dmercer

Making Connections

Blog Post created by dmercer Employee on May 28, 2012

All the connections to the Analog Discovery lab instrument hardware are made though the 30 pin male header (0.1 inch centers) connector. This is a very common, generic connector and is simple to attach wires to as with the various female to female cables supplied in the kit. Double length square male pins are included to change the female end of the wires into male pins that can be easily inserted into the solder-less breadboards often used in the lab for building prototype circuits. Using these male adapter pins can be less than ideal when they fall out and get lost. I’ve found that having a set of wires where the female connector on one end is replaced with a permanent (i.e. soldered on) male pin to be more convenient when connecting Discovery to breadboards.


But there are many cases where unshielded wires with simple male and female square pins are just not sufficient. It might be desirable to connect Discovery to other conventional Lab instruments or generic 1X:10X scope probes for example. Figure 1 is a schematic of a small adapter board I’ve put together. It provides single ended BNC connections to the two scope inputs (C1+ and C2+) with jumper selectable AC or DC coupling. For the two AWG outputs (W1 and W2) again two BNC connectors are provided with jumper selectable 50 ohm series termination resistors. A three pin header (JP5) is included to provide connections to the two user power supplies and ground.

AD2BNC_sch.jpg

Figure 1 BNC to female header adapter schematic


The two sided PC board layout is shown in figure 2. The board is notched out to allow access to the remaining connections (mainly the digital I/O) on Discovery. Note that the female header connector should be mounted on the bottom of the board, so it can plug into the connector on Discovery and the rest of the components go on the top of the board as usual. The BNC footprints are set up for a couple different styles of PCB BNC connectors. It would be simple to swap out the BNC connectors for other connector variations like SMA or SMB or even RCA connectors.

AD2BNC_brd.jpg

Figure 2 BNC to female header adapter layout


I’ve found this adapter very useful and have built three variations with female BNC, SMA and RCA connectors. The RCA connectors are especially convenient for attaching Discovery to home audio equipment and analog video signals (from DVD players for example).


The Discovery hardware itself is rather small and light weight and special care should be taken when using this adapter with heavy and stiff coax cables. It is probably best to avoid using stiff coax when possible but one thing that might work somewhat better would be to insert the BNC connectors on the bottom of the board so that they extend back over the top of the Discovery board rather than out in front of it.


I’ve attached a zip file containing the Gerber PCB files for the board shown in figure 2 to this blog. As always I welcome comments and suggestions from the user community out there.


Doug

 

 

PS:

BatchPCB.com where I put this board up for public sale has gone out of business. They are directing all their customers to http://www.oshpark.com/

for prototype runs of boards. OSHPark takes Eagle CAD board files directly ( in addition to gerber files ). So I've appended a .zip file containing the Eagle CAD files to this blog.

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