Garmin GPS?
- Thread starter Squintz
- Start date
Rupp
Senior Member
I just got finished using my GPS receiver that plugs into my com port as well as my mouse port (GPS unit that came with Street Atlas USA 5 years ago) and it works perfectly. My wife isn't to keen to hold the laptop for hours on end though. We made a trip over to Destin, FL to see a bit of the hurricane damage but it wasn't bad there.
Ok, so I am finally finished with the design of the PC, and decided not to use a case at all. I am mounting it in my glove compartment box , so I have no case to deal with. I finally started looking at the GPS again, and started thinking, is there any reason why I Can't just use the power from the serial port? If I am not mistaken, it puts out about 10VDC, and the range of this device is 6-40VDC. This way I could just use the serial port. If that won't work, then I will just use the 12V rail as Ski suggested.
Here is a link to the manufacture site with more info:
http://www.garmin.com/products/gps35/
I have the GPS35-HVS model.
Here is a link to the manufacture site with more info:
http://www.garmin.com/products/gps35/
I have the GPS35-HVS model.
Squintz
Senior Member
The only problem i could see is that it would draw to much current. Like i said before... When i tried to plug it into the Serial Keyboard port it would only work if i had an inverter pluged in. Using just the laptop battery was not enough to power the GPS and the laptop shut down that port.
Pictures...Pictures...Pictures and details
Pictures...Pictures...Pictures and details
rocco
Active Member
Does the GPS specs state anywhere how much current it draws?
I've designed a number of devices that were powered from the modem-control lines on the serial port. Here is my experience, FWIW.
Data-Terminal-Ready (DTR) and Request-To-Send (RTS) can be used to power external circuitry, as long as the circuit does not use these signals as modem control.
These lines were designed as signals, not for power, so they are not always reliable.
The software needs to set these lines to the level required by the circuitry, or the circuitry needs to be designed around the levels that the software will set these levels to. The latter is not always feasible. Most of the devices I have built required it's own drivers anyway, so I could set the modem control lines to what I needed.
The voltage is typically around +/-10 volts, but can be as high as +/-15 volts or as low as +/-5 volts. Many laptops put out only +/- 5 volts.
Each line can typically provide 10 milliAmps. If the circuit requires both positive and negative voltage, each rail is limited to around 10 milliAmps. If you only need a positive supply, you can parallel DTR and RTS to get 20 milliAmps.
ALWAYS use series diodes on these two lines to prevent the incorrect polarity from burning things down.
And now, E, for your GPS:
I will assume you need only a positive supply, and that you have no control over what the GPS software does with DTR and RTS.
If your GPS draws more than 20 milliAmps, you may be out of luck.
If your GPS draws less than 20 milliAmps, check the voltage in pin 4 (DTR) and pin 7 (RTS) with your GPS software running. If they are both positive, you are good to go.
If only one of them is positive, you are still good to go if the GPS draws not much more than 10 milliAmps.
Your mileage may vary. I've seen serial port pins supply much more than 10 milliAmps, and I've seen devices draw much less than their specifications state. So the only way to know is to try it. Don't forget the diodes.
I've designed a number of devices that were powered from the modem-control lines on the serial port. Here is my experience, FWIW.
Data-Terminal-Ready (DTR) and Request-To-Send (RTS) can be used to power external circuitry, as long as the circuit does not use these signals as modem control.
These lines were designed as signals, not for power, so they are not always reliable.
The software needs to set these lines to the level required by the circuitry, or the circuitry needs to be designed around the levels that the software will set these levels to. The latter is not always feasible. Most of the devices I have built required it's own drivers anyway, so I could set the modem control lines to what I needed.
The voltage is typically around +/-10 volts, but can be as high as +/-15 volts or as low as +/-5 volts. Many laptops put out only +/- 5 volts.
Each line can typically provide 10 milliAmps. If the circuit requires both positive and negative voltage, each rail is limited to around 10 milliAmps. If you only need a positive supply, you can parallel DTR and RTS to get 20 milliAmps.
ALWAYS use series diodes on these two lines to prevent the incorrect polarity from burning things down.
And now, E, for your GPS:
I will assume you need only a positive supply, and that you have no control over what the GPS software does with DTR and RTS.
If your GPS draws more than 20 milliAmps, you may be out of luck.
If your GPS draws less than 20 milliAmps, check the voltage in pin 4 (DTR) and pin 7 (RTS) with your GPS software running. If they are both positive, you are good to go.
If only one of them is positive, you are still good to go if the GPS draws not much more than 10 milliAmps.
Your mileage may vary. I've seen serial port pins supply much more than 10 milliAmps, and I've seen devices draw much less than their specifications state. So the only way to know is to try it. Don't forget the diodes.
From the technical specifications PDF file:
Input current: 120 mA typical 140mA max -LVx versions, 20mA while in power down mode. 870mW typical 1000mW max -HVx version, 300uA while in power down mode.
I have the HVS model, so doesn't look like the serial port is an option. I am surprised that the PS2 port could provide this much current. I will just hook it up to a molex connector, thanks for the detailed info tho, learn something every day.
Input current: 120 mA typical 140mA max -LVx versions, 20mA while in power down mode. 870mW typical 1000mW max -HVx version, 300uA while in power down mode.
I have the HVS model, so doesn't look like the serial port is an option. I am surprised that the PS2 port could provide this much current. I will just hook it up to a molex connector, thanks for the detailed info tho, learn something every day.
