RC Allen Trim Indicators in Parallel

[Tom_RV10]

I am in the process of wiring my RV-10 with 3 HDX displays, SV-AP, SV-COM, X-Ponder, SV-ARINC, and SV-EMS. As part of this I have wired the roll and pitch trim servos to the RC Allen Indicators. I also wired the wiper outputs to pins C37_P22 and C37_P23 of the EMS respectively. I read elsewhere in the forum that these are 12V outputs. However, I tested them and, when functioning properly, the output only varies between ~0.25V and ~1.25V.

- I added a sensor definition with id= RC ALLEN for these pins as function=VOLTS with low resistance set to NONE.
- I set the configuration file for C37_P22 and C37_P23 to use this new definition

What is unexpected is that the EMS inputs don't behave as if they are a high impedance. When I power up the HDX system the voltages on the trims rise as if the EMS side is still connected to a pull-up. The high end goes to about 1.8V with the EMS connected.

I plan to isolate and amplify the EMS inputs using a simple op-amp circuit I found elsewhere in the forum but would still like to understand how to correctly configure a type C input to read a voltage.

Also, does Auto trim require the feedback from the trim position to function?

 

[Raymo]

Auto trim uses feedback from the AP servos.

I'm not clear on what you are attempting to accomplish with the EMS connections. Are you trying to display trim position on the HDX? if so, see page 7-66 of the install manual (rev AE) for more information on EMS connectivity. Any general purpose input can be used. Pins 22 and 23 are enhanced general purpose inputs (see page 7-16), which I would suggest saving for other purposes unless you are out of GP inputs.

Once connected, you'll need to perform the trim calibration.

 

[Tom_RV10]

I am trying to add the trim positions to the HDX display in addition to the RC Allen indicators to accomplish this only an active analog input (Type C) to the EMS will work.

 

[djones]

Tom,
You really shouldn't need all of this. There are thousands flying around with Ray Allen servo's using our position sensor file. The problem is, you can't use both HDX and the Ray Allen indicators(without doing as you describe). I actually looked at doing this when I built mine and decided it wasn't worth all the extra work and complications required. I only have them displayed on my HDX. I still have the Ray Allen LED's in my tool box.
Oh, and if you want to keep going down this path, you shouldn't use VOLTS, POSITION lets you take advantage of the Calibration procedure and the pre-configured trim widgets. Volts won't

 

[jakej]

I'm with Don on this. The good thing about EAB is you can do what you want however complicated you want to make it. the KISS method works really well IMO. Another thought - if you are using the 'old' RP3 displays then don't bother as they will have led 'failures' , use the new RP4's instead.
Personally I've wired 60 + aircraft & have never been asked to do what you propose - I just don't see a need for the extra expense, work & using panel space

 

[DBRV10]

Besides, the Ray Allen indicators are the most unreliable thing you could use. You really should not use them.

 

[Tom_RV10]

Thanks you all for taking the time to give me your opinions. However, I would like answers to the actual questions I asked. Can pins c37_p22 and c37_p23 be configured to read a voltage, i.e. high impedance inputs?

BTW, Auto trim does not use the trim position feedback. The calibration procedure only does a phasing check.

 

[djones]

Tom,
Yes, with the pull up set to NONE you can read voltage. The calibration I was talking about is the trim position calibration, not auto trim.

 

[Tom_RV10]

I have both resistances set to NONE (I understand having is_piecewise=0 should have only the low_resistance be relevant). Here is my sensor config after changing function to POSITION. The voltage still changes when the EMS powers up. Is there an error here?

sensor={
id=RA TRIM VOLTS
function=POSITION
pins=C37_P22 C37_P23
name=ROLL
name=PITCH
min_val=0.0
max_val=2.0
resolution=3
round=.001
is_piecewise=0
low_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=1
c_x0=0
}
low_resistance=NONE
low2high_cross=0
high_coeff={
c_x4=0
c_x3=0
c_x2=0
c_x1=0
c_x0=0
}
high_resistance=NONE
high2low_cross=0
}