Analog Discovery Breadboard Adapter
All the connections to the Analog Discovery design kit are made though the 30 pin male header (0.1” centers) connector. This is a very common, generic style 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. These fly-wires are several inches long and can be awkward to use at times given the relatively light weight of the Discovery box and a small solder-less breadboard. A more convenient arrangement would be an adapter PC board that connects to the 30 pin male header of Discovery and brings all the connections to a female header positioned right alongside the breadboard area. By using a female header simple 22 gauge wire jumpers can be used to connect to the breadboard rather than the long female to female fly-wires supplied with the kit. An example 3.1” by 3.4” adapter PC board layout is shown in figure 1.
Figure 1 Breadboard adapter layout
The board consists of a grid of 21 by 30 plated through holes on 0.1” centers which can be used to solder test circuits. Three of the columns of holes on the left side of the grid are shorted together and tied to the +5V, -5V and ground connections on the 30 pin right angle female connector that mates with Discovery. Three of the columns of holes on the right side of the grid are shorted together and tied to the +9V, -9V and ground connections for use with external batteries or other sources of power. The 30 Discovery connections are brought to a breakout space for a 40 pin vertical female header positioned alongside the breadboard area.
The 21 X 30 grid is sized to accommodate the popular 30 position (400 total connection points) solder-less breadboards with power buses along both sides which are 2 1/8” by 3 ¼”. These breadboards come with adhesive backs that will stick the breadboard to the adapter PC board.
The schematic of the adapter board is shown in figure 2. The signals and power supplies that Analog Discovery can generate are limited by the USB power available from the computer. The analog inputs can measure much larger +/- 20 volt signals. This board provides a place to connect external power sources such as a pair of 9V batteries. A socket for a dual op-amp is included with the two amplifiers configured as non-inverting gain stages and are powered from the external power supplies. A pair of resistors for each amplifier sets the gain. Depending on the choice of amplifier it can be used, for example, to boost the voltage and/or current available from the AWGs or for other purposes in the circuit being breadboarded. The external power supplies along with the inputs and outputs of the two amplifiers fill out the extra 10 pins on the 40 pin header.
Figure 2 Breadboard adapter schematic
I’ve found this adapter to be very useful and have built a couple example versions. The layout of the resistors around the dual op-amp are arranged such that rather than two independent amplifiers, a single resistor can be inserted between the two inverting inputs, in place of the two resistors (R1,R4) to ground. Configured this way the two op-amps form the input section of an instrumentation amplifier. The amplified differential signal at the outputs of the two amplifiers can then be connected to the differential scope inputs on Discovery. Another possible use would be to generate complementary or differential signals from one of the AWGs. By connecting one input to ground, with the other input connected to one of the AWG outputs and adjusting the resistor values the first amplifier acts as a non-inverting stage to generate the in phase or true output and the other amplifier acts as an inverting stage to generate the 180º phase or complement output. To make it easy to swap resistor values individual pin sockets could be installed rather than directly soldering the resistors to the board. Likewise using a socket for the op-amp would allow you to interchange different devices optimized for the intended application.
The Discovery hardware itself is rather small and light weight and special care should be taken when using this adapter. It might be useful to add small stick on rubber feet to the underside of the adapter board to help prevent it from tipping or sliding around on the work surface. Figure 3 is a picture of the finished breadboard attached to Discovery with two 9V external batteries.
Figure 3 Finished product
I’ve attached a zip file containing the Gerber PCB files for the board shown in figure 1 to this blog. As always I welcome comments and suggestions from the user community out there.
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.