Allegro CX Bluetooth Conversion
Awhile back I wrote about converting an Allegro CX from the stock spread-spectrum radio to a long-range bluetooth radio. I did this because the Leica radio that it communicated with died, and the repair was quoted at around $1,200.00. I’d had good results with the DC50 bluetooth arrangement, and I figured it’d be a lot less expensive, so I forged ahead. Below are some photos of the process and results.
The radio housing on the Allegro is fairly roomy as these things go, but getting to the comm ports from there was kind of tricky. I probably should have taken the time to run wires inside the unit, but opted for the expedience of coming in from an external comm port. It was the first kludgy decision in what proved to be a long line of kludgy decisions.
Here’s a shot from the front of the finished job. You can see the comm port wiring looping up from the port and back down into the radio housing in back. Ugly, but it worked. The base of the external 5dbi bluetooth antenna is on the right.
Below is a photo showing the inside of the radio housing. The yellow cable is the comm port wiring; upper left is a power switch for the BT radio; and the BT radio on the right.
As noted in my earlier posts, one of the big challenges was getting power to the bluetooth radio. The radio wants 5v, but I wasn’t able to find a reliable 5v source anywhere near the radio housing. I ended up installing a 3.2v-5v converter board (visible on the lower left in the above photo). It only cost about $11, so money wasn’t an issue, and it was small enough to fit the space.
The trickiest part was getting reliable 3.2v power to the radio housing. I ended up going directly to the battery, which is in the bottom of the Allegro. Below you can see the red and white wires I ran from some pads on the main board to tap the power:
This shot shows a closer (if somewhat fuzzy) view of the battery pads. They go directly to the battery contacts in the battery housing.
Here’s a photo of the Allegro main case buttoned back up, with the power wires extending into the radio housing space:
I installed a radio switch and a LED to remind me that the radio is powered up. In the photo below, the switch (push on, push off) is on the lower right:
Below are front and side views of the completed installation:
I originally thought I’d have to run a terminal window to initialize the BT connection before running SurvCE every time I lost a connection. However, after finally paying attention to the BT radio manual, I realized that I could set them up to reconnect every time they’re powered up or lose connection. That makes usage a whole lot simpler.
Using the 5dbi antennas (which are about 8″ long) on both radios, I can get a solid connection out to 1/4 mile or so, and a pretty good (a bit slower) out as far as 1,900 feet in open-field conditions. With a 9dbi patch antenna at the gun, I’ve gotten as far as 2,500 feet, which is much farther than I’ll usually be working robotically.
The BT radios were around $100 apiece, and I probably spent another $30 on the converter board and miscellaneous parts, so I’m well ahead of the stock radio repair. I wouldn’t have messed around with this if I didn’t enjoy doing this kind of tinkering, so it’s not really about the money. And I’m happy with the performance result despite the oddball appearance.
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