GB2090509A - Device for reading digital waveforms - Google Patents

Abstract

The present invention concerns a device for reading a plurality of multi level digital waveforms represented one below the other including calculation means responsive to the relative movement of a reading head (1) transverse to the waveforms to generate in digital form data representing the levels of the waveforms. The calculation means (3) are operative to determine the level of the waveforms by comparison of the spacing between the lines of the waveforms and at least one reference level. The results of the waveform level determination may be used by the computer to reproduce accurately the waveforms or to generate data in suitable form for test equipment. <IMAGE>

Description

SPECIFICATION Device for reading digital waveforms The present invention concerns a device for reading electronic waveform diagrams and converting them to electronic signals suitable for input to a computer. Typical uses of the device would be in producing good quality drawings from freehand sketches of waveform diagrams and providing data for automatic test equipment.

The traditional procedure in the design of electronic circuits is for a design engineer to produce his design in sufficient detail for a prototype to be made. Tests carried out on the prototype may lead to modification of the design before it is made in final form. The increased complexity expected of modern electronic designs requires sophisticated test aids to be used in the evaluation of the prototype so that its responses can be monitored. A problem exists in setting up the test equipment, often computer based, to produce the required stimulii, particularly if changes are required during the evaluation phase.

The designer can often describe the required stimulii as two-level or binary waveform diagrams. Currently these diagrams are not readily translatable into machine language compatible with the test equipment. This causes problems in that entry of the data can be cumbersome and, for prototype testing, it is often a prohibitive task requiring manual code conversation and keyboard typing.

The present invention has for an object to provide a device for obviating or at least reducing the above problems.

Accordingly the present invention consists in a device for reading a plurality of multilevel digital waveforms represented one below the other including calculation means response to the relative movement of a reading head transverse to the waveforms to generate in digital form data representing the levels of the waveforms.

Preferably the calculation means determine the level of the waveforms by comparison of the spacing between the lines of the waveforms and at least one datum.

In accordance with a feature of the invention the calculation means may include a source of clock pulses and at least one counter to which the pulses are applied when the reading head detects a line which may be a waveform or a datum.

The counter may be reversible so as to count in opposite directions in response to each passage of the reading head over a line. In such a case the calculation means may include a circuit for detecting the sign of the count in the counter at appropriate times so as to derive the level of the last waveform crossed by the reading head.

Alternatively the calculation means may include a pair of counters one or the other of which is supplied with clock pulses in accordance with the position of the reading head relative to the waveforms and the or each datum, and comparator means for comparing at appropriate instants the counts in the counter so as to derive the levels of the waveforms traversed by the reading head.

It is also possible for the calculation means to comprise a pair of generators generating constantly varying voltages one or the other of which generators being switched on in accordance with the position of the reading head relative to the waveforms and the or each datum, and comparator means for comparing the levels of the voltages generated at appropriate instants to derive them levels of the waveforms traversed by the reading head. Yet another possibility is that the calculation means may comprise a digital processor programmed with an appropriate algorithm so as to derive from the output signal of the reading head the levels of the waveforms traversed by the reading head.

In order that the present invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a device for reading digital waveforms constructed in accordance with the present invention; Figure 2 shows a typical handrawn waveform diagram; Figure 3 shows a diagram of Fig. 2 with added reference lines together with the path of a reading head; Figure 4 shows in greater detail the electronic circuitry of the device of Fig. 1, Figure 5 shows counter values reached in a modification of the reading device described with reference to Figs. 1 to 4., Figure 6 shows a flow diagram for an algorithm for use in a digital processor to carry out the present invention, and Figure 7 shows a typical freehand sketch of waveform levels which can be read using the algorithm of Fig. 6.

Referring now to Fig. 1 of the accompanying drawings there is shown a reading head 1 which can be held in a users hand and wiped or passed over a waveform diagram drawn on a sheet 2.

