freeconnect

freeconnect is a project that aims to provide a family of no mating required, small footprint connectors for in-circuit connection, providing a means to program and debug pcbs without the added cost and assembly of traditional mating connectors. The main focus of the project is to provide an open, free to use, cheap, reproducible at home alternative to existing (expensive, and unobtainable) solutions on the market.

I hope to help community develop their projects by providing an accessible solution without having to worry about issues like availability, prohibitive cost, or proprietary IP.

The aim is to also provide Footprints for most/all EDAs.

Planned is also a cheat sheet of connections for the various connectors and applications (JTAG, SWD, UART, SPI, etc…)

State of the project

I have prototyped connectors with 6 and 10 connections, with very positive results.

The internal pcbs were made with 2 layers, which made it impossible to do odd-even pinout, 4 layer is a consideration, but the 0.6mm thickness is a requirement making this a slighlty harder problem.

As is the connectors are ready for early adopters, improvements need to be made.

Roadmap

• Mechanical design [Done!]

• Internal pcb design [WIP]

• Footprints

• Snap-in versions

• Snap-less holding solution (flexible material? pcb with sockets?)

• clean up the OpenSCAD scripts

• Compile a cheat sheet of recomended connections

Early prototypes

Mechanical design

Stack up

Available Solutions (planned)

Name	No pins	Pinout
fc203u	6	DIP style
fc203z		Odd-even
fc204u	8	DIP style
fc204z		Odd-even
fc205u	10	DIP style
fc205z		Odd-even
fc207u	14	DIP style
fc207z		Odd-even
fc208u	16	DIP style
fc208z		Odd-even
fc210u	20	DIP style
fc210z		Odd-even

Making the connectors

arquitecture/Core technologies

There are some technologies and specific materials that allow this to be possible:

2 Row by X column design with 1.27mm pitch:

This choice allows compatibility with existing solutions, and relies on a dimension.

Automated/scripted generation:

I am trying to rely on scripting/automation were possible, this allows for a consistent range of connectors, and allows me or annyone to easily modify them for specific needs.

Right now the 3 model is completely reliant o OpenSCAD, and many parameters are costumizable.

Resin 3d printing:

After unsuccessful attemps at making the required mechanical parts with fdm 3d printing, It is clear the detail/resolution allowed by resin 3d printing is a requirement to reproduce them.

The equipment i had success with so far:

• creality LD-002R printer.

• Anycubic clear resin.

• SIRAYA Tech Blu resin.

Pogo pins:

This is core to the connectors, there are some details this current solution relies on, for instance the diameter of the pogos chosen is 0.68mm this is rather convinient, because at 1.27mm spacing, this allows almost exactly 0.6mm between them, which is a standard thickness for PCBs, one which is available from pototype manufacturers without added cost.

The pin I have chosen to work with is the P50-Q1, It seems to be reasonably standardized and available, at least from chinese suppliers (example Listing).

There are other viable options from the same series, I chose this model because the tip seemed to be the most appropriate for me.

If you are looking for an alternative, make sure it is aroun 0.68mm in diameter and around 16.35mm long to allow use of the standard models i will provide You can ofcourse generate your own with different dimensions

Dowel/Alignment pins:

The alignment pins are arranged in a “triangle” of sorts, one single centered on one end, two equally spaced on the other end.

The spacing from the alignment pins to the pogo pins is 1.27mm, the distance between the two alignment pins on one side is 2.03mm, the dowels are standard 0.8mm diameter 16mm long pins readily available (Chinese supplier Listing, also available from mcmaster).

The dimensions were chosen to keep compatibility with existing solutions.

cable:

The wires/cable the design was made around is standard p``1.27mm`` ribbon cable, nothing special about it. The cable is folded in half in order to conserve space, and make a more direct connection with the pogo pins. It should be possible to use other solutions, like for instance individual wires.

PCB:

There Exists a PCB in the Middle of the connector, it serves a couple of important purposes: - mechanically holds the pogo pins in place - holds the wires to the connector - provides the connection between the wires and the pogo pins

This last item is important, it allows us to control the pinout of the connector, if we were to for instance make a direct connection between the wires and the pogo pins, we would be stuck with a U shapped pinout (similar to a DIP package), because of the way the cable is bent, when a odd-even arrangement is probably more desirable in most circumstances.

The plan is to provide both options for every connector, a U (pinout following a U shape) and a Z option (pinout following an odd-even arrangement).

Getting the models

Standard renders of the models should be available on github releases.

If you need a different model, like for instance a different pogo pin diameter, you can generate your own, take a look at Development.

Printing

To be documented.

Assembly

To be documented.

Development

To be documented.