Update README.md

README.md

@@ -21,7 +21,21 @@ This is a great board; I would highly recommend it for NRF52 projects.
 
 This board comes flashed with a Serial DFU bootloader and it has an onboard USB-to-Serial converter.  This allows you to program it simply with a USB cable.
 
-## Custom board with Segger J-Link
+## Custom boards
+
+If application requirements don't allow you to use the Feather board from Adafruit, you can also build custom boards around the available NRF52 modules.
+
+The Adafruit board uses the <a href='http://www.raytac.com/download/MDBT42/MDBT42Q%20spec-Version%20C.pdf'>Raytac MDBT42Q</a>, available from Digikey (PN 1597-1434-ND) for $14.
+
+Fanstel also makes a variety of modules with the NRF52832 as well as the NRF52840 (with USB 2.0 support).  The BC-832 is a very small module (7.8mm x 8.8mm) available for $7.60 in quantity 10.  The BT-832 is slightly larger, but comes in a variety ranges and sells for just $5 in quantity 10.
+
+Below is a custom board using the Raytac module.  It is designed to use a serial DFU bootloader for programming with a standard FTDI cable.
+
+<img src='raytac-ftdi/raytac-nrf-ftdi-layout.png' width=60%>
+
+
+
+## Programming with Segger J-Link
 
 The Segger J-Link is a very helpful tool, but it's quite expensive.  With it, we can use Nordic's command line utilities, including `nrfjprog`.  I wrote a shell script with three commands to erase, flash the adafruit bootloader, and then start the chip running.  
 
@@ -36,7 +50,7 @@ nrfjprog -f nrf52 --run
 
 The J-Link requires a wire to ensure the target has power.  In the image above, red is target power (3.3V), black is ground, green is SWDCLK, and blue is SWDIO.
 
-## Custom board with OpenOCD and Raspberry Pi
+## Programming with OpenOCD and Raspberry Pi
 
 You don't have to spend hundreds on a J-Link (even though it is very nice).  Using <a href='openocd.org'>OpenOCD</a>, we can make a Raspberry Pi bit-bang the programming protocols.