Updating Light Gun Commando to ESP-IDF 5.0 and simulating a Guncon 2

Sunday, 25th December 2022

I've continued working on the Light Gun Commando project that I hope to be able to use as a system for playing light gun games on old consoles with Wii remotes.

The Wii remotes are connected to an ESP32 microcontroller using Bluetooth, and I had a few small issues with this arrangement, most obviously with a cheap third-party Wii remote that refused to pair. I had also encountered a few other quirks and oddities along the way, such as the timer capture's interrupt (used to measure the horizontal scanline period for timing purposes) crashing the whole system if it received too many pulses in a short while (e.g. by inserting or removing the video sync cable producing lots of fast glitchy pulses). I'd found some clumsy workarounds, but when I saw that the ESP-IDF 5.0 development tools for the ESP32 had been released I thought it would be worth updating to that to see if it improved matters.

As well as a lot of improvements and bug fixes ESP-IDF 5.0 did introduce quite a few breaking changes and I couldn't get the project's existing Bluetooth code to compile at all under the new environment. Much of it was based on sample code and rather than try to get this old copied-and-pasted code that I didn't fully understand up to scratch I ended up writing my own code to handle searching and connecting to devices. Fortunately this is quite straightforward to do with the Bluetooth APIs provided, and I even got my cheap 3rd-party knockoff Wii remote to pair alongside my official Wii remotes.

I use the Motor Control Pulse Width Modulator (MCPWM) and Pulse Counter (PCNT) peripherals on the ESP32 to generate the waveforms that approximate what a light gun would see if it was pointed at a CRT based on where the Wii remote is aimed. The old drivers for these peripherals have been deprecated in ESP-IDF 5.0, and though my old code still worked it threw up some compiler warnings and as I'd experienced crashing issues I thought it best to update my code.

I've found the new drivers provide much better control over the peripherals, at least for my use case, and are quite a bit easier to use. I was able to remove some of my clumsy workarounds and improve overall performance, as well as properly handle the timing for a range of different video modes: 240p, 480i, 288p, 576i and 480p are now all supported. Separate sync is now also supported for Dreamcast VGA compatibility, as the following video demonstrates:

One light gun I hoped to support was the PlayStation 2's Guncon 2. This uses a USB connection and USB is not something I have very much experience with, though I have used V-USB in a few projects before to add USB support — I'd been using standard device classes (e.g. HID or MIDI) where it's a case of simple "fill in the blanks" coding to get a working USB device, rather than a vendor-specific class device like the Guncon 2.

Fortunately I do have a real Guncon 2 and by plugging it into my PC I was able to get a device descriptor from the Windows SDK's usbview. From this I could see the device IDs that I'd need to include as well as see that the Guncon 2 has an interrupt endpoint. Armed with this information I was able to set up a USB device descriptor that closely matched the Guncon 2 by editing V-USB's usbconfig.h.

Of course, having a matching device descriptor is not much use without sending the approprate data back to the console. I'd seen a few places mention that the gun's data is six bytes long: two bytes of button data, two bytes of 16-bit X coordinate data, two bytes of 16-bit Y coordinate data (least significant byte first). I was able to find a mapping of button names to bit indices in the button status data, but nothing clear about the coordinates. I started by just using the same coordinates as the original Guncon, which appears to work for Y but squished the X coordinates into the left half of the screen. I tried doubling the X coordinate range (from 384 units to 768 units) but this seemed a little too wide. I ended up settling on an X coordinate range of 640 units, which seems to provide good results:

The only USB-handling code I've got in there at the moment is a basic poll/check interrupt ready/write interrupt data loop, though, which is likely not enough to properly implement all of the Guncon 2's functionality. Time Crisis 3 and Virtua Cop: Elite Edition seem happy enough so far, but I'll need to do some further digging into the Guncon 2's USB protocol. I've also ordered an original Xbox controller extension cable to cut in half as I'd very much like to see if I can build an Xbox gun adaptor, and the Xbox uses USB like the Guncon 2.

Electronics Guncon 2 Light Gun Commando Light guns Namco Sega Sega Dreamcast Sony Sony PlayStation 2

Light Gun Commando: LCD-compatible light gun support for original console hardware?

