Resitive Fuel Sensor not recognised by HS74 GP

[jwachman]

I am having problems getting my fuel system to work using the HS74 GP inputs. There are 4 tanks on the aircraft, all with identical resistive sensors. The sensors should read approx 70 ohms empty an 10 ohms full. Both have these readings when disconnected from the Dynon system. (I am able to disconnect the wires at the wing root for testing).
I was able to calibrate my inboard left tank. When empty the Dynon shows a reading of 135 and about 40 when full. However, when I connect the left outboard tank and start the calibration it shows 1.
So I have completed some fault finding. If I earth the inboard tank during the start of calibration it reads 0, when not earthed it reads 500. When I connect the tank sensor it reads 135.
When I connect the earth to the outboard sensor and earth it, it reads 0, when not earthed it reads 500. When I connect the sensor it reads 1 or 0, yet the ohms are at 70.
The inboard sensor is connected to the EMS fuel input, and the outboard is connected to the #1 GP input for the HS74. The GP sensor is set to Fuel Tank 3, and is displayed on the EMS tank display. So the EMS display appears correct. I have earthed each input line during the start of calibration, and all run from 0 (earthed) to 500 (not earthed). So each wire to the EMS and HS74 seem OK.
But I have cross connected the inner and outer sensors. When connected to the EMS input both sensors show about 135. But when either sensor is connected to the HS74 GP input, neither register and both show 500.
So why doesn’t the HS74 GP input (wire #7) recognise the resistive fuel sensor. But does recognised earthing the wire.
Thanks for your help.
:-/

 

[jwachman]

Or even the HS34. Sorry!

 

[dynonsupport]

Connecting a fuel level sensor to the GP inputs on the HS34 must be done in the same way as hooking a fuel level sensor to the GP inputs on the EMS. The GP and fuel level inputs on the EMS are not the same.

To hook them up, you must hook a 1K pull-up resistor from the GP input to the 5V output on the HS34. This is covered on page 3-15 of the D120 install guide and in the D10 and D180 install guides as well.

Given that your sensors are 10-70 ohms, I would recommend something more like a 200 ohm resistor instead of a 1K. The exact value is not important since we will calibrate it out.

 

[jwachman]

Many thanks for your reply. I reread the manual again last night, and found the GP and resistor requirement. So I figured that was the problem. Thanks for taking the time to reply.

Love the kit. (HS34, EFIS D-10, EMS D-10A)

Jon