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MINI ARCADE PONG WITH SIX ‘CLASSIC’ BUGS FIXED 3 5 by Dr Hugo Holden Pong was one of the first commercially successful video games, and I reckon that Arcade Pong was the best version ever made. So I decided to make a fun home version of the game, copying the arcade version as closely as possible, but on a significantly smaller board. While I was at it, I thought I’d fix six bugs that were in the original design! A rcade Pong is the most sophisticated and brilliant version of Pong ever created. Mr Allan Alcorn created this masterpiece at Atari in 1972. It completely outclasses any coded or software-based Pong, and also outclasses any hardware-based Pong on a single LSI chip. Editor’s note: there was also the Magnavox Odyssey, a home video games console which was released a few months before Atari released the Pong arcade machine. The Odyssey featured a “table tennis” game. Original Arcade Pong boards are large and becoming rarer, so for history’s sake, I decided that I wouldn’t modify one. Instead, I would create my own, more compact version based on that design. I used discrete logic ICs placed in a neat grid, in the same arrangement as the original. This way, when an IC is referred to at a particular location in the Atari documentation, it matches up with my board. My design eliminates the six bugs present in the original, and it also provides some simple onboard diagnostics via two TIL311 hexadecimal displays. I have seen PCB designs from others aiming to recreate Arcade Pong, 38 Silicon Chip but they have the ICs in a completely different configuration, and they are generally larger than my design. The bugs in the original design did not detract at all from the brilliance and creativity of the original circuit from 1972. For a circuit of such complexity, needing to get to market quickly, some unresolved problems are to be expected. How a Pong machine works The original circuit (including bugs, which as described below, I fixed) is shown in Fig.1. It also includes an onboard rectifier and regulator, which I didn’t bother with in my version, since regulated DC power supplies are now readily available and inexpensive. The paddle architecture alone in Pong’s arcade version was more complicated than any home Pong version, with 42 possible states of ball motion. The ball motion “vector” (to think of ball motion in analog terms) is formed from combined horizontal and vertical motion components. On the vertical side, there are three up and three down ball motion components. There is also a state of zero vertical motion, leaving a horizontal motion component only in that condition. Australia’s electronics magazine There are three horizontal motion components too, determined by the HIT counter, which combine with the vertical motion components to produce an overall perceived motion vector for the ball that a player observes on the video screen. Although the ball motions are generated digitally, the player perceives the motion in a more analog manner, due to the persistence of the phosphor on the CRT screen and other factors. The three horizontal and three vertical motion components combine to produce a motion vector, and this occurs in four screen quadrants because the ball could be travelling up or down, or left or right. So this gives 36 states of motion or ball ‘velocity vectors’ (4 quadrants x 3 x 3 components). However, there are three additional states of motion that have zero vertical velocity. These are the horizontal states of motion on their own, determined by the HIT counter during gameplay. This adds another six states of possible ball motion during gameplay (3 x 2), giving 42 total unique ball velocity vectors. This is more than enough to convince the player that the game is functioning in a smooth and analog fashion. siliconchip.com.au The genius of the game was that the vertical components of ball motion were determined by where on the paddle the ball made contact. When this interaction occurs, data relating to the condition is clocked into the vertical velocity encoder circuitry, one of the many very clever sub-circuits. The further away from the paddle centre that the ball and paddle interact, the higher a vertical velocity is encoded. The upper half of the paddle is encoded for increasing vertical velocity upwards, while the lower half is encoded for increasing downward motion. The paddle centre is encoded for zero vertical velocity. Also, the horizontal motion speeds up in a volley when there