Page last updated: 02/02/2010

This page presents an interface to a Bluetooth headset for Amateur radio application. The key advantage in my solution is that the Bluetooth headset's answer/hang up push-button can be used to control the radio PTT. This is very convenient inside and around the shack.

My Jabra A210 - Radio interface schematic is shown on the right hand side. The circuit is quite straightforward. The headset microphone audio signal flows from left to right, from the Jabra A210 to the radio microphone input. A coupling capacitor C1 is added to eliminate possible DC contention on that line. The headset earphone audio flows from right to left, so from the radio speaker to the A210 earphone input. I have populated an optional attenuator made of R3 and R4 to reduce the audio level going into the A210.

Click on the figure to enlarge it.

I have created a PCB layout that custom-fits a Hammond 1551RBK enclosure. This is a neat and compact solution. The PCB layout is shown on the picture to the right. The PCB is made of single-sided copper clad glass-epoxy material of 0.062" thickness. The copper pattern resides on the PCB bottom side. The components are located on the top side. When hand-making the PCB, drilling of holes is required to solder the components to the copper pattern.

Click on the figure to enlarge it.

A210 interface PCB_v1_top.pdf    A210 interface PCB_v1_bot.pdf

Bluetooth_PTT_PIC_v2.zip

• Open up the unit. This is a delicate task if you want to preserve the looks of your A210. Using a sharp knife, carefully crack open the casing. It is easier to start on the side where the casing has a long recessed slot. Work your way to the corners and the ends. Go gentle. The glue should give pretty easily. Watch out for the flying white button! Work over a table and make sure to recover the white button that falls off when you spread the two covers.
  
• Remove the old battery. If you intend to connect the unit to the voltage regulator for external battery operation or 12V DC, you must disconnect and remove the old battery. Simply cut off or desolder the battery wires. There is hot-melt glue on the contacts so take that off first. The battery is also glued to the casing; use a small flat screwdriver and gently pull it off.

Remove the coiled signal cable. Simply desolder or cut off the four wires attached to the PCB. There is hot-melt glue on the contacts and wires so take that off first. Preserve the rubber grommet to plug the cable hole after completion. Simply cut off the cable from the grommet with a sharp knife. Implement VE3LC's modification. The A210 normally transitions to a power-saver mode after 60 seconds without any audio fed into it. For an amateur radio application, we do not want this. To keep it alive, install a 47K resistor as shown on either of the pictures to the right. I recommend using a surface-mounted resistor. I used an 0805-size resistor and some AWG-30 "wire-wrap" wire. Implement the solution you are more comfortable with. In either case, the result is a 47K resistor connected between pin one of that chip and ground. If you are still unwilling to deal with surface-mounted components, implement VE3LC's mod using a regular leaded resistor as shown in his PowerPoint presentation.

Click on the figure to enlarge it. Click on the figure to enlarge it.

Attach new wiring. Desolder any old pieces of wire from the PCB and connect new wires to the six PCB pads shown on the picture to the right. Use long enough wires to allow interconnecting with the interface PCB inside the Hammond box. Using colored wires is a good idea. Drill a hole in the A210 to feed the wires to the Hammond enclosure. You want to send all the wiring to the Hammond enclosure located underneath. Drill a hole through the bottom cover that is big enough to accommodate all the new wires. The best location is somewhere in the center of the area where the battery used to be located.

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• Assemble the interface PCB as per the parts list provided below.
  
• I highly recommend using an i.c. socket in the PIC micro-controller location.
  
• The PCB is quite small, so I had to keep the pad size to minimum. This makes re-work (replacing components) difficult without damaging the pads and traces. Make sure that the components are in the right locations before soldering!
• Depending on the electrolytic capacitor package used in C2, it may or may not fit in the proposed enclosure when mounted vertically. Install C2 last and bend its leads 90 degrees to mount it horizontally (parallel to the PCB surface), and above the other components.
• Install the PIC micro into its socket only after the entire soldering process is completed.

Install the momentary PTT push-button and the PTT LED (optional) on the top face at one extremity of the Hammond enclosure. Make sure that the PCB will still fit inside the enclosure with the proposed push-button and LED locations. See the picture to the right for the proposed location. Note that I used a push-button with built-in LED. Drill a hole to feed the wires from the A210 inside the enclosure. You want this hole to be located on the top face of the enclosure, underneath the interface PCB. Position that hole to align with the hole on the bottom cover of the A210 so that the A210 is neatly positioned on top of the enclosure. Use the A210 bottom cover to mark the location on the enclosure for an exact hole line up. Once again see the picture on the right hand side for a suggested A210 location.

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• Drill a hole on one side of the Hammond enclosure to feed the DC power cable and the radio speaker cable.
  
• Feed the A210 wires inside the enclosure.
  
• Attach the A210 to the top of the Hammond enclosure. I used Coax-Seal putty. Use something that can be easily removed. Velcro is also fine. Remember that the Bluetooth pairing pin-hole is located on the bottom cover of the A210!
• Install the interface PCB. Bring all the wiring underneath the PCB and above it by routing it to one of the open corners in the Hammond enclosure.

Solder the wires and cables to the proper locations. Follow the wiring diagram shown to the right. If you do it right, you should be able to take the PCB out of the enclosure when all the wiring is still attached.The result should look similar to my assembly shown below. Install the proper connectors for the radio interface. Follow your radio manufacturer's wiring instructions or the radio schematic diagrams for the microphone connector pinout.

Click on the figure to enlarge it.

• There is a one-second delay between depressing the headset push-button and the radio PTT action occurring. This delay is generated by the A210 and there is nothing that can be done to reduce it. In a typical simplex or repeater conversation, this is not much of a problem, but forget about contesting using the headset push-button! If you need fast PTT action, just use the wired PTT push-button instead. Note that the headset microphone audio is always present at the radio connector. 
• Powering up the Bluetooth headset will put the interface in transmit mode, the LED will turn on and so will the transmitter. Just remember to quickly revert to receive by pressing on the PTT push-button once. Again, the A210 causes this and nothing can be done to remove it...
• I have verified that the range is around 10m (30 feet) in line of sight. Walls and floors will reduce the range though. So I would not claim that you can walk around everywhere inside the house and expect it to work flawlessly. But "inside and around the shack" is probably a better way to describe the range.
• I have noticed that there may be a low-level constant-pitch whining noise present on the transmit audio. The intensity of that noise seems to be dependent on the headset type used. It is quite low, certainly not enough to annoy the people listening to you, but it may show up.