VOR2 Indicator : ARC-IN-514R

Introduction

I already had won a VOR2 indicator on eBay, but the indicator had a square shape, and this indicator had the shape that all my other indicators had. I won the auction for $26, and the good part was that it included the connector with some 20 cm of cables attached.
Another good thing was that a small schematic label was glued on the housing of the indicator showing the connections. If there are two things to look for, first it is the connection information and on second place a mating connector for the indicator. Both items save you a lot of work!
The information given here probably applies to several types of VOR2 indicators, so the data might be useful ...

Connection information

The indicator has a 10 pin female connector on the rear side, labeled A thru J.
The label glued on the side reveals the following data.

pin label indication text A   GND symbol B   C.S potentiometer 90° C   C.S potentiometer 180° D   C.S potentiometer 270° E   C.S potentiometer 0° F   C.S potentiometer wiper arm G   LOC PTR RIGHT H   LOC PTR LEFT I   AMB FLAG TO J   AMB FLAG FROM		With an Ohm meter I found out that pin A, which only had a "ground" symbol, has infinitive resistance with all other pins. The five pins B thru F all have a separately shielded wire. I assume that the shield of those five wires is connected to pin A, but I can not measure that when the connector is plugged in the socket on the indicator. The PTR LOC Needle connections G and H show approximately 900 Ohms and the needle moves to the left or the right depending on how I connect the Ohm meter. The AMB FLAG connections I and J show approximately 300 Ohms and depending on the connection of the Ohm meter the flag indicator moves down to show "TO" or moves up to show "FROM". The 4 potentiometer connections B, C, D, and E all vary the resistance between their pins and the common potentiometer wiper arm pin F, when the "OBS" knob is turned. When you turn the "OBS" knob, the internal dial rotates. The following table shows the resistance at 30° delta settings. The four measurements give an indication of what the setting is.

Hardware interface

With the measured data and the information from the indicator I concluded that I need the following hardware to interface the VOR2 indicator.

• 1 analog output   -- to control the needle indication.
• 4 analog inputs    -- to read the 4 potentiometer resistance values.
• 2 digital outputs   -- to move the AMB flag to "TO" and "FROM" and have the "OFF" position available too.

needle indicator

The analog voltage must have a range from some negative value to some positive value.
The analog output of the PHCC Daughterboard is an "open-collector" transistor, so a resistor is needed to have flow of current through the transistor and develop a voltage across that resistor. The 100 nF capacitor makes the edges of the PWM signal of the analog output less steep (prevents influences onto other signals). The OpAmps are powered with a symmetrical +/- 12 Volt power supply. The analog output voltage is connected to the inverting input of the first OpAmp, and with a preset voltage level on the non-inverting input the voltage range of the output of the OpAmp can go positive and negative. With the small amount of amplification it is assured that the output level is kept within the swing range of the OpAmp. The second OpAmp is simply a buffer. The fixed resistor limits the maximum current to prevent (permanent) damage to the coil of the needle indicator, and the adjustment potentiometer sets the maximum deviation of the needle.

Setup and Adjustment procedure
First of all, make sure that all power supplies are off!   Connect the chosen AnOut output of the PHCC Daughterboard to the circuit below. Set the "CENTER" potentiometer to mid-position and set the "MAX" potentiometer to the maximum resistance.
Start the PHCC TestTool and check that the Motherboard makes connection with the TestTool. Go to the "Analog Output" tab and set the correct device address (I have chosen address hex 0x10). To prevent "funny" things (strange behavior), move the GAIN slider a little down and then back up, then move the slider "CHNL x" (where "x" stands for the chosen analog output) a little up and down. These 2 adjustments makes the PWM signal functioning correctly. Move the "CHNL x" slider to "75%". You should get some meter movement, else adjust the "MAX" potentiometer so that the meter deflects approximately 3/4 of full scale to the right side. Now move the "CHNL x" slider to "25%". The meter should now be at approximately 3/4 of full scale to the left side. Trim the "CENTER" potentiometer so that the needle deflection is approximately equal on both sides. Fine tuning can be done by setting the "CHNL x" slider to 50% and the use the "CENTER" potentiometer so that the needle deflection is zero (stays in the middle).
Set the "CHNL x" slider to zero and adjust the "MAX" potentiometer so that the meter deflects to its maximum position at the left side. I have set it so the needle is just at the end of the blue indication field. Then set the "CHNL x" slider to almost maximum and check that the meter deflects to its maximum position at the right side; just at the end of the yellow indication field. If there is a small difference you can tune the "CENTER" potentiometer a little.
Do not set the "CHNL x" slider to the maximum position. The analog output will be zero, as if the slider is set to the minimum position.
I do not know if this is a bug in the Analog Output firmware or in the Test Tool.