Tuesday, 13th December 2022

As the previous entries on this site might indicate, I do enjoy a good light gun game. Unfortunately, when it comes to playing them on home consoles you usually need to use a CRT television for the gun controllers to work. I have a CRT or two at my disposal but I'm well aware they won't last forever and they're not really the most convenient devices even when they are working at their best.

Bearing this in mind I decided to try to find a way to get light guns working on LCD TVs. My experiments back in early 2015 – called DC-LiGuE, the "Dreamcast Light Gun Emulator" – never amounted to much. I was able to build a circuit that I could feed coordinates into and translate that into light gun inputs without involving a CRT display, but I had a couple of major issues. The first was that I was unable to talk to the Dreamcast directly; its controller protocol is much too fast to decode reliably using the ATmega microcontrollers I favour in my projects, so my interface involved shining a bright white LED into the end of a regular Dreamcast light gun. The second issue was disappointment in the Wii remote I was hoping to use as the light gun input; I'd tried some homebrew programs that translated the data from its IR tracking camera into pointer events as well as the Mayflash DolphinBar (which shows up as a regular USB mouse on a PC) and the accuracy was generally pretty poor and not subsitute for a light gun.

More recently I was made aware of other IR-based light gun solutions such as GUN4IR from Boojakascha's YouTube video on the project. I thought I should give the Wii remote another chance! I'd also realised that Mayflash's DolphinBar has a fourth mode intended for use with the Dolphin emulator in which it presents the four paired Wii remotes as four USB HID devices. This makes experimenting with the Wii remote very easy, as you don't need to worry about any of the Bluetooth pairing side of things. I stuck some IR LEDs around my monitor in the GUN4IR configuration and knocked together a quick prototype in C# that analysed the tracked points and translated them into pointer coordinates. Having the four LEDs around the monitor (instead of just two in the Wii sensor bar) makes the aim tracking much easier and much more accurate.

Skipping ahead in the story a bit, the video below shows the C# prototype running in the monitor on the left. The diamond shape is drawn around the four tracked IR emitter points. If the Wii remote is aimed far enough away from the centre of the screen it may lose sight of one or more of these points, but the software does a reasonable job of reconstructing the diamond based on the remaining points it can see. The large bright white dot is the calculated pointer position.

In example the Wii remote is being used to play Time Crisis II on the PlayStation 2. This is a happening on a real PS2, not an emulator on the PC. To achieve this a circuit that mimics a Guncon light gun is connected between my PC and the PS2, and the PC sends button and pointer data to this circuit. Different circuits could be built that could mimic different light guns for different consoles, providing a somewhat universal light gun solution. One issue is that my PC isn't anywhere near my consoles, though, and not everyone is going to have a DolphinBar so replacing the PC side with a dedicated unit seemed like a good idea.

If I was going to use Wii remotes then I'd need something that could speak Bluetooth. The ESP32 microcontroller is cheap and provides a system-on-a-chip with Bluetooth (and a corresponding software stack) that seemed somewhat easy to get into. There was a simple Bluetooth HID host demo that served as a good starting point, and once I'd got the Wii remote paired with the ESP32 and transferring HID reports I translated the C# prototype code I'd written into C and got the ESP32 talking to the simulated Guncon instead of my PC.

The choice of the PlayStation Guncon was deliberate, as simulating this sort of light gun if you know the pointer coordinates you wish to send is very easy. The Guncon is quite unusual compared to other light guns of the era in that it handles the position calculation within the gun itself and then transfers the coordinates directly to the console over the standard controller protocol used to normally send button statuses or analogue joystick positions. Most other light guns just send a pulse on a dedicated "light gun" input pin when they see flashes of light from the CRT's raster scanning pattern and rely on the console to handle the position calculation, which the console can do as it can ask the video chip which part of the frame it was sending to the TV at the moment the light gun saw the light and from that determine where the gun was aimed. For the Guncon to be able to do this without direct access to the video chip it needs to have access to the generated video signal, which is why the Guncon has an RCA connector on it to pass the console's video signal through it. To be able to make most other light guns work, I'd need to generate the pulses seen when the Wii remote is pointing at the part of the screen that the console is currently outputting, and to do that I'd need to be syncronised with the console's video output.