are no misses by either player. After four consecutive hits, the horizontal component of ball velocity increases. By 12 hits with no misses, the horizontal velocity component speeds up yet again. These ball motion features, combined with the sound effects and score-keeping, make for a version of Pong that outclasses all other versions. One of the earliest prototypes made for the Pong circuit. Clever design Out of all the circuits I have seen after a lifetime of interest in electronics, Pong is up there in the top two most impressive. One reason for this is the combination of technical creativity and fun, making the best out of the current technology of the time, seldom seen together, all wrapped up in one design. To give you an idea of how cleverly the sub-circuits are implemented, a single standard binary-to-7-segment display encoder IC is multiplexing the video for both players’ on-screen score displays. Also, the size of the player paddles and score segments on the screen in the arcade game were a well-proportioned use of the video display area; much better than in some home Pong versions where the scores and paddles (bats) appeared larger. Clearly, some compromises were made when this arcane circuit of around 66 TTL ICs was miniaturized down into a single integrated circuit for home Pong versions. Bugs in original Pong The original Arcade Pong “Syzygy E” PCB contains six known bugs. My version, besides being considerably smaller, also addresses and fixes all six. siliconchip.com.au Another later revision prototype PCB being tested before the final design. 1960s and 70s plastic TTL ICs aren’t made of the same kind of plastic as modern chips; it is a much harder type of resin. I find them reliable; these new-old-stock parts were 35-45 years old, but worked perfectly the first time I powered it up. 60Hz displays on 50Hz mains power Like the original Arcade Pong, this design produces a more-or-less NTSC-compatible composite video signal, using the American frequencies of 59.97Hz for vertical sync and around 15,750Hz for horizontal sync. But many small monochrome PAL (50Hz/15,625Hz) monitors have sufficient horizontal and vertical hold adjustment range to lock onto this signal. Sometimes with vintage 50Hz CRT monitors, you need to reduce the value of the vertical oscillator timing capacitor a tad to get the vertical hold control into range. Australia’s electronics magazine June 2021  39 Fig.1: the original circuit diagram for the arcade version of Pong. 40 Silicon Chip Australia’s electronics magazine siliconchip.com.au siliconchip.com.au Australia’s electronics magazine June 2021  41 Fig.2: this modification to the original Pong circuit fixes one of the bugs whereby the ball becomes ‘trapped’. This can occur if the paddle range pot is out of adjustment. 1. The Ghost in the Machine Bug This bug was not found for over 40 years. It came about due to a mistake in the original PCB design. Pin 10 and pin 1 of IC A6 (a 7450) had reversed labels on Atari’s original schematic, and the original PCB designer copied this. This meant that the least significant bit of paddle data, processed by the vertical velocity encoder, was switched between the two players. The result was that one player’s paddle could influence the other player’s interaction with the ball. Also, this reduced the number of possible ball motion states. It produced a “spooky” and unpredictable effect, in that sometimes the ball would bounce from an unexpected angle from the paddle, depending on where the other player’s paddle was positioned. This bug was fixed by connecting the tracks correctly to the 7450 IC at location A6, ie, swapping the connections to pins 1 & 10. This bug is not present in Arcade Pong Doubles, only the original Pong E Syzygy boards. 2. Ball Trapped in Blanking Bug This is a very complex and infrequently presenting bug. In effect, it represents a ‘logic race’ that the game cannot escape from if it gets into it. The result is that the ball can become ‘trapped’ inside the vertical blanking interval instead of inside the active raster scan time interval. It can occur if the paddle range potentiometer is out of adjustment (or the paddle range is increased; see below). In this case, the ball oscillates between the paddle edge and vertical blanking. The ball becomes ‘trapped’ in synchronicity with the vertical blanking interval and appears in a vertically elongated form (if the vertical blanking area is visible on the monitor screen), moving horizontally to and fro in the vertical