via SCART or other connector, or using an RF modulator (typically on in Europe and in North America) to TV receivers that do not natively support the services. They provide outputs via composite, S-video, or component video. Many can be used with video monitors that do not have a TV tuner or direct video input. They are often part of a VCR or digital video recorder (DVR, PVR). Many home computers in the 1970s and 1980s used an RF modulator to connect to a TV set. Personal computers may be fitted with expansion cards (typically with PCI or USB interface) providing a TV tuner and digital signal processor (DSP). They may be dedicated TV tuner cards, or incorporated into a video card. These cards allow a computer to display and capture television programs. Many earlier models were stand-alone tuners, designed only to deliver TV pictures through a VGA connector; this allowed viewing television on a computer display, but did not support recording television programs. Smartphone and tablets can use a Micro USB DVB-T receiver to watch DVB-T TV. Electronic tuner An electronic tuner is a device which tunes across a part of the radio frequency spectrum by the application of a voltage or appropriate digital code words. This type of tuner supersedes mechanical tuners, which were tuned by manual adjustment of capacitance or inductance in the tuned circuits. In a more practical and everyday sense, a radio or television set which is tuned by manually turning a knob or dial contains a manual tuner into which the shaft of that knob or dial extends. Early model televisions and radios were tuned by a rack of buttons; some of the earlier types were purely mechanical and adjusted the capacitance or inductance of the tuned circuit to a preset number of positions corresponding to the frequencies of popular local stations. Later electronic types used the varactor diode as a voltage controlled capacitance in the tuned circuit, to receive a number of preset voltages from the rack of buttons tuning the device instantly to local stations. The mechanical button rack was popular in car radios of the 1960s and 1970s. The electronic button rack controlling the new electronic varactor tuner was popular in television sets of the 1970s and 1980s. Modern electronic tuners also use varactor diodes as the actual tuning elements, but the voltages which change their capacitance are obtained from a