Hi all,
I'm looking to build (for a personal project) a system that requires a sort of "cartridge connector" or rather a gumstick sized, quickly patchable, hot plug, resilient up to 100k mating cycles, 50-pin, pcb-carrier, low frequency (DC..200 kHz), normalizable connector with a sturdy shell that will carry the cable. The idea is to have a relatively thick pcb the size of a stick of chewing gum, and have it mate with a port on the front panel of a piece of equipment. I might also want to add a run of fiber optic cable with associated mating hardware on the connector.
Let me go through the requirements a little first:
1. gumstick sized - this is going to go on a control panel where the user will be patching and unplugging a lot of connections. The control panel is very busy and front panel real estate is at a premium. The size shouldn't be much larger than a quarter inch jack, so something like a stick of chewing gum (see attached image) would be perfectly fine. I wouldn't like something huge like a D or Centronics-style or automotive multipin or military circular multipin Lemo connector. Those are just huge because they arrange the pins next to each other in the surface of the front panel they attach to. So the logical conclusion is to instead arrange the contacts depth-wise.
2. quickly patchable. one issue with all existing high pin count connectors is that they are very slow to patch. eg with milspec and lemos you have to aim the connector (it's not self-aligning) and then pray that you put it on at the right angle, and then screw it down. That's waaaay too much work for this use case which requires being able to add a patch within seconds.
3. hot plug. this will carry low analog voltages and should be hot pluggable. I don't see any issues.
4. resilient up to 100k mating cycles - on some ports, this will get plugged in and out dozens of times a day. I want it to last 20 years.
5. 50-pin. The pins will carry DC..200kHz signals at up to 50Vpp, but I could settle for DC...50kHz at a much lower voltage if there are unsurmountable issues, but I wouldn't necessarily really want to.
6. pcb carrier. It seems like the only way to really do this is to have a pcb mate another pcb using spring contacts, but I'm open to other suggestions.
7. low frequency - this will only carry audio
8. normalizable - the audio connections should by default be routed to another place rather out of (or in from) the connector. Just like a normalized audio patch bay. This can be done by having a mechanical feeler and switching using transistors, but it would be nice if the connector did it on its own in some way.
9. sturdy shell that will carry a cable - a 50 pin cable is pretty heavy and a bit of a boa constrictor, but if you have a heavy connector it should be able to carry the weight of up to 2-3 meters of such a cable.
10. fiber optic connection - I'd like this to ideally also patch a slow digital signal (~1-10 MB/s). As the signal runs together with sensitive audio, I can't have it run in electrical form, which would create very unwanted EMI in the analog wiring. It would mostly be used for carrying stuff like DC signal values to be put out via DAC, simple control values that don't change a lot, or digital configuration.
My main issue is that I don't know of any connectors that would fulfill this combination of needs. I've been looking for a bunch of years on and off and always come up empty handed. Maybe someone has a good idea of a connector that would work like this? But otherwise, I am looking at manufacturing this myself. I have a low initial need - in the tens to hundreds for the first set, later maybe single thousands over the next ten years.
I don't really know how to do a few things:
A. how to create the mating interface? If I have two PCBs above each other, I want them to connect using an elastic pin of some sort. Pogo pins feel like they'll have a failure rate that's too high. In addition, the two PCBs will most likely be sliding past each other. So I'm probably looking at something like leaf springs, like eg mobile phone battery connectors (see attached image). Is that a good idea? What are some better ideas to make this? Should I try to get the spring contacts themselves, without the plastic carrier package? Where would I get something like this? I've only seen them in the SMD package. Do they come in through-hole? that would likely make them more sturdy.
B. The connector shells for both the cable-bound plug and the front-panel socket will have to be sturdy. I made a simple design that includes locator pins and makes the connector slide in most of the way, and then in the final bit of travel it creates force to mate the two electrical contact surfaces. I'm not sure whether the rails should perhaps be on the front panel connector, since it requires thicker metal. I think mechanical retention of the connector could be accomplished by a spring loaded bearing ball in the underside of the connector. I guess either way the design means they'll have to be CNC milled, unless there's a better way of making them. I've included a crude mechanical drawing in the attachments - what would the best way be to create something like this? Is there a better design?
C. How to measure the reliability of the connectors? Or of the cable itself? I would like them to meet a certain amount of cycles. Obviously there's going to have to be a lot of testing, but other than that, how can I make an initial set of calculations to make sure I'm not doing something that'll obviously fail after ten uses?
D. What does everyone think of the design? It's pretty ambitious but I hope that with enough time and work I can figure out how to make something like this reliably and to good quality. Are there other designs you would suggest?
E. What sort of costs could I be looking at?
F. What is the best way to strip and solder 50 wires to a pcb, if you have to do this a dozen times? A thousand times? Ten thousand times?
G. Are there other places I should ask about this, or is this the correct place to go?
Thanks for reading and looking forward to the replies.