DIY DB25 - RJ45 converter

[VDX]

... why not expand the BOB for one or even two more connectors for the remaining signals?

Viktor

[area51t]

I don't know if you are referring to the manufacture or Me
well the picture I inserted was the possible pin map of the RJ45 connector and
the actual Back looks like this. they are unexpandable

[VDX]

... OK - if its from an RJ45-Output to the 25pin, then there's no other way ... I thought, it was the other way round

Viktor

[lasermaster1977]

as they are not using 'All the signals' do you think there could be a flaw that can be caused by it?

Your projector appears to only need those primary laser signals in order to produce RGB laser scanned images or beams. The software you use determines whether it matters. Most likely, it won't matter.

[buffo]

I remember an early Chinese laser projector called "The Big Dipper 2000" that also used a standard ethernet port as the only connection on the back of the unit. This would have been around 2005-ish. George Mack had one, and when he showed it to me, I was surprised that it did not have the standard 25-pin ILDA connector. He was using Full Auto at the time, and he had to build a DB-25 to RJ-45 adapter so he could connect to the projector.

I know that the color signals were all single-ended with a common ground, but I think the X and Y signals were also single-ended and used the same common ground. If that's correct, then the projector only used 6 of the 8 conductors available on the RJ-45 jack. (Meaning you had X+, Y+, R+, G+, B+, and GND.)

Obviously this is not ideal, but it would work.

It's also possible that they did use differential signaling for X and Y, (which would use up 4 conductors) and then used the remaining 4 wires for single-ended color with a common ground. (So you'd have X+, X-, Y+, Y-, R+, G+, B+, and GND.) I honestly can't remember exactly how it was wired up...

Regarding your projector, it's very possible that the RJ-45 connector is wired similarly to one of the two examples above. if you remove the cover you should be able to ring out each pin on the RJ-45 connector and see where the signals are routed to inside the projector. Pay attention to the inputs for the scanner amps - that will tell you if the projector is wired for differential X and Y, or if they went with a single-ended connection.

Adam

[lasermaster1977]

The norm in RJ-45 use for high frequency network communication is to use Unshielded Twisted Pairs (UTP) of wires, 4 pairs, each pair twisted 8-9 twists per inch for CAT5, CAT5e and CAT6 cables with all four pairs encased in a vinyl sheath, no braided shield sheathing the 4 pairs. This takes advantage of balanced, differential signal lines such as used in Ethernet communications to reduce crosstalk and induced noise pickup in the balanced transmit and receive wire pairs. Ethernet cables only use 2 pairs for transmit and receive, while the other 2 pairs are sometimes used for Power Over Ethernet (POE), a way of providing operating voltages on those pairs, such as +5v and Ground and +12v and Ground. 100 meter cables lengths are the practical limit for CAT5-CAT6 cables and includes any additional "patch cables lengths" between end point Ethernet port connections. Pins 1 & 2 are one pair, pins 3 & 6 are the second pair, pins 4 & 5 are the third pair and pins 7 & 8 are the fourth pair. The first two pairs are the "signal" pairs for Ethernet transmit and receive.

Ethernet cables come in two varieties, straight-through and cross-over. Straight-through cables map the wire connecting to each RJ-45 pin pair to the same pin pair on the opposite end. Cross-over cables swapped the pin 1 & 2 pin pair with the 3 & 6 pin pair on one end of the cable terminated with RJ-45s on both ends.

Older uses of RJ-45 connectors may have used 8 wire, flat cables akin to flat ribbon cables in a vinyl cable sheath. These were more commonly used with 300-9600 baud modem communication speeds and do no provide good noise rejection characteristics.

Outside the realm of "Ethernet communications", how an RJ-45 jack is wired has no rules, but maybe some loose conventions. Assume the 4 twisted wire pairs in a CAT5-6 cable are simply connected like:
Pair 1 - pins 1 & 2 (white-green, green)
Pair 2 - pins 3 & 4 (white-orange, orange)
Pair 3 - pins 5 & 6 (white-blue, blue)
Pair 4 - pins 7 & 8 (white-brown, brown)

If the cable is sold as an "Ethenet CATn" cable then the pairs would be the T-568A standard
Pair 1 - pins 1 & 2 (white-green, green)
Pair 2 - pins 3 & 6 (white-orange, orange)
Pair 3 - pins 4 & 5 (blue, white-blue)
Pair 4 - pins 7 & 8 (white-brown, brown)


The ILDA +X and -X signal pair could be assigned to Pair 1, while +Y and -Y is assigned to Pair 2. This leaves RGB and Ground signal lines. If the RGB signals are 0-5v TTL or single-ended analog signals, R & G might be Pair 3 and B & Ground as Pair 4. Having any two of the RGB lines as a twisted pair isn't ideal for noise reduction in those two signals but it probably does not matter for short cable length (but this is a generalization).

