GB2054301A

GB2054301A - Generating digital signals; ADC with non-volatile input

Info

Publication number: GB2054301A
Application number: GB8019602A
Authority: GB
Original assignee: GEC Elliott Automation Ltd
Current assignee: Roadside Technology Services Ltd
Priority date: 1979-06-19
Filing date: 1980-06-16
Publication date: 1981-02-11
Also published as: GB2054301B

Abstract

An apparatus for generating any selected one of a plurality of digital signals comprising: a non- volatile setting means (1) whose setting is continuously variable through a range; detecting means (3, 5, 7) for determining in which of a said plurality of discrete bands within said range said setting means is set; output means (5) connected with the detecting means for producing a different digital signal for each said detected band; and indicating means (9, 11) connected with the detecting means for indicating the detected band. <IMAGE>

Description

SPECIFICATION Apparatus for generating selected digital signals This invention relates to apparatus for generating selected digital signals.

Such apparatus is used, for example, for setting desired numbers into digital devices, e.g. the number which makes up a batch into a batch counter or the time at which alarm signals are required into a timing device.

One known form of such apparatus comprises a non-volatile multi-position setting means e.g. a thumb wheel switch, which is operated into a particular position according to the required number, and an associated coding means which generates a digital signal corresponding to the number selected by the setting means. Such an apparatus is expensive but has the advantage that the selected number is not lost on power failure.

Another known form of such apparatus comprises means for causing the device display to step rapidly through the possible number settings until the required number is reached. The number reached is then stored electronically and the device display returns to its normal function. This arrangement is relatively inexpensive but the selected number is lost on power failure.

It is an object of the present invention to provide an apparatus for generating any selected one of a plurality of digital signals in which the selected signal is not lost on power failure and which can be relatively inexpensive.

According to the present invention an apparatus for generating any selected one of a plurality of digital signals comprises: a nonvolatile setting means whose setting is continuously variable through a range; detecting means for determining in which of a said plurality of discrete bands within said range said setting means is set; output means connected with the detecting means for producing a different digital signal for each said detected band; and indicating means connected with the detecting means for indicating the detected band.

In an apparatus according to the invention the detecting means is preferably arranged so that, after initial detection of the band within which the setting means is set, the width of said band is increased to reduce the possibility of the setting of the setting means moving outside said band as a result of drifting of the setting of the setting means.

The advantage of the invention lies in the fact that the setting means can be an inexpensive analogue variable device such as a potentiometer. The detecting means and output means are suitably constituted at least partly by a microcomputer. Where the apparatus is required to select from a large number of signals the apparatus may comprise a single microcomputer associated with a number of setting means.

It will be appreciated that the microcomputer may form part of a digital device which uses the selected signal. Similarly the indicating means may form part of a digital device which uses the selected signal.

One apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawing in which:~ Figure 1 is a block schematic diagram of the apparatus; and Figure 2 is a diagram illustrating the operation of the apparatus.

The apparatus is adapted to generate any selected one of ten digital signals.

Referring to Fig. 1, selection of a signal is made by variation of the position of the wiper of a potentiometer 1 connected across a voltage V.

The potential at the potentiometer wiper is applied to a first input of a comparator 3 whose second input is derived from a microcomputer 5 by way of a digital to analogue converter 7.

The microcomputer 5 is arranged to determine in which of ten discrete spaced bands 13 in the range 0 to V volts (see Fig. 2) the potential at the potentiometer wiper lies. To this end the microcomputer 5 applies to the converter 7 in turn a succession of 8-bit binary words so as to supply to the second input of the comparator 3 a succession of voltages corresponding to the limits of the discrete bands, the voltages being applied in order of increasing magnitude. The 8-bit words applied immediately before and after the comparator output changes state indicate in which band, or gap between bands, the wiper potential lies.

Having determined the band in which the wiper potential lies the microcomputer 5 generates a predetermined corresponding digital signal.

To indicate the selected signal the microcomputer 5 operates a display device 9 via a driver means 11 to display an appropriate symbol e.g. one of the digits 0 to 9.

When the wiper potential lies in a gap between bands the microcomputer 5 blanks out the display or flashes the display symbol corresponding to the band above or below the gap, as desired.

To allow for drift in the potentiometer wiper potential, e.g. due to variation of the voltage V or temperature, after determination of the band in which the wiper potential lies the upper and lower limits of the band are respectively increased and decreased by an amount larger than any likely drift, but without encroaching on the adjacent bands. For example with bands of width 0.2 volts centred on potentials of 1, 2 and 3 volts etc., the width of the detected band may be increased to 0.8 volts after detection.

