Arduino driven VOR

[meatbomber]

OOPS Wrong thread... was late yester day night..

[Zlatko]

Hey, that is a great topic to read. Nevertheless – I have something to say:
I am not sure if I am right or not, but what I think I’ve noticed from the video above – the deviation needle goes as far as two –tree dots in its maximum deflection ( that is 4 – 6 degrees instead of all 5 dots = 10 deg. ) If this is the case, it might be due to the reduced voltage margin ( between 0-5 volts instead +5 … -5 ). I don’t want to criticize , since you have done a great job , especially with the reading of the OBS knob
(To be honest – I didn’t quite understand how you achieved that one. ) .
As I said – if this is the case – I would like to offer a possible solution – so – for you to achieve +5…. – 5 range and provide over-current protection to the circuitry in one go . Theoretically – it is practicable to use a ready made motor shield for Arduino ( H –bridge) like this one –
http://www.ebay.com/itm/Mini-Motor-D...item2ecb760b85

They are used to change direction and speed of dc motors. For your needle you’ll need to provide signals to three of the shield pins - in1 , in 2, en 1. When FSUIPC offset value is positive – set in1 LOW, in 2 HIGH. When is negative – vice versa . And use the number 0-127 to provide pulses to en 1 pin . This changes the motor speed ( needle deflection in your example) . I am not sure if it is going to work that way, worth trying though.

All the best.
Zlatko

[hyamesto]

As an old teacher once told me:
"Think twice, there is always a more complicated way to do", or like the american says. K.I.S.S. (Keep It Simple Stupid)

You can experiment virtually in:

https://123d.circuits.io/circuits/10...r-flag-to-from

With this, you have -5v, 0 and +5 v. (look the motor running clockwise, and anti-clockwise) (sorry, no needle voltimeter in library).
The OFF Flag is at rest (0 volts, output 7 low, output 8 low), the TO Flag, is +5 volts (output 7 high, output 8 low), and the FROM flag is -5 volts (output 7 low, output 8 high).
And you can have the OFF Flag, with output 7 and 8 ON too.
Only 1 resistor, 2 Digital outputs, No current divisor.

Warnings: The resistor is approximate. Try with a potenciometer to find full scale, measure and replace by a resistor.

[hyamesto]

Hi Zlatko:

The full deflection depends on serie resistor, and value of the PWM output. You can handle this by soft.
Or you can use the board found inside of micro-servos.
Just replace the motor with the needle´s galvanometer, put a resistor in serie, and use the feedback pot to center the needle. In this way, you just use 1 PWM output. (your shield needs 2 digitals and 1 PWM output)
The value of the H-Bridge Motor shield is almost the same of the cheap chinese micro-servo, and you have a couple of gears,and a motor to buid another thing......
Regards.
Horacio.

[Zlatko]

Well , more thinking for me to be done. I'll answer tomorrow, when i figure it out how PWM + resistor would work for controlling needle range
If i don't say anything by then, it probably means you were right

[hyamesto]

Zlatko:

You are right. For the needle, you need a solution like Simsupervisor (one PWM and some voltage divider), or a H-bridge like your solution, or the micro-servo board (its a H-bridge too, with a pulse width sensor to define rotation)
The flag TO-OFF-FROM is another story. That´s what i have made work with only 2 digital outs, like the example post earlier.
Regards.
Horacio.

[SimSupervisor]

As an old teacher once told me:
"Think twice, there is always a more complicated way to do", or like the american says. K.I.S.S. (Keep It Simple Stupid)

You can experiment virtually in:

https://123d.circuits.io/circuits/10...r-flag-to-from

With this, you have -5v, 0 and +5 v. (look the motor running clockwise, and anti-clockwise) (sorry, no needle voltimeter in library).
The OFF Flag is at rest (0 volts, output 7 low, output 8 low), the TO Flag, is +5 volts (output 7 high, output 8 low), and the FROM flag is -5 volts (output 7 low, output 8 high).
And you can have the OFF Flag, with output 7 and 8 ON too.
Only 1 resistor, 2 Digital outputs, No current divisor.

Warnings: The resistor is approximate. Try with a potenciometer to find full scale, measure and replace by a resistor.

As I said earlier, you can't achieve it with only one digital output, you need at least the two outputs you used in that simulation... Can't make 3 states with only two distinct values.
-- I realise I mentionned voltage divider, and really this isn't needed. For some reason it made sense when I typed the message on my cellphone.
I personally went with a single PWM output when I made it, mainly because I was copying the needle, and didn't think about making it otherwise. I am using a perfboard to put all the avionics, but will want to make it out of a protoshield instead, as the arduino pins don't fit perfectly on normal perfboards... and sometimes it will stop working, which is frustrating. When I do the migration, I'll likely remove the TO-FROM PWM in favor of two properly tweaked digital out. There's not that many PWM available on a MEGA.

