Internal GPS Mod Tech Support/Q&A

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jonwienke

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Since I've modded scanners with internal GPS units for several RR members, I thought it would be useful to start a thread to cover any technical support issues that may arise, as well as answer questions people may have regarding the process. The following is sampled from the documentation I include with the scanner when I mod it, with a few comments in brackets:

1. [This is specific to the 436. Other scanner models' power taps may behave differently.] The internal GPS module is only powered when the scanner has completely booted and scanning has started. It is NOT powered when the scanner is in Mass Storage mode (such as when updating the scanner with Sentinel) or while the scanner is booting (including loading favorite lists).

2. [This does not apply to Ladybird module installs, which do not require a cutout in the case.] The internal GPS module uses a 25x25mm square ceramic patch antenna installed flush with the rear of the scanner case. Avoid placing metal objects near the GPS antenna, as this will interfere with the received GPS signal, and may prevent the GPS module from getting a satellite fix. Also, while the antenna will withstand reasonable handling, you must protect the antenna from being scratched, crushed, or struck by foreign objects, as this may damage the antenna and/or the GPS module.

3. [The switch location is specific to the 436.] The power switch for the internal GPS is a small white push button on the left side of the scanner just above the battery door. It is flush with the side of the scanner when the GPS is on, and protrudes slightly when the GPS is off. Do not press the switch button with excessive force, or you may damage the switch.

4. When the GPS is active and the baud rate is set correctly in the scanner, you will see a “GPS” indicator in the bottom-right corner of the screen. The on-screen “GPS” indicator does NOT mean the GPS has a location fix, it only means that the GPS is on, and is communicating with the scanner. You must use the GPS status indicator LED to determine whether the GPS has a location fix or not.

5. [The indicator light location is specific to the 436. The color and blink pattern varies, depending on the GPS module installed.] The internal GPS status indicator light is located opposite the scanner’s alert LED under the keypad. It lights up green continuously while the internal GPS is on and acquiring satellite lock. Once the internal GPS module has a satellite lock, the light will flash red briefly once per second.

6. [The Ladybird GPS module does not have a backup battery, and always cold starts.] The internal GPS module has a backup battery to maintain satellite orbit information for a few days when it is turned off. The backup battery is charged when the internal GPS is powered on. When the internal GPS has not been used for a few days, the backup battery will be depleted, and it will take longer to get a location fix—up to 5 minutes if GPS reception conditions are poor. But if the internal GPS power is only off for a minute or so (e.g rebooting the scanner or changing batteries), the internal GPS will reacquire a fix in a few seconds.

7. Running the internal GPS will decrease battery life by about 15%, depending on your scanner backlight settings, volume level, and the amount of scanner traffic you receive. To conserve battery power, you can turn off the internal GPS in situations where it is not needed, and the scanner will continue to use the last location it received from the GPS.

8. You may hear faint electronic noise in the background on some channels while the internal GPS is active. Shielding and other components have been installed with the GPS to minimize this noise, and comparison testing indicates that the internal GPS does not significantly affect receiver sensitivity in digital or analog modes. The noise can be eliminated completely by switching off the internal GPS. When using the scanner as a base, the GPS can be turned off once a location fix is achieved at the base location. The same is true of handheld operation, unless you are riding in a vehicle, or going on an unusually long walk.

9. The internal GPS module operates at 9600bps, which is NOT the default NMEA 4800bps rate. You will need to change the baud rate setting in the scanner profile in Sentinel (it’s in the Location Settings tab) or the scanner setting will revert to 4800bps next time you write to the scanner from Sentinel, and the internal GPS will not be recognized.

10. If you turn the internal GPS off with the GPS power switch, you can still use an external GPS. But be aware that most external GPS units, such as the Uniden BC-GPSK GPS receiver, operate at 4800bps. Therefore, you must change the baud rate in the scanner’s GPS setup from 9600bps to 4800bps when switching to most external GPS receivers, and you must change the setting back to 9600bps before you can use the internal GPS again. In the scanner menu:

Set Your Location
Set Up GPS
Set Serial Port

and then select 4800bps (for most external GPS units) or 9600bps (for the internal GPS). The scanner’s baud rate setting must always match the baud rate setting of whatever GPS is being used, or the scanner will not recognize the GPS.

