Electrically-operated dispensing modules capable of dispensing small volumes of a viscous liquid at high operating frequencies and reproducibly among successive dispensed volumes of viscous liquid without the occurrence of stringing. The device comprises an external structure, in which external structure a first and a second pressure-influenced bellows device is mounted, where the first and second pressure-influenced bellows devices are in fluid connection with each other via a support device. 02 Hz-5 Hz and wherein the ratio between the first AC frequency and the second AC frequency is 2 or more. Thus, the rays distributed by the lamp include both red infrared rays and white visible rays, and therefore a red color is not particularly noticeable. The output node is connected to the input of the demultiplexer. The method locates R-waves by searching for maximum slope values and cycle lengths that satisfy certain threshold values.