Pixel String Data Extender

[erm213]

Hello,

This is my fist shot at making a board. The intention is to make a transmitter/receiver pair that will allow a RGB controller board (such as the E680, or the PropController) to be far away from the start of the pixel string. My plan is to have it be 24 VDC input to the transmitter. A voltage regulator will output 5 VDC to a 485 transceiver. The 24 VDC, common, and A & B outputs of the 485 chip will be connected to a RJ45 jack.

Cat 5 cabling will connect it to the receiver. The 24 VDC will connect to a voltage regulator to drive the 485 transceiver, and ultimately the pixel string. The data out of the 485 will be connected to the data line of the pixel string. I am initially making it 5 VDC, as thats what I need. It could probably easily be adapted for 12 VDC.

I have drawn up a schematic of what I believe it should look like. I am sure I missed things, and am looking for feedback.



Thanks,

Erik

[David_AVD]

A few comments:

• Add decoupling capacitors to RS485 chips and regulators
• The resistor on the sending end is not required
• The resistor on the remote end should be 120 Ohms
• The regulator on the remote end will not cope with the current / power dissipation
• Won't you need two data paths for most pixel types?

[n1ist]

A few more comments:
- On the transmitter, tie ~RE high
- On the receiver, tie DE and DI low
- You don't show the RJ45 pinout. Make sure A and B are run on a twisted pair (say pins 4 and 5). Parallel the remaining lines for +24 and GND
- On the LM1085-5.0, pin 1 is GND, not ADJ
- For the kind of power draw you are looking at, you will likely want a switching regulator on the receiver

[erm213]

A few comments:

• Add decoupling capacitors to RS485 chips and regulators
• The resistor on the sending end is not required
• The resistor on the remote end should be 120 Ohms
• The regulator on the remote end will not cope with the current / power dissipation
• Won't you need two data paths for most pixel types?

Thank you for the feedback. I will make the changes. Do the capacitors go between the Vcc and ground correct?

The part on the voltage regulators is wrong. For the transmitting side, I plan on using a LP2950-50LPRE3 and a LD1085V50 on the receiving side. Should these be ok, or would you recommend something else?

I am going to be prototyping this on the GECE strings, they have one data line, as they do not use the clock line. I should probably include the clock line. Would that need to go through a RS485 chip as well.

I used ExpressSCH to make the diagram. I installed Eagle, and am going to try to remake the diagram in there. It seems like better software. Hopefully I can make a better and more accurate schematic.

Thanks again,

Erik

[erm213]

A few more comments:
- On the transmitter, tie ~RE high
- On the receiver, tie DE and DI low
- You don't show the RJ45 pinout. Make sure A and B are run on a twisted pair (say pins 4 and 5). Parallel the remaining lines for +24 and GND
- On the LM1085-5.0, pin 1 is GND, not ADJ
- For the kind of power draw you are looking at, you will likely want a switching regulator on the receiver

High means supply it the 5V, and low means ties it to ground, correct?

I will add the RJ45 pin outs. As far as the parallel comment, do you mean make 3 lines +24, and 3 lines GND? Should the +24 be paired with a GND?

I will fix the ADJ in the schematic, I think the Eagle software will work a lot better.

Is this the kind of switching regulator you mean? LM2576TV-5G

I will post the updated schematic once I get all of the changes incorporate.

Thanks,

Erik

[David_AVD]

Thank you for the feedback. I will make the changes. Do the capacitors go between the Vcc and ground correct?

Correct. Maybe use a 1uF monolithic cap on the 485 chip supply and a 100uF electrolytic cap on the regulator input.

The part on the voltage regulators is wrong. For the transmitting side, I plan on using a LP2950-50LPRE3 and a LD1085V50 on the transmitting side. Should these be ok, or would you recommend something else?

The transmitter side is probably fine. The problem with the regulator on the right is that it will be dropping 19V @ whatever current the pixels draw. That's 19W of pure heat (and 19W power wasted) for just 1A of output! As n1ist says, use a switching regulator to get the high efficiency (and low heat) you need.

I am going to be prototyping this on the GECE strings, they have one data line, as they do not use the clock line. I should probably include the clock line. Would that need to go through a RS485 chip as well.

You'd need as many differential data lines (with 485 chips) as you have data signals to send.

As for the pinout, I would use:

1. D1+
2. D1-
3. D2+
4. +24
5. +24
6. D2-
7. GND
8. GND

This allows for 2 differential signals, correct pairing and doubling up on the +24 and GND wires. It's also compatible with DMX over CAT5 wiring and PoE with respect to the power.

[erm213]

Correct. Maybe use a 1uF monolithic cap on the 485 chip supply and a 100uF electrolytic cap on the regulator input.


The transmitter side is probably fine. The problem with the regulator on the right is that it will be dropping 19V @ whatever current the pixels draw. That's 19W of pure heat (and 19W power wasted) for just 1A of output! As n1ist says, use a switching regulator to get the high efficiency (and low heat) you need.


You'd need as many differential data lines (with 485 chips) as you have data signals to send.

As for the pinout, I would use:

1. D1+
2. D1-
3. D2+
4. +24
5. +24
6. D2-
7. GND
8. GND

This allows for 2 differential signals, correct pairing and doubling up on the +24 and GND wires. It's also compatible with DMX over CAT5 wiring and PoE with respect to the power.

I made the new diagram last night in the Eagle software. It's much better. I think I had made all of the changes you suggested, but it was late. I will check again tonight, and add the second data line into the schematic.

I found the LM2576TV-5G and plan on using that on the receiving side.

Thanks,

Erik

[erm213]

Ok,

I have updated the schematic. Here is the image:



I have made a BOM from Mouser as well.

Would it be helpful to have the sch file from EAGLE?

Thanks,

Erik

[P. Short]

At first glance it appears that you are transposing the A and B on the data signals between the transmitter and receiver. Is that your intent?

[erm213]

At first glance it appears that you are transposing the A and B on the data signals between the transmitter and receiver. Is that your intent?

Oops, that is not my intention, and I double checked on the data sheet, I do not want to be doing that. Good catch.

Thanks,

Erik