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bitvision CV mods?
MUFF WIGGLER Forum Index -> Video Synthesis  
Author bitvision CV mods?
looking at the LZX bitvision specs, I see it has an voltage-controlled color phase shifter as well as an envelope follower. It'd be great to be able to patch those out for some CV inputs.

lars, dunno if this kind of info is stuff you'd be comfortable sharing or having people share if we figure it out. let me know if that's the case.
BitVision is meant to very open as far as user community, mods, alternate -software, etc. It's a crude (but effective) generator trying to get the most out of the parts count as possible -- as opposed to the Visionary modules, which use lots of expensive components. The only reason the schematics, code, etc aren't online yet are that they are kind of messy and I need to find time to clean them up!

You could have plenty of fun inserting external voltages into the color phase shifter, but you'd want to be very cautious about voltages too high since it all runs off +5V power. The audio/CV input is protected with a zener diode against over-voltage, so it can already be used with Euro oscillators and so on.

I'll attach a PDF of the schematics for the time being.
awesome, I'll see if I can dig into this and figure anything out...
my bitvision is alive as of tonight! it is great, and before I get into any hardware mods, I am gonna learn it fully, and get my own images onto it.

the left LED just seems to be blinking steadily no matter what the input signal is doing, although the input signal seems to make the image glitch a bit.

what is the trimmer for? i'll look through the docs again, but so far this thing is a lot of fun and trippy
Cool! Yes, read thru the documentation in full. The trimmer is to adjust color phase response (turn it counter-clockwise until you see the palette go black & white, then ease it back to the desired point.) Left LED (with buttons facing you) should only be flashing if the input signal is peaking, so with gain all the way down you shouldn't see it. Make sure "param #2" knob is all the way down to get full response from the audio input (it's like an offset control.)

E-mail when you're ready and have an AVR programmer, and I can send you the code. smile
i don't have an AVR programmer yet but I'll pick one up, you think the SparkFun Pocket AVR Programmer would work? gle&utm_medium=Product+Search&utm_campaign=Product+Search+(Jan11)

i'm gonna go read up on what AVR even is
thumbs up
That's the programmer I use, works great! smile You'll need AVR Studio (from Atmel's site, you have to register) and WinAVR downloaded and installed.

I have a script right now written in Adobe Flash that takes an input image (jpg, bmp, etc) and basically quantizes it to 16 brightness levels and spits out the image "code". You can copy/paste this code into the project code in AVR Studio, over one of the existing images, and recompile. That's the basic process. There's a LOT of potential for alternative applications for this little board. Anyway, shoot me an e-mail when you're ready and I can send everything over.
Is it a major task to mod the bitvision for PAL?
or are plans for PAL version still being hatched?
The only changes are using a different part for the crystal and changing some code on our end. Do you have an AVR programmer? If so, you can update any code changes yourself.

All the units Switched On has in stock are built/preprogrammed for NTSC. E-mail me at and we may be able to arrange the direct sale of a PAL version kit. It's been something I've been needing to do anyway!
Thanks - email sent
oh +1 for pal smile
+1 for pal too!
I've got PAL crystals coming in this week and will have this sorted for you guys very soon. smile
drew up a simple circuit to give CV inputs to replace param 1&2 knobs.
EDIT - have built the CV input circuit, the input resistors need to be adjusted as suits the builders system

Find the latest version on my homepage

Its basically a two stage mixer, but the second stage attenuates the input and can be setup so the output should be 0-5V.
If i trusted my design chops fully it probably doesn't need the 5v1 zener and diode on the output.

I want to learn more about the
'cycle current counter action'
'cycle current display mode'
'cycle current palette'
functions that are obtained by holding one button and pressing another.
I would like to develop gate/trigger circuits to drive these. Does there need to be a delay between closing the 'hold' button with a gate signal and triggering the other button? Or can they just get a trigger/gate at the same instant?

thanks Lars for all your help with this device
Hey Andrew, yeah that schematic looks good to me!

