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While it is easy to bulk produce PCB's with sensors attached directly on the PCB how do you bulk produce PCB's that area attached with a length of wire (up to 1.5m) to sensors?

One solution would be to have PCB headers on the PCB and the wire but I cannot find anywhere that sells wire in this form. We could build it ourselves but when scaling to any significant number this becomes infeasible. You can see how we solved the problem in our prototype in the photo below.

enter image description here

How would you solve this problem?

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The answer more-or-less hinges upon what a "significant number" of devices is.

If the sensors you're using are commercially-available and you truly are making a significant number of devices, then the sensor manufacturer or vendor is likely willing to discuss selling you the sensor modules with pre-attached wiring harnesses and connectors to your specification (likely at an increased cost.) This is something to work out before getting the boards made because it will likely drive your layout and part selection based on the manufacturer's or vendor's capabilities.

The sensor you mentioned, the DS18B20, is a discrete part and I would be surprised if Maxim were willing to sell them pre-attached to a harness/connector, but it's not something I'v tried with them previously. That said, making a simple interface PCB that is not much larger than the size of one of your sensors plus the connector of interest would be quite easy and at the scale you're talking about not much more expensive.

If the sensor is something you've designed yourself, the quantity of boards to be manufactured is too low for the manufacturer/vendor to assemble a custom harness (or they just can't/won't), then your best bet is sticking to a connector schema that's already readily available in required length and conductor number/thickness such as CAT-5 cables, EIA-485, etc., so that you don't have to assemble them yourself. Interfacing this cable to your sensor module is probably going to increase part cost and complexity, but if you don't have the manufacturing infrastructure to assemble the boards as you've shown in your prototype, then it may be the best and only option. The sensor you're using is a common one among hobbyists and as such, there are some good examples of cable interfaces to be found such as this one. The author of that page cites standard 4-wire flat telephone cable and shielded 2-wire microphone cable as potential options (in addition to CAT-5). Personally, I would avoid the microphone cable because although the shield is nice for signal integrity, microphone cables typically come with bulky pre-attached connectors because of their intended application.

If none of these are sufficient and you decide you want a custom cable for your application, then st2000 does bring up the option of working with a custom cable manufacturer, of which a quick google search turns up quite a few.

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  • \$\begingroup\$ Thank you, we would be looking to build around 1000. The sensors come from Maxim (DS18B20) so I will contact them now. Thank you I will look into the cables, do you know of any more that would be worth investigating (beyond the CAT-5)? \$\endgroup\$ – PaulBarr Mar 30 '16 at 12:39
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    \$\begingroup\$ I updated my answer with information about your specific sensor. A similar option to CAT-5 would be standard telephone cable with either 6P4C or 4P4C connectors on the end, both of which should be readily available much like CAT-5 cables. \$\endgroup\$ – Cheibriados Mar 30 '16 at 13:43
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CAT-5 CAT-6 Ethernet cables and headers are easily found maybe you can consider using them if sufficient.

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Some sensor OEMs support their products by providing cables. But often this work is farmed out to cable houses which produce custom length cables with custom connectors for the specific product.

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Often the same assembly house that you would use for your boards will have the equipment to produce a similar quantity of cables.

If not there are specialist harness and cable makers who can assemble cables including connectors, shielding, strain reliefs and even provide thermoplastic elastomer overmolding using vertical injection machines.

1,000 is a reasonable quantity for outsourcing, but you can't expect to get a really low price and good quality at that relatively low quantity, so you may have to pick one of the two (quality or price).

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