As shown in Fig. 2, the top and bottom bands are preferably made relatively wide to allow for manufacturing tolerances in the end settings of the potentiometer wiper.

The microcomputer 5 may be arranged to respond to a change in the wiper position by generating the appropriate new output signal and display corresponding to the new wiper potential. Alternatively, to guard against tampering with the wiper setting the microcomputer 5 may be arranged to reject any change in wiper potential to a value outside the detected band and operate an alarm e.g. by flashing the display. With such an arrangement a reset control is provided for use when it is desired to select a new output signal.

It will be appreciated that, while the selected digital signal generated by microcomputer 5 may be used solely to operate the display, the selected signal will more commonly constitute an input to an associated digital device (not shown). In such a case the microcomputer 5 may form part of the associated device, as may the display device 9, and the selected signal may be used by the microcomputer as an input in performing its role as part of the associated device.

In such a case the only extra components required to input a selected signal are the potentiometer 1, the comparator 3 and the converter 5, and in some cases only the potentiometer 1. Furthermore, the potentiometer 1 is not required to be closely toleranced and no associated scale or calibration is required. It will further be appreciated that on power failure, the selection of a digital signal is retained so long as the wiper position is not disturbed.

By using two or more potentiometers and associated display devices co-operating with a common microcomputer on a time multiplex basis, selection from a large number of possible signals may be effected. The display of multi-digit numbers is one example of such an arrangement, a separate potentiometer and display device being used for each digit.

It will be appreciated that in an arrangement according to the invention the setting means may be any non-volatile continuously variable means. However potentiometers are probably at present the most inexpensive such setting means.

Furthermore the detecting means may be arranged to detect a quantity other than voltage. It may for example be arranged to determine the resistance between a potentiometer wiper and one end of the potentiometer.

It will also be appreciated that whilst the indicating means in an apparatus in accordance with the invention will normally comprise a visual display means, the indicating means could alternatively or additionally provide another kind of indication e.g. aural.

Claims

1. An apparatus for generating any selected one of a plurality of digital signals comprising: a non-volatile setting means whose setting is continuously variable through a range; detecting means for determining in which of a said plurality of discrete bands within said range said setting means is set; output means connected with the detecting means for producing a different digital signal for each said detected band; and indicating means connected with the detecting means for indicating the detected band.

2. An apparatus according to Claim 1 wherein the detecting means is arranged so that, after initial detection of the band within which the setting means is set, the width of said band is increased to reduce the possibility of the setting of the setting means moving outside said band as a result of drifting of the setting of the setting means.

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3. An apparatus according to Claim 1 or Claim 2 wherein the setting means comprises a potentiometer.

4. An apparatus according to Claim 3 wherein the potentiometer is connected across a potential source and the detecting means is responsive to the potential at the variable tapping point of the potentiometer.

5. An apparatus according to any one of the preceding claims wherein the detecting means comprises comparator means having a first input to which the output of the setting means is applied, and a second input to which a succession of signals corresponding to the limits of the discrete bands are applied, the comparator means output indicating the ones of said succession of signals which lie nearest above and below the setting of the setting means.

6. An apparatus according to Claim 5 wherein said succession of signals are applied to said comparator means in order of magnitude so that said nearest signals are the signals applied immediately before and after the comparator means changes state.

7. An apparatus according to Claim 5 or Claim 6 wherein the comparator means is an analogue signal comparator and said succession of signals are supplied to the comparator means via digital to analogue converter.

8. An apparatus according to any preceding claim wherein each said discrete band is spaced from the or each adjacent band.

9. An apparatus according to Claim 8 wherein the indicating means is arranged to indicate when the setting of the setting means lies in a gap between adjacent discrete bands.

10. An apparatus according to Claim 9 wherein the indicating means is a visual display means and indicates that the setting of the setting means lies in a gap between adjacent discrete bands by flashing the display corresponding to the band above or below the gap, or blanking out the display.

11. An apparatus according to any preceding claim wherein the discrete bands nearest the ends of said range are wider than the other bands.

12. An apparatus according to any preceding claim wherein, after initial detection of the band within which the setting means is set, the output means requires to be reset before responding to a change in the setting of the setting means outside that band.

13. An apparatus according to Claim 12 wherein, before being reset, the output means operates an alarm in response to the setting of the setting means moving outside that band.

14. An apparatus according to any preceding claim wherein the detecting means and output means are at least partly constituted by a microcomputer.

15. An apparatus for generating any selected one of a plurality of digital signals substantially as hereinbefore described with reference to the accompanying drawings.