The waveform diagram may be a freehand sketch. The reading head 1 may, for example, be a well known bar code reader. The output of the reading head is taken to an electronic circuit 3 shown in greater detail in Fig. 4 of the accompanying drawings. The circuit 3 processes the signal from the reading head 1 into suitable form so that it can be inputted to a computer 4.

The computer 4 may be programmed so as to generate a computer-drawn diagram of the waveform scanned by the reading head, or to generate data in suitable form for test equipment.

In operation of the device shown in Fig. 1 the waveform on sheet 2 is examined by wiping or scanning the reading head manually over the diagram to determine whether the portion of the diagram being scanned at any moment is at a "high", or a "low" level. Each part of the waveform is examined sequentially and a decision for each part is presented by the circuit 3 to the computer 4.

Fig. 2 shows a typical waveform diagram in simplified form, the diagram containing three waveforms each of which varies between a high level, marked "T", and a low level marked "0".

In order to utilise the more detailed circuits shown in Fig. 4, reference lines marked R1, R2 and R3 are added to the waveform diagram of Fig. 2 as is shown in Fig. 3. This figure also shows a typical path for the reading head 1 over the diagram, this path being marked P.

Referring now to Fig. 4 of the drawings it can be seen that the output from the reading head 1 is taken to a control circuit 10. The reading head 1 gives a pulse each time it crosses a line and the control circuit 10 decides whether the pulses from the reading head 10 were caused by crossing a reference line R or a waveform. As shown in Fig. 3, the active portion of the path P of the reading head is shown in unbroken lines whilst the inactive portions of the path, i.e.

those portions where the reading head is returning are shown in dotted lines. The operation of the reading unit may be controlled by a suitable switch which renders it unresponsive during the inactive portions of the scanning path. As shown during each active portion of the path P the first line crossed by the reading head 1 is a reference line or datum, the second a waveform, the third a reference line and so on.

When the first reference line R1 is crossed the control circuit 10 receives a pulse from the reading head 1 and clears a pair of counters 11 and 1 2 and a latch 1 3. Furthermore a switch 14 is operated so that pulses from a clock generator 1 5 are fed to counter 11. The counter 11 counts the clock pulses from the geenerator 1 5 until the control circuit 10 detects that the reading head 1 has crossed the next line which is known to be a waveform line. On the crossing of the waveform line the switch 14 is changed so that the clock pulses are routed to the counter 1 2 instead of the counter 11.Counter 1 2 then counts the pulses from the generator 1 5 until the reading head crosses the second reference line R2. If the waveform line was low counter 11 will have counted fewer pulses than counter 1 2 and, conversely, if the waveform line was high the count in counter 11 will be greater than that in counter 12. This result is detected by comparator 1 6 which loads the result of the comparison into a store 1 7. This result is now available to the computer 4 whilst the circuitry repeats the operation for the next line of scan.

In a modification of the circuit shown in Fig. 4 the two counters 11 and 1 2 may be replaced by a single reversible counter which counts in one direction on the passage of the reading head over a reference line and in the other direction on passage of the reading head over a waveform line. Thus the final state of this counter when the reading head reaches the next reference line, either positive or negative, will denote the high or low position of the waveform line between reference lines.

In another modification of the embodiment described with reference to Figs. 1 to 4 the clock generator 1 5 and the counters 11 and 1 2 may be replaced by analogue circuits which produce incrementing or decrementing levels of voltage which are compared by suitable comparator means at the moments at which the reading head crosses the references lines lying on either side of a waveform.

In a further modification of the embodiment described with reference to Figs. 1 to 4 the necessity of providing a reference line for each of the waveforms is avoided.

Thus, only a single reference line may be provided beneath the first waveform. When the reading head crosses this single reference line the circuitry of the device is switched on and the position of other reference lines computed from the crossing times of the waveform lines as detected by the reading head during its movement.

