Rechargeable External GPS Project

[jonwienke]

I've gotten several comments and inquiries about developing an external GPS device that has its own rechargeable battery, and so I'm putting together a preliminary design. It includes the following tentative feature list:

•At least 24-hour battery life. Can go 36+ if desired.

•Auto power on/off. The unit will only turn on when it is connected to a powered-on scanner. If it is unplugged from the scanner, or the scanner is powered off, the GPS will shut down as well.

•Magnets in the case to secure the GPS to a dashboard, console, etc.

•Charging and GPS status LEDs clearly visible through the top of the unit.

•Single wiring harness with GPS and USB power plugs for HomePatrol, 436, SDS100, etc. so the scanner and GPS can be powered/charged from a single USB port. Preferably without creating a total rat nest of cabling.

•Weather-resistant enclosure for the GPS receiver and battery.

Any feedback on the relative importance of various features would be welcome.

 

[dave3825]

•Magnets in the case to secure the GPS to a dashboard, console, etc.

This would use a longer cable i would imagine, to achieve the ability to stick to the dash if the scanner resides in a console cup holder between the seats. How long of a cable might this be?

Would there be an option to Velcro the gps to the the scanner and have a shorter cable for that purpose? In my state its not legal to have the scanner in the car. So this would be good if one had to hide a scanner in hurry.

Also, when I ride either quads or snowmobile, I do travel many miles from the county I stay in. So totally portable could be nice.

 

[phask]

Agree- make it with a short lead, then use an extension cable.

This would use a longer cable i would imagine, to achieve the ability to stick to the dash if the scanner resides in a console cup holder between the seats. How long of a cable might this be?

Would there be an option to Velcro the gps to the the scanner and have a shorter cable for that purpose? In my state its not legal to have the scanner in the car. So this would be good if one had to hide a scanner in hurry.

Also, when I ride either quads or snowmobile, I do travel many miles from the county I stay in. So totally portable could be nice.

 

[jonwienke]

The USB cable I have with the correct end for the scanner GPS port is 10 feet long. So that's kind of an upper limit.

For your last two items, doing an internal GPS install would probably be better than velcroing an external device to the scanner or having any external device at all--fewer cables to unplug and snag.

 

[BigWonton]

If it could utilize user serviceable rechargable batteries, specifially 18650 type batteries that would be great since I already carry a bunch around for use with flashlights.

 

[jonwienke]

The trick is doing user serviceable and weather resistant. The enclosure I have is weatherproof, but the batteries need to be inside to keep it that way.

I can do 14500 (AA form factor) or 123 batteries inside the enclosure with a USB charging port, and keep it weather resistant.

A 18650 would be a bit overkill, battery life would be about a week of continuous on.

 

[JamesO]

I was considering doing something like this using a standard 9 Volt battery. Rechargeable might be a better idea.

I would skip the magnets or allow a way/option for people to put magnets on the bottom or inside. The problem with magnets is when they get near something they should not be near like credit cards.

For the HP1 & HP2 if the case was small enough it could be attached to the rear of the scanner with Velcro.

I have some small 9 Volt battery cases that I would possibly fit the GPS module inside. Have all the parts, just not the time.

What kind of price range would you expect this to be in?

 

[mancow]

I was thinking that it might be viable to use one of the cheap tracking devices you can find on ebay and elsewhere then just disable the components that might consume power such as an SDR data logger and/or cellular GPRS module. You would be left with a case and battery already built.

 

[jonwienke]

No on the 9V battery. The modules run on 3-5V, so a Li-ion battery is a much better option--no additional voltage converter needed. A 14500 or 123 will give you about 24 hours of GPS runtime.

 

[jonwienke]

I have some p-channel FETs on order (needed for the auto power-on/off function) that should arrive tomorrow. I will put together a prototype when they arrive and see how it works.

 

[jonwienke]

OK, I got all the parts, and put together a prototype. It has magnets in the base, is weather resistant, plugs into any Uniden scanner with a mini GPS port, and automatically powers on when plugged into a scanner and the scanner is on. Note that the GPS is NOT powered by the scanner, it just receives a signal from the GPS port when the scanner is on which turns on power to the GPS module.

I had a pack of 3 14500 cells already wired together that fit perfectly, so I threw it in as-is. Battery life should be about 3 days of continuous use.

Here's a video in action, showing the auto power off:
https://1drv.ms/v/s!ApJIS-l4xqPtgvBkSXAhDwPw-ouoPw

 

[dave3825]

Now thats hot!!! Do you have an estimated price range ? Love the clear..

 

[jonwienke]

Exact price will depend on the number of batteries you want (approximately 24-30 hours runtime per 14500 cell, up to 3 cells) and whether you want magnets for mounting. I'm thinking somewhere around $70 for a single-battery unit with magnets.

For the same price, the unit could have a DB-9 connector to fit a mobile.

 

[jonwienke]

I have started a battery life test with the triple-14500 battery pack. Check back on Saturday...

 

[jonwienke]

The auto power on/off circuitry--a BSS84 P-channel FET and a 100K resistor. The resistor is connected between the source (right) and gate (left) of the FET. The drain (center) isn't connected yet.

https://1drv.ms/u/s!ApJIS-l4xqPtgvB2Y0X9Nm9vxqiiCg

The gate is connected to the RS232 data out from the scanner, which is a logic 0 (~-5V) when the scanner is powered on. So when the GPS is plugged into the scanner, the gate is pulled ot -5V, which turns the transistor on, and activates the GPS. When the scanner is powered off, the -5V is disconnected, and the transistor and GPS shut off.

In order to solder the transistor connections, I have to super glue it to the charger board, or it is nearly impossible to hold in place.

 

[buddrousa]

This may something I want to get.

 

[jonwienke]

I'm considering some design changes. Specifically, putting a DB9 female on the GPS module instead of a cord. So if you have the Uniden 4-pin-DB9 GPS cable, you could connect that between the GPS and the scanner, or connect a longer or shorter cable as needed.

There is also an unused connection in the factory cable that could be connected to the scanner +5V USB power so that when the scanner is plugged in to USB power, it could charge the external GPS battery as well. This would require a minor mod to the scanner--connecting the V_USB +5V power to the unused GPS pin, and then connecting the corresponding DB9 pin to the charger board. But it would reduce the number of cables needed to keep all the batteries charged when USB power is available. The same setup would allow the GPS to charge/power the scanner if the GPS was plugged into USB power, and also plugged into the scanner.

 

[bryank104]

Will this work on 536 also

 

[jonwienke]

Yes. You would use a DB9 straight-through cable with a male connector on one end and a female on the other.

The GPS would not be able to power the 536 because it runs on 12V rather than 5V. An unmodded 536 would be able to use the GPS, but would not be able to charge its batteries.The GPS would have to be recharged periodically.

If the 536 was modded to supply +5V power on pin 9, then it could power the external GPS and charge its batteries.

 

[buddrousa]

Jon the one you made me works great got out Monday got to run it on a 260 mile road trip just love it one less thing to power. I like the idea for a 9 pin serial for the 536 on road trips.