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Siemens Hall sensor ICs

Siemens produced a range of different Hall effect sensor ICs. These appear to be the Hall sensors used in RAFI switches, before RAFI started using HFO Hall ICs instead. As RAFI RS 74 C was introduced around 1975, that suggests that at least part of this range was in production at that time.



Wolfram Zucker in Germany provided some photographs of various Siemens Bauteile Service price list pages. Having now been able to identify the origin of the PDF in the Documentation section—and along with it, a description of its contents—we now also have the dates of the details it contains. From this, we get the first indications of the product history:

It seems that Siemens had discontinued most of the range by 1985, including the types with enable input that RAFI were using. Some of the models seem to have had very short production lives. This may indicate why RAFI switched over to using HFO’s products instead. Wolfram conjectures that the S-variants represent items that do not meet the required tolerances, and are downgraded to lower-specification products rather than be discarded; this may relate to the coloured-stripe markings and why they are always accept a lower supply voltage than the non-S base model. This may also indicate why, from SAS 231 onwards, the S-variants are not given in the price lists. Unfortunately, Siemens practice seems to have been inconsistent and there is no definitive pattern to the markings.

Product range

The following table lists all known types. The Documented column lists the range of years within which each type has been found in Siemens literature. It does not indicate when each type entered production or was discontinued; ranges are used only to conserve column space. Years marked with an asterisk (*) indicate products not intended for new development (products that will be ending production).

Model Type Terminals Temperature range Supply voltage Marking Documented
SAS 201 S2 Digital, dynamic VCC, GND, dual outputs Not yet known 1977, 1978
SAS 201 S4
SAS 211 S2 Digital, static
SAS 211 S4
SAS 221 S2 Digital, unspecified VCC, GND, Q and Q̅ outputs
SAS 221 S4
SAS 231 W Linear, bipolar VCC, GND, zero point, sensitivity, output, unused 0–70 °C 4.75–15 V None 1981–1985*
SAS 231 L Linear, bipolar (MIKROPACK) Blue/green 1982, 1985*
SAS 241 Digital, dynamic, open collector, bipolar VCC, GND, dual outputs 0–70 °C 4.75–18 V SAS 241 1981–1983, 1985*
SAS 241 S4 4.75–5.25 V White 1982, 1985*
SAS 250 Digital, static, open collector, bipolar −40–125 °C 4.5–27 V SAS 250 1982, 1983, 1985*
SAS 251 0–70 °C 4.75–27 V SAS 251 1977–1985
SAS 251 S4 4.75–5.25 V SAS 251 S4 1982
SAS 251 S5 4.75–18 V Orange 1982
SAS 261 VCC, GND, enable input, output 0–70 °C 4.75–18 V Blue 1981, 1982, 1985*
SAS 261 S4 4.75–5.25 V Green 1982, 1985*

Most types use the same IC package, 10 mm wide, 6.5 mm tall and 2.1 mm deep. SAS 201 has 0.3 mm extra leg length, with four terminals. SAS 231 has six terminals instead of four, and uses two separate form factors: a miniature 3.9 × 4 × 2 mm package, and a MIKROPACK version. Most if not all models are bipolar: they are switched on by the south pole, and then switched off by the north pole. (Unipolar Hall sensors simply detect the presence of the south pole.)

Some SAS ICs are marked by nothing other than a line drawn across the front, without branding or any mention of the model number or production date. The colour of the line indicates the model. OleVoip’s lone RS 76 C switch has such a sensor, marked with merely an orange stripe. This indicates that it is SAS 251 S5. Wolfram Zucker has a collection of Siemens Hall ICs for sale; he has helpfully posted photos on his analog ICs page of various SAS types, and although most are blank or marked normally, some SAS 261 chips are marked with only a blue stripe, which is the expected colour from the catalogue.


Some models were copied by VEB Halbleiterwerk Frankfurt (Oder):

Siemens model Signals Supply voltage HFO model
SAS 251 Dual in-phase outputs 4.75–27 V B 451 G
SAS 251 S4 4.75–5.25 V B 453 G
SAS 251 S5 4.75–18 V B 452 G
SAS 261 Single output, enable input 4.75–18 V B 462 G
SAS 261 S4 4.75–5.25 V B 461 G


In 2013, Christoph Kessler produced a PDF containing portions of three Siemens documents:

This shows up on other sites, and it seemed impossible to find where it originated. Now that the source is known, it remains archived here.