Fortunately the ESP32 has a motor PWM controller that can be synchronised to external sources and so by adding an LM1881 sync separator circuit to extract the composite (horizontal) and vertical sync pulses to give it something to synchronise itself to I was able to generate pulses that looked like they might have come from a light gun based on the point on the screen the Wii remote was aimed at. I first tested this with the Master System, pretending to be a Light Phaser, before feeding the signals into a circuit that pretends to be a Mega Drive Justifier.

The point I'm aiming for with all of this is to have a central unit sitting under my TV that has the Wii remotes paired to it and the video signal passing through it. It will then have a socket on the front that can be connected to the console-specific light gun simulating cables which will then be plugged into their corresponding consoles. One system that can hopefully cover all the possible combination of light guns on original hardware. When I think of being prepared for any eventuality with a large collection of guns I naturally think of the classic Arnold Schwarzenegger film Commando, and so I've decided to call this project the Light Gun Commando.

Unlike John Matrix, however, I prefer to go into battle with a friend and so it's very important to me that not only does this system cover as many light gun types as possible, but also more than one player. I can't think of any console light gun games that support more than two simultaneous players so at the moment I'm concentrating on two player support but will probably leave space in protocol specifications for more. The following video shows a demonstration of two simultaneous guns in action:

In the video we're back to the PlayStation, but now simulating a Hyper Blaster instead of a Guncon. This is using the same circuit as the Guncon adaptor, but the firmware now supports different gun modes. Before the main host device sends any data to a console-specific gun adaptor it asks it to describe its capabilities. The adaptor replies with a block of formatted data describing each gun it can simulate; this includes a list of all buttons it has (including a descriptive name and a generic button type such as "trigger button", "start button" or "back button") and any axes it has (such as the pointer X and Y for the Guncon). These gun descriptions can then be repeated for multiple players if an adaptor can simulate more than one gun at a time, and then these player/gun descriptions can be grouped into different modes (e.g. "Two Guncons", "Two Hyper Blasters"). Pressing a button on the host device can then cycle between the different gun modes. The host device can use these mode, player and gun descriptions to construct status reports based on the current state of the Wii remotes, and by using generic button types (e.g. "trigger button" or "start button") the Wii buttons can be mapped automatically to suitable simulated gun buttons.

This automatic mapping is not just a matter of convenience, but is also intended to keep the host device and simulated guns separated. The simulated guns only need to worry about the guns they are simulating and not about button mapping from a Wii remote specifically. This is to allow the host device to be replaced by other hosts but still be able to use the same console-specific adaptors; the idea is that a GUN4IR or Sinden light gun host could be put together in the same way that I'm putting together a Wii remote host, and as long as the communication protocol between them is sensibly designed this should be a pretty straightforward endeavour.

To this end I'm currently trying to hack together as many different simulated light guns as I can to ensure that the communication protocol works well for them all. I've already mentioned the Sega Master System's Light Phaser, Mega Drive's Justifier and PlayStation's Guncon and Hyper Blaster. I did also get the Saturn's Virtua Gun working:

This all started back in 2015 with an attempt to mimic the Dreamcast's Light Gun, though, so if it's nearly eight years later and still no closer to that goal it's surely a bit disappointing? The main problem I had with the Dreamcast is that its controller bus uses a wire protocol that's not directly compatible with any existing standard that might be built into a microcontroller (the PlayStation uses a minor variation of SPI, for example) and is too fast to decode reliably in software on the microcontrollers I typically use. I have seen projects that perform clever tricks to work around this, such as dumping the bus state to RAM in a tight loop before decoding it (slowly) afterwards but these never seemed particularly robust and I didn't want to risk dropping data coming in from the host via the serial port if I was busy spending all available CPU time on speaking to the Dreamcast.

My solution was to look into the dsPIC33, specifically a model capable of running at 140MHz (up to 70 MIPS) which has sufficient grunt to decode the controller protocol in software with cycles to spare, enough RAM to store large data frames and DMA capabilities to be able to keep receiving data from the host device with zero CPU overhead if we're otherwise busy talking to the Dreamcast – all in in a hobbyist-friendly breadboardable DIP28 package!