Thus when the reading head is wiped across the drawing containing the waveforms the value reached by a counter which starts to count in response to the reading head crossing the base reference line will be a function of the frequency of the clock pulses, the speed of the wipe and the position of the next line crossing as detected by the reading head.

Thus the clock frequency can be set such that for a predetermined rate of movement of the reading head that successive transitions of the reading head over the base reference line and a low level waveform will produce a count of O to 30 units, a transition between the reference line and a high level waveform produces a count of 70 to 100 units, and that there is a gap of 20 to 30 units between waveforms. Such a range of values will permit some wander of the lines which may well occur if they are drawn freehand.

Starting from the base reference line, if the first crossing occurs with a ccounter value 0 to 30 the level of the waveform is low, if it occurs with a counter value of 70 to 100 the level is high.

If only two levels are being detected the second crossing will result in one of two sets of values as set out in the following table.

As can be seen from the table the range of values are discrete and the second level can be determined without the presence of an intermediate reference line.

In a further modification particularly suited to determining the levels of a large number of waveforms with a single reference line or datum that may be arranged that the counter is reset after each detected waveform.

Fig. 5 of the accompanying drawings shows the counter values which could be used to indicate the presence of high or low waveforms. It will be appreciated that in this arrangement it will be necessary for the counter to be reset at an appropriate instant after the reading head has passed the base reference line and the detected waveform whether the latter be high or low.

Such an instant would correspond to the presence of a second reference line if the latter were present. One method of determining the instants at which the counter is reset is the provision of a learning algorithm in a digital processor to which the data derived from the reading head is supplied and which takes note of the total number of transitions over lines, namely the base reference line and the waveforms, made by the reading head so as to deduce suitable average values for the presence of notional reference lines lying between the waveforms being read.

It will of course be appreciated that the specific embodiment described with regard to Figs. 1 to 4 and the modifications thereof also described herein could be replaced by a suitably programmed digital processor containing an algorithm for determining the levels of the waveforms scanned by the reading head.

The digital processor utilising the algorithm includes a counter with the count rate of the counter normally related to units of time which can in turn be related to the crossing of the lines of the diagram by the reading unit. Thus in relation to an expected rate of movement of the reading head across waveform diagrams the counter values will represent distances and in the diagram of Fig. 7 and in the following table a counter unit approximates to a millimetre on the diagram., CROSSING NO. COUNTER VALUE (A) TEST LEVEL (B) TEST (C) DECISION (D) O O (REF) 1 4 5.9 A < B 'O' 2 16 17.7 A < B 'O' 3 33 29.5 A > B '1' 4 42 41.3 A > B '1' 5 49 53.1 A < B 'O' 6 59 (REF) As can be seen in Fig. 7 the diagram contains upper and lower reference lines 20, 26 between which extend five waveforms 21, 22, 23, 24 and 25 the levels of which are to be calculated.In carrying out a calculation of the levels of the five waveforms it is first necessary for the processor to obtain the number of lines to be crossed by the reading head together with the total spacing occupied by the waveforms. In the present example this spacing is the distance between references lines 20, 26. Once the number of wavelines and the spacing between the two references lines is known a set of notional test levels T1, T2, T3, T4 and T5 can be calculated against which the actual line crossings can be compared to arrive at the necessary decisions as to the values of the waveforms. The number of lines on the waveform diagram, including the reference lines, can either be entered into the processor before a scan or determined by a preliminary scan, or simply stored during the main scan with the user of the device indicating the end of a scan.Thus, in the following table it can be seen that the actual counter values for each line crossing are given in column A. The final counter reading gives the distance between the two references lines 20 and 26 so that with five waveforms the average waveform separation is 11.8 counter units.

The first test level T1 is set at half the waveform separation on the assumption that a "O" value will be below this level and a "1" value above this level. Accordingly the first test level T1 as shown in the table is at counter reading 5.9.