11. The scanner will receive the correct time from the GPS. However, it is important that the time zone and Daylight Savings Time are set correctly for your location, or the scanner clock will be off by an hour or more. In Sentinel, these settings are located in the Miscellaneous tab of the scanner profile under Clock Options. These settings are also found in the scanner menu:

Settings (you’ll have to scroll down to the bottom of the menu to find it)
Set Clock
Set Time Zone
Set Daylight Saving

Time zones are not named in the scanner menu; they are just listed as the number of hours offset from GMT. Eastern time is -5, Central is -6, Mountain is -7, Pacific is -8, Alaska is -9, and Hawaii is -10.

12. Keep in mind that when you write to the scanner from Sentinel, the scanner settings will be overwritten by the settings in Sentinel, and if you read from the scanner in Sentinel, the settings in Sentinel will be overwritten by the scanner settings.

13. If you have any questions or issues, I can be reached by email at jonwienke@yahoo.com.
 

jonwienke

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Here's a mod I'm working on--rewiring the Uniden GPS puck so that it gets its power from the DB-9 connector on the back of the radio. The first step is to replace the PS2 connector on the puck with a DB-9...
 

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jonwienke

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Of course, that requires that 5V power be supplied to the DB-9 connector. Conveniently, there is a 5V pad on the circuit board not too far from the DB-9 connector. I connected power to pin 9, which is traditionally used for the ring indicator, and is not connected to anything in the Uniden GPS cable assembly.

The pinout on the female DB-9 connector is as follows:
1 NC
2 Scanner data RX (serial data from GPS to scanner) - Green wire
3 Scanner data TX (serial data from scanner to GPS) - White wire
4 NC
5 Ground - Black wire and shield
6 NC
7 NC
8 NC
9 +5V (power tapped from scanner) - Red wire
 

jonwienke

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Some notes about the MAX3232 TTL-RS232 serial converter modules:

1. The board has 2 TTL-to-RS232 circuits, and 2 RS232-to-TTL circuits. It is why the power pads on each end of the board have thru-holes, but the data pads do not. The circuits on the top of the board are independent from the circuits on the bottom of the board.

2. They strongly dislike open RS232 inputs.There are 2 of them, one on the top of the board, and one on the bottom. The MAX3232 chip has an autosense feature where it looks at the signal voltage at RS232 inputs, and uses that as a reference level for generating the RS232 output level. If the inputs are open, the chip will try to max out the RS232 output voltages, draw excessive power (>100mA), and fry itself. The simplest solution is to tie all unused RS232 inputs to VCC. They are not needed for GPS data. No data connection from the scanner to GPS is required, so both RS232 inputs should be tied for GPS applications.

3. They strongly dislike startup voltage spikes or fluctuations of the sort generated by dirty switch connections, or switches with significant keybounce. If you don't have a decent-sized decoupling capacitor across the power leads, and a filter inductor between the power source and the module, the chip will randomly start in a failure mode where it outputs a random RS232 voltage, draws excessive power (>100mA), and fries itself.

4. Normal power draw for the converter module (not counting GPS power rdaw) is under 10mA. If it is pulling more than that, you have one of the problems described in #2 or #3.
 

JamesO

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Comments & Questions

1. I might suggest using a resistor for the power feed/tap for to the DB9 connector. This would be a current limiting resistor that would protect the scanner/cable/GPS puck in case of a problem. Not sure the value but if the GPS puck draws very little current, then the resistor value could be fairly high. A bit of experimenting to make sure there is not too much current drop would be all that is required.

2.For the 536HP, what about using the USB port to power the GPS puck? You would just need a small "Y" cable and you could route the USB power feed into the DB9 headshell.

3. The comments on the MAX232 chip/board in the post above, this is to do with 536HP GPS mod or the 436HP mod?

4. I know you are doing conversions to the 436HP for people, do you foresee that you might offer a parts kit for conversion?

Keep up the good work, sometimes just getting people thinking outside of the box is a good thing even if they do not want or need the internal GPS mod sometimes other ideas are born out of hacking.
 

jonwienke

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The Uniden puck draws about 50mA. I haven't tested how much of a voltage drop it can tolerate and still function, so I don`t know how much of a resistor could be put inline or how that would affect reliability/function.