As the video above hopefully demonstrates, the dsPIC33 seems to have done the trick and I can join the dogs of the AMS and hopefully not suffer like G did.

There's quite a lot work to go but I'm already feeling slightly less worried that if my CRT TVs all conk out I'll be stranded with no way to play my light gun games.

Electronics Light Gun Commando Light guns Sega Sega Dreamcast Sega Mega Drive Sega Mega-CD Sega Saturn Sony PlayStation

Connecting pedals to a Sega Dreamcast Race Controller

Friday, 30th September 2022

I recently built some Dreamcast Race Controller "De-Dead Zone" mods for people and before popping them in the post I tested them in my wheel. During this process I noticed an unpopulated region of the main PCB:

Photo of unpopulated region of the Dreamcast Race Controller PCB

I remember reading that some versions of the Race Controller had a socket on the back for the connection of a set of pedals, however those pedals were never released and games instead rely on a pair of analogue paddles mounted behind the wheel for braking and acceleration. I wondered if the pedal functionality was still available on my wheel, even though it lacks the relevant socket on the back. I traced the connections of the unpopulated components and made a guess of their values, based on their name (e.g. FB9 is presumably a fuse, C22 is presumably a capacitor) and comparing their function to other similar sections of the circuit. This is the circuit I arrived at:

Circuit diagram of the missing components on the Dreamcast Race Controller PCB

FB9 and FB10 connect +5V and GND to CN5's pins 1 and 5 respectively and are presumably the power connections for the pedals. R22 and R23 are 1MΩ pull-down resistors that were already present, and based on the thick traces from CN5's pins 2 and 3 and connection to two adjacent pins on the main microcontroller these are part of the analogue inputs from the two pedals. CN5's pin 4 is eventually connected to another pin on the microcontroller with a 10KΩ pull-up resistor, and my assumption is that the pedals should connect this pin to ground so the wheel can detect whether they are plugged in or not.

Other parts of the wheel use 100Ω resistors in series with their analogue inputs so I followed their lead. I'm not sure of the capacitor values; I picked 100nF for the C25 capacitor across the power supply lines and 10nF for the capacitors to ground on the other inputs (C22, C23 and C24) but these are complete guesses as I don't own a capacitor meter to test the similar components on other parts of the board.

As I also don't have the small surface-mount parts in stock I connected wire links across FB9, R17, R18, R19 and FB10 and then soldered five wires to CN5 so that I could build a small circuit on a breadboard with the resistors and capacitors on it. I then connected this to my racing wheel pedals:

CN5 Pin Function
1 +5V
2 Pedal 1 analogue voltage
3 Pedal 2 analogue voltage
4 Pedal detect (connect to GND)
5 GND

With the pedals connected like this the race controller does detect them and sends their status back to the Dreamcast console, however no game software I have tried has been able to work properly with the pedals. Games either ignore the pedals entirely or complain about an unsupported or disconnected controller. However, if you run the 240p Test Suite's controller tester you can see the pedals reported as two additional axes that operate independently of the existing analogue paddles.

Video thumbnail showing wheel and pedals being tested in the 240p Test Suite

The video above shows a demonstration of how the wheel and pedals perform in a handful of games and the 240p Test Suite, with that test suite being the only software I've found that can show the status of the pedals. It's a bit disappointing that no games seem to support the wheel and pedals together, but I thought it was interesting to see that the functionality is at least present in the wheel hardware.

Electronics Race Controller Sega Sega Dreamcast

Making your own Dreamcast MIDI Interface Cable

Saturday, 1st May 2021

I love an unusual accessory for a video game console or computer, and one such accessory is the Dreamcast MIDI Interface Cable, HKT-9200, which allows you to connect MIDI devices to the Dreamcast console's serial port. Only released in Japan and with only one piece of software released for it — the O･to･i･re (お･と･い･れ) sequencer – these are a somewhat hard to find accessory nowadays and prices for second-hand units are far beyond what I could hope to afford (at the time of writing there are two on eBay, both for over £300).

Fortunately, the user darcagn on the Obscure Gamers forum took some photos of the insides of the interface box and from that I could make a pretty good guess as to how the cable works.