blanking interval, unable to escape. This can usually be corrected by turning the game off and on again. It 42 Silicon Chip is a rare bug to appear, but the game ‘locks up’ when it does. Very rarely, the bug would appear at switch-on, disabling the game until it is reset. The cure is to deploy an unused 74107 flip-flop in IC A2, as shown in Fig.2. Flip-flop A2a is used to reverse the ball’s vertical velocity after the ball signal V.VID and vertical blanking V.BLNK become coincident. The addition of the second flip-flop, A2b, and rewiring A2a solves the problem, allowing enough time for the ball to always escape the vertical blanking interval without remaining trapped there. Also, flip-flop A2b with both J and K tied high toggles very reliably. More details on this can be found in the link at the end of the article. 3. Paddle Range Limitation The original paddle range was limited. This has the effect of allowing the ball to travel above a player’s paddle no matter how hard they rotate the control against its stop. This made some players angry as they knew they could have hit the ball if the control had allowed them. The designer pointed out that this ‘feature’ always meant the game would finish, as two experts could otherwise play it for a very long time. But even with good players, someone usually misses, especially when the ball’s horizontal velocity is at maximum after 12 consecutive hits (especially if the player has a beer or a hamburger in the other hand and they are chatting to friends). The modification made here allows full range of the paddles close to the vertical blanking intervals, so that the ball cannot get around (over or under) the paddle. It does not cause any problems, provided the ball trapped in blanking bug fix, described above, is present. If not, the extended paddle range can more likely push the ball into blanking, where it can get trapped. This change is made by replacing one Australia’s electronics magazine 1N4148 in the original design with three in series, as shown in Fig.3. Note: do not attempt to use any other variant of the 555 timer IC than the NE555N; preferably, use an early Signetics unit. Many other 555 types, whether CMOS versions, the NE555P or the LM555, have small differences that show up in the timing and generation of the paddle image, with the paddle appearing early or late or exhibiting non-linear control. 4. Screen Video Horizontal Image Displacement Bug The horizontal sync pulse is located with respect to horizontal blanking so that, with the horizontal hold setting of the monitor properly adjusted, the screen image is displaced to the left (especially the ‘net’ line). To improve this, the horizontal hold control on the monitor can be turned a little. This is because most monitors have a horizontal AFC circuit with a DC control to their local horizontal scan oscillator, so any offset in the sync timing with respect to the video (image) signal causes a horizontal phase shift or displacement of the video image on the scanning raster. However, when the horizontal hold control is centred, the monitor can sometimes lose horizontal picture lock when first turned on from cold, as the AFC circuit goes out of “capture range”. Therefore, the sync pulse is better repositioned within the blanking time to be closer to video industry standards (NTSC). There are several ways to do this with the spare gates and flip-flops available in the circuit. The method I used is simple, as it just uses one spare flip-flop – see Fig.4. The NEW H.SYNC signal replaces the HSYNC signal that feeds into pin 12 of the sync-pulse-mixing XOR gate at location A4. Although this arrangement doesn’t exactly give a standard sync pulse to blanking relationship, it is very close, and the picture centring is much better on the monitor. siliconchip.com.au ► The 16H signal is available from pin 4 of the IC at location E4, while 32H is from pin 9 of the IC at location F9. HBLNK is available at pins 4, 8 and 12 of the IC at location H5. This bug was fixed in Atari Pong Doubles, but that particular circuit fix required three extra gates, as well as the flip-flop, to achieve the same result. Also, I found that if a modification is made to place the sync pulse almost identically to industry standard (NTSC video), and the net line is centred almost perfectly, then the score images appear to be displaced a little to the right. So the better picture position is with the net displaced a tiny bit to the left and the score a little to the right, when the horizontal hold