A free & open framework to help speed along the discovery, design, implementation & testing processes for Makers of all skill levels.

Follow the project at retromodules.com!

You should be able to throw your prototypes in a backpack. You should be able to tweak their code while at the coffee shop. There is no need to make or buy a 3D printer or CNC machine. No need to do a circuitboard production run. No need to crowdfund your idea or deal with the challenges of said campaign. This community-maintained specification is (and will always be) free!

Think the spec needs some revision? Please submit a pull request. Your feedback is truly appreciated.

Take a look at some sample projects, module ideas and popular interfaces if you want to dive in now.

"Upcycling is the process of converting old or discarded materials into something useful and often beautiful." -hipcycle.com

The Retro Modules framework provides many great opportunities to modify junk-bin hardware or to tranform it into an entirely new product. Re-use these objects. Save them from the garbage heap if possible. If the internals are no longer useful, send them to reputable e-waste facilities & re-use the enclosure.

This concept is certainly worth an interweb search. It is the idea that a product can be used while lacking certain functionality. Some features of the product may be minor & can be finished later. Headed to a demo with a grip of modules? Only demonstrate module features that are functional. This approach has roots in theater & beyond. The audience won't know something is missing from a production unless they expect it to be there. The audience is your user base... which may just be you. You can start using all sorts of not-quite-finished modules in the near-term, while slowly building toward completion of your grand scheme.

A stable spec among a group of people is a very valuable thing. It becomes easier to hack on a project with your friend on the other side of the world. When you meet up at Burning Man, your big group project could come together with greater ease. One of the modules failed? Ask someone to make & send a backup!

Many projects require redundant systems to allow fast repairs if part of the project fails. Retro Modules meets that need by reinforcing modular design patterns, such as using proxy microcontrollers which respond to data on industry-standard communication protocols.

One of the worst feelings, when starting to work on an old project, is when realize you forgot how you wired things before. When using a stable external spec, problems like these are minimized. That old robo-eyeball module you made for that Comic-Con puppet? It probably still works! Just plug it back in, load your old code & use it in a new project!

You may not need to buy anything to start building Retro Modules! Check your parts bin. If you have a 3V microcontroller (or similar), an I2C device (such as a port expander or accelerometer), & some DE-9 connectors, you're ready to begin!

• Cables & connectors used by this framework can often be found:
  • in a garage
  • at an office
  • at a maker space
  • at discount electronics stores
  • at nearly any online electronics vendor
  • at E-Waste processing facilities
• Refer to the tool list for tool recommendations.
• Refer to the style guide for overall style recommendations.
• "Ground" is referred to as "common" in this specification.
• Power contacts feature positive DC unless stated otherwise.
• Use a DC-DC Regulator for devices requiring specific voltages (e.g. "AMS1117", "MP1584EN", or "LM2596")
• I2C & SPI logic level is 3.3V.
• Unbalanced analog audio sources should provide line level signal
• Analog signals near digital signals will be subject to some interference. Some connectors support balanced & digital audio signals for pro audio applications. On most connectors, however, unbalanced line-level analog signal contacts are used to help facilitate easy experimentation with analog audio signals. These analog signal contacts have been arranged to help reduce risk of interference.
• Modules can be daisy-chained together with ease.
• Modules which provide power should only ever have socket-style connectors.
• Modules should typically have one pin-style connector.
• Modules may have zero or more socket-style connectors.
• If you're putting your client modules in an enclosure, put a sticker on the module describing what the module is & some of its capabilities.
• Typical ribbon cables support up to 1.2A per wire.
• A typical d-sub contact can only support up to 3A. Premium d-sub contacts typically support up to 5A.
• Add fuses to help protect power sources & small wires.
• Use polarizing keys in headers to help prevent incompatible connections.
• Unless explicitly recommended, do not connect connectors of one type directly to connectors of another type -- even if their pins line up.

