Par-Can Retrofit: fitting the Luxapel "Primo" PR75 LED module

  I don't remember how I first learned of this product's availability, but a directly-installable LED retrofit for old PAR64 or PAR56 fixtures did seem like an intriguingly sensible thing.  I could immediately think of two or three venues and gear inventories that could benefit from something like this, radically cutting power requirements and having full color capability by simple reclamation of lights whose usefulness would otherwise keep declining.  And there were strong hints that this wasn't typical cheap offshore crap, but rather of domestic design and manufacture.

The website had a phone number, so I called it with some questions ready.  I wound up talking to the founder, which in retrospect made sense since Luxium / Luxapel appears to be two or three guys working out of someone's garage.  But the conversation was pleasant and reasonably technical, which I always appreciate.  Later I sent some email with further questions as they'd come up, and got a reasonably coherent reply from the same fellow.  The LED units could be equipped with wireless DMX, and the claim was that in the wireless mode, the physical wired ports would act as repeaters and relay the DMX as local signal sources.  Think about that -- anywhere at least one of these units was deployed, no physical long DMX wire would in theory be needed to reach that position from the console!  This feature was quite attractive given the setup of several events I routinely work on, where cabling paths around the venues are often a bit of a design headache.

Since larger purchase quantities could bring deeper per-unit discounts, I tried to get some other par64-owning collaborators interested, but that didn't really go anywhere constructive.  The quantity I personally would need was only four, but I inquired about how to start the purchase process based on that anyway.  Then the flaws within Luxapel began to emerge, specifically that of being really disorganized from an actually-doing-business perspective.  I received a quote for way more per-unit cost than we had discussed via email, and the pricing on a wireless DMX transmitter was exactly the same number so that distinctly looked like a copy/paste typo.  We were also trying to work out how I could test various optical diffusion media kits they could offer, and figure pricing for that.  Back and forth some more, and finally on the *third* emailed PDF quote they seemed to actually get it right.  Almost.

But at least the buying process had been launched -- they asked for half the total up front, and accepted Paypal which I had finally and grudgingly set myself up with.  The shipment showed up about a week later, except minus the wireless DMX transmitter, so to begin testing I would have to take apart at least one unit and pull out its wireless receiver to enable the RJ45 wired DMX ports to receive from a controller.  [More on this particular travesty below.]

Primo 75 unit apart Four corner screws out and the back comes off the module, bringing all the works and the ribbon cable from the LED plate with it.  The bulk of the parts volume is an off-the-shelf power supply, which produces a surprisingly high 22 VDC.  But I suppose that's appropriate to running strings of LEDs in series.  Inserted into a header on the control board is the wireless "W-DMX" module [blue arrow].  That's another off-the-shelf part from "Wireless Solution" or Lumenradio or or whoever they are this week.
W-DMX daughter board pulled off Better look at the PR75 control board
Pulling the W-DMX off reveals the rest of the control board -- not a lot to it.  There's a small Atmel processor here, a RS485 transceiver chip, and LED driver transistors.  Addressing and a couple of other settings are done with a 10-position DIP switch on the back panel, and there's a socket for a Bluetooth module that can also do some of that with an app.  The ribbon cable going out to the LEDs is not particularly robust, and uses those stapled-through insulation displacement lugs that seem likely to fail under repeated flexing.  So we'll try to not flex this assembly too much...

LED matrix, separate color emitters Leaving the W-DMX module out and partially reassembling did allow for wired DMX control, and then I could actually hook up a console to one of the RJ45 jacks and start playing with the module. 

Here's the emitter matrix: separate red, green, blue, lime, and white, as opposed to multi-output chips like in the Rokboxes.  Each LED chip on the output board has basically 180 degree emission, which is all caught by a lenslet that sends it into a roughly 20-degree beam.  The white emitters produce a surprisingly warm color temperature, more like that of the par lamps these are intended to replace than the cold blue-whites we normally expect from white broadband phosphor emitters.  The units normally occupy 4 DMX slots, so we don't directly control the lime emitters -- they come on automatically at an appropriate level to augment the spectrum between red and green.