control on the monitor is set correctly. Some monitors (very few) have an internal horizontal phasing control, so the image horizontal picture centring can be adjusted after the horizontal hold control is correctly set. 5. The Weak Net Bug This bug occurs due to the propagation delays in the two 7493 counters in the horizontal sync generator. Cumulative delays in this ripple counter system can upset the timing in the generation of the net signal. When specimens of the 7493 counter IC had shorter propagation delays in each flip-flop, typically the 7493AN counter chips, a timing error developed in the drive to the flip-flop pulse synchroniser circuit (F3 and G3) that generated the net pulses. The result is weak-looking, thin or faint net on the screen image. The fix is to clock the flip-flop at pin 9 of the IC using the 1H signal rather than the clock signal. This way, the timing errors or differences in 7493 ICs do not affect the net pulse width. This modification is shown in Fig.5. The earlier 7493 counter ICs had about 18ns delay per internal flip-flop, siliconchip.com.au Fig.3 (left): this modification is used in conjunction with the ‘fix’ in Fig.2 to extended the paddle range so that it can be used close to the vertical blanking intervals. This means the ball can’t get around the paddle in edge cases. ► Fig.4 (right): a new horizontal sync pulse is made with a spare flip-flop to improve the horizontal hold control and fix screen displacement. Fig.5: propagation delays in the 7493 counter ICs (F8/9) cause a faint net on the screen image. This is fixed by clocking pin 9 (CLK) of flip-flop F3 using the 1H signal from one the horizontal sync generators. and there being eight flip-flops in two 7493s, this yielded a delay of about 144ns. Add about 16ns for the 74107 flip-flop, giving a total of 160ns between the 256H going high and the clock pulse going low. The clock pulse has an interval of about 140ns, so in this case, the 256H signal rises about 20ns after the clock pulse goes low. This results in a typical Australia’s electronics magazine net pulse length of about 120ns. However, the 7493AN counter IC is often faster than the earlier 7493N, with a delay of about 13ns per flipflop, giving a total delay of 120ns. So 256H rises about 20ns before the clock pulse goes low, upsetting the net pulse generator. This results in a net pulse of only about 20ns long, which looks very weak on the screen image. June 2021  43 Fig.6: gates at C1 and D1 are used to create a NEWBALL signal to help deal with screen tear due to the ball being visible during blanking periods. The final PCB, with a bit of glare from the camera flash. Since this was originally a 1970s design, it seemed fitting to populate the PCB with vintage TTL ICs. Clocking flip-flop F3 with the 1H signal, instead of CLOCK, results in a net pulse in the range of 140 ±20ns, with the variability caused by the difference in the 7493 counter IC specimens. It always gives a normal-looking net pulse on the screen, regardless of the properties of individual ICs. 6. The Ball Monitor Sync Disturbance Bug In the analog video signal, picture information should not appear inside the horizontal and vertical blanking periods. These intervals are the province of the sync pulses during the monitor’s beam fly-back time. In the original Pong design, the ball was not gated out of the blanking intervals, and appeared in this area when the ball ‘bounced’ off the screen edges. This makes the picture on the monitor jump vertically a little sometimes, or get a small horizontal picture tear as the ball bounces, depending on how vulnerable the particular monitor is to a sync disturbance. The designer had given thought to the vertical blanking interval, because the net pulse is gated out of vertical blanking. But the ball signal is not gated out of horizontal or vertical blanking. The BALL signal appears on output pin 4 of the IC at G1. Unused gates at locations C1 and D1 are deployed to create a NEWBALL signal, gating the ball signal out of both the horizontal and vertical blanking time (Fig.6). Making it more compact An Apple IIc monitor undergoing modifications so that it can be powered from the same 12V DC supply as the rest of the Pong game. 44 Silicon Chip Australia’s electronics magazine With no negative reflection on the genius of the original design implied here, the arcade PCB design was large and cumbersome at 395 x 220mm. Of course, there was plenty of space inside an arcade game cabinet, so it hardly mattered. This