Device for displaying a parameter value

A device for displaying a parameter value has at least one row of light-emitting diodes in which each light-emitting diode has a position input, and the device has a control circuit with address outputs connected to the position inputs. Faults, such as a short-circuit can be detected more easily by an improved interconnection of the address outputs and position inputs such that two adjacent address outputs are connected to two position inputs physically separated by at least one position input.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a device for displaying a parameter value, of the 
type having at least one row of light-emitting diodes each having a 
position input, and a control circuit with address outputs connected to 
the position inputs, whereby a signal sent from the control circuit 
through an address output connected to a specific light-emitting diode's 
position input causes illumination of that light-emitting diode. 
2. Description of the Prior Art 
Devices of the type described above are known for use in a number of 
different application fields for different kinds of indications. In 
general, such devices have one row of light-emitting diodes, also known as 
a bar graph, and a control circuit to turn on individual light-emitting 
diodes. For this purpose, the control circuit has address outputs 
connected to position inputs on the row of light-emitting diodes. 
One problem is that an undetected fault could occur, for example, a 
short-circuit between two lines, since the display does not change very 
much. The nearest diode neighbor then 20 lights as well, which is not 
necessarily interpreted as a fault. In addition, an undetected erroneous 
indication could have consequences, such as for example termination of a 
process at the wrong point or operation of a process with an incorrect 
parameter value, such as temperature, etc. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a device of the general 
type described above, which provides a clear indication of any faults 
which may occur. 
The above object is achieved in accordance with the principles of the 
present invention by inter-connection of the address outputs of the 
control circuit and the position inputs of the light-emitting diodes in 
such a way that two adjacent address outputs are hard-wired connected to 
two position inputs physically separated by at least one position input. 
Accordingly, the normal display format is distorted when a fault occurs so 
the row of light-emitting diodes shows that a fault is present. Especially 
when the intended indication is only at the parameter value with one or a 
few light-emitting diodes and not in the form of an illuminated bar, the 
special connection between the address outputs and the position inputs 
ensures that a fault can be quickly identified. Indication only at the 
parameter value also has the additional advantage of reducing the power 
requirements of the device. 
In an embodiment of the invention at least two parameter values are 
displayed in the row of light-emitting diodes, such as a reference value 
and an actual value, and the control circuit causes display of the 
respective parameter values with different illumination modes, such as 
continuously lit diodes, diodes lit with different intensities for 
different parameter values, blinking diodes, different blink rates and/or 
blinking at different levels for different parameters or different numbers 
of light-emitting diodes in the illumination modes. This can be 
accomplished by appropriate modulation of the electrical signals supplied 
to the address outputs. 
The use of a plurality of different indications in the same row of 
light-emitting diodes saves space. The different values are distinguished 
by the use of different illumination modes, such as continuous lighting at 
one intensity, blinking on and off, blinking at different intensities, 
different colors, different numbers of light-emitting diodes in the 
illumination modes etc. 
The device can be equipped with a parameter value scale parallel to the row 
of light-emitting diodes in order to indicate the magnitude of a parameter 
value. 
A linear parameter value scale is normally sufficient, but indication in a 
large parameter value range using one light-emitting diode row may be 
useful in certain instances. To emphasize a specific interval in this 
range, it would be advantageous to have a partially high-resolution 
parameter value scale, in which each scale segment or the distance between 
two light-emitting diodes in the most interesting parameter value 
intervals corresponds to a smaller value than in other intervals in which 
the same accuracy is not required for the parameter value. In other 
instances, a non-linear parameter value scale might be more useful, e.g. a 
logarithmic or quadratic scale. 
In another embodiment of the invention, two parallel rows of light-emitting 
diodes are employed, these light-emitting diodes forming a matrix with one 
x coordinate and one y coordinate comprising each position input, and the 
address outputs of the control circuit each comprising one X coordinate 
and one Y coordinate. The address outputs and the position inputs are 
connected so that two adjacent X coordinate addresses are connected to two 
x coordinate positions separated by at least one x coordinate position and 
so that two adjacent Y coordinate addresses are connected to two y 
coordinate positions separated by at least one y coordinate position. In 
other words, no two adjacent X coordinate addresses will be physically 
connected to x coordinate positions which are adjacent, and no two 
adjacent Y coordinate addresses will be physically connected to y 
coordinate positions which are adjacent. 
The use of two rows of light-emitting diodes increases the number of 
possible parameters which can be displayed simultaneously without any risk 
of mixup and without increasing the risk of misinterpreting a fault 
indication. The matrix system reduces the number of connecting lines 
between the control circuit and the row of light-emitting diodes. Each X 
coordinate constitutes, for example, part of an address output or a 
position input for every individual Y coordinate. The intersection of both 
x and y coordinate lines ensures that there is at least one empty row of 
light-emitting diodes on both sides of the indicated symbol. 
Analogous to the description above regarding the use of different 
illumination modes in conjunction with the indication of two parameter 
values, the first parameter value can now be indicated with two adjacent 
light-emitting diodes which emit light at a fixed intensity, and the 
second parameter value can be indicated with the alternating blinking of 
two adjacent light-emitting diodes. Again, this can be accomplished by 
modulating the respective electrical signals supplied to the address 
outputs. 