On the trigger/gate signals and the CV input ("param" knobs, etc):

All of this can easily be changed to work however you want in the software. It's all written in C, and is pretty straightforward what is doing what (hopefully moreso, when I comment and clean it up a bit better.) The only real limitation is the number of input pins on the AVR.

A note on the CV input ("param" knobs, etc.):

In the current application, these are sampled once per frame. So 30 times/second (or 25 times/second for PAL.) So they're not sampled fast enough to do actually visualize the input CV, so best used for low frequency modulation.

The envelope follower output, however, is sampled at line rate -- or ~15.75 KHz. This allows you to actually visualize the waveform. It's quantized by how many bits are in the image, so its a little crude. One useful modification might be a switch to select AC or DC coupling with the envelope follower's input if you want to run CV in here.

On the 3 buttons:

Once per frame, the current state of all of these inputs is read. It looks back one frame to see if you're still holding down a button from the previous frame. If you pressed down all 3 buttons at -exactly- the same time (all gates are high simultaneously), it would be the same as if you had pressed them separately at different times. So there has to be a one frame delay between one gate going high, and the other going high.

My suggestion is that you just do some generic logic inputs + pushbuttons (similar to how you've drawn up a CV input + bias), and then modify the code to get them to do what you want.

If you want to get a video clock signal, in order to clock sequencers off a division of the line rate (or try to sync your oscillators), you could patch out Pin 16 of the AVR (going to pin 6 of the HC4053.) Pins 18 and 19 currently just drive LEDs (for peak detect and frame counter pulses) but those would also be potentially useful patched out logic inputs as well! (Frame counter output with frame counter at max speed, fully CCW, would be a frame rate clock.)
So a summary for "patching it out" experimentation:

Replace Param #1 & #2 pots with CV inputs + bias (as per your schematic)
Replace all three buttons with Logic inputs + gate pushbuttons (or just OR the logic input with the output of the current switch+debounce circuit.)
Patch out pin 16, 18, 19 as logic outputs
Add toggle to bypass C41 (ac-coupling on audio input)

Other note:
For the audio input/envelope follower circuit, if you've got external envelope follower(s) you'd rather use, just replace this whole thing with another CV input + bias like you've got already. Having a bias control here basically makes the "Param #2" knob's function redundant, which means you can use that whole ADC channel to do something else by modifying the software.

P.S. Got PAL crystals in the mail today. smile
cheers Lars
Definitely a clock out signal would be useful too.

just ordered my pocketAVR programmer, better dig out my old nemesis; the 'C' programming textbook
Brownian Lotion
Can I be a +1 for a PAL version?

I live in Australia and have a friend who needs kickstarting in video..
Sure, no problem. I'll send a note to everyone on this thread that's mentioned it as soon as I have them ready.
Kit assembled last night here on Vancouver island Canada, direct from Austin. First test was running a Casio sk-1 through it and then a Suonio. thumbs up
I think I've finally found the perfect partner for my Benjolin.... CVing & clocking one another love love love
Hmm, same flashing left led issue, regardless of source, reheated for cold solder joints, nope that's not it.
still have that bitvision led issue? me too, a puzzlement, not cold solder issue. parts issue, something reversed? ?
Does the flashing rate of the left LED seem to be connected to the flash rate of the right LED at all? I'm wondering if some sort of crosstalk might be happening.
No its a fairly steady rapid flash that does not vary with the gain pot. Sort of one-one-one-one. Gain makes no changes to it, nor do any of the buttons. It blinks when there is no audio input hooked up or if there is, its at the same reate, quite constant.

The led on the right is quite slow and only slows a bit with parameter 1, no change with parameter 2. Its rate is sort fo waltz time, one and two, one and two.

Possibly related the trim pot to counter-clockwise never seems to get to black & white after dozens of turns.
Hi sealion -- solder job looks nice and clean, good job! Yeah that doesn't sound right about the LEDs. Double check the orientation if you can. As for the trimmer, do you see the color scaling changing as you adjust it? It is a 6-turn trimmer. You're basically scaling the DAC voltage going to the phase shifter. If you could, do you have a way to take some snapshots of the output or capture a clip, going thru different images?