MIDI uses a serial protocol running at 31.25Kbps (a speed that can be easily derived by dividing a 1MHz clock by 32). Rather than signal "0" or "1" bits with different voltage levels (as with a PC's RS-232 serial ports, for example, which commonly uses +12V for a "0" and -12V for a "1") it uses a current loop, with 5mA current on for a "0" and current switched off for a "1". To avoid ground loops, which are a big concern when working with audio as they can introduce intereference (e.g. a mains hum) on recordings, the two connected devices are electrically isolated with an optoisolator in the receiver.

At the very least I therefore expected to see some sort of optoisolator circuit on the adaptor's MIDI IN port and some sort of output buffer circuit on the adaptor's MIDI OUT port to convert between MIDI's current loop signalling and the Dreamcast's 3.3V logic on its serial I/O pins, and that is indeed what you can see from darcagn's photos. My worry was that there might be some additional Dreamcast-specific hardware inside the box, but fortunately there isn't – it's all off-the-shelf parts. My main concern was how everything was connected, as this can't be completely seen from the photos: would sending MIDI IN data to the console's serial port RX and relaying data from the console's serial port TX to MIDI OUT be enough? Some experimentation would be necessary!

Building a serial port connector

As mentioned above, the MIDI interface cable's box doesn't contain anything Dreamcast-specific, however this box is connected to the Dreamcast's serial port using a proprietary connector. To try anything out I'd need to find a way to connect a circuit to this port:

The serial port on the back of the Dreamcast

Fortunately, the port's contact pitch is the same as a PCI Express slot, and I was able to find a PCI Express slot for £5 which could be used to make multiple connectors! It will need to be cut down to size (and in half, as the Dreamcast's serial port only has contacts on one side rather than both sides of a PCI Express card) but with a bit of work will do the job.

Cutting the PCI Express connector to make the serial port connector

The above photos show the process of cutting the PCI Express slot down to size. The Dreamcast serial port has 10 connectors in it, so a block is cut that is 12 connectors long using a cutting disc – as this is quite a rough process an extra sacrificial connector is left on each end as it doesn't matter if this gets mangled by the cutter. The block is then cut in half, leaving more of the support structure from the bottom of the slot on the side of the slot we're going to be using. The outer two connectors are then removed if they haven't already been damaged, leaving the central 10 connectors, and the outer plastic is brought to the final width and tidied up with some hand files. The fit of the connector should be tested against the Dreamcast's serial port:

Testing the fit of the connector inside the Dreamcast serial port

There shouldn't be too much side-to-side movement but the connector will be very loose without something to hold it down against the contacts. In my case I found some 2mm thick ABS plastic sheet was the perfect material to make the backing piece for the connector, though you may find your choice of material depends on the thickness of your PCI Express slot. It will need to be 13.5mm wide (about ½") and a decent enough length to fit inside the enclosure you're going to use for the plug – in my case 4cms was about right. The plastic can be cut by scoring it with a knife and then snapping it over the edge of a table.

Backing support piece to hold the connector against the serial port contacts

You should also drill some shallow holes in the plastic, with the centres of the holes being 3mm from the end and 3mm from the sides. The serial port has a couple of bumps stamped into the metal surround of the serial port and these matching holes in the plastic piece allow it to snap into place. A stripboard track-cutting drill is perfect for this task!

Groove filed into the end of the piece for the raised ridge on the PCI Express slot

In my case the PCI Express slot also has a slight lip that prevents it from sitting flush against the backing support. I could have filed this flat but the connector is quite fragile so I didn't want to risk damaging it so I ended up filing a corresponding channel into the bottom of the backing support piece.

Test fit of the connector and support piece

At this point make sure that everything fits. If it does you can start wiring up! The photos below show the process – heat-shrink tubing and strain reliefs are very useful, so don't forget to install them before soldering!

Soldering the wires to the connector

Putting a scrap piece of circuit board material between the two rows of pins also makes soldering much easier. In my case I only soldered the six pins required for this MIDI interface cable:

  • 1: +5V
  • 3: GND
  • 4: RX
  • 5: TX
  • 8: GND
  • 10: +3.3V

Pins are numbered from left to right when looking at the serial port at the rear of the console (if in doubt, you can check the voltages of the end pins against the console's metal chassis ground).

