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Browse Prior Art Database

1-PIN GAUGE DRIVER

IP.com Disclosure Number: IPCOM000007275D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-11
Document File: 3 page(s) / 128K

Publishing Venue

Motorola

Related People

John Pigott: AUTHOR

Abstract

Vehicles use small air-core gauges as oil-, temperature-, or fuel-gauges. Typically, these auto- motive air-core gauges have less than 90" of pointer movement, which is insufficient for some applica- tions because of the effects of bearing friction and because some vehicle styling options require more movement.

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MO7VROLA Technical Developments Volum@ 23 October 1994

l-PIN GAUGE DRIVER

by John Pigott

  Vehicles use small air-core gauges as oil-, temperature-, or fuel-gauges. Typically, these auto- motive air-core gauges have less than 90" of pointer movement, which is insufficient for some applica- tions because of the effects of bearing friction and because some vehicle styling options require more movement.

  Usually, these gauges do not have to be as accu- rate as standard 270" gauges (e.g., speedometer and tachometer), but to achieve more than 90" of pointer movement a similar drive circuit is required because operation on three quadrants is required (from < 0" to z 90").

  l-pin gauge drivers are also useful because of the saving in IC pins used. Many instrument clus- ters use four of these smaller gauges. Using a l-pin instead ofa 3-pin gauge can save 8 pins per package.

HOW IT WORKS: [

  The combination of RTOP, RMID and RBOTTOM biases the top of one coil slightly below Vdd, and the bottom of the other slightly above ground. Typical values would be 90% and 10% of Vdd respectively.

  The drive voltage can drive the junction of the coils from near ground potential up to Vdd poten- tial. When the drive voltage is greater than the volt- age at the top of the upper coil, the current in this coil is reversed, and the needle points at an angle less than 0".

Similarly, when the drive voltage is close to OV the current in the lower coil is reversed, and the

NEW SOLUTION:

This new circuit requires just a single IC pin to achieve greater than 90" ofpointer movement:

  The l-pin gauge driver achieves greater than 90" of pointer movement because the resistors bias the ends of the coils at voltages between the rails. This allows the driver circuit to easily reverse the direc- tion of current flow in the coil, thus driving the pointer into another quadrant.

26 Q Motorola. 1°C. ,994

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MOIY)ROLA Technical Developments Volume 23 October 1994

needle points at an angle greater than 90". Thus pointer movement in three quadrants is achieved.

  The control circuit drives the junction voltage as a fraction of Vdd determined by the desired pointer angle. The values of RTOR RMID and RBOTTOM determine how much movement is allowed.

There are two other features ofthis circuit:

  1) For certain values of the external resistors, a fairly linear pointer indication vs. drive voltage can be obtained. This can be useful in simple systems where the accuracy is sufficient and it is not desired to have the extra complication of a ROM lookup table. In any case, the nearly li...