How to safely pass the SPI signal over long distances? – The Symmetrizer
Almost all LED strips are using TTL signal (data, GND) for communication. This signal is very sensitive to pick up noise, crosstalk and especially to ground shift problems. With standard TTL signal, you can’t use longer distances between LED Controllers and LEDs or LEDs and LEDs.
For typical LED installation like on the picture above, you are not able to use 1 controller. You need at least 2. That means you can’t use the whole potential of LED controllers, what costs you money and time. Check the solution #2. It looks easy, so logical and saves some money :).
Differential data
The solution for passing SPI for long-distance is to use differential signal data, which are not referred to GND but to negative data (D- / B).
Differential data transmission advantages
- High immunity to crosstalk
- High immunity to noise
- Ground noise rejection
- Longline length (100m+ can be normally achieved with twisted pair cable)
Our recommendation for differential data transmission is to use a twisted pair cable.
Not all LED controllers can send symmetrized data / or differential data transmission. However, our LED Ethernet Controller 3, SPI Matrix and LED Ethernet Powered are able to do so with no difficulties. To convert Differential signal to TTL signal, you’ll need The Symmetrizer (symmetry board).
THE SYMMETRIZER specs
- Convert Differential signal to TTL level (de-symmetrizer)
- Convert TTL level to Differential signal (symmetrizer)*
- Wide power supply range 5-24V by default
- POWER indicator LED
- TTL data level H/L LED indicators
- Overvoltage / ESD protections on all lines & power included
*setting by solder pad needed
Standard connection usage diagram of The Symmetrizer
Note: Please note that LEC3 controller (SPI Matrix) has a built-in differential signal buffer (symmetrizer) which can be enabled in the web configuration tool. Using this you need THE SYMMETRIZER only on LED strip/pixel side.
For long cable runs use twisted pair cable (e.g. CAT5e) where you have to connect signals A & B to one twisted pair! Connect all remaining wires (and shielding if exists) to GND on both ends. Using power cable for longer signal runs is also possible, but not recommended.