Similarly test level T2 is calculated to be 11.8 + 11.8/2 or 1 7.7 counter units and level T3, 2 x 11.8 + 11.8/2 or 29.5 counter units. Similar calculations can be made to provide a test level for every waveform crossed by the reading head. Naturally the number of waveforms which can be handled can vary from 5. In the present example the test levels are set out in column B of the table.

Once the test levels have been calculated the processor then carries out a simple comparison between the actual waveform crossings and the calculated test levels to assign a value to each waveform.

The results of the tests are shown in Column C of the table and the final decision in Column D.

It will be appreciated that the digital processor referred to in the above description can be any type of programmable computer but could also include other devices such as integrated circuit testers and automatic test equipment which include or use calculating or control circuits of the computer type.

It will also be appreciated that the description given so far has been directed to waveforms having two levels. However it will be a relatively simple matter to alter the device described, or the modified versions of the device described or in fact a computer algorithm so as to be capable of distinguishing between the levels in waveforms having more than two levels such as "high", ''low" or "intermediate" levels.

Furthermore the preceding description has been given on the assumption that the reading head is either a known bar code reader or a similar device which incorporates its own light source.

It will be appreciated that known bar code readers are normally used to read many lines over short distances.

The application of bar code readers as described hereinbefore requires the reader to read fewer lines at substantially greater spacing than is normal. Accordingly it may be found necessary to add some circuitry to the output of a standard reader to suppress spurious "crossings" due to marks in, or on, the paper. Alternatively, the sensitivity of the reader could be reduced. However it is equally possible for the waveforms to be drawn on a translucent sheet which is illuminated from the rear. In such a case the reading head may be a simple hand held photodetector possibly provided with a suitable on-off switch.

Claims (10)

1. A device for reading a plurality of multilevel digital waveforms represented one below the other including calculation means responsive to the relative movement of a reading head transverse to the waveforms to generate in digital form data representing the levels of the waveforms.

2. A device according to claim 1, wherein the calculation means are operative to determine the level of the waveforms by comparison of the spacing between the lines of the waverms and at least one datum.

3. A device as claimed in claim 2, wherein the calculation means include a source of clock pulses and at least one counter to which the pulses are applied when the reading head detects a line which may be a waveform or a datum.

4. A device as claimed in claim 3, wherein the counter is reversible so as to be capable of counting in opposite directions in response to each passage of the reading head over a line.

5. A device as claimed in claim 4, wherein the calculation means include a circuit for detecting the sign of the count in the counter at appropriate times so as to derive the level of the last waveform crossed by the reading head.

6. A device as claimed in claim 2, wherein the calculation means include a source of clock pulses and a pair of counters one or the other of which is supplied in operation of the device with clock pulses in accordance with the position of the reading head relative to the waveforms and the/or each datum, and comparator means for comparing at appropriate instants the counts in the counter so as to derive the levels of the waveforms traversed by the reading head.

7. A device as claimed in claim 6, comprising a control circuit connected to the reading head and operative to clear said counters on receipt of an initial pulse from the reading head, and to switch the clock pulses from said clock pulse source to a selected one of the counters, the control circuit switching the clock pulses to the other counter on the receipt of a second pulse from the reading head indicating the passage of the reading head over the next line, the comparator means being operative to prepare the counts in the counters when the control circuit receives a third pulse from the reading head and to give a decision as to which count is higher to a latch circuit.

8. A device as claimed in claim 2, wherein the calculation means comprises a pair of generators each generating in operation a constantly varying voltage, one or the other of which generators is arranged to be switched on in accordance with the position of the reading head relative to the waveforms and the/or each datum, and comparator means for comparing the levels of the voltages generated at appropriate instants to derive the levels of the waveforms traversed by the reading head.

9. A device as claimed in claim 1, wherein the reading head is associated with a digital processor programmed with an algorithm for determining the levels of the waveforms scanned by the reading head.

10. A device for reading digital waveforms substantially as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.