variant of Arcade Pong, with all the above bugs corrected, fits on a PCB measuring just 245 x 165mm, as shown overleaf – including the details of all the components. It has been possible to design a much smaller version than the original arcade PCB by altering the track design and running the IC power rails down the long IC axes, unlike the original design, which had them perpendicular to the long axis of the ICs. I designed this new PCB by hand, like the original arcade game PCB. I worked on this design for about two years on and off. siliconchip.com.au I added some ‘onboard diagnostics’ via two TIL311 hexadecimal displays. One display monitors the 4-bit data from the vertical velocity encoder output, while the other shows the 4-bit data from the hit counter. This is useful to see that everything is working normally, but most, perhaps not all faults, if present, are usually evident in gameplay. Another advantage of the new PCB is that it can be powered from any common garden-variety 5V switchmode power supply. This saves space by not having the power supply components on the PCB, as in the original Arcade version. It still uses the original 74-series DIL TTL ICs. LS-TTL ICs can also be used, reducing the power consumption to around 360mA <at> 5V rather than about 1.2A with standard TTL. However, there is something quite wonderful about the power-hungry 74-series TTL ICs. This is the sort of robust technology which comprised the computers in the Apollo spacecraft. They are very trustworthy chips. If you are keen to build your own copy of my Mini Arcade Pong, you can do so. You can get the PCBs from the Silicon Chip Online Shop, and all the other parts are easy enough to obtain. The possible exceptions are the TIL311/DIS1417 7-segment displays, but they are not necessary – they are mainly for ‘debugging’ purposes. You can get them from sellers on eBay if you feel you need them. Fig.7: the upper half of this circuit is an optional buffer transistor which is used to help drive a 75W input impedance for the monitor. The lower half is the audio amplification and volume control. sync tip to sit just at +50mV to +100mV or thereabouts. A reasonable starting value is 1kW. The original coupling capacitor should be linked out. The 33-75W resistor is chosen so that when the output is terminated with 75W, the overall amplitude (sync + video) is about 1V peak-to-peak across the termination resistor. Audio-wise, in my Mini Arcade Pong ‘cabinet’ (pictured), I just used the Champ amplifier (February 1994; siliconchip.com.au/Article/5303), which uses an LM386 IC, to drive the speaker. A small single or two-transistor amp would be fine, as long as there is a volume control. Some video monitors have sound and a speaker built-in, but not all. A simplified version of the basic arrangement I used for volume control and audio amplification is shown at the bottom of Fig.7. Another possible solution would be to use a video buffer IC like the MAX497. This contains four buffers; one could be used for the video, with the other three paralleled for the audio. These ICs work fine with Video buffering The video output is formed using just three resistors to mix the sync pulses and video. This was simply fed into the high-impedance video input of a domestic TV set, which would have had an impedance of a few kilohms. Most newer video monitors, CRTs or other types, have a 75W input impedance, although some have a switch select ‘High Z’ mode. So you might need to add a buffer transistor to this design to feed the signal into your display, to make sure that the video output can successfully drive a 75W cable that is terminated with 75W. This can be done simply with an emitter-follower, as shown in Fig.7. This circuit (or a similar one) could be built on a small daughterboard. The pull-up resistor value (X) needs to be adjusted to get the bottom of the siliconchip.com.au The finished product has a retro vibe, except perhaps for the LED-illuminated start button! Australia’s electronics magazine June 2021  45 Parts List – Mini Arcade Pong 1 double-sided Pong PCB coded 08105211, 245 x 165mm 1 5V DC 1.5A regulated supply 1 monochrome TV or monitor with composite video input 2 5kW 24mm linear panel-mount potentiometers (for paddles) 1 50kW 24mm logarithmic panel-mount potentiometer (volume control) 1 small amplifier module (eg, the Champ) 1 speaker to suit amplifier module 1 enclosure to fit all assemblies 2 large knobs, to suit 5kW pots, for paddles (larger is better for ease of use) 1 smaller knob, to