steute enables users to operate different devices in parallel, without any interference. Besides numerous techniques for the automatic detection and correction of transmission errors, Bluetooth also provides additional safety by avoiding sources of interference using its frequency hopping technique.

The frequency band used by Bluetooth is divided up into 79 channels (Fig. 1), which can all be used for data transmission equally. During transmission these channels are permanently changing (Fig. 2), so that data batches with interference can be retransmitted on another channel (with no interference).

If two wireless devices use the same radio technology, they can communicate with each other and swop information. This feature, which at first sight seems extremely positive and which was the motivation behind the Bluetooth development, also involves a whole series of dangers.

Controls with wires are either firmly connected to a device or are at least coded by a particular plug or a particular configuration as belonging to one device series. If you take the cable away, you also lose this special device coding.

In order to ensure that transmitter and receiver definitely match, steute has included a configuration area in its RF/BT module where the origin and functions of each different module can be individually entered (Fig. 3).

Besides classification data like manufacturer, device type and device class (e.g. foot control), the modules configuration data can also be stored. These are the number and function of digital and analogue I/Os, operational settings like alarm duration and warning delay, as well as the baud rate of the serial interface.With these configuration data the transmitter and the receiver can establish during the connection process whether they are compatible and whether safe operation is therefore possible.

All input and output signals are handled at the edge of the board on a 26-pin connector. With a minimum of external configuration, up to 4 digital functions are possible.

Additional peripheral components can be connected via the I²C bus. In this way, up to 14 digital and 2 analogue signals can be transmitted. The maximum reaction time is 50 ms.

A serial interface with adjustable transmission speed (baud rate) is also integrated. Depending on the external configuration, asynchronous interfaces with cables (e.g. RS232) can be replaced by the RF/BT. The module requires a stabilised voltage of 2.9-3.4V. Peak power consumptionis approx. 150 mA.

In order to increase operational safety even further, steute has integrated a whole series of innovative functions. To enable Bluetooth controls to be »connected« ad hoc to any device as with a cable, steute employs a special initialisation procedure. Via an infrared path a second data channel is established, along which the transmitter and the receiver can exchange data. In addition to an individual and globally unique identification number, manufacturer and configuration details are also exchanged. In this way any incompatibility is detected before operation commences and can thus be effectively prevented.

Wireless foot controls have no cables to tie them down to one location. In order to rule out incorrect operation, in-house sensors permanently monitor the location of each control. If one is lifted off the floor, all functions are automatically blocked and a warning signal emitted. If the control is not replaced within a certain period (configurable between 1 and 60 seconds), radio transmission automatically ceases.

The wireless foot control is powered by a conventional rechargeable battery. Depending on the size of the control, different types of rechargeable batteries can be used, facilitating different operating times. In order to keep down electricity consumption, thus guaranteeing operation for as long as possible, energy-saving components were consistently employed throughout the development of the module.With a double-pedal foot control and three 1600 mAh cells, an operating time of approx. 10 hours could be achieved.

The way the battery is monitored can be adjusted to suit individual needs. From a simple digital display of the battery level or the monitoring of voltage, to complex measuring procedures with automatic actuation of a test load, different concepts suitable for all manner of applications have been incorporated.

An intelligent charging procedure additionally guarantees fast and careful charging, and thus longer battery life.

The charger used can charge all types of battery with extreme precision. Even partly empty batteries can be charged; the special charging procedure prevents a memory effect from occurring. Once the battery has been fully charged, the processor automatically switches to a careful trickle charge.

Voltage 2.9 – 3.4 V, 150 mA

• Battery level as a digital and/or analogue signal
• IR transmission signal for additional signal amplifiers
• Serial interface up to 19200 baud
• 4 bidirectional digital signals
• Position sensor
• LEDs for displaying module state
• I2C bus expands port for up to
  14 bidirectional digital signals
  2 analogue signals