The deviation needle goes as far as two –tree dots in its maximum deflection ( that is 4 – 6 degrees instead of all 5 dots = 10 deg. ) If this is the case, it might be due to the reduced voltage margin ( between 0-5 volts instead +5 … -5 ).

Nah, I was limiting it to these few dots. From memory I tought the VOR had its needle always visible, that's what I was aiming for. I can double its range without any issues.
Would you happen to have a video of an actual VOR being tuned?

(To be honest – I didn’t quite understand how you achieved that one. ) .

Probing the values to deduce the internal wiring, then figuring out a way to use it. It took some time, but I am very happy with the result.

[Zlatko]

Would that video be of any help? : https://www.youtube.com/watch?v=zzXXxG-BKgA

Still can't figure it out how placing a resistor to the PWM pin would make the needle travel all distance to the very end ( 5 dots ).
In my understanding placing a resistor makes voltage "steps" measured to PWM pin smaller and in that way - needle movement - more precise but wouldn't enlarge the overall distance travelled. It would be like a man, who covers a certain distance from premise A to premise B in 10 normal steps. On the next day he is weak and capable of doing only 5 steps ( cover half distance) . So - he is trying to cheat by doing 10 small steps - still half distance travelled.
The only way i can think of -if the wires inside VOR are not going directly to the needle motor, so it is not a voltmeter working on -5 ... + 5 v , but sort of galvanometer instead, working on millivolts and connected to additional internal circuitry. That way - if you cheat the circuitry, it would provide same millivolt range .

@Horacio , i admit - your solution with servo H-bridge is more elegant one, especially if you are short of Arduino pins, but most motor shields provide outputs for 2, 3, 4 or more motors and that mean - all VOR needles driven by one shield. I am still curious about simSupervisor solution with a voltage divider and one PWM pin - if that works to its full range, that probably is the easiest way.

@SimSupervisor i meant 4 dots needle travel with your "Narco VOR, not 5 dots. Still well within visible area. Take a look at minute 1.30 with this Narco Gauge
https://www.youtube.com/watch?v=mvX6zMUQMj4

[hyamesto]

Zlatko:

The TO-OFF-FROM flag, the CDI Needle, the Glidescope Needle, and GS-OFF flag, are galvanometers. No motor, no internal circuits. Just a galvanometer connected to cables to exterior connector.
Look this series of pictures :


According with specifications manuals, the data are:


Another instrument table:


The resistor go in serie, to obtain 150 milivolts, in 1k ohms, 150 microamper galvanometer. Maybe you can add some capacitor to dampen needle´s movement.


This squematics work only from 0 to full scale.
Tomorrow i can send you a squematics for connect the needle as Simsupervisor, but the side of the galvanometer connected to ground, must be connected with a resistive divisor like a pot, with one side to ground, the other side to 5 volts, and the wiper to the galvanometer original ground.
And about the "elegant solution" of servo board, now in my country, its very difficult to find others alternatives. I know about hundred shields, and some fantastic absolute encoders to replace the OBS, like this:

http://www.usdigital.com/products/en...tary/shaft/ma3

but goverment´s import laws make impossible to find, and/or buy online. Last time (6 years ago) make a internet buy with credit card.
Original cost x3, now its x 5 times.....
I hope this can help.

Regards.
Horacio.

[hyamesto]

Zlatko:

I think Simsupervisor make this way:

The circuit:



The 5 volts on centering pot and ground, must be taken from the same arduino. (or from external power supply, with common ground with arduino.
How its work? Supposed 2,5 volts in PWM (50% dutty cicle), centering pot to obtain 0º deflection on needle.
Now:
If PWM is 5 v, one side of galvanometer is 5v and the other is 2,5v, you get full right (or left) deflection. (left side potencial is +2,5 volts up relative to the right side)
If PWM is 0 v, one side of galvanometer is 0v and the other is still 2,5 v, you get full left (or right) deflection, (right side is +2,5 volts up relative to the left side at 0 volts).
I know i can´t take a PWM like a lineal variable volt, but it´s for simplify the concept.
And the condenser, can be used if the needle got "nervous"....

Maybe Simsupervisor can help if any mistake has be done here...

Regards.
Horacio.