Non-WiFi Radio Link (2)

silo2Figure 1: Homemade sleeve (made of .75 inch PVC plumbing pipe) protects the 2.4 GHz communication board’s antenna.

Ok, so the PVC for the antenna silo is a little crude.  It’s what I had in the junk drawer, and it seems to work OK.  It was necessary to put a spacer between the PVC and the tap hole for the screw. I couldn’t find anything of the right size, so I used a plumbing seal (meant for a faucet).  It was from a spring and seat set meant for single handle faucets.  It works well as a little shock absorber.

Here I show the protection sleeve again, from the photo on the previous page.  The screw for the tapped hole is on the bottom, and not really visible.  I could have made another trip to the home improvement store, and purchased threaded feed-thru pipes, but I didn’t.  The threaded pipe setup would probably have been bulkier inside the case, but may have been the prettier option.  I could still do that if I want:

rf-unit-2-4ghz-thru-sleeve4Figure 2: 2.4 GHz communications board, shown inside of homemade protection sleeve, with female header ends affixed by conductive glue. This is done because the end of the PCB contains the antenna, and the enclosure is aluminum. The PVC is affixed with a screw and tap hole underneath it (click to enlarge).

Note: Never use an aluminum enclosure to contain batteries (especially lithium batteries).  Aluminum makes nasty shrapnel.

The other end of the female header connectors go to the 40 GPIO header on the Odroid. Below, I show those connections, made in a similar way, inside of the aluminum enclosure.

headersfor2.4ghz-3Figure 3: Connecton of 2.4 GHz communication board to the 40 pin GPIO header (click to enlarge).

The Odroid’s GPIO is pretty compatible with the Raspberry Pi2’s.  Only a few pins are different. By the way, the box I’m using for one of the communication boards is the one I named “Yellow box droid” or some such thing on another of my blog pages.  It has been set up with various things like navigation software.  Here’s a photo from that other article, and shows it running the nav software and some other communications software:

yellowboxfinal4Figure 4: The yellow box has been getting use around here for a while. This pic is from another blog page of mine (The Homemade Tablet’s Little Brother, IIRC).  Of course it doesn’t show the comm board silo we’ve just added.

The circuit hook-up is simple.  The 2.4 GHz transceiver is controlled via the SPI bus.  The wiring on the Odroid is therefore:

  • Xcvr   —  GPIO header
  • pin 1  —  pin 25  (GND)
  • pin 2  —  pin 1    (VCC)
  • pin 3  —  pin 15  (CE)
  • pin 4  —  pin 24 (CSN)
  • pin 5  —  pin 23 (SCLK)
  • pin 6  —  pin 19 (MOSI)
  • pin 7  —  pin 21 (MISO)

OK, so it’s wired (we still need to tidy the wiring a bit, and put the leads down along the edge of the board.  That will wait until we know it’s * really* working).  For the first trials, I’ll use Linux.  I’ll need some added configuration to set up the SPI bus, and some software.  We’ll need some pull-down resistors (see the next page of this blog post for details on that).

git clone git://
cd wiringPi
sudo ./build

These actions should look familiar, as we needed the same software library to test our membrane keypad on the Raspberry Pi2 homemade tablet project, in another blog post.

Read More …

Note: the author does not have a recent, applicable background in circuit building, or battery related issues, so this is presented as the work of a hobbyist, and is not meant for duplication by others. Readers should look elsewhere for design advice and info.

Note: The Odroid is a product made by Hardkernel at They are not affiliated with this site in any way. The nrf24 is a product of, and they are not affiliated with this author or website in any way.  The Raspberry Pi2 is a product of the Raspberry Pi foundation ( and this author and site has no affiliation with them. “Raspberry Pi” is a trademark of the Raspberry Pi Foundation.

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