We're currently running a Vertical Power PPS and attempting to tie the fault lights into the GAD27 discrete inputs. The PPS is meant to output 12V to a fault light on the dash when there's an error. We setup the GAD27 with discrete inputs, active high. The problem is, it's always showing the faults are active. The PPS and the VPX have a habit of putting phantom voltage on the line unless there's a load on it, and I'm wondering if this circuit needs a pull down resistor added in order to make it operate correctly. I've contacted Astronix and they've suggested I contact Garmin. Hoping someone here has done this before, or that G3Xpert can chime in. Thanks.
Van's Air Force
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Vertical Power PPS faults into GAD27
- Thread starter agent4573
- Start date
Depending on which inputs you use you get different behaviour
From page 26-5 of the manual.
The GAD 27 has 9 discrete inputs that can be configured as Active Low or Active High. The GAD 27
discrete inputs conform to the following specification:
Low: Vin < 3.5 VDC, or Rin < 375 Ω
High: Vin > 8 VDC, or Rin > 100k Ω
Note that a floating (disconnected) input on Discrete Inputs 1-7 will be treated as High, while a floating
input on Discrete Inputs 8-9 will be treated as Low.
I suspect you are not connected to pins 8 or 9, in which case you will need a pull down resistor.
Derek
From page 26-5 of the manual.
The GAD 27 has 9 discrete inputs that can be configured as Active Low or Active High. The GAD 27
discrete inputs conform to the following specification:
Low: Vin < 3.5 VDC, or Rin < 375 Ω
High: Vin > 8 VDC, or Rin > 100k Ω
Note that a floating (disconnected) input on Discrete Inputs 1-7 will be treated as High, while a floating
input on Discrete Inputs 8-9 will be treated as Low.
I suspect you are not connected to pins 8 or 9, in which case you will need a pull down resistor.
Derek
From page 26-5 of the manual.
The GAD 27 has 9 discrete inputs that can be configured as Active Low or Active High. The GAD 27
discrete inputs conform to the following specification:
Low: Vin < 3.5 VDC, or Rin < 375 Ω
High: Vin > 8 VDC, or Rin > 100k Ω
Note that a floating (disconnected) input on Discrete Inputs 1-7 will be treated as High, while a floating
input on Discrete Inputs 8-9 will be treated as Low.
I suspect you are not connected to pins 8 or 9, in which case you will need a pull down resistor.
Derek
I missed that note. Thank you for that. I'm not an electrical guy, I know there's a calculation for the correct pull down resistor, but is there a recommendation on what value resistor to use? 1k, 5k, 10k?
Last edited:
TLAR answer since I don't know the internals.....
PPS says the following about these pins.
Specification Min Typ Max
Output Voltage 0 V – BUS
Output Current (at VO=BUS/2) – – 10 mA
Low Output Resistance – 10 kΩ –
It's a bit of a strange formulation, but it looks like they designed it to be current limiting, so that you could put an LED directly on the terminal.
TLAR would be a 10k resistor. WAG is anything between 5k and 50k would work, as the resistance drops you will get less voltage across the resistor, and eventually you won't have enough volts for the Garmin to register high, too big and the internal pull up resistor in the Garmin eventually wins.
PPS says the following about these pins.
Specification Min Typ Max
Output Voltage 0 V – BUS
Output Current (at VO=BUS/2) – – 10 mA
Low Output Resistance – 10 kΩ –
It's a bit of a strange formulation, but it looks like they designed it to be current limiting, so that you could put an LED directly on the terminal.
TLAR would be a 10k resistor. WAG is anything between 5k and 50k would work, as the resistance drops you will get less voltage across the resistor, and eventually you won't have enough volts for the Garmin to register high, too big and the internal pull up resistor in the Garmin eventually wins.
PPS says the following about these pins.
Specification Min Typ Max
Output Voltage 0 V – BUS
Output Current (at VO=BUS/2) – – 10 mA
Low Output Resistance – 10 kΩ –
It's a bit of a strange formulation, but it looks like they designed it to be current limiting, so that you could put an LED directly on the terminal.
TLAR would be a 10k resistor. WAG is anything between 5k and 50k would work, as the resistance drops you will get less voltage across the resistor, and eventually you won't have enough volts for the Garmin to register high, too big and the internal pull up resistor in the Garmin eventually wins.
Awesome. Thank you for the help.
Aussieflyer
Active Member
Regulator spike
I'm not sure if this directly related to your problem. I'm not electronically inclined. However my Plan Power Alternator caused havoc with my VPX and Garmin instruments. The alternator was showing 14.2 volt charge and looked like it was working OK, yet my voltage sensitive instruments, transponder and radio kept tripping out. Luckily my next door neighbor is very electrically savvy and suspected the regulator was giving off a dirty/spikey charge. The oscilloscope revealed a momentary high spike occurring regularly. Whenever the spike occurred the VPX doing what its meant to do, protecting my valuable avionics, tripped the circuit. If it wasn't for the oscilloscope revealing the dirty spike I would have been tearing my hair out.
I had a friend with the identical issue a short time later, he sent his VPX back to the factory for checking only to have it returned with a note that it was operating perfectly. He changed his alternator out, all fixed.
Then my buddy a few hangars up had the identical issue, changed the alternator out, all fixed.
Do you have a Plane Power alternator? If so I suggest you get a B & C, it would appear that Plane Power have a regulator problem.
I'm not sure if this directly related to your problem. I'm not electronically inclined. However my Plan Power Alternator caused havoc with my VPX and Garmin instruments. The alternator was showing 14.2 volt charge and looked like it was working OK, yet my voltage sensitive instruments, transponder and radio kept tripping out. Luckily my next door neighbor is very electrically savvy and suspected the regulator was giving off a dirty/spikey charge. The oscilloscope revealed a momentary high spike occurring regularly. Whenever the spike occurred the VPX doing what its meant to do, protecting my valuable avionics, tripped the circuit. If it wasn't for the oscilloscope revealing the dirty spike I would have been tearing my hair out.
I had a friend with the identical issue a short time later, he sent his VPX back to the factory for checking only to have it returned with a note that it was operating perfectly. He changed his alternator out, all fixed.
Then my buddy a few hangars up had the identical issue, changed the alternator out, all fixed.
Do you have a Plane Power alternator? If so I suggest you get a B & C, it would appear that Plane Power have a regulator problem.
I'm not sure if this directly related to your problem. I'm not electronically inclined. However my Plan Power Alternator caused havoc with my VPX and Garmin instruments. The alternator was showing 14.2 volt charge and looked like it was working OK, yet my voltage sensitive instruments, transponder and radio kept tripping out. Luckily my next door neighbor is very electrically savvy and suspected the regulator was giving off a dirty/spikey charge. The oscilloscope revealed a momentary high spike occurring regularly. Whenever the spike occurred the VPX doing what its meant to do, protecting my valuable avionics, tripped the circuit. If it wasn't for the oscilloscope revealing the dirty spike I would have been tearing my hair out.
I had a friend with the identical issue a short time later, he sent his VPX back to the factory for checking only to have it returned with a note that it was operating perfectly. He changed his alternator out, all fixed.
Then my buddy a few hangars up had the identical issue, changed the alternator out, all fixed.
Do you have a Plane Power alternator? If so I suggest you get a B & C, it would appear that Plane Power have a regulator problem.
I do, but I haven't done the first engine run yet, so I can't say if it's going to cause an issue. This problem was found during initial checks after the panel install and is coming up on battery power only. It's good to know about the PP issue though, and I'll keep an eye out for it once the engine starts to run.
