|Re: HP31E, charging circuit and flex-cable versus discrete wires |
Message #7 Posted by Ellis Easley on 1 May 2003, 3:32 a.m.,
in response to message #6 by Ellis Easley
I opened up my 97 and I see that there is not a lot of clearance above the PCB at either end, so a right angle connector would be needed. The opening in the middle plastic is 0.180" X 1.490". The red Molex connectors measure 0.196" thick so that's too much. The black ones, which are actually the ones used for PC chassis front panel harnesses now that I look at it, are exactly 0.1" thick - they need to be since common PC motherboards use a dual row header (0.1" centers both ways) and plug single row sockets on both rows - so they would fit through the slot in the middle plastic. If you had a bunch of PC chassis harnesses, enough to add up to 2 X 13 pins, you could cut the wires to length, tape the plugs together to make two 13 pin single row sockets, solder 13 wires into each PCB, and then use a double-header to join the two sockets. Page 4 of this .pdf from DigiKey shows single row headers with many combinations of lengths above and below the plastic strip (drawing calls them "A head" and "B head"):
The black connector is called "C-grid" by Molex, you can see it on this page:
The single row version only comes in up to 10 circuits and you have to buy the contacts separately and you have to have the right tool to crimp them right.
An idea that came to me when I looked in my junk box is to take a 28 pin machined pin open frame DIP IC socket, cut it into two strips, cut one pin from each (to make two 13 pin strips), bend the pins on one strip at a right angle and solder it into one of the PCBs. Then push 13 wires into the sockets of the other strip and solder them in place, and solder the other ends of the wires to the other PCB. Now you can plug the pins from the second strip into the sockets of the first strip. Page 5 of this .pdf has the kind of IC sockets I'm talking about:
The pin and the socket should be either both gold plated or both tin plated for reliability. Catalog number ED56283-ND or ED56286-ND are both all gold plated 28 pin sockets, one is 0.3" wide and the other is 0.6" wide, both cost $2.07. Catalog number ED3128-ND or ED3728-ND are both all tin plated 28 pin sockets, one is 0.3" wide and the other is 0.6" wide, both cost $1.13. The drawing for these parts, labeled "Solder Tail", shows the pin is .021" diameter but it doesn't say what range of pin sizes the sockets accept.
On page 3 of this .pdf are "single row sockets" which are strips made of machined pin sockets:
The drawing "Fig.1" shows that these parts have a pin .021 diameter and a socket that accepts pins from .015 to .025 diameter, which means you can plug one of these into another reliably (the contacts in the IC sockets are probably the same thing). The 7400 series has gold plating on both the pin and the socket. You can either order a 64 pin strip and cut it or order "custom" sizes - the price works out the same for a 64 pin ordered as custom. A 13 pin "custom" would be $1.04 ($0.26 base + $0.06 per pin).
I think I'm going to do this to my 97. To me, it makes sense to solder the wires to the card reader PCB and solder the socket to the main PCB, then you can unmate the connector before you remove the middle assembly to get to the card reader. Also, it looks like there is more room near the main PCB. It's probably a good idea to use a small screwdriver to separate the two connectors a little at a time to avoid bending the pins.