16 switche med 16 taster
Mål, switch: 15x15mm (totalhøjde: 28mm)
Mål, tast: 18x18mm (totalhøjde, monteret på switch: 33mm)
Micro Switch offered a variety of output options. Sink level, sink pulse, source level and logic scan were all available with SW and SN series and are explained on that page, as well as briefly below. (It is possible that logic scan was introduced with SD and then adapted for SW; the sequence of events is not yet known.) Two additional output types were introduced with SD Series, timed repeat and three-terminal, covered on this page below.
No documentation has been found for these. These have been sighted in keyboards, but at present there are no documented examples of how they behave, and no such switches have been found for sale.
Three-terminal switches date to around 1979 and are a special adaptation of the logic scan type that is designed to greatly reduce the power consumption of a keyboard. They function either as source level or logic scan. The ground terminal is renamed “input”, and when the input is high or disconnected, there is no potential difference across the switch and it is inoperative. When the input is pulled low, the switch powers up and the output reflects the key state (low when inactive, high when active). If input is hard-wired to ground, the switch functions as a source level type. When input and output are connected into a matrix, the switches are only powered up when their row is active. A standard logic scan switch requires 3.5 mA current when idle, and for 100 switches there would be a total of 350 mA of idle current. The ability for switches in active matrix rows to be powered off saves a considerable amount of power. There is only one output on these sensors, as they are targeted at matrix keyboards, while the original sensors are designed for two-of-N wired encoding which requires dual outputs per switch
Keyboards featuring a Hall-effect device, magnet and plunger in each keyswitch position (Fig. 1) are available from Honeywell’s Microswitch Division, which recently introduced a three-terminal Hall-effect module that helps reduce power consumption by a reported 60%. The module’s “scan” input shares a pin with the negative power supply, so deselected modules draw no current. An on-board µP activates only eight keys at a time. The modules themselves come individually or in completely built, intelligent keyboards.
Although figure 1 depicts SW Series, SD Series is implied here (as three-terminal SW is not known), and this gives a rough idea of when the three-terminal types were introduced. The diagram below shows how the switches operate:
The diagram above is not an official Micro Switch diagram, but rather a traditional SW Series diagram adapted to depict a three-terminal sensor, for consistency with the SW-era diagrams. The faint portion on the right shows how the switch is wired into the surrounding circuit to form the logic scan arrangement; without this portion, it is a single-output source level sensor.
Three-terminal sensors are physically smaller and have tighter pin spacing, and cannot be swapped with any other SD sensor type: