The only connection needed between GPS and the scanner is RXD, which you connect to the TXD of the RS-232 converter chip. The NMEA serial data protocol doesn't require any handshaking or acknowledgment from the recipient.
Small DIY GPS powered by BCD-436HP -- make it yourself!
- Thread starter rbn_rr
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The only connection needed between GPS and the scanner is RXD, which you connect to the TXD of the RS-232 converter chip. The NMEA serial data protocol doesn't require any handshaking or acknowledgment from the recipient.
I'm going to go the route of using a HC-05 Bluetooth module and Max3232 installed in the BCD436 paired with a like HC-05 / GPS module with external antenna installed in my car.
In that scenario, all I need to do is bring the radio with me into the car, and it auto pairs with the GPS module and enables GPS.
In that scenario, all I need to do is bring the radio with me into the car, and it auto pairs with the GPS module and enables GPS.
Meh.
You still have to have GPS infrastructure in the vehicle with that approach. With the GPS inside the scanner, its much easier to move the scanner from one vehicle to another and still maintain GPS functionality. Plus, using Bluetooth adds complexity to the communication path, and increases the probability of RF interference between the Bluetooth module and the scanner's main receiver (because the bluetooth module transmits, but the GPS module only receives).
You still have to have GPS infrastructure in the vehicle with that approach. With the GPS inside the scanner, its much easier to move the scanner from one vehicle to another and still maintain GPS functionality. Plus, using Bluetooth adds complexity to the communication path, and increases the probability of RF interference between the Bluetooth module and the scanner's main receiver (because the bluetooth module transmits, but the GPS module only receives).
I've taken into account that there might be some interference with the RF subsystem of the radio.
However, I won't have to worry about placement of the radio or acquisition time of a GPS lock. I drive a rather sporty car (BMW M5) which doesn't allow much visibility in the "cockpit" for the radio to have a GPS lock. I might just choose to toss it into the armrest storage area.
Plus, the BCD436 is a portable radio. I don't have a need for any GPS capabilities outside of a mobile/car environment.
And, I'd rather not have a bastardized case...
However, I won't have to worry about placement of the radio or acquisition time of a GPS lock. I drive a rather sporty car (BMW M5) which doesn't allow much visibility in the "cockpit" for the radio to have a GPS lock. I might just choose to toss it into the armrest storage area.
Plus, the BCD436 is a portable radio. I don't have a need for any GPS capabilities outside of a mobile/car environment.
And, I'd rather not have a bastardized case...
I get that not everyone wants to mod their case. The opening I cut in the back of the case for the antenna eliminates the possibility of using the factory belt clip. I decided that was an acceptable tradeoff because I never use the factory belt clip anyway--it's rather flimsy. I use a case with its own much sturdier belt clip instead when going walkabout. The bumps on the back of the scanner case for the factory belt clip block the scanner from snapping into the RAM mount all the way, so I sanded them mostly flush with the rest of the case.
The antenna works quite well, even when the it has an obstructed sky view. The test I did yesterday involved a 6-hour drive in the back of an SUV in a cradle sitting on the seat, where the scanner was angled back about 30 degrees so the antenna was facing the floor of the vehicle somewhat, rather than the sky. But despite those disadvantages, the scanner had no trouble keeping up with where it was at.
Here's a view of the back of the scanner with the antenna in its cutout. I painted the antenna to give it some scratch and static protection, and to blend it with the rest of the case. The paint I used is actually a spray-on truck bed coating formulated for toughness and abrasion resistance. I also drilled a small hole so that the GPS status LED on the module is visible. The GPS module generally shows having a satellite lock by the time the scanner boots up.
The main advantage to this setup is that the scanner can be used in vehicles without GPS infrastructure, including trains and buses, and can easily be moved from vehicle to vehicle with minimal hassle.
The antenna works quite well, even when the it has an obstructed sky view. The test I did yesterday involved a 6-hour drive in the back of an SUV in a cradle sitting on the seat, where the scanner was angled back about 30 degrees so the antenna was facing the floor of the vehicle somewhat, rather than the sky. But despite those disadvantages, the scanner had no trouble keeping up with where it was at.
Here's a view of the back of the scanner with the antenna in its cutout. I painted the antenna to give it some scratch and static protection, and to blend it with the rest of the case. The paint I used is actually a spray-on truck bed coating formulated for toughness and abrasion resistance. I also drilled a small hole so that the GPS status LED on the module is visible. The GPS module generally shows having a satellite lock by the time the scanner boots up.
The main advantage to this setup is that the scanner can be used in vehicles without GPS infrastructure, including trains and buses, and can easily be moved from vehicle to vehicle with minimal hassle.
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tumegpc
Member
That looks like UPMan's avatar. Uniden will be all over this with a 100.00 snap on GPS module.
There are GPS modules available that are thin enough to install without modding the case, but they have much smaller antennas with significantly worse specs. I decided to get the module with the best available antenna type, and mod the case to make it fit.
The initial breadboard setup is positive. I'm streaming over Bluetooth NEMA GPS data at 9600 baud to my Mac, after pairing the HC-05 using the default code of "1234". Decoding using GPSxY on the Mac.
What you see here is a breadboard for the "host GPS." The GPS setup is powered by a USB power supply which is a USB serial port adapter that provides +5v and +3.3v.
What you see here is a breadboard for the "host GPS." The GPS setup is powered by a USB power supply which is a USB serial port adapter that provides +5v and +3.3v.
It appears that the Home Patrol 1 and 2 are packed pretty tightly into their cases, such that placing an internal GPS would not be possible. But, would it be possible to attach an outboard GPS to its plastic base holder, with a very short (< 4") connection to the HP which both controls and powers the base-mounted GPS?
Upon further testing, we're both right, sort of.
When the scanner is on battery power, the 3.7V pad is switched. If the scanner is off, the 3.7V pad is off.
But when a powered USB cable is plugged into the scanner, the 3.7V pad is constantly on, regardless of whether the scanner is on, off, or off and charging the batteries.
Running the GPS module off the 3.7V pad will not drain your batteries when the scanner is off. When there is USB power available, the GPS will be active. This will keep the GPS module's backup battery topped off, which will accelerate getting a fix when you start the scanner on AA battery power and the GPS has been powered off.
The same is true of the 436--there is little unused space. That's why I had to cut the hole in the back of the scanner case to fit the GPS module into the available space. The circuit board itself will fit, but the patch antenna is too thick if attached to the module board. There are modules available with antennas attached by a short pigtail instead of soldered to the module board. One of those could probably be made to fit without cutting holes in the case:
https://www.amazon.com/dp/B01I1JDCJ2
Good deal. I tested with USB since the battery clips wouldn't hold the batteries outside the case... was just easier to plug USB in.
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Drilling the hole in the case so the GPS status light is visible made the pad behavior a lot easier to track. I'm going to leave the GPS module connected to the 3.7V pad to accelerate satellite fixes when the scanner starts.
You can preconfigure the HC-05 modules in a master/slave configuration where the two are only paired with each other.
Yes, I've interfaced the HC-05 installed in the scanner with the scanner's main CPU using a couple extra pins on the CPU that Uniden uses. You'll need a 10K resistor to protect the HC-05 module when the CPU pulls the programming pin high.
I then patched the firmware to allow for a menu option to pair to a new master GPS HC-05 in cases where the GPS broadcaster just suddenly decides to "fail"
You can download the patched firmware here
Got me. 
KC4RAF
Member
LOL!!!
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