Need bipolar (-5v...+5v) output to interface to vintage Frasca sim

[brianbarr]

I recently picked up a 90's vintage Frasca simulator(see cockpit building forum below) .. I'd like to reuse many of the high quality hardware instruments in the panel, however quite a few of them need bipolar inputs (either -5 to +5 volts) or a strange 4 wire reverse resolver input where the sim sends two outputs to the gauge -- sin(indicator angle) * 5v = vSin, and cos(indicator angle) * 5v =vCos. vSin and vCos then vary between -5 to +5 volts.

So I need some way to get these voltages generated using Air Manager.

I'm looking at maybe 10 instruments total to reuse.

The obvious alternative is to just gut the panel and put a flat screen monitor behind and use virtual instruments.

Any suggestions ?

[Sling]

I guess the answer to this is do you want the flexibility to have different instruments for different aircraft. To get the most flexibility an LCD is the way to go. However If the existing gauges are in good condition and you are happy to use them for all your flying then I’d stick with them. As for the interface it shouldn’t be that difficult once you figure out exactly what those signals are. It’s sounds a bit like the sin and cos an ADF indicator uses. You’ll likely need to produce your own hardware interface to generate these signals and/or perhaps use the AM message port as the interface.

Tony

[brianbarr]

I actually have figured out exactly what the signals are. I have a complete set of manuals and engineering drawings for this beast. The simulator maintenance manual actually has calibration instructions for each instrument with test voltages and expected gauge readings. Many of them are simple unipolar 0-+5v devices and can be handled with standard hardware and software. But to make this thing fly as is,I need to somehow output an array of bipolar voltages to various other instruments (such as the tachometers and manifold pressure gauges). The bipolar devices are the ones I don't yet have a solution for.

[Ralph]

There are surely circuits that do this. Like this:
http://www.usbmeter.com/Electronics_Kit ... ly_Reg.htm

But you might have to get your hands dirty on schematics and PCB design to get exactly what you need.

[brianbarr]

It is a pretty interesting piece of hardware.. it has a complete enclosure and a servo driven "force feedback" system for all three control axes.

So I'd enjoy keeping it as original as possible. But the flat screen behind the panel is the big fallback option.

[brianbarr]

So with a bunch of research I found a DAC board with 16 bipolar outputs (16 bit resolution!) for ~$100 ! The Linear/Analog Devices DC2025A evaluation board.
Most DAC boards with a large number of outputs are super expensive. This looks like it should do the trick at a reasonable cost.

There is a way to change a unipolar DAC to bipolar with a fairly simple op-amp circuit, but the analog output of the Arduino is not true variable voltage levels - it is PWM.
Unsure if PWM would work for this and setting up 16 channels of op-amps and associated support circuitry would really require a custom PCB design IMO.

The DC2025A has a SPI interface for receiving commands and there is an Arduino board they also sell ("Linduino One" DC2026C) that it plugs together easily (custom connector) with along with providing a working sample code library to play around with.

So I'm going to give this a try and either use the Air Manager message port API to send dataref updates to the board via an arduino - or use a raspberry pi talking to the sim with "x-plane connect" software and then talking over the pi's SPI interface to the DAC board and do it all in python that I am more familiar with.

Getting Messageport working looks a little daunting but I'll give it a go.

[jph]

is this, as you describe, a fairly linear 10v variation > (-5 to +5 ) or a 3 phase with shift variation ? as in an 'oldish standard aircraft synchro / resolver (which tend to work on 400hz) > or - a combination of both ?
many were synchro / resolver phase shift ... I played with this 20 years ago.... yikes !. the issue was that the instruments were 'real' and designed to be driven from a phase difference synchro. a bloody nightmare.....

[jph]

ps - -- nice rig - love the tennis balls

[jph]

there is a way to change a unipolar DAC to bipolar with a fairly simple op-amp circuit, but the analog output of the Arduino is not true variable voltage levels - it is PWM.
Unsure if PWM would work for this and setting up 16 channels of op-amps and associated support circuitry would really require a custom PCB design IMO.

I am unsure what you mean by ' but the analog output of the Arduino is not true variable voltage levels' - using PWM, the variations as near as damn it linear. it depends on the res' of the pwm as to the step value you require > ?
the standard RC output from PWM is the norm. tends to do the job. the impedance is reasonably important and may require a buffer, but, as you intimate, each channel would be treated with the requirements of your output.
the pwm output of the arduino is not an issue though, just avoid the esp32... yuk... it should be buried along with nuclear waste............................

[brianbarr]

is this, as you describe, a fairly linear 10v variation > (-5 to +5 ) or a 3 phase with shift variation ? as in an 'oldish standard aircraft synchro / resolver (which tend to work on 400hz) > or - a combination of both ?
many were synchro / resolver phase shift ... I played with this 20 years ago.... yikes !. the issue was that the instruments were 'real' and designed to be driven from a phase difference synchro. a bloody nightmare.....

There are several gauges that use the "reverse resolver" interface I mentioned. A simplex gauge has two - two wire inputs. There are duplex gauges for twin engine use (such as the twin needle manifold pressure gauge) that has four two wire inputs.

The maintenance manual for this thing specifies the following for the manifold pressure gauge for example:
LEFT MANIFOLD PRESSURE sin 0.00v, cos +5.00v = 0 degrees (upward)
sin -5.00v, cos 0.00v = 90 degrees (right)


So it looks like if I power the cos input pair with 0v, and the sin pair with +5v the gauge should move to a position certain.

What is different from normal avionics is that this is sort of reversed. You are sending discrete sin/cos bipolar signals TO an instrument for needle movement instead of decoding sin/cos values FROM an instrument's twist knob setting. I'm guessing that if I do a little math on the needle angle in degrees and send the sin, cos of that angle x 5v to the gauge then I will get something usable (unless it is expecting radians!)

The ADC & DAC converter chassis in this thing a a massive 100 channel + monster with mil-spec wiring everywhere. The motherboard is wire-wrapped. The converter boards in the chassis are using muti-bus. Very Vintage. Discrete components all over the place. These days all the work is done with multi function ICs. The circuit diagrams are mostly all there in the docs.

Yes that is a REAL KI-206 in the panel. The system generates the proper signals to drive the needles and the system decodes the resolver signals for the OBS setting. The rest of the avionics are simulated with "Frasca design" boards with real King faceplates. The KMA-24 looks like the real thing with a oddball connector on it.

All three control axes have a chain sprocket drive attached to them with a huge low inertia servo motor attached to each axis to provide force feedback. Getting that system reimplemented I'll save for last.

I'm not seeing any real synchros on this thing [EDIT - yes there are synchros as well}

Position is sensed by 10k pots everywhere. This will be interesting.

The whole mess is enclosed in an airplane cockpit like fiberglass pseudo-airplane with two nicely padded seats and a single small window out the pilots side that looked out to a fresnel lens box that made the tiny computer monitor placed out there for visuals look bigger.