I don't see the point of using a Y cable off the USB port. The whole point of the mod is to cut down on external wiring, and a Y cable would defeat that purpose, as well as eliminate the use of the wifi dongle while using the GPS. IMO it's a doubly bad idea. There is plenty of room inside for a wire between the +5V bus and the DB-9 connector.

The MAX3232 is not needed if directly connecting the Uniden puck to the DB-9; the Uniden puck already outputs RS-232. Most modules on ebay output TTL, which is opposite polarity and a different voltage level. So if installing TTL module, you need the MAX3232 to convert the TTL output to RS-232.

I`m still refining my component choices, so I wouldn't do a kit until that is ironed out to my complete satisfaction. Perhaps in the future though...
 

JamesO

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Appreciate the reply.

If the Uniden Puck only draws around 50 mA, then a fairly high value resistor could be used. I prefer to use resistors to protect circuits or current limit them when there is some sort of outside chance something could go wrong. Since this jumper is feeding the DB9 connector, I would prefer to have some form of protection.

Simple way to test this is use a variable resistor and/or substitute different resistor values in until you start to drop the Voltage, then you know you have gone too far.

The reason I mentioned the "Y" cable approach for the 536HP is not everyone wants to open up their scanner and modify is. Just another thought to give people options. There would be a short jumper from the DB9 headshell to the USB port, probably only 8 inches long. As for using the WiFi dongle, this is more often than not used in a fixed situation unless for a portable operation someone is using the WiFi dongle for a remote head. But I find that you would typically only run GPS while mobile anyway.

So your comments on the MAX232 chip are if you integrate this internal to the scanner?

I know the MAX232 boards are pretty small, could they be incorporated into the DB9 headshell??

Might want to consider a GPS kit it you would consider it. I know there may be many people that are capable and willing to do their own modifications and might like to consider something like this.
 

jonwienke

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Operating mobile is when remote head and GPS function would likely both be used.

MAX3232 use has nothing to do with internal vs external install, but whether the GPS outputs RS-232 or TTL. If the GPS outputs TTL, you need the MAX3232 to convert to RS-232. If the GPS outputs RS-232, then you don't need it.

I have some DB-9 shells on order, when they come in, I will see if the MAX3232 module could fit inside.
 

SteveSimpkin

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Appreciate the reply.

If the Uniden Puck only draws around 50 mA, then a fairly high value resistor could be used. I prefer to use resistors to protect circuits or current limit them when there is some sort of outside chance something could go wrong. Since this jumper is feeding the DB9 connector, I would prefer to have some form of protection.

Simple way to test this is use a variable resistor and/or substitute different resistor values in until you start to drop the Voltage, then you know you have gone too far.
The GPS is rated for 5V at 50mA. Assuming a +/-5% tolerance, the 5V series resistor would have to be 5 ohms or less. Even if the tolerance was +/-10% the resistor could not be more than 10 ohms. And that is not taking surge current into consideration. Neither value would likely provide much protection.
 

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When I did this mod to my BCT15 using a standard BR-355 GPS puck, or whatever model it was, I used a 7805 12-to5 volt regulator soldered to the underside of the circuit board. I didn't want to put any extra load on the 5v power supply and the 7805 is current limiting if I accidently would make a mistake while fumbling with the connectors. On the BCT15 the RI pin was also unused by the scanner and used to feed the GPS with 5v.

/Ubbe
 

jonwienke

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That is a better approach than a resistor. The 5V bus is adequate to handle an additional 50mA load.

I suppose shorting the DB-9 is a possible issue, but unless you try to insert a plug with a paperclip jammed in the connector, IMO it's pretty unlikely. If you keep the GPS plugged in when the scanner is on, it should never be an issue.
 

jonwienke

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On a separate note, If your scanner has the display or clock issues, and you want to send it in for the repair campaign, it would probably be best to have the scanner sent in to Uniden first, and then have the GPS mod done. I'm not sure how Uniden would handle a campaign repair on a modded scanner.

Upman?
 