This is mostly from memory so double-check me.

[buffo]

If the cable is sold as an "Ethenet CATn" cable then the pairs would be the T-568A standard
Pair 1 - pins 1 & 2 (white-green, green)
Pair 2 - pins 3 & 6 (white-orange, orange)
Pair 3 - pins 4 & 5 (blue, white-blue)
Pair 4 - pins 7 & 8 (white-brown, brown)

This used to be the case; the 568A standard is an older standard that was designed to be compatible with twisted-pair telephone wiring.

However, today nearly all "CAT-n" Ethernet cables are wired using the 568B standard as it offers better signal isolation for high-speed digital signals.

568 B looks like this:

Pin 1: White-Orange
Pin 2: Orange
Pin 3: White-Green
Pin 4: Blue
Pin 5: White-Blue
Pin 6: Green
Pin 7: White-Brown
Pin 8: Brown

Regardless, I don't think this projector is using the RJ-45 jack for any sort of network connection. Rather, I suspect it's wired to accept analog signals straight from the controller (DAC) using the fewest number of conductors as possible. Definitely not an ideal solution, but it's cheap at least...

Absent a diagram from the owner's manual, the easiest way to figure out which pins go where is to pop the lid and trace or ring out each pin. (With the power disconnected, of course!)

Adam

[lasermaster1977]

This used to be the case; the 568A standard is an older standard that was designed to be compatible with twisted-pair telephone wiring.

However, today nearly all "CAT-n" Ethernet cables are wired using the 568B standard as it offers better signal isolation for high-speed digital signals.

568 B looks like this:

Pin 1: White-Orange
Pin 2: Orange
Pin 3: White-Green
Pin 4: Blue
Pin 5: White-Blue
Pin 6: Green
Pin 7: White-Brown
Pin 8: Brown

Regardless, I don't think this projector is using the RJ-45 jack for any sort of network connection. Rather, I suspect it's wired to accept analog signals straight from the controller (DAC) using the fewest number of conductors as possible. Definitely not an ideal solution, but it's cheap at least...

Absent a diagram from the owner's manual, the easiest way to figure out which pins go where is to pop the lid and trace or ring out each pin. (With the power disconnected, of course!)

Adam

You are right. The 568B standard is the most current but the only difference between them is that the orange and green pair positions are swapped. The 568A and 568B have identical performance characteristics with the caveat that they both use the same cable types with the same number of twists per inch. From a telephony point of view of using RJ-45 connectors, the difference had to do with backward compatibility between one pair and two pair phone connector jacks. The US Gov't requires the 568A standard for all wiring under federal contracts.

I only brought up this network cabling standard for RJ-45 cables to bring awareness of the difference between it and a straight-through RJ-45 cable. I also wanted to point out potential issues with the color mod signals where a long RJ-45 network cable was used for connection for single-ended RGB signals.

We can hope that this projector manufacturer provided some insight for how the RJ-45 jack was wired or as you suggested, provided the DAC and the cable to connect the two.

The photo @area51t provided from Banggood's website was a cabling/pin assignment solution that may have been used.

[HankLloydRight]

The ILDA +X and -X signal pair could be assigned to Pair 1, while +Y and -Y is assigned to Pair 2. This leaves RGB and Ground signal lines. If the RGB signals are 0-5v TTL or single-ended analog signals, R & G might be Pair 3 and B & Ground as Pair 4. Having any two of the RGB lines as a twisted pair isn't ideal for noise reduction in those two signals but it probably does not matter for short cable length (but this is a generalization).

Regarding your projector, it's very possible that the RJ-45 connector is wired similarly to one of the two examples above. if you remove the cover you should be able to ring out each pin on the RJ-45 connector and see where the signals are routed to inside the projector. Pay attention to the inputs for the scanner amps - that will tell you if the projector is wired for differential X and Y, or if they went with a single-ended connection.

Absent a diagram from the owner's manual, the easiest way to figure out which pins go where is to pop the lid and trace or ring out each pin. (With the power disconnected, of course!)

We can hope that this projector manufacturer provided some insight for how the RJ-45 jack was wired or as you suggested, provided the DAC and the cable to connect the two.

Guys -- @Area51t posted the answer in Post #8 with the adapter he got from Banggood!!! .

[lasermaster1977]

@HankLloydRight...what? We can't digress?