A typical microcontroller board (e.g. Arduino, Teensy, etc.) is pretty modular as-is. To make your microcontroller board into a Retro Module, you will often use the contacts which communicate easily with other modules, while leaving most other contacts disconnected. In this example we'll use a 3.3V Arduino-style microcontroller board, a "Pin-Style" DE-9 connector for power supply modules & a "Socket-Style" DE-9 connector for client modules. We're using devices & connectors that are easy to hand-solder. If you wish to design printed circuit board Retro Modules, no problem! There are headers for that.

Please refer to this section for the DE-9 Connector spec.

• Connect the SCL contact on the microcontroller to the i2c-clock contact on the "Socket-Style" DE-9 Connector.
• Connect the SDA contact on the microcontroller to the i2c-data contact on the "Socket-Style" DE-9 Connector.
• Connect the VIN contact on the microcontroller to the fifteen-volts-max contact on the "Pin-Style" DE-9 Connector.
  • Use a DC-DC converter if the microcontroller requires a supply voltage lower than 15V.
• Connect the common contact on the "Socket-Style" DE-9 Connector to the common contact on the "Pin-Style" DE-9 Connector.
• Connect the common contact on the microcontroller to the common contact on the "Socket-Style" DE-9 Connector.
• Connect the fifteen-volts-max contact on the "Socket-Style" DE-9 Connector to the fifteen-volts-max contact on the "Pin-Style" DE-9 Connector.

Congratulations! You've created your first Retro Module! Let's power it up!

You'll need a power source, of course! You will need a 9V Battery Clip Connector, which will be soldered to a "Socket-Style" DE-9 Connector.

Please refer to this section for the DE-9 Connector spec.

• Connect the red wire of the 9V Battery Clip Connector to the fifteen-volts-max contact on the "Socket-Style" DE-9 Connector.
• Connect the black wire of the 9V Battery Clip Connector to the common contact on the "Socket-Style" DE-9 Connector.

That's it! You now have a 9V Battery Module! Feel free to power up your microcontroller module.

A good example I2C device is a MPU-6050 board, which creates & sends its accelerometer data to other device(s). Since the Retro Modules specification requires 3.3V logic levels, your MPU-6050 Retro Module will require a 3.3V voltage regulator (such as "AMS1117-3.3").

Please refer to this section for the DE-9 Connector spec.

• Connect the SCL contact on the MPU-6050 board to the i2c-clock contact on the DE-9 "Pin-Style" Connector.
• Connect the SDA contact on the MPU-6050 board to the i2c-data contact on the DE-9 "Pin-Style" Connector.
• Connect the GND contact on the MPU-6050 board to the common contact on the DE-9 "Pin-Style" Connector.
• Connect the VCC contact on the MPU-6050 board to the output of the 3.3V Voltage Regulator.
• Connect the common contact of the 3.3V Voltage regulator to the common contact on the DE-9 "Pin-Style" Connector.
• Connect the input contact of the 3.3V Voltage regulator to the fifteen-volts-max contact on the DE-9 "Pin-Style" Connector.

You now have your third Retro Module ready to go! Power down your Microcontroller Retro Module, connect your Accelerometer Retro Module, power them up & start coding!

This framework is not just for microcontrollers, microcomputers & peripherals. It is for small vaccuums, fume extractors, soldering irons, 3D printers, laptop power supplies, power tools, audiovisual devices, lighting, robotics & more!

Consider taking a closer look at I2C, SPI and CAN bus. There are many inexpensive I2C devices out there (accelerometers, LED displays, etc). Consider I2C & SPI for short to medium-range digital communication. CAN bus is better for longer distances & greater reliability. The one-wire-data communication protocol is unique & may prove useful in wearable modules and/or modules that need to send basic messages.

Consider having 'proxy' microcontrollers in certain modules. Say you have an SPI-based MP3 player board, but you want to avoid using SPI pins among your set of modules. Build your module with a proxy microcontroller connected to the I2C contacts, and only connect your MP3 player SPI wires to that internal proxy microcontroller. You can then craft simple programs to serve as interfaces on the I2C bus. If you're comfortable with CAN bus... choose that instead of I2C.

If you have a few minutes to spare, take a look at projects, module ideas and popular interfaces.