suit 50kW volume control pot 1 SPDT momentary pushbutton switch 2 50kW mini horizontal trimpots 1 14.31818MHz crystal (X1) 1 red binding post 1 black binding post 14 PCB pins (optional) Various lengths & colours of medium-duty hookup wire Hardware to mount PCB, power supply & other components in the enclosure Semiconductors 2 TIL311 or DIS1417 hexadecimal 7-segment displays with inbuilt logic (optional – A1, B1) [eBay] 10 7400 or 74LS00 quad 2-input NAND gate ICs (B2, B7, C1, C3, E1, E6, G3, H1, H4, H5) 7 74107 or 74LS107 dual JK flip-flop ICs (A2, C8, D9, F3, F6, G6, H2) 4 74161, 74LS161 or 9316DC synchronous 4-bit counters (A3, B3, G7, H7) 1 7486 or 74LS86 quad 2-input XOR gate IC (A4) 5 7474 or 74LS74 dual positive-edge triggered flip-flop ICs (A5, B5, C2, E7, H3) 2 7450 or 74LS50 dual 2-input AND-OR-invert gate ICs (A6, B6) [Rockby] 2 7420 or 74LS20 dual 4-input NAND gate ICs (A7, H6) 7 7493 or 74LS93 dual 2-bit up-counter ICs (A8, B8, E8, E9, F1, F8, F9) 4 NE555N timer ICs (A9, B9, F4, G4) [eBay] 1 7483 or 74LS83 4-bit binary adder IC (B4) [Rockby, Futurlec] 6 7410 or 74LS10 triple 3-input NAND gate ICs (C4, D4, D5, D8, E2, G5) 1 7448 or 74LS48 BCD to 7-segment decoder IC (C5) [Futurlec] 2 74153 or 74LS153 dual 4-input multiplexer ICs (C6, D6) 2 7490 or 74LS90 modulus-10 decade counters (C7, D7) 3 7404 or 74LS04 hex inverter ICs (C9, D1, E4) 3 7402 or 74LS02 quad 2-input NOR gate ICs (D2, F5, G1) 2 7430 or 74LS30 8-input NAND gate ICs (D3, F7) 3 7427 or 74LS27 triple 3-input NOR gate ICs (E3, E5, G2) 1 7425 or 74LS25 dual 4-input NOR gate with strobe IC (F2) [Rockby, Futurlec] 2 2N3904 NPN small signal transistors (Q1, Q3) 1 2N3906 PNP small signal transistor (Q2) 1 6.8V 1.5kW unidirectional TVS (eg, 1N6267) 1 1N4004 400A 1A diode 9 1N4148 small signal diodes Capacitors 2 220μF 10V axial electrolytic 1 4.7μF 10V tantalum or multi-layer ceramic 1 4.7μF 10V axial electrolytic 1 1.0μF 10V tantalum or multi-layer ceramic 2 120nF 63V MKT 33 100nF 50V ceramic 1 100pF ceramic or greencap Resistors (all mini 1/4W 1% metal film) 1 330kW 3 1kW 46 1 220kW 2 470W Silicon Chip 2 56kW 3 330W 1 2.2kW 4 220W 2 1.5kW 3 100W 1 1.2kW Australia’s electronics magazine high-value input resistors in the range of 5kW, but most circuits show the inputs terminated with 75W. Their input impedance is actually very high. Building the cabinet Once I confirmed it worked, the next step was to mount the PCB in a housing and pair it up with a suitable monochrome monitor. A suitable monitor for this job is the small monitor used with the vintage Apple IIc computer. I got my hands on one of those old Apple IIc computer monitors and modified it to run from 12V DC rather than mains power. This way, the monitor can be powered from the same power supply as the rest of the Pong console. This is also convenient because the Apple IIc typically runs from 115V AC. The Apple IIc monitor also has a handy stand that elevates it to a good viewing level. Apple IIc monitors generally come with a green phosphor (P31) CRT; however, I changed this for a white phosphor CRT, since monitors used with Pong were generally modified TV sets with white (P4) phosphor CRTs. I then mounted the completed Pong PCB, power supply (compact switchmode PSU), speaker and Champ amplifier module in a high-quality Hammond painted aluminium enclosure for the final result. I also added an illuminated push-to-start button. Once all the components are mounted in the cabinet, it’s just a matter of wiring them up. The power supply outputs go to the binding posts (positive to red). Connect either the VID & GND terminals to your display input (possibly via a buffer circuit, as described above). GND & SND go to the amplifier input, with its output going to the speaker (and whatever power supply arrangement the amplifier requires). Wire the N/O, GND & N/C terminals to your momentary game start pushbutton switch (which was a coin detector in the arcade version). The remaining two pairs of three terminals are wired across the two controller paddles, with PLL to the wiper of the left-hand player’s pot and PLR to the right-hand player’s. Connect the +VE terminals to the clockwise track ends, and GND to the anti-clockwise ends. A full circuit analysis can be found at www.worldphaco.com/uploads/ LAWN_TENNIS.pdf Continued on page 85 siliconchip.com.au siliconchip.com.au Australia’s electronics magazine June 2021  47 The T0053298599 is well-suited for heavy-duty usage. It is solid and includes a settings lock feature to prevent tampering