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GRT HX Ray Allen trim indicator problem

RedRaider94

Active Member
I am about to pull my hair and could use some guidance. I have 2 GRT HX screens and trying see aileron and elevator position on the EFIS.

Problem: can?t get the change in voltage from the Ray Allen servo to register on the Efis to then show trim position.

What I have done:

1) installed two male pins in the B connector in analog 5 and 6. Position 16 and 17 on the Primary HX.
2) wired the three servo wires. Blue to ground, green/orange to efis in analog 5 or 6.
3) set analog 5 to elevator trim in general setup.
4) Turned pull up resistor ON

When I go into trim setup, it shows volts for both elevator and trim around 9.65 but rapidly fluctuates from 9.58 to 9.67 without my hitting the trim button. When I hit the trim button, nothing different happens so it is not registering a change in voltage from the servo.

I can put the green wire from servo to red on multimeter and blue to black and set to resistance. I can work the trim and see the resistance change from 2 at far left to 5 far right trim and hold its resistance number when I release trim button so the servos are sending a signal.

Can I only wire this to secondary display instead of primary? Is there something else I am missing as this is so frustrating.

Thanks
Shawn
 
It sounds like it should work. Be sure the green and orange wires are connected together, for each sensor. And then connected to pin B17 or B16.
Pin 17 is analog 5; pin 16 is analog 6.
Check your ohmeter scales; the readings are probably 5000 ohms, not 5.
 
Any idea what the voltage should read in the calibration menu on the EFIS? Mine is showing above 9 with the pull up resistor on. My friend wired his HX the older way of adding a resistor to one wire, running another through the EIS, and the the third wire to the EFIS with pull up resistor off and his voltage is between 1 and 2 as you move the trim.

Any other thoughts on what it could be as this is so frustrating.
 
Measure voltage

You should be able to measure the voltage from the trim servo directly, and see it change as you change the position. Not sure what resistance you would see, you should be getting voltage. I can't recall exactly mine, but I believe it was between close to 0 and up to 4.something - I used the 4.8v "excitation" connection to the EIS. I wired it like they suggested in the book:

img_4519-1024x1024.jpg
 
Played with it some more this morning and no luck.... Here is what I do know. I am not getting any voltage from the actual green or orange service indicator wires that I can tell. I can see the resistance change from 0 to 5 on the multimeter from the green wire as I operate the trim with the blue wire connected to other multimeter probe.

Question: should I see any voltage from the servo indicators alone? I am guessing not since they want that orange wire powered either by 4.8 volts reduced with an inline resistor for the older HS EFIS or with ~9.7 volts directly from the HX EFIS when you connect the orange and green to the analog input.

Is the Orange wire supposed to take voltage into the servo and then send it to the green wire for voltage indicator? If so, it seems odd to me they want the green and orange connected together into the same analog input.

Maybe I should try the HS version and put a resistor in-line and then connect to EIS constant 4.8 volt? Not sure which pin that would be in my EIS 4000.

Any additional thoughts welcome and definitely any opinions about how these servos work from an position indication perspective.

Thanks!
 
trim indicator

...Question: should I see any voltage from the servo indicators alone? I am guessing not since they want that orange wire powered either by 4.8 volts reduced with an inline resistor for the older HS EFIS or with ~9.7 volts directly from the HX EFIS when you connect the orange and green to the analog input.

Is the Orange wire supposed to take voltage into the servo and then send it to the green wire for voltage indicator? If so, it seems odd to me they want the green and orange connected together into the same analog input. ...
I don't think they want the green and orange connected.

Keep in mind what is happening - you are putting a voltage into the servo on the orange wire - either 12v or 4.8v - and the indicator is sending back a range of voltages that tell you where it physically is on the green wire. This range in theory should be from 0-12 or 0-4.8. I used 4.8v input since it was handy. I believe the EFIS can take up to 12v. Adding the resistor may not be needed with the EFIS, but I put it in since I used the same technique for my inputs to the EIS (fuel flow, current sensor, fuel pressure).

Keep in mind this is totally independent of the two white wires that make the servo move.
 
Okay, here’s the deal:
The best set up is shown in post #4, except that the 1K resistor is not needed. Wire the orange wire directly to the 4.8 volt source. You should see the voltage on the green wire vary between 0 and 4.8 volts, more or less. Pull up resistor in the HX OFF.
You can also wire it per the GRT manual, green wire directly to the HX (no EIS needed), with the pull up resistor ON. The orange wire can be connected to the green wire and the HX, or the orange wire can be left open. BUT, if you leave orange open, put some heat shrink over the end so it cannot accidently touch ground. Since the internal pull up resistor is large (10K??) the EFIS will only see a variation of something like 0 to 3 volts. Not quite as good as the first option, but it works.
Note to OP: Since you are looking thru that internal resistor, your multimeter will read low if it has a low nominal input impedance. Likewise, the resistance readings must be higher than 5 ohms. Check the scaling, it’s probably 5,000 ohms. Double check your HX settings, make sure the pull up resistors are on for those analog inputs. Some inexpensive multimeters require you to move the red probe input from ‘ohms’ to ‘volts’, to measure volts. Put the meter on a AA battery and make sure you see 1.5 volts.
 
