Category: design

i’ve spend the last two weeks house-sitting at my parents place while they are on holiday. this has given me time to deep dive into some larger topics i have been meaning to get around to.

one of these topics was the design and fabrication of panels for underscores circuits (having unlimited access to a laser cutter over this time helped!). i made a half vlog / half tutorial style video to document this exploration – you can see on videos.scanlines or on youtube:

types of panels

sometimes i get asked if there are enclosures/front-panels available for the pcbs i sell (there actually have been a few community contributed designs for the recurboy and i_n_c_u_r circuits) but so far nothing from me. this will change soon with the addition of two enclosure options – stand-alone sandwich and eurorack front-panel for the following circuits:

• sync_ope
• recurboy
• _rupture_
• two_comparator_effect
• i_n_c_u_r

originally i planned to prototype with laser-cut MDF (and share these files so others can laser-cut also) but only stock the FR-4 versions in the shop (since these would be cheaper and tend to look quite professional) – however after seeing the MDF i think i prefer them to FR-4.. i wonder if there would be any interest in stocking MDF (or even bamboo) lasercut panels too ?

euro-friendly designs

although definitely not eurorack modules themselves a number of these underscores circuits were designed to be euro-friendly, in the sense that you could mount them in eurorack case with the appropriate front-panel if you wanted to.

all the interfacing parts of these circuits are vertically mounted and the pcbs are at most 100mm tall. all circuits run on single-rail power (mostly 5v) but some have footprints for euro-power headers anyway and the others you could mount a vertical barrel-plug on the bottom of the pcb allowing a small eurorack-to-barrel-jack converter to sit inside your case and power from beneath:

as i mentioned in the video there are a few other things to consider when adapting to eurorack – the small slide switches i usually use sit a bit too low for comfortable switching (i would love to try 3d-print some switch-caps for these when i get a printer!) and i would recommend choosing longer shafts on the pots than the ones usually supplied with my kits…

its fun to see them mounted together in a rack like this however this conversion is not the same as an actual eurorack module version of these circuits – which i do plan to design one day (closer to that day now that i finally have a euro-case built) the true eurorack versions will:

• use smd components and be designed to conserve hp
• have interface parts chosen to fit panels better rather than prioritizing what is cheapest
• layout of interface optimized for rack use
• have proper eurorack power headers
• hopefully expose some more of the controls with CV

my workflow for creating panels

this is shown with more detail in the video, but here is a written overview:

copy the pcb footprint into a new project and delete everthing except for the edgecuts, silkscreen and any footprints of interface parts

then replace each interface footprint with a edgecut hole to access it from the panel (based on a table of known hole sizes)

arrange the silkscreen however you want the panel to look – 3d viewer in kicad is useful!

when you are happy with how the panel looks you can export it – use the usual GERBER export if you want to get it fab’d in FR-4. my method for getting designs into lightburn was to first export from kicad as SVG and then open these SVGs with inkscape and save a copy as DXF (it seems like lightburn didnt like some of the SVG format that kicad creates)

once in lightburn put the edgecut and silkscreen imports on different layers – you can add thickness to the silkscreen using the offset tool

then set your laser speeds, check the material is lined up with the cutting area and make the cut!

we have a number of new projects in the works – im hoping to release three more circuits before the end of this year – heres a preview and small overview of one of them!

underscores presents an adaption of Rob Schafer’s two_point_one_colorizer:

history of the project

the original circuit was designed by Rob Schafer on breadboard and shared on the facebook group Video Circuits :

since then Rob has moved on from working with composite video – (check out his youtube channel to follow his exploration of HD analog video) – but my interest in this circuit remains!

how it works

the way this circuit creates colour is both genius and extremely hacky!

the first stage is very similar to another underscores circuit adapted from Rob Schafer – the two_comparator_effect :

the signal passes through two comparator stages – reducing the signal down to this posterized effect with only white, grey and black visible – two_point_one_colorizer is similar but instead creates two colours plus black (hence the two point one)

colour on composite video is created with a sub-carrier signal – an extremely fast sine wave that runs over-top of the luminance signal:

the hue is selected by the phase difference between this sub-carrier signal and the colour burst reference.

on the next stage of the two_point_one_colorizer a sub-carrier signal is approximated using high-speed monostables and overlaid over these ‘white’ and ‘grey’ portions of the comparator outputs:

monostables generate square waves with variable pulse widths -which at this speed can approximate the sub-carrier signal with variable offsets (hue) – inverters are also used to shift the offset by 180 degrees – since this approximation is not perfect some colours are easier to generate than others – and some displays are more or less picky than others.

what i love about this approach is that it is less precise and predictable than (for example) generating colours with an rgb encoder – you end up getting some really unexpected results – and also some great colour glitches as the tv decoders struggle to make sense of the out-of-spec signal:

the adaption

back in 2020 i made a start trying to adapt this design to pcb with help from Rob and others from the scanlines community – a few of the mods made to the original design include:

• simplifying the sync and burst pulse portions by using lm1881 instead of doing this more ‘manually’
• swapping out the monostables for another ic – similar in spec but around 1/10th of the price (can still swap out for robs original ic if you would like!)
• adding video by-pass toggle – making the circuit more usable in larger signal chains
• adding more control over colour selection – a master colour offset that changes both channels together and sub-carrier amplitude that changes colour saturation
• (attempting to) adapt the circuit to also work on pal cvbs – adding a switch to select sub-carrier frequency and also logic to implement Phase-Alternating-Lines

PAL troubles

i got a bit stuck on the PAL compatible part of the mod and ended up shelving this project for a bit while i focused on working towards the shop launch and polishing other projects..

..im still not sure that the PAL version is perfect – the Phase-Alternating-Lines mod never quite worked how i expected and the range of colours seems a bit less (could be just due to PALs faster sub-carrier though since the monostables are already being pushed to limits with NTSC). im sure there will be some displays that wont show any colours for PAL but to my surprise the three monitors i tested it on in my studio all worked with NTSC and PAL (a crt tv, a small car-reversing lcd and a easycap capture card)

the nature of this project is hacky and experimental so it is already wishful thinking to have it running consistently on all displays – I think the current version would be a useful tool in the studio of many composite video artists and im excited to see it out in the world!