JamesO

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The GPS is rated for 5V at 50mA. Assuming a +/-5% tolerance, the 5V series resistor would have to be 5 ohms or less. Even if the tolerance was +/-10% the resistor could not be more than 10 ohms. And that is not taking surge current into consideration. Neither value would likely provide much protection.
We are talking about a current limiting series resistor which is different than a simple Ohms Law circuit formula crunching exercise. I expect the resistor value would be higher than 5-10 Ohms, but probably not over 100 Ohms. Put a small enough Wattage resistor in, probably a small surface mount take off and it will become a fuse at the end of the day. I prefer to protect things the best I can especially during modification.

While I may want to calculate something like a current limiting fuse, I will almost always bench test it because at the end of the day, ANY calculation is only as good as the values and assumptions provided. Often things are over looked, mis-understood or not taken into consideration, so a Real World test is really the final determining factor of how something should be implemented and what the final value of a component should be.

Everyone has ideas, some may or may not agree on whether or not this may be needed or is a wise idea. But the DB9 connector on these radio has Male uninsulated pins exposed when a connector is not present and I would not want a wire off a 5 Volt source constantly making a Male pin hot. Too much at chance when a few extra minutes and a few pennies could safeguard the radio for the long term from any possible accidents.

Even a low current Pico fuse would be better than a wire.

Something to think about, I would rather be safe than sorry in the long run.
 

jonwienke

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If you specify 0.2V drop through the resistor at 50mA, that is 4 ohms. If the pin got shorted, that would be a current of 1250mA--probably enough to overload the power supply. A larger value is probably going to cause the GPS to run unreliably because it is designed to run on 5 volts. So I don't see much point in putting in a resistor. If you put one in large enough to prevent damage to the power supply, you aren't going to have enough voltage on the downstream side to run the GPS reliably. It is pointless.

Only run the scanner with the GPS plugged in, and don't stick pennies in th DB-9 connector when the scanner is turned on. Problem solved.
 
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JamesO

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Only run the scanner with the GPS plugged in, and don't stick pennies in th DB-9 connector when the scanner is turned on. Problem solved.
This is clearly going to go nowhere.

You do realize that there may be many times when there is no GPS or DB9 connector mated?

My point is might as well make things as robust and safe as possible.

The way to solve the problem is to not set yourself up for a problem to begin with.

Current limiting resistor if it makes sense, if not a Pico fuse and then the problem is solved!

As I stated before not everyone will agree, but lets have some open minded discussion and kick some ideas around for the best and safest modification possible unless this becomes a typical not invented here situation.
 

jonwienke

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A fuse or a separate current-regulated power supply makes sense, as I noted earlier in post #12. A resistor does not, for the simple reason that a resistor with a large enough value to limit short-circuit current to safe levels would also prevent the GPS from operating properly.
 

jonwienke

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It's also worth noting that the 996P2 has two 12V power connectors--a 3-pin power jack and a coaxial 2-pin jack, both of which are wired in parallel. Whichever jack is not used has 12V battery power connected to an exposed male pin.
 

Ubbe

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It's also worth noting that the 996P2 has two 12V power connectors--a 3-pin power jack and a coaxial 2-pin jack, both of which are wired in parallel. Whichever jack is not used has 12V battery power connected to an exposed male pin.
Maybe Uniden took notice of this, because my 536 have these connectors isolated by diods so there can only be currents going into the scanner and none out.

BTW. The 7805 never gets hot and doesn't need any cooling, so I guess all these GPS pucks use very little current.
I never use the GPS for scanner control, only warning about dangerous crossings and speeding and things like that.

/Ubbe
 

JamesO

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If the coaxial and 3 pin power jacks are not isolated, sounds like this was an oversight or just plain bad design practices.

I assume steering diodes could have been used if there was no need for a full 12-15 Volt supply Voltage and a 0.6 Volt loss would not be a problem, most devices are regulated down these days anyway.

The other option might have been to use a shorting plug in the multipin position to allow the coaxial port to function, then when the shorting plug is removed for the multipin cable connection the coaxial port would be isolated.

Either way, I prefer to have things as safe and idiot proof as possible. Good design practices go a long way to allow the product to have a long and useful lifespan.
 
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