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Thanks Bob. What I don?t understand is when I tried the green and orange together into the EFIS Analog input and went to calibration, I could see it have voltage around 9.6 - 9.8 and rapid fluctuations of about .5 constantly. This was without me touching the trim. When I disconnected the green and orange, the voltage stayed exactly the same. When I hit the trim button, the voltage wouldn?t change other that the rapid change of about .5 that happens constantly in the calibration screen.

I tried this with two Ray Allen services, in both Analog 5 and 6.

I may try running the orange wire to voltage but not sure which pin in the EIS to run it too for 4.8 volts.

What I don?t understand is if the green wire is actually getting its voltage from the orange wire? If so, is leaving it open going work? I did try to leave it open and just connect the green wire to the analog and grounded the blue wire (I grounded the blue directly to the negative battery terminal just to make sure I had a good ground). It just read the 9.6 - 9.8 volts like the other way.

Note: the 9.6 to 9.8 difference was just over time which I think is changing due to the battery charge draining while I am messing with this thing and no engine running. I played with it (the Efis) for so long this afternoon that the voltage was down in the 9.4-9.5 range.

Basically, the green wire is simply not providing a voltage indication to the Efis. The only way that I haven?t tried is putting the orange to a constant voltage and then put the green to an analog input.

I installed 4 analog wires. I could turn on the pull-up to analog 5 and then run the green wire to analog 6 and 7 for elevator and aileron with pull-up off on both of those. Thoughts on testing it that way?

Thanks for your help Bob!
 
The sensor is just a potentiometer-a variable resistor. The blue and orange wires go to the two ends of the resistor. The green wire goes to the variable pick-off, also called ?slider?.
Please measure the resistance between the blue and orange wires, with the HX connector unplugged. Try to measure it from the connector pins. If you?re measuring 9 volts one possibility is that the sensor (or a wire) is open-circuited. It will not be 5 ohms. Maybe 5000 ohms? Let me know.
I have no idea about the actual circuits in the HX, but it may be that the regulated 12 volts doesn?t work at all if the battery drops below 12 volts. Put a battery charger on it and see if anything changes.
I have this exact set up and it works fine, so something is not right here.
 
how does it work?

Bob, just for my education, how can the HX sense two wires at the same time? I've seen circuits like this but I don't understand how that works. Is there a technical name for this so that I can google it? Thanks!
 
The HX analog inputs don?t sense ?wires?, they sense voltage. Since the orange and green wires are tied together, and are good conductors, they will both be at the same voltage, and that voltage is what the HX will measure. Since there is no voltage difference between the orange end of the resistor and the green slider connection, no current will flow thru that part of the resistor. It is exactly the same as if the orange wire were cut off. Of course, current does flow thru the resistor between the green slider connection and the blue ground connection.
 
where does the voltage come from?

The HX analog inputs don?t sense ?wires?, they sense voltage. Since the orange and green wires are tied together, and are good conductors, they will both be at the same voltage, and that voltage is what the HX will measure. Since there is no voltage difference between the orange end of the resistor and the green slider connection, no current will flow thru that part of the resistor. It is exactly the same as if the orange wire were cut off. Of course, current does flow thru the resistor between the green slider connection and the blue ground connection.
Thanks - if the orange wire is cut off or connected to the green wire, where does the voltage that the green slider wire outputs come from? Is it from one of the other 12v wires used to actually move the servos? I visualized electrical separation between the two white wires that move the servo and the three wires for the sensor, but perhaps that's a mistake.
 
Thanks - if the orange wire is cut off or connected to the green wire, where does the voltage that the green slider wire outputs come from? Is it from one of the other 12v wires used to actually move the servos? I visualized electrical separation between the two white wires that move the servo and the three wires for the sensor, but perhaps that's a mistake.

You only tie the wires together, or cut off the orange one, if you have the GRT set to ?Pull up ON?. Internal to the grt, there is a 12 volt power supply, which is connected to the analog port by a resistor (10K, I think), when you select pull up on. Current flows thru that resistor, and also thru the position sensor, to ground. So the green wire will have different voltages, for different positions. For example, if the position sensor is at 5K: Total resistance is 10K + 5K=15K, green wire will see 12*(5/15) volts = 4 volts. If sensor is at 2K, green wire will see
12*(2/12) = 2 volts, etc.
 
Magic in the EFIS

You only tie the wires together, or cut off the orange one, if you have the GRT set to ?Pull up ON?. Internal to the grt, there is a 12 volt power supply, which is connected to the analog port by a resistor (10K, I think), when you select pull up on. Current flows thru that resistor, and also thru the position sensor, to ground. So the green wire will have different voltages, for different positions. For example, if the position sensor is at 5K: Total resistance is 10K + 5K=15K, green wire will see 12*(5/15) volts = 4 volts. If sensor is at 2K, green wire will see
12*(2/12) = 2 volts, etc.
Got it - thanks for the clarity. I also spent a bit of time on the web and I believe I understand the magic that's happening here. :)
 
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