At this point you may wish to double check that your solder connections are made correctly and that nothing is shorted out – try with the cable plugged into the Dreamcast as well, and check that adjacent pins are not shorted together (the only two that should be shorted are pins 3 and 8, the two GNDs). If you're happy with that you can glue the connector onto the backing:

The connector is now glued to its supporting backing

You may notice that this is actually a different connector in the photo to the previous one, and that's because I accidentally got glue into the connector's springy contacts and jammed them so had to start again – definitely not a fun mistake to make, so be careful!

Fortunately, the second one went more successfully. The glued connector snaps in and out of the console with a nice reassuring click thanks to the two holes drilled into the top surface. Before switching on the Dreamcast I tried wiggling the cable around to ensure that even when treated roughly it woudn't short out adjacent pins. When I was happy this was the case I switched on the Dreamcast and ensured that I was getting a consistent +5V from pin 1 and +3.3V from pin 10 – as these pins are at the far end of the connector these are the ones that are more likely to have problems with crooked connectors. In my case I found there was an intermittent fault with pin 1's +5V. This was because I hadn't glued the connector on particularly straight and so pin 1's connector was slightly back from the edge of the backing piece. I very carefully filed the backing piece's edge so that it was flush with the slightly wonky PCI Express connector, after which pin 1 made reliable contact.

Potting the connector inside a small enclosure with hot glue

When you're completely happy with the connector, you can make it more robust by putting it inside an enclosure. I have some very small project boxes that are perfect for this sort of thing, it's a bit bulky when compared to the official Sega product but it does its job well here and doesn't bump into the power connector or AV port connector.
I cut a slot in one end of the box for the connector to stick out of and a notch in the other for the cable strain relief to clip into. I surrounded the console's serial port with a few of layers of masking tape to ensure that when the connector was inserted there was still a small gap between the case and the plug to make sure that it could always be fully inserted and not held back by interference from the case (it also protected the console shell from accidental strings of hot glue!) I then plugged the connector into the Dreamcast, made sure that everthing was neatly lined up, and secured the parts in place with copious amounts of hot glue. Once this had set I added more hot glue to the rear of the connector to make sure it was all held as securely as possible, and then screwed the enclosure shut.

The finished serial cable

With all the effort spent on the Dreamcast end of the cable, don't forget about the MIDI interface box end! I'm fond of JST-XH connectors so crimped one onto the end of the cable, ready to plug into the circuit board. The finished cable is seen above!

Building a prototype MIDI interface cable

With a Dreamcast serial port cable to hand I was able to experiment and see what happened when using the O･to･i･re (お･と･い･れ) sequencer. Here's the circuit I ended up building on a breadboard:

The prototype MIDI interface cable on a breadboard

On the very left is the first serial cable connector I tried constructing. It looks more yellow than the final version as I used a piece of pad board for the backing piece instead of the 2mm ABS plastic – I thought I was going to solder the PCI Express connector piece to a circuit board rather than directly to the cable's wires, this turned out to be a mistake. One advantage is that it does have eight wires soldered to it – I thought I'd see what RTS and CTS were doing, but I ended up not using them. The MIDI port to the left is for MIDI OUT and has a large black chip to act as a buffer, the port to the right is for MIDI IN and has a small white chip as an optoisolator. Here's the corresponding circuit diagram:

The schematic for the MIDI interface cable

The position of the ports is flipped in this diagram when compared to photo of the breadboard, but it otherwise matches up!

On the left is the MIDI IN port. This uses an H11L1 optoisolator as they are still reasonably easy to get hold of today, are fast enough for use with MIDI and can be run directly from +3.3V. Its output on pin 4 is open collector so it needs the 270Ω pull-up resistor to the +3.3V rail. A +5V-demanding optoisolator could also have been used if it had an open collector output and the pull-up resistor on its output was still tied to +3.3V (we don't want to run +5V into the Dreamcast's +3.3V logic!) but this makes the wiring a little more complicated so sticking to a +3.3V-compatible part makes life easier.

