Wireless Technology FAQ‘s
To connect a wireless transmitter and a receiver, they have to be coupled. This is called pairing. The receiver is switched to pairing-mode by pressing a push button. If a signal is triggered with one or more wireless transmitters, all the transmitters will pair with the one receiver.
Transmitting and receiving reliability of wireless signals depends on various factors. In addition to technical values, e.g. transmission power of the wireless transmitter and sensitivity of radio receivers, environmental conditions are essential.
Barriers – like walls and ceilings in buildings – dampen and reflect radio waves affecting the transmission reliability. Interference of radio transmission can be caused by other radio participants when they are using the same frequency bands. Instructions for operation and installation of our wireless technology can be found in the application notes.
Barriers – like walls and ceilings in buildings – dampen and reflect radio waves. Therefore it is important to ensure that as few walls and ceilings are between the wireless transmitters and receivers, as possible. To minimize the disturbance caused by other radio participants, the radio telegrams should be transmitted several times. Instructions for operation and installation of our wireless technology can be found in the application notes.
Up to 32 wireless transmitters can be paired with one radio receiver for products using the proprietary ZF Protocol. For special applications the quantity can be increased to a maximum of 256 wireless transmitters.
To increase the transmission reliability, products with proprietary ZF Protocol transmit three redundant radio per operation. For special applications the number of telegrams can be increased to a maximum of 7 radio telegrams.
Every ZF wireless product transmits at a specific radio frequency.
Only the radio receiver working at the same frequency can receive and evaluate the signals. At the beginning of each ZF radio telegram there is a so-called preamble. This preamble is a defined sequence of data bits. Only radio receivers familiar with this preamble react to the ZF radio signal. Therefore radio signals can only be evaluated by the receivers using the same frequency and can identify the ZF radio protocol. Details on the structure of the ZF radio protocol can be found in the application notes.
Every ZF wireless transmitter includes a unique identification number (Unique IDentifier = UID). This UID consists of 32 data bits. In every radio telegram the transmitter sends to the receiver, the UID is transmitted. During pairing of the transmitter to the receiver, the receiver saves this UID. The receiver evaluates only the signals of the radio transmitter for which the UID was saved. Details on the structure of the ZF radio protocol can be found in the application notes.
For products with ZF Protocol there is no limit to the number of receivers that can be served by a single transmitter.
Currently the ZF protocol is not encrypted.
To pair a transmitter with a receiver, both devices have “to speak the same language“. This means in the field of wireless technology that both devices have to use exactly the same radio frequency, and be able to understand the protocol. Therefore the telegrams of ZF products with ZF protocols can only identify with receivers that have the ZF protocol implemented, e.g. the ZF-specified-receiver.
Basically, there are two different operating modes: Direct Control Mode (DCM) and Interface Mode (IFM). In Direct Control Mode, the module can be operated without an external controller. In this mode, the module does not have regular UART interface and the received telegrams are evaluated and four output channels are directly switched. Using the connections “Pairing”, “Reset”, and “Status LED”, a maximum of 32 RF switches can be paired. Paired switches can be deleted individually or all together. In Direct Control Mode two different modes can be selected for the pairing of RF switches. In other words, different functions (Toggle, Tipp, On, Off) can be assigned for the four output channels.
In the interface mode, the received sub telegrams of RF switches will be combined in one data telegram and sent via the UART interface.
Principally, the receiver only communicates via UART and transmits the data of each radio reception from paired transmitters directly as TTL signal, or directly on the USB port to a connected computer. A connection to an industrial bus system like Modbus must be created by means of an additional converter.
Two factors are important for selecting a frequency: the technical propagation characteristics and regularity and legal aspects. Regarding the technical propagation characteristics, it is generally correct that lower frequencies have a greater transmission range.
In addition, the propagation characteristics in buildings get better with lower frequencies. These so-called Sub-GHz-Frequencies, which means below 1 GHz, become therefore very attractive.
Due to national and international regulations, not all frequencies can be used everywhere. Only the 2.4 GHz band is based on the definition of the ITU (International Telecommunication Union), a so-called ISM Band. It is applicable all over the world. The 868 MHz frequency band is just applicable in Europe and China. In USA and Canada this band cannot be used. In this case it is necessary to use the 915 MHz band.
The task of the antenna is to radiate the produced transmission power with minimal losses into the surrounding environment (transmitting antenna) or to capture maximum transmission power (receiving antenna). As a consequence, the orientation of the antenna can have a critical effect on the radio characteristics. ZF wireless products use a wire antenna or a PCB antenna. In the case of a wire antenna, the insulated wire leads out of the switch housing. To ensure an optimal radiation it is important that the antenna is not twisted. Direct contact or indirect shielding through metal surfaces should also be avoided. This also applies for products with an integrated antenna that is directly implemented into the conducting path on the electronic board. For these products you will find information with regard to the installation in the respective application notes.
The so-called resonance frequency is a very important factor of the antenna construction. At this resonance frequency the losses from the antenna are minimal. The resonance frequency is usually the requested communication frequency and confirmed in the settings by the radio chip. The antenna was precisely designed for this frequency which means the length of the wire antenna corresponds exactly to the constructive design. Therefore, reducing the length of the antenna will lead to transmission losses and should be avoided.
The radio communication could either work from transmitter to the receiver (unidirectional) or from the transmitter to the receiver and reversed (bidirectional). A bidirectional communication is useful if the transmitter sends, providing that it receives an acknowledgement from the receiver.
The wireless switch produces electrical energy through the actuation or release of the inductive generator. The entire electrical energy produced is required for the transmission of one or more radio telegrams. No energy remains. There is no energy left for the receiving of radio telegrams. The ZF wireless switch is only capable of unidirectional communication.
The ZF wireless switch products for industrial applications and the generator module support the ZF proprietary protocol. The light switch pushbuttons support standard protocols KNX-RF, ZigBee Greenpower and EnOcean. Bluetooth, Z-Wave and WiFi are not supported.
Energy Harvesting FAQ’s
The inductive generator transforms mechanical force into electrical energy in the form of inductive voltage pulses. The energy management of the soldered electronics changes this voltage pulse through rectification and intermediate buffering into a constant operating voltage for the radio chip.
The produced electrical energy is not saved. The energy is buffered using a capacitor to ensure the availability of the radio chip for as long as possible. All available energy is used to transmit the radio telegrams.
ZF has various patents filed for Energy Harvesting. These patents include technology, design and structure of the products, as well as applications. Details of the filed patents are available here.
A tight fit of the Energy Harvester has to be ensured over the whole life time. During the assembly of the Energy Harvester in the application you must consider the guidelines for the “press-in position” to avoid possible damage, as the functionality of the Energy Harvester could be affected. During assembly the mechanical parts should not be be pinched or their movement impeded. The specified lifetime and energy yield are only ensured if the exact actuation point is observed. All relevant information is detailed in our technical specification.
The unique characteristics of the ZF energy generator are the compact size and high energy yield. The generator is therefore suitable for installation in industrial switch applications and integration for building automation applications.