GPS use while soaring

[edwalker]

I'm about to put a Skyview system into a new Phoenix U-15 SLSA touring motorglider. It's a hybrid aircraft that can run under power with a Rotax 912 engine and then transform into a 32:1 glider for soaring. I have to have two avionics configurations to make the most of it. For powered cross country the Skyview system does the work, but when I switch off the engine I need a GPS-based soaring flight computer and a variometer. For this configuration I have a PDA-based soaring flight computer that feeds an LX Nav V7 variometer.

Here's my question. I'd like to have only one GPS receiver. If I power down the Skyview system I assume that it takes the GPS down with it. Is there a way to wire the system so that the Skyview GPS can stay on while the Skyview main unit is off? The V7 variometer is often used to power both the PDA and GPS and it will put out 5v for a PDA as well as 12v for a GPS as part of the RJ connector wiring.

I"m assuming I can split the NMEA output between the two devices. Will I need to have a panel switch to select the power source for the GPS, and is 12 volts an acceptable input for the GPS? Any problems "borrowing" the GPS for this other function? Thanks for your thoughts.

 

[dynonsupport]

The GPS puck needs 6-8V. 12V is too high and it will overheat, plus it isn't designed for the 30V spikes you can see on a 12V line if it isn't regulated 12V. 5V is too low and it won't work. So if you can get us a well regulated voltage at 6-8V, it will work. You can actually hook this voltage right to the red power wire while hooked to SkyView at the same time. There's a diode inside SkyView so you won't hurt it.

The other thing to check is that your other system can take NMEA at 38,400 baud. This is fast and non-standard, but we use it so we can send out data at 5Hz. Most devices are 1Hz so they use 9,600 baud. There's no way to change the output of the SkyView puck.

 

[edwalker]

Thank you. This is good news since both the V7 variometer and the PDA soaring software will operate at that baud rate. I'm sure the 12v coming out of the back of the variometer through the RJ connector is already regulated, so I might be able to drop it to 6-8v with an additional voltage regulator. I'll pass this on to the avionics tech.

 

[dynonsupport]

If it's regulated, a cheap and easy way to get it down to 8V is to use 6-7 diodes in series. Each one drops about .7V, so this will get you the 4-5V of drop you need.