Vectrex Lissajous cartridge

[froogy]

Hi! On the Muffwiggler forum there's a thread for modifying Vectrexes (Vectrexi?) into XYZ monitors. Would something like this be possible through a cart instead? What do you think?


Check out the thread here

[gauze]

ok, I don't know what this is suppose to be, do the sounds relate to the onscreen pattern at all?

[froogy]

The original modification described in the Muffwiggler thread requires disconnecting the XYZ wires from the CPU board and adding three external inputs each representing X, Y and Z. External equipment, like oscillators, is then connected to produce the patterns you see in the video above. For example one input could be a sine wave and another input a triangle wave etc.

I'm wondering if it would be possible to do something similiar with a cartridge instead. Imagine a cartridge with 3 mini jack inputs allowing control voltages (+/- 5V) to be displayed as Lissajous curves.

Lissajous curves: en.wikipedia.org/wiki/Lissajous_curve

Here's something similar, a GameBoy Oscilloscope:

[kokovec]

I can't think of a way to send a signal through the cart port unless you add some electronics that converts signals into 6809 instructions that drive the monitor.
The Vectrex is not fast enough to do that anyway in my opinion.
Another possibility for slow signal analysis by the Vectrex is using the analog inputs of the joystick port. Again, the Vectrex may not be fast enough to sample high frequency signals at high resolutions.
Lissajous curve calculations are not considered complex for modern computers but I don't think the Vectrex would be able to keep up with drawing refresh cycles.

[christophertumber]

It really depends what "something like this" means. If you want to be able to input a signal you're going to need to do some electronics hacking. I'm not aware of any way to access the VIA or anything else directly from the cartridge port, however, I'm definitely not a hardware guy. So whether you build an interface for the controller port or you create a custom cart with some kind of signal processor that feeds the data into a program on the fly you need to be pushing bytes onto the VIA.

If you just want to do some curves in software, that's not that big a deal:



You should probably try this on real hardware. Results are mixed on emulators:

Curve.bin (687 B)

(Calcs are in real time every frame, though I am using a lookup table for sine).

[froogy]

Interesting! I think I begin to understand the difficulties involved if external signal sources are required. It never occurred to me to use the joystick port. Clever! Beautiful demo BTW!

So, you're saying that even if the input hardware bit was solved, the Vectrex is probably too slow to process and display the result?

Here's another example where you can hear the sound that is producing the Lissajous pattern on a Vectrex screen: 

http://instagram.com/p/wHdH_CrRcD

[vectrexmad]

Christopher, full marks again for your programming prowess! Works really nice on a real Vectrex.
Froogy - all you would need is a voltage converter to take the sound from a mp3 player and convert it to the -3.4V to +3.4V accepted by the joystick analogue input.
I think you could could certainly make the Vectrex react to signal threshold values and change the display accordingly.

We can turn the Vectrex into an oscillocope! Funny, it was the Vectrex that inspired Walter LeCroy, originator of the company LeCroy Corp. which is famously known to many electronic test engineers for its oscilloscopes to this day (the company has since been taken over by Teledyne). LeCroy took inspiration for the company's oscilloscopes from a Vectrex on display in Toys R Us at the time. Assimilating the Vectrex's magnetic deflection technology, LeCroy created oscilloscopes that could perform tests and draw results on screen for engineers to evaluate. A fuller story can be found here.

[christophertumber]

Dec 7, 2014 9:25:31 GMT -5 froogy said:

So, you're saying that even if the input hardware bit was solved, the Vectrex is probably too slow to process and display the result?

No, but if a software intermediary is required to process the signal, the result is never going to be as quick and clean as the direct hardware approach in the OP.


My demo is drawing curves based on parameters (a, b and δ) that are being changed every frame in order to create animations. But there's no signal processing going on. If it needed to (for example) poll a joystick port and then interpret that signal in some way then that would be additional overhead. I can only speculate on the cost (cycles) of that.

[kokovec]

Well done Chris!
So the question is how fast can the Vectrex sample the voltages at the joystick port in order to capture the two signals and properly display a Lissajous pattern. Like the ones in Chris'demo.
With proper voltage translation ahead of the joy port it should work.
If all the Vectrex is doing is forwarding the voltages at the joy port to the VIA then it's a matter of how fast the Vectrex can do it. I'm not sure what the maximum frequency would be given the physics of the X-Y integrators.
To be clear this is for driving the X-Y beams. The brightness would not be controllable unless the processing circuit translates that voltage as well. But that would take more cycles for the Vec.
As for LeCroy, he gets major points for his honesty.

[froogy]

Having an MP3 as an input reminded me of Vib Ribbon for Playstation, it featured Vectrex style graphics and the levels were generated on the fly from whatever music you played.

[froogy]

BTW this also works on a Vectrex (if you mod it) it would be interesting to try and see if the joystick inputs could be used instead of modding the Vectrex.

[gauze]

Jan 5, 2015 7:30:32 GMT -5 froogy said:

BTW this also works on a Vectrex (if you mod it) it would be interesting to try and see if the joystick inputs could be used instead of modding the Vectrex.

I looked quickly at the cartridge slot schematic and from there you have access to the via6522 pin 16 (PB6) which is one of the serial interfaces, possibly could be used for additional input bandwidth.

also to give you a visual representation of how the vectrex is set up here is a block diagram