OBS - dial setting read-out

The 4 resistance values must be converted to a voltage level suitable for the analog inputs on the PHCC Motherboard.
As can be seen from the table, the resistance range of each of the 4 pins varies from roughly 2518 Ohms to almost 0 Ohms. So, if the common wiper is connected to GND you need a resistor on each of the 4 pins connected to +5 Volt to obtain a voltage level representing the setting of the dial. (Note that if the common wiper contact was connected to +5 Volt, you would still need the resistors now connected to GND). The voltage level on each pin now depends on the resistance ratio of the dial position and the fixed resistor. For accuracy the 4 fixed resistors have a tolerance of 1%. The voltage level will have a range of almost 0 Volt up to the ratio of the resistance. To limit the current I chose a fixed resistor value of 2700 Ohm, thus the maximum output voltage will be almost 2.5 Volt. The OpAmp amplifies this level to obtain a maximum swing on the analog inputs of the PHCC Motherboard. The output of an OpAmp is at best approximately 1 Volt lower than its power supply voltage, thus the OpAmp is powered by +12 and -12 Volt. As the input will not go negative, the output can at best be 0 Volt. However, depending on the amplification, the output can go well over +5 Volt and that would damage the analog input on the Motherboard. On the other hand, you want the output to go to almost +5 Volt, and not just 2.5 Volt, because that would limit the voltage span, thus decrease the measurement resolution, so amplification is needed.
Note that the resistors in the dashed-line box are needed 4 times, the LM324 package contain 4 OpAmps.
Setup and Adjustment procedure
First of all, make sure that all power supplies are off! Connect the common wiper contact of the indicator to GND and connect one of the 4 potentiometer outputs. Set the "FS.ADJ" potentiometer to minimum resistance. Connect the +/-12 Volt power supply and the +5 Volt from the Motherboard.
Do not yet connect the output to an analog input on the Motherboard!
Connect a Voltmeter at point (X) and GND. Switch on the +5 and +/-12 Volt power supply. Turn the OBS knob on the indicator. The measured voltage must change. Check (for the connected potentiometer output) that at the lowest resistance setting the measured voltage is practically 0 Volt, and at the highest resistance setting the voltage is at its maximum (turning the OBS knob back or further will decrease the voltage level).
Set the OBS knob so that the measured voltage is at its maximum. Check a few times to make sure that the setting is indeed at its maximum. Now measure the +5 Volt level of the PHCC power supply on the Motherboard. It will probably read something like 4.97 Volt, not exactly 5.00 Volt. Trim the "FS.ADJ" potentiometer until the voltmeter reads the voltage level that you measured on the Motherboard.
Do this setup and adjustment for the other 3 potentiometer outputs.
Now you can connect the 4 outputs to the analog inputs on the Motherboard. Start the PHCC Test Tool and check the lowest and highest value obtained from the analog to digital conversion. These are needed for the conversion table in the software. More on that topic later ...

AMB flag setting: "OFF" / "TO" / "FROM"

As 3 positions are possible, you can not realize that with one single digital output.

OUT1 OUT2 desired AMB flag indication 0 0 OFF 0 1 TO 1 0 FROM 1 1 OFF

As you can see from the table, if both digital outputs are "0", the flag should be "OFF". If one of the outputs is "1", the flag must either indicate "ON" or "OFF", depending on which output is active. If both outputs are active (which could be prevented in software, but hardware might do this when the power supply is turned on and the software does not yet control the outputs), the flag must also indicate "OFF". The mutual exclusive behavior of the outputs is realized with an EXOR gate. If both inputs to the EXOR gate has the same logic level, the output of the EXOR gate is "0". This signal is used to control a relay (#1) that connects/disconnects the AMB flag pin J to the power supply. If digital output OUT1 is active the relay #2 is activated, else the relay is in rest. The contacts of relay #2 switches the polarity of the power supply voltage of the AMB flag, thus realizing the "TO" or "FROM" indication. A series resistor limits the current as the small current from the Ohm meter was already sufficient to move the AMB flag!

Setup and adjustment procedure
Connect the 2 chosen DigOut outputs of the PHCC Daughterboard to the circuit below. Set the "ACT" potentiometer to its maximum resistance. Do not connect the VOR2 "TO/FROM" indicator yet.
Start the PHCC TestTool and check that the Motherboard makes connection with the TestTool. Go to the "Digital Output" tab and set the correct device address (I have chosen address hex 0x30). When both DigOut outputs are inactive the bi-color LED is off. Activate "DigOut 2". Check that the bi-color LED turns on. I have soldered the LED so that when Relay 2 is not powered the LED is green, and when the Relay 2 is powered the LED is red. Activate "DigOut 1". The color of the LED must change. De-activate "DigOut 2". The LED should turn off again. If this is the behavior, everything is wired correctly, so you can connect the VOR2 "TO/FROM" pins.
Activate "DigOut 2". Depending on the "ACT" potentiometer setting the flag should move from "OFF" to "TO" or "FROM" depending on how the wires are connected. With the "ACT" potentiometer you can set how fast the flag changes from "OFF" to the other indication. Do not set it too fast! There is no reason for a fast change and you might set the current too high, damaging the indicator.

VOR2 - PHCC  interface board

Software interface

more to come ...