Dimming is very smooth, with no evidence of "quantization" or flicker in the output, especially where it tends to be most noticeable at the bottom in other LED fixtures.

Sharp fringing in hand shadow Diffusion added to smooth out fringing
Because the color sources are fairly widely separated, the near-field output is anything but uniform.  This causes fairly sharp fringing in shadows, worse the closer we are to the unit.  Makes my hand look like a weird rainbow monster.  Luxapel has a variety of diffusion plastic panels that they can provide, with intent that they would mount on standoffs at a little distance from the emitters and smooth the output.  This does actually work, and I spent quite a while playing with diffusers, random frost gel I had around, and distances from the array.  Note that my ceiling lamp is in focus in both comparison images; this is showing the effect of *some* diffusion vs. the raw array output.

With two stages of gentle diffusion -- one on the module standoffs inside the par-can and then something more across the gel slot, output can be made decently uniform without objectionable edge fringing.  And the throw for this testing was only modest residential ceiling height, so it would be better at real stage distances.

  After a little back-and-forth with the Luxapel guy who was convinced that he had shipped the wireless DMX transmitter when in fact he had not, I found a related inconsistency on his invoice where our agreed-upon price for it wasn't even included in the total.  He finally found it still sitting around the shop, said "Oops", and overnighted it.  So now I could start testing the wireless functionality, pairing and unpairing lights, and the claimed re-transmission of a full DMX universe out the wired side of every unit.  If this worked as I assumed, it would be a super-handy feature for events, eliminating DMX cable runs to any part of the rig where these units were hung.
Luxapel/Luxium TRW-1 W-DMX transmitter So here's the "TRW-1" transmitter.  It's actually a fairly smart little unit, with various auto-run functions as well as controls to pair and unpair with any receivers in range.  It has a rotary-plus-push encoder to navigate the menus.  The Luxapel guy was able to sell me this particular transmitter at a discount, because the rotary encoder would only output in one direction so it was thus considered "flakey".  Apparently this is a common problem with them.  But fortunately, all the menus wrap around correctly, so I can still get to every function -- and really, only one function is needed here, that being to simply boot up and talk to the lights.
TRW-1 circuit board One end plate looked a little crooked with a screw not seated right, so I decided to have a look inside on general principles in the process of fixing that.  I also wanted to look at the encoder to see if anything might be done, but it's basically a sealed-up component with nowhere to, say, squirt in a little DeOxit.  The Luxapel fellow actually suspects it's a soldering defect somewhere else, blocking the direction output from reaching the processor.  Anyway, here we have the W-DMX transmitter board, a small display, and some glue logic.

RJ45 to XLR adapter, for DMX *output* To effect bridging DMX from wireless to wired, I would need a couple of these adapters.  Note that it's a female XLR, because this is an OUTPUT!  I cut apart a short RJ45 patch cable which turned out to be made of stranded wire anyway, so aside from the typically disparaged "RJ45 vs. gigging" aspect, these should hold up okay with a little attention to strain-relieving our cabling.

I actually made the first one of these early on, and then converted male-to-male via XLR to temporarily use the RJ45 as input when the W-DMX module was out.  Unfortunately there's no easy external way to switch that functionality in the Primo module -- if the W-DMX daughterboard is in, the RJ45 is hard-set as an output that actively messes with any DMX line plugged into it.  The fellow from Luxapel seemed to believe that un-pairing would revert the ports to high-impedance input mode, but such is not the case.  We discussed; I think wound up sending him into a bit of a re-design project.

DMX frames received over wireless, TTL level Before installing the W-DMX back in the one unit I'd been testing with, I did a little probing around to confirm some of these findings -- ohming out the direct path from the W-DMX module to the data-enable pins of the transceiver chip instead of being controlled by the processor like it should have been ... and watching the TTL-level DMX signal arrive wirelessly from the board in the other room.  What fun!