I've personally handbuilt over 20 of these with this same board revision/BOM, so I'm sure we'll get it sorted. smile
Here's a quick preview of the Bitvision image & palette editor tool I've been working on. It's going to be pretty bare bones at first, but we'll keep improving it. In addition to defining a custom image and palette for each "program", I'd also like to be able to reconfigure the actions of the param knobs and mode/action buttons on a per-program basis (so kind of like a modular control patch that you set up in this editor, and gets encoded with the image+palette.) So you could have 16 different image/palette/control patch combinations loaded on the BitVision at once.

That's one of the coolest dang things I ever did see. applause
Can't wait to try it out! You rule Lars!
sealion wrote:
still have that bitvision led issue? me too, a puzzlement, not cold solder issue. parts issue, something reversed? ?

sounds like we have the same issue. maybe an issue with this run??

this thing is still great but I'm not sure I am getting modulation through the external input.

honestly I have not had a chance to power mine up since I built it, since I am planning to use my own images on it for performance, and I have been slacking on picking up the AVR programmer thing.

Hey Giorgio, it looks like some bad AVR chips may have gone out with these kits! I've been looking into this with sealion and believe that I didn't pack the AVRs well enough, and it's potentially been damaged during shipment (I apologize for that.) I had a BitVision here that I just did rework on (leftover one that didn't test OK from the last building run) and it had the exact same issue that you're both describing. New AVR fixed it right away.

You guys are both definitely not seeing the correct behavior out of your BitVisions yet. Shoot me an e-mail and we'll get it sorted out, either you can send it to me and I'll install a new chip and confirm it's all good -- or I can send you a new chip.
IIRC the AVR chip was just floating in the bag of parts, which I kinda found odd, but in any case, I am not worried about it at all thanks to your support!

i'll drop you an e-mail now

thumbs up
I've just uploaded the source code, the editor utility, and some very brief step-by-step instructions for adding your own images and color palettes on the BitVision webpage here:

Keep in mind this is a big work in progress! BitVision is meant to be a development board for "vintage audiovisualizer" type applications, and there is much more to be explored. Let me know if you've got questions and looking forward to feedback.
Thanks Lars
got my programmer yesterday
think I will start making up some 32x32 bit images and get some hex files ready.

This is such a fantastic project! love
I'm also happy to report that I have BitVision working in PAL now too. This requires population of an alternative crystal (17.73MHz) and different code. Given the really grungy response of the color phaser, I was wondering how this would look and it's surprisingly very interesting.

The downside is that I'm not getting the full range of color shift that the NTSC version has, something that may be able to be improved -- I'll look into it, but it seems like the NTSC version is more tolerant to the upper extremes of the chroma shifter. PAL is only getting green and blue parts of the spectrum, with hints of orange and purple coming through at times.

If you are DIY'ing the circuit, one solution (and this goes for the NTSC version to) is to lengthen the stages in the phase shifter delay line. Currently it is 4 stages, lengthening to 8, 12, etc. will allow a smoother response.

On the other hand, PAL speeds are allowing me to show a few more pixels and increase the image (but not buffer) size a bit.
I've uploaded a version of the source code for PAL here:
The only hardware change required is changing the crystal to a 17.73MHz part, such as this one.

Due to the fact that I may not be able to get the full color palette range for PAL with the current hardware design, I'm going to wait and get some field reports of anyone willing to test it out and see if it can be improved first, before I start offering an official PAL version. There is always the option to use an NTSC to PAL converter, like this one (maybe cheaper options out there) -- always something useful to have around anyway! But I'm betting we can get this running full speed with a little tweaking.

