Help with connectors

Discussion in 'The Projects Forum' started by av8or1, Mar 31, 2014.

  1. av8or1

    Thread Starter New Member

    Jul 6, 2013
    Hi again-

    Over the past few months I have learned a great deal from this forum, so thank you! I began studying this forum because about a year ago I embarked on a project to develop a digitial electronic automotive engine compression tester. I had to take a 4 month break due to other issues, but have resumed work a few months ago.

    Anyway, I have a design for my PCB that I am happy with. Initial boards work as expected. During the past week I have removed the test points (via headers) that I had on what I was calling my "development board", though I'm not sure that this is actually how one goes about developing such an animal. This effort is being done to move from the "development board" to what I am calling a "production board."

    Which ultimately leads me to connectors and this is where I could use some explicit help. I've done several Google searches and I've seen lots of connectors. I'm getting lost in the sea now really. Therefore I'll explain what I have and what I need and see if anyone has any suggestions.

    The components of my device are:

    1) my custom PCB
    2) an LCD that comes already mounted to its own PCB off-the-shelf
    3) a 4x4 membrane keypad (8 pin single row female connector)
    4) SD card
    5) +9V battery
    6) 8 light pipes
    7) 4 analog inputs in the form of 3-wire cables (+5V, GND, signal)
    8) The custom enclosure

    In the "production board" there are a total of 4 connectors that are located on my custom PCB, all of which are currently through-hole type that I am populating with male pin headers:

    1) custom PCB to the LCD's PCB. This is a 21 pin connector (could be 20 if I wanted/needed it to be) through which all interfacing with the LCD is done, as well as the two potentiometers for LCD backlight/contrast and the pushbutton for device power. The LCD's PCB has a single row 16 pin through-hole type to mount something to.
    2) custom PCB to/from the membrane keypad. This is an 8 pin connector single row. The end of the keypad's tail is an 8 pin female header.
    3) custom PCB to/from a serial interface. This is a 6 pin standard style header to provide serial interface capabilities. Currently I have it as a single row.
    4) analog inputs to the custom PCB. This is obvious as to its nature and purpose. Currently I have it as 4 separate connectors, but I am thinking of combining them into one.

    So. What to do. I dunno. The original plan was to have male pin headers on the board and use ribbon cables for everything. But they don't make single row ribbon cable connectors so that's kinda out of the window. I've made-do during testing, but now that I'm coming to production level, I need to progress into something more solid and reliable. I was thinking of using positive lock connectors but can't find anything that makes sense to me right now. I've seen a few 90-degree "low profile" connectors that seem to have promise. I only have 18mm from the top of my custom PCB to the bottom of the enclosure, so that limits connectors somewhat.

    And that's just half of the battle, specifically the PCB connector half, if you will. To measure compression, I use a pressure transducer. This transducer is the source of the analog input. But to connect it in the spark plug hole way down in the depths of an engine bay with a long 3-wire cable extending all of the way back to the enclosure presents obvious problems. Therefore I decided to "break" the cable into two parts. I am calling this splitting-of-the-cable an "inline cable connector". The first part of the split or break is quite short and consists of the transducer, a short amount of 3-wire cable and one end of the "inline cable connector." The second part is much longer. It consists of the other end of the "inline cable connector" plus a good length of 3-wire cable. This part will extend into your enclosure. Thus the "inline cable connector" will be in the depths of the engine bay and therefore it cannot be too big in size. I've come to learn that this can be a problem.

    And if that wasn't a tall enough order, I need this "inline cable connector" to capable of being installed with one hand and with little-to-no visual reference (blind installation), so that if you have very little room to twist the adapter/transducer into place, you can do that reliably. And you can do it reliably because you can feel how the connectors are supposed to go together, once you put them together they stay that way, and then when you want them to separate, they do.

    So there it is. I've spent a good month trying to work this out but I'm just not confident in what I've come up with. Does anyone have any suggestions? They are very much appreciated and most welcomed!