Wiring Smart Pixels

The most important part of your show is the wiring. This heavily affects the cost, ease of setup/take down, and how easy it is to fix problems. It is important that you thoroughly understand wiring, before you choose how you want to layout your show.

Basic Recommendations

First, let me list some of the basic recommendations as a starting point for your display.

1) Only drive fifty 5Vdc pixels without power injection (assumes standard 60mA per pixel).

2) Only drive one hundred 12Vdc pixels without power injection (assumes standard 60mA per pixel).

3) Do not use ground loops in your power.

4) Use Ethernet cable, a twisted pair, for control signals (control/ground)

5) Multiple small controllers around the yard minimize wiring and cost.

5a) Wi-Fi controllers based on the ESP8266 and ESP32 have become a common alternative to Ethernet controllers for individual props. Placing small controllers close to each prop can greatly reduce wiring, power injection requirements, and setup time.

6) Measure both the voltage and current under load at the end of each pixel string. Actual voltage drop depends on pixel type, wire gauge, wire length, brightness setting, and whether the pixels contain internal voltage regulators. Always verify your design with measurements rather than relying solely on calculated values.

Wiring Methods

Direct Power

By far the least expensive method to drive smart pixels is with a large power supply powered through your controller. The only other components required is a power cable to the pixels. It is recommended that you use 16AWG extension wire in lengths of 10-15 feet, which is cheapest bought as an extension cord. The only cost for this layout is the controller, large power supply and the wire. This has become one of the most common wiring methods for medium and large displays because inexpensive controllers can be placed close to the props they control, minimizing voltage drop and reducing the need for additional power injection. Many modern displays use smaller distributed power supplies or power supplies integrated with individual controllers instead of one large centralized supply. This reduces long power cable runs and often simplifies installation and troubleshooting.

Local Power Supply

If the pixels are further away from your controller, it is best to use a local power supply and Ethernet cable for the control lines. If you use Ethernet cable to drive the control signals, with 100 ohm source termination, it has been demonstrated to work to at least 100 feet. The drive chip used was an 74ACT541 versus the standard 74HCT541. The ACT parts have more current drive, which will improve your ability to drive the signal further. The local power supply adds some additional cost for power.

Local Power Supply with Pixel Extender

In electronic engineering, best practice for signals that go more than a couple feet is to add a differential driver/receiver pair (RS-422/485). These drivers make the signal more immune to noise and allow the signal to be driven further. For pixel data rates (approximately 1MHz), the expected distance is 1000 feet. These also add the benefit of allowing the ground between your lights and controller to vary up to ±7Vdc. By far this is one of the best methods to drive strings. It will always work at any distance, the input to the display element is an Ethernet cable and power is through an extension cord. There are a couple controllers available with pixel extenders built in. This adds additional cost for the buffer/receiver boards. Differential pixel extenders continue to be widely used for long cable runs where controllers cannot be located close to the props. Many modern controllers also offer built-in differential outputs or expansion receivers using the same concepts described here.

Power Over Ethernet

This method allows you to use one cable for both power and control lines. The power over Ethernet specifications is written for use with 48Vdc and 56Vdc power supplies at 600mA maximum current. The higher the voltage, the longer you can make the cables with out any issues. For use with 5V and 12V strings without the DC to DC converter, you need to check current in the cable and voltage at the last pixel. This method is not recommended for 5V pixels.

This is really best used with two power supplies, a high voltage power supply at the controller and a small DC to DC converter at each string. The high voltage on the cable minimizes the current required to drive the lights. For example, if you have a string of 50 - 5Vdc pixels, the current at the string is 3 amperes maximum (power = voltage x current) or 15 watts. The amount of current varies with the voltage as shown below:

12V = 1.25 amperes

24V = 0.625 amperes

36V = 0.417 amperes

48V = 0.313 amperes

The Ethernet jacks are rated at 1.5 amperes, and normally two pins are used. Nominally for commercial equipment the connectors are derated by 15 percent to 3.0 x 0.85 = 2.5 amperes. This would be the peak current through the cable.

When choosing a DC to DC converter make sure that the module can support 3 amperes of continuous current. The LM2596 is a good example of what not to buy, it supports 3 amperes peak, with 1 ampere of continuous current.

This method should not be confused with the IEEE 802.3 Power over Ethernet (PoE) standard used for networking equipment. In most DIY holiday displays, the Ethernet cable is simply being used as a convenient multi-conductor cable to carry custom power and pixel data.

Power Over Ethernet with Pixel Extender

This is just a repeat of the above version with pixel extenders. This adds the benefits as previously mentioned of distance and ground variance.

Distributed Controllers

Modern holiday displays frequently use multiple small controllers distributed throughout the display instead of a few large centralized controllers. Placing the controller close to the pixels minimizes long data cable runs, reduces voltage drop, decreases the amount of power injection required, and often makes installation and troubleshooting easier. The availability of inexpensive ESP8266 and ESP32 Wi-Fi controllers has made this approach practical for displays of all sizes.

Wiring and Controllers

Another aspect of wiring to consider is the type of controller you buy. A controller may support 1 to 4 universes of lights or 170 to 680 pixels per output. So this would affect your layout of your wiring. For example, in the picture below, you can wire four mini-trees with each using one output, or all four using the same output. The first version allows you to use a common power supply if the trees are close, and the second requires power to be injected into the string.

Modern pixel controllers support a wide range of output capacities, from a single output for small standalone props to dozens of outputs capable of controlling tens of thousands of pixels. Choosing the proper controller often depends as much on the physical layout of the display as on the total number of pixels.