Here's more confirmation that the SD50 only sends 48-slot DMX frames, too.

Mounted R114 diffusion on standoffs All this aside, it was time to quit goofing around and actually assemble these into a set of gig-ready units with all the other trappings they'd need.  The extensive experimentation with diffusion had indicated a reasonable "frost density" compromise of Rosco 114 at the distance of the provided standoffs.  Since Luxapel had sent a full complement of those I decided to use some gel stock I already had, and simply clamp a piece of same across four standoffs per unit.  This somewhat fragile setup would be safely contained inside the par-can body, so it would work fine.

To somewhat re-create the traditional oval beam of MFL and WFL par lamps, I also cut some *circular* 10" pieces of Rosco 113 silk, which could be rotated to arbitrary orientations in a gel frame.  Not perfect, but does visibly spread in one axis.

Foam 'ear covers' for mounting tabs The four "ears" on the LED unit would nominally fit into the lamp housing section of a Par 64, but actually fall a little short of that diameter.  [They're designed to be broken off for installation into a PAR56 housing instead.]  Because of what I've experienced with PAR lamps rattling around in these things and that I wanted a nice firm mounting for these units, I cut a bunch of little padding pieces from Luxapel's original high-density packing foam.  A blind slot cut "the hard way" into the inner curve could accomodate the unit ear but keep it padded a bit away from the lamp ring.  These were not constructed with any particular precision; the idea was simply to keep the LED module from moving around once installed.
PR75 mounted in an old PAR64, with padding So here's what it looks like installed, without the retaining ring.  Works fine for now, and of course the foam pieces won't undergo any undue heating since whatever heat produced is blown out the back by the fan and the module plate stays completely cool.  The fan is dynamically controlled based on cooling need, and doesn't come on until the LED board and the big heatsink behind it starts to warm up.

Scope hookup to watch DMX transmitters In the process of playing around with wiring and relaying the re-generated wired DMX output, I happened to notice a different appearance of the LED in the back of my "happy light" terminator when being driven from one particular unit.  It was significantly dimmer than what I expected, where the same signal from other units looked completely normal.  So I decided to scope all of their wired outputs to see if there was some explainable difference or defect.

This terminator [blue arrow] is basically a 100 ohm resistor in series with a red/green bi-color LED, and the running differential RS485 signal is usually enough to flicker the red/green outputs in a characteristic way.  But from a couple of the Primo units, that output looked "weak".

Those two units were producing decidedly degraded waveforms, with weird leading-edge overshoot spikes and a lower overall voltage differential.  It was barely within RS485 spec and could still likely drive a downstream wired fixture, but over what kind of distances and conditions in the field?

Weak transmit waveform with ringing and low voltage
Degraded DMX output signal

The other two units produced a nice solid DMX signal with completely in-spec voltage and a clearly slew-rate-limited waveform to help eliminate ringing.

Solid transmit waveform with clean slew-rate-limited edges
Solid DMX output

Upon briefly taking one of the "weak" units apart, I found that the transceiver chip inside was indeed a different part than in the first unit I'd been playing with.  "SP3072EE" vs generic "83072", for what that's worth.  I didn't try to pursue what actual component manufacturers either was from, as there are so many knockoffs that come up in search results.  Luxapel had simply made a questionable choice over some part of their production run, and never sanity-checked what those chips were doing.  So the RJ45 ports on two units are labeled "WEAK", such that the other two should preferentially be used as the local DMX sources instead.

LED par coloring smoke column And here's where one of the units got its first "show": enhancing the backyard fire-pit I had on Halloween, and it was even cooler once it got truly dark.  It served as a nice attractant for people to venture past the house to the backyard for their treats [energy bars, we do *nourishing* snacks here] rather than go up to the door.  The light ran off a portable power box, with the control board and wireless sender sitting on a reachable windowsill back at the house, so no wires across the yard!

_H*   231024, 231031