The 36Ω resistor between the output of the MIDI IN circuit and the serial port's RX pin is there because it is in the official cable. The official cable also places ferrite beads on every I/O pin (and has a ferrite bead clipped onto the cable itself) which I have not replicated in my own cable, but they can't hurt and I suppose it could protect the console from certain direct shorts!

The MIDI OUT port uses a 74HC365N to convert from the serial port's +3.3V logic to +5V to drive the MIDI output. MIDI signals can be run from +3.3V (it's the flow of current that's more important than the selected voltage) but +5V seems more typical so I thought I'd stick with that, and as we need to buffer the signal anyway (I'm not sure how much current the Dreamcast's serial ports are designed to sink or source) using the +5V supply we have available to us made sense. The voltage threshold for a "high" input signal is probably a bit too high with the 74HC365N – +3.3V is pretty close to the recommended values in the datasheet, so the 74HCT365N version of the chip would give you more margin for error and would be a drop-in replacement. In my testing the 74HC365N does work well, though, and it's what I had available.

The cable used in this prototype has eight connections rather than the six in the final. This is because I did experiment with the RTS (pin 6) and CTS (pin 7) signals from the console, however as far as I can see these are just pulled low and high respectively and do not change from the moment the console boots, even when sending and receiving MIDI data within the O･to･i･re (お･と･い･れ) software. If they were planned to be used for some purpose then I'm not sure what, and with only one piece of software released to test with I'm not sure I'll find out.

In any case, with this circuit data from the MIDI IN port is translated to +3.3V logic levels suitable for the Dreamcast's serial port input (RX) and translated back from the serial port output (TX) to a current loop suitable to drive a device connected to the MIDI OUT port. In practice it seems this MIDI OUT port acts more like a MIDI THRU with the O･to･i･re (お･と･い･れ) sequencer – any data sent to the MIDI IN port comes straight back out of the MIDI OUT port, however if you record some notes in the sequencer and play them back afterwards they aren't played back out of MIDI OUT. At first I wondered if I'd made a wiring error (accidentally connecting MIDI IN straight to MIDI OUT) but the MIDI OUT is indeed under control of the software as it will stop relaying messages on certain screens.

Putting it all together in a nice box

I ended up using my usual pad board construction technique to build the final device:

The assembled circuit board for the adaptor

I followed the circuit diagram I'd drawn earlier (rather than copy the breadboard circuit) to ensure the diagram was correct. This was all assembled to fit in a ready-made ABS enclosure, into which I cut some holes. Historically I've had a hard time cutting neat round holes in plastic enclosures – I have a few hole saws and these are great for cutting through wood or acrylic but when trying to cut ABS they tend to bind and either rip the box out of the vice or just shatter it. I normally resort to drilling lots of very small holes around the perimeter of the circle and then try to file it to size, which is OK for buttons or sockets with overhanging parts to hide the inaccuracies but wouldn't do here! For this project I bought a very cheap step drill set on eBay (three bits for a fiver) with zero expectations but it did an excellent job, it kept the centre hole I'd started from and didn't need very much cleaning up. I wish I'd bought one sooner!

Using a step drill to make the MIDI port holes

The other enclosure challenge to deal with was labelling the two ports. I normally get away without labelling my projects because the function of each port can be guessed quite easily (e.g. inputs and outputs normally only plug in one way, or player 1 is on the left and player 2 is on the right) but in this case there's not much convention for where MIDI OUT and MIDI IN go (though the original Dreamcast MIDI interface cable puts MIDI OUT on the left, as does my M-Audio Midisport). For this I thought I'd try using some dry transfer lettering designed for model-making, and it seems to do a great job!

Dry transfer decal lettering marks the OUT and IN ports

I'm pretty happy with the final outcome – it's a bit of a pain making the serial cable for connection to the Dreamcast, but the end result works well and it saves spending an absolute fortune on the original Sega accessory.

The completed MIDI interface cable/box

Now I can get on with making music with my Dreamcast!

Electronics MIDI Music Sega Sega Dreamcast

Subscribe to an RSS feed that only contains items with the Sega Dreamcast tag.

FirstLast RSSSearchBrowse by dateIndexTags