In another embodiment of the control circuit only energizes one 
light-emitting diode at a time, the time elapsing from the energization of 
one light-emitting diode until it is reenergized being so brief that the 
light-emitting diode appears to remain continuously lit, and the intensity 
with which a light-emitting diode driven in this manner appears to emit 
light depends on how often it is addressed and how long it remains lit in 
the time interval when addressed. 
Lighting only one light-emitting diode at a time further reduces power 
consumption. Control of the intensity also ensures that intensity 
increases and any fault is discovered if a short-circuit should occur 
between two normally lit diodes. 
The device according to the invention is not limited to the display of only 
one parameter. A plurality of rows of parameter value light-emitting 
diodes can be added to the system and controlled by the control circuit. 
In order to increase the system's reliability even further, the control 
circuit can contain a parity check circuit which checks to ensure that the 
signal generated in the control circuit to light a specific light-emitting 
diode is correct. The parity check circuit can block the emission of the 
signal and keep the light-emitting diodes turned off if a fault occurred. 
One advantageous employment of the device is as an indicator on a 
ventilator. 
The correct display of values is particularly important with a ventilator. 
The safety of a connected patient depends on the administration of gas at 
a specific pressure and flow rate, correct gas composition etc. If any 
parameter is indicated erroneously and the error is not detected, there is 
a risk an attendant changing a parameter setting in the belief that the 
setting is incorrect. This change could have grave consequences for the 
patient. 
Parameters have hitherto been displayed with analog dials or digital 
numerical displays. Analog instruments are incapable of displaying many 
values at the same time. One dial for the actual value and one dial for 
the reference value or an alarm level are normal. More dials increase the 
difficulty in making correct readings. In addition, the reference value or 
alarm level must be set manually on analog instruments. Digital numerical 
displays can only indicate one value at a time. Thus a plurality of 
displays must be used when a plurality of values have to be displayed or 
the displays must be resettable to permit indication of other values. 
Moreover, a fault in the indication device could result in the display of 
an erroneous numerical value. A break in one line could cause, for 
example, an 8 to be displayed as a 0. 
With use of the device according to the present invention, a plurality of 
values can be indicated and read easily and simultaneously, since the risk 
of erroneous indications has been minimized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the case of ventilators, obtaining information about, for example, 
pressure and volume must be fast and easy. The information must be readily 
accessible, and detection of any faults must be simple. FIG. 1 shows a 
device 1 for this purpose in accordance with the invention. Device 1 
includes a first light-emitting diode bar 2 for indication of pressure, a 
second light-emitting diode bar 3 for low-resolution indication of volume, 
a third light-emitting diode bar 4 for high-resolution indication of 
volume, and a control circuit 5. The control circuit 5 is connected to the 
three light-emitting diode bars 2, 3, 4 by an X coordinate address data 
bus 6 and a Y coordinate address data bus 7 which are described in greater 
detail below. 
A multiplexer 8 supplies the control circuit 5 with parameter values for 
pressure and volume via a data bus 101. The multiplexer 8 sends the two 
actual values to the ventilator as well as the reference value and alarm 
levels which have been set. Data flow to the multiplexer 8 is via a data 
bus 102. 
In the control circuit 5 the data bus 101 is connected to a microprocessor 
11 in which each parameter value is processed and transformed into a data 
instruction which consists of two bytes, one odd and one even, for each 
light-emitting diode which is to be lit, and which contains the address, 
intensity level and parity check bits. The data instruction is sent from 
the microprocessor 11 to a double port RAM 12 (DPR) via the data bus 104. 
The data instruction is fetched from the data output f the DPR 12 in two 
stages, controlled by a pulse sender 14. The pulse sender 14 controls the 
switching between the two addresses for the respective odd and even bytes 
in the DPR 12 and also controls transmission to first and second 
intermediate level memories 15 and 16. A counter 13 controls the 
transmission of each new data instruction from the DPR 12. The counter 13 
and pulse sender 14 are clocked by a clock signal cl at a rate of, for 
example, 15.625 Hz, i.e. a period duration of 64 .mu.s. When the counter 
13 addresses data transmission from the DPR 12 at the beginning of a 
period via the data bus 103, the pulse sender 14 emits a negative pulse 
with a duration of 8 .mu.s through a first signal line 105 and also emits 
a negative pulse with a duration of 4 .mu.s through a second signal line 
106. The first signal line 105 connects the pulse sender 14 to the 
microprocessor 11, the DPR 12, the first intermediate level memory 15 and 
a third intermediate level memory 17. The second signal line 106 connects 
the pulse sender 14 to the DPR 12 and the second intermediate level memory 
16. The connection between the pulse sender 14 and the microprocessor 11 
is to enable the microprocessor to synchronize transmission of the data 
instruction to the DPR 12 via the data bus 104. 
When the positive-going edge of the signal in the second signal line 106 
appears, i.e. 4 .mu.s into the period, the even byte from the data output 
of the DPR 12 is transmitted via the data bus 107 to the second 
intermediate level memory 16 which is also activated by the positive-going 
edge. The DPR 12 is simultaneously re-switched in order to emit the odd 
byte from its data output. 
