumper 1 and Kicker 1 to ground. Assuming the display works, hold the Self-Test button (S1) on the Control Board while powering the system up. This puts the controller into test mode. It provides serial data via a USB serial port regarding its status and relevant data for a series of tests for the inputs, LED outputs and power outputs. You really should use this for all testing and debugging. In Self-Test mode, data is also written to the score display, but considering we have four display digits to work with, the output is pretty brief. The controller emulates a serial connection, so all you need to do is plug it into a computer and run a terminal like PuTTY or Tera Term Pro to display what the controller is sending. On a Windows PC, you can go into Device Manager and look at which serial port your computer has assigned to the Pico 2. This varies – search for and open Device Manager, then look at Ports (COM & LPT), which will show you the serial port number. Tera Term also shows the available ports and their names when you launch it. We ran PuTTY on our computer, clicked on serial connection and then “Open”. This opens a window that prints out data on the serial port – see Screen 1. In test mode, you will get relevant data sent out about once per second, depending on what test you are running. You will know that you are in Self-Test mode as the heartbeat LED does not blink. Instead, data is sent on the serial line and to the Score display. Input tests Screen 3: testing the LED ports one at a time. Screen 4: testing the high-current (‘power’) output ports, one at a time. 64 Silicon Chip Australia's electronics magazine The first test is reading the inputs. This will present data to you on the serial console as shown in Screen 2. Simultaneously, the Score display will scroll the value of the inputs in two four-character HEX numbers. These are arranged as MSB first, LSB last. There is a space in between to let you see the two words. We have inverted the logic in the display, so 1 means the input is active, ie, pulled low. You can stimulate each input to the controller by shorting that input to ground and you should see the corresponding input value change. We used the General Input PCB for this, as it breaks out all eight inputs run from the ribbon cable to eight two-pin headers. We shorted each in turn with siliconchip.com.au a screwdriver. You could also use a jumper shunt. A quick-and-dirty test is to short each input in turn and look for the reported input state changing. Even if you don’t bother decoding the input, if the value changes each time you short a different input, it’s likely that all the inputs are working. If an input does not work, check the associated input soldering, resistor, cabling and diodes. If a whole input bank does not work, check that IC’s soldering. Before desoldering chips, check the soldering and the control lines carefully, as getting those ICs off the board realistically requires a hot air gun or snipping every lead off and individually desoldering them. Output tests Once you are satisfied that all the inputs are working, press and hold the Self-Test button for a second or so to progress to the output tests. A quick press might not work because of how the software works in test mode. A message will be presented on the serial output and also the score display. Press the Self-Test button again; this makes the Player LED port blink on and off at 1Hz. A second press runs each LED in series for that port. The serial report on your computer should show something like Screen 3. Repeat this test for the four Score board headers, the three Bumper headers, the two Pattern LED headers; then the Rollover LEDs, Target LEDs and General LEDs (those three are on one header each). If a whole port does not work, debug the control lines and check your soldering, especially around the associated IC. If individual LEDs do not work, look from the output IC through the transistor to the output connector. Power Output tests Next come the power outputs. These tests make the output active for 100ms, then off for 600ms. We run the test this way, as if you have a solenoid connected, it will be driven very hard, and we do not want to leave power applied for an indefinite period. If you have the serial port connected still, you will see these states reported on the terminal, as shown in Screen 4. The next three button presses will start bumpers 1-3 pulsing on and off. Connecting a bumper or LED with a 1kW series resistor to see these operate. siliconchip.com.au Photo 9: this photo gives you an idea of the size of the Pinball Machine. It stands 153cm tall (71cm for the legs alone), 60cm wide and 112cm deep. After that are the two kickers, then the left and right flippers. The eighth press activates the second kicker, although I didn’t use that in my machine. A ninth press triggers the ball load solenoid, then after that the ball release solenoid. The bell comes next; this operates at 50% duty cycle since we use a 12V bell, and if you run this test with the bell plugged in, we don’t want to melt it. If all of these fail, then we need to look at the SER and SRCLK lines (although if you got this far, surely they are OK). If the first eight or second four fail but not all, look at IC22-IC23 plus the L_Power0 and L_Power_1 lines. If an individual output fails, check Australia's electronics magazine for soldering problems and wiring problems, especially around the Mosfets. These Mosfets are pretty chunky, so it is very unlikely that they will fail if you have the diodes installed correctly. Now plug the speaker into CON10 and turn up the volume to a moderate level. Apply power and listen for a tune at start-up. If this fails, look around the power amplifier and volume pot. Next month You should now have the controller up and running. Next month we will start describing how to 3D-print and assemble parts like the bumpers, kickSC ers, targets and flippers. July 2026  65