in production environments. can be beneficial when working with solder wick. So having a good variety of tips available at reasonable prices (around $8 each) is definitely a plus in our books. Safety rest Included with the station is a PH70 safety rest, which is also equipped with rubber feet. Like the power unit, the safety rest feels weighty and is not likely to slide around. The rest has a generous space for the included sponge and several holes to store spare tips. Controls The three buttons form a simple and intuitive interface. The menu button cycles between standby time, offset, units and lock, with the up and down buttons changing the selected value. The lock feature is intended for a production environment, to prevent operators from adjusting the settings, although you might also find it useful to avoid accidental changes. The manual is quite thick, but mostly from including almost 30 languages. There are detailed pictograms, so even if there weren’t any words, the unit would be easy to use. Hands-on testing The manual states that the iron can heat from 50°C to 350°C in 28 seconds. We timed it at 50 seconds from ambient (around 20°C) to 380°C; perhaps this varies depending on the type of tip fitted. The nominal operating range is 100°C to 450°C with a stability of ±6°C. That’s a reasonably wide range, and if you need to work with a range of low-melt solders, for example, in constructing white-metal models, then the Weller T0053298599 should have the range and accuracy to do so. We had no trouble using the iron with a typical 99.3% tin/0.7% copper lead-free solder, which has a much higher melting point than standard tin/lead solder. Even working along rows of closely spaced pins, the iron was able to keep up the heat. Having said that, our work typically doesn’t involve really heavy-duty soldering. But based on our experience, we think that it would handle larger jobs reasonably well, as long as you used a suitable tip. We found that the default standby timeout of two-minutes was a little short, but it can be increased to 99 minutes, which we think should be sufficient for most cases. Conclusion We would certainly have no complaints about using this station for our everyday soldering tasks. It is sturdy, adjustable and responsive, and would be well suited to duties much more intensive than we could throw at it. The Weller T0053298599 kit is available at Bunnings Warehouse for $249, including GST. This unit was provided for review by Weller Tools. Visit www.bunnings.com.au/ weller-70w-240v-soldering-station_ p0248144 to purchase the station and/ or spare parts, including tips. Here’s a short link to the above: siliconchip. SC com.au/link/ab8n Suite 201, Level 2, 184 Bourke Road Alexandria NSW 2015 www.weller-tools.com.au/ Arcade Pong: the ANT terminal (continued from page 46) You might be wondering about the purpose of the "ANT" terminal on the PCB. It's close to the VID terminal, so you might think it's meant to drive a TV set's antenna input. But that is not its purpose. In the arcade machine, the ANT terminal was connected to a wire about a meter long, leading nowhere in the arcade cabinet. It connects to the base of the transistor that resets the game, which is floating, except for the tiny leakage of a diode. So the base voltage can float to be just on the verge of causing the transistor to conduct. siliconchip.com.au Back in the 1970s, it was surprising how resourceful teenagers were at trying to get free credits on arcade games. One trick was to deliver an electrostatic charge, or burst of RF, into the machine to clock up credits, as though multiple coins had been put in the coin mechanism. It was possible to prevent this with extensive RF filtering on all the logic circuits and wires leading to coin mechanism, switches etc. In Pong, however, one coin gave one game play credit. Atari decided to simply detect any electrostatic or RF burst, using Australia’s electronics magazine that antenna wire, and reset the game, making it impossible to get a free credit. That is one reason why the original transistors used (2N3643 and 2N3644) in the game's reset circuit were RF types. I left the "ANT" connection on my design so that my PCB could be used to replace/ repair a genuine arcade game console. It is surprising how few people can fix the original boards and run around in circles until they have replaced nearly every IC. The originals were not socketed, and many original arcade machine PCBs have been destroyed by botched repair jobs. SC June 2021  85