Eight .mu.s into the period, the positive-going edge of the signal appears 
at the first signal line 105, and the odd byte is sent to the first 
intermediate level memory 15 at the same time as the four lowest bits in 
the second intermediate level memory 16 are sent to the third intermediate 
level memory 17 via the data bus 108. These four bits, plus the sixth bit 
in the odd byte, constitute the X coordinate information, whereas the four 
highest bits in the even byte constitute the intensity 5 information. 
The third intermediate level memory is connected via a data bus 109 to a 
parity check circuit 18 and an addressing circuit 19 to which the four 
bits are sent. The address in circuit 19 may contain a signal modulator 
19a, if needed, to modulate the electrical signals supplied via the 
respective data lines to the light-emitting diode bars 2, 3 and 4 to 
provide the different illumination modes. This function could 
alternatively be undertaken in the microprocessor 11. 
The odd byte, in which the five lowest bits constitute the Y coordinate 
information is sent to the parity check circuit 18. The sixth bit 
constitutes a part of the X coordinate information, as noted above, and 
the two highest bits constitute special purity bits used for the parity 
check. If a parity error occurs, the parity check circuit 18 sends a 
signal via the signal line 111 to the microprocessor 11 and to the 
addressing circuit 19. All light-emitting diodes will then be turned off. 
This prevents the overloading and destruction of individual light-emitting 
diodes if the same light-emitting diode is addressed continuously due to 
some fault in the data instruction. The light-emitting diodes re-light as 
soon as all the information in the DPR 12 is correct. 
The four bits in the even byte which constitute the intensity information 
are sent from the second intermediate level memory 16 via a data bus 112 
to an 30 intensity pulse former 20. Intensity information is 
transformation in the intensity pulse former 20 into a pulse whose width 
designates the time the light-emitting diode is to be lit during the 
period. The pulse width can vary, for example, from 0 to 56 .mu.s, 56 
.mu.s constituting maximum 35 intensity. The intensity pulse is sent to 
the addressing circuit 19 via a signal line 113. 
X and Y coordinate information is read in the addressing circuit 19, and a 
signal is sent to the respective coordinate address bus 6 or 7 to light 
the addressed light-emitting diode for the duration of the intensity 
pulse. 
When this period has elapsed, the counter 13 is incremented by one step so 
as to address the next byte pair identifying a new light-emitting diode. 
With, for example, a 7-bit counter, 64 light-emitting diodes can be 
addressed in one cycle, the first light-emitting diode thereafter being 
addressed once again. The cycle period could also consist of six or eight 
or some other number of bits, and the same light-emitting diode could be 
addressed many times during a cycle in order to increase the intensity. 
A parameter value scale 22 is disposed next to each light-emitting diode 
bar 2, 3 and 4 to permit the numerical values for pressure and volume 
respectively to be read. 
As FIG. 1 shows, the light-emitting diode bars 2, 3 and 4 each consist of a 
number of light-emitting diode segments 9. FIG. 2 shows one of these 
light-emitting diode segments 9. The light-emitting diode segment 9 
consists of forty light-emitting diodes 10, each having a unique position 
coordinate in the light-emitting diode segment 9, as shown in FIG. 2. 
The light-emitting diodes 10 are sub-divided into ten y coordinate groups, 
y0 to y9, each having four x coordinates, x0 to x3. In principle, each 
individual light-emitting diode 10 could have its own signal line, but the 
total number of lines can be reduced with a coordinate system, i.e. from 
forty to fourteen lines in this instance. 
FIG. 3 shows the light-emitting diode bar 9 in matrix form to illustrate 
the manner in which fault indication is performed according to the 
invention. The positions are indicated with lower case letters and 
addresses with upper case letters. Each intersection 21 of two position 
lines corresponds to a light-emitting diode, and each combination of an x 
and a y coordinate constitutes a position input for the light-emitting 
diode at the intersection of the two coordinates. 
As FIG. 3 shows, an address coordinate X0, for example, has been connected 
(hard-wired) to the position coordinate x2, address coordinate X1 to 
position coordinate x0, X2 to x3 etc. 
If a short-circuit should occur between two address coordinates, for 
example, Y3 and Y4, a signal on either of the lines will also lead to 
transmission of the signal to the second line via the short-circuit point. 
A signal to light a light-emitting diode via the address coordinate XOY4 
also results in a signal with the address coordinate XOY3. In FIG. 2, the 
position coordinate x2y8, which is lit by the address coordinate XOY4, has 
been identified. The address coordinate XOY3 lights the position 
coordinate x2y6, also identified in FIG. 2. It can be seen that there are 
three rows of light-emitting diodes between the two positions. This 
discrepancy would be quickly interpreted as a fault. 
In principle, the cross-connection of the address and position coordinates 
can be achieved in any way. It is essential that two adjacent address 
coordinates must not be connected to two adjacent position coordinates. As 
FIG. 1 shows, the first light-emitting diode bar 2 consists of six 
light-emitting diode segments