If you're one of the several who want this running in PAL, send me an e-mail if you'd be willing to give it a shot and I can put a bare-bones kit together for you with both crystals, just realize it's not fully there as far as color response goes just yet.
Pulled it back out to try to clean up the PAL code a bit today and got it working much better, so I think it's good to go -- just need to populate a 17.73MHz crystal instead of the one included in the kit. So those of you that want a PAL kit can go ahead and order one from Switched On. If you need the 17.73MHz crystal, I bought several, so just e-mail me with your address and Switched On receipt and I will stick one in the mail to you. Next time I do a production run of these (it may be a while), I'll include PAL & NTSC crystals in all the kits.

The PAL color subcarrier is a lot touchier than NTSC as far as valid ranges go, so it can't get as grungy and bleeding as the NTSC version, but we're seeing the full color palette now, which was the important part. I encourage anyone with the PAL circuit to play with resistor values in the HC4053/HC14 areas of the circuit -- there's a lot there to be modified and played with that will alter the color response.

I've uploaded the improved PAL code over the original zip file linked in the last post.
+1 on the PAL Version!

also emailed you! this looks fantastic!

Lars, this look pretty damn cool.

I'll email you to discuss some bits including a PAL one of these.

Hi everyone! I'm very pleased to announce that I've solved the bug issue that a few of you were experiencing with your BitVision kits with a firmware update (available for download on the website here:

I've e-mailed the few of you I promised new AVRs too, but just mentioning it here in case anyone else pops up with the same problem!
Got my BitVision up and running last night with CV inputs for the parameter pots, gate inputs for the momentary switches, DC bypass and separate clock input.

The CV input cct I posted previously has been slightly changed to get a better range out of the input CV
This and the gate cct are both on my site, if they get updated the date of the latest version will be on the link.
The gate cct is VERY simple, I didn't even need a PCB, just twisted the leads together and soldered them to the jacks.

See vidsynth page for pics and PDFs

Switches out of some 50s lab gear
THANKS Lars for the kit and sharing this great design.
AWESOME!! Looks great, Andrew! Can't wait to see some video! smile

Keep in mind, if you have a way too display it... consider swapping out for the NTSC crystal and reprogramming the AVR to see the difference. I still haven't got nearly the full color response out of PAL yet (how does it look to you?)
to be honest, in my rush to try it out, I forgot to setup the trimpot. The colours seemed okay, but I cannot say for sure until I set it up correctly.
Will do so today
Cool! You should see close to 16 distinct shades (not on all patterns.) the one page with the gradiated bars (pattern #2 or #3?) should show all palette colors.
just a simple bit of info on modifying the code in my BitVision using a Sparkfun Pocket programmer

hopefully it will be of some use to others who are new at this

Thanks for the help....and the BitVision, Lars

mine now has SouthPark jesus and daffy duck It's peanut butter jelly time!
Thanks Andrew!! I'll probably put this up on the BitVision page if that's cool.

I wanna see Daffy Duck and Jesus!! One simple alternate program I want to do at some point is an animation player, designed to use the 16 images as animation frames, and change the palette modulation LFO control to a playback speed control.
creatorlars wrote:
Thanks Andrew!! I'll probably put this up on the BitVision page if that's cool.

no worries

Maybe we can get an image thread going for people to share code.
If anyone missed it the page for creating new images is here -

for anyone wanting to mod their BitVision: a good way to find images is use google search, select images, then in the left side column, under "Any size" select 'exactly' and input 32 pxl by 32 px, then search away.
images need to be in gif or jpg, but can be easily converted in Paint.
It is even worth just looking for B&W images, as the image converter works off brightness, so these tend to turn out better in Bitvision. Colour images can be hit & miss, some are ok, some don't work at all. Of course if you are creative you can draw your own.
daffy and SP JC are near the end

andrewF wrote:
Maybe we can get an image thread going for people to share code.
I like this idea, will have a few to contribute soon.

Wonder how well QR codes will work, looking forward to making time to play with them.
old gregg

is tere some equivalent diode to the SMV1255. I'm about to order stuff from Farnell but, obviously, they don't have those.
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