- Product range
As with other contemporary contactless switches, RAFI’s magnetoresistive keyboard switches were mostly likely created to be able to directly drive logic circuitry without the problem of contact bounce. These switches are described in German patent 7024643U filed in July 1970, and US patent 3668596 filed in October 1970. The oldest reference to the product range is an advertisement in Electronics magazine in October 1971.
The design as described in the patents uses a magnet (with ALNICO 450 given as a successful magnetic material) to control the resistance of a semiconductor junction, whose resistance increases when the magnetic flux passes through it. A separate logic element is placed within the switch to interpret the resistance and provide suitable output. The resistance is said to increase by a factor of five when the switch is actuated. The principle of magnetically-controlled resistance pre-dates switching, and was previously described in RAFI patents from 1966 for non-keyboard switches.
The series offered a choice of positive and negative logic, and three different operating voltages (5 V, 12 V and 24 V). Momentary and alternate action were offered, as was illumination. Mechanical switches were also included in the range, although these are not depicted.
Non-illuminated types have a square section keystem. Illuminated types have a central lamp surrounded by a large, hollow, square section plunger.
These switches were only current for around three years, before RAFI introduced RC 72 Hall effect switches.
Force and travel are given as “Operating stroke” and “Operating force”, so the forces given appear to be the total travel force.
|Total travel force||70 cN max (momentary)||150 cN max||180 cN max|
|100 cN (alternate action)|
|Lifetime (momentary)||More than 100 million||More than 10 million||50 thousand|
|Lifetime (alternate action)||50 thousand|
The part numbers take the following format:
The following parts were given in the 1972 catalogue:
|Part number||Type||Action||Keystem||Operating voltage||Output||Logic|
|3.11705.001||Non-illuminated||Momentary||0°||5 V 50 mA||Transistor||Negative|
|3.11712.001||12 V 50 mA||Transistor||Negative|
|3.11724.001||24 V 40 mA||Transistor||Negative|
|3.11805.001||Alternate action||5 V 50 mA||Transistor||Negative|
|3.11812.001||12 V 50 mA||Transistor||Negative|
|3.11824.001||24 V 40 mA||Transistor||Negative|
|3.11705.101||Momentary||13°||5 V 50 mA||Transistor||Negative|
|3.11712.101||12 V 50 mA||Transistor||Negative|
|3.11724.101||24 V 40 mA||Transistor||Negative|
|3.11805.101||Alternate action||5 V 50 mA||Transistor||Negative|
|3.11812.101||12 V 50 mA||Transistor||Negative|
|3.11824.101||24 V 40 mA||Transistor||Negative|
|3.16705.001||Illuminated||Momentary||0°||5 V 50 mA||Transistor||Negative|
|3.16712.001||12 V 50 mA||Transistor||Negative|
|3.16724.001||24 V 40 mA||Transistor||Negative|
|3.16805.001||Alternate action||5 V 50 mA||Transistor||Negative|
|3.16812.001||12 V 50 mA||Transistor||Negative|
|3.16824.001||24 V 40 mA||Transistor||Negative|
The mechanical switches use illustrated as having an illuminated plunger in all versions.
The dummy switches use standard (non-illuminated) plungers.
- RAFI contactless keyboards advertisement, Electronics, Vol. 44 No. 21, October 11 1971 (scanned for or by WorldRadioHistory.com
- RAFI Contactless Keyboards (excerpt from the Contactless Components 103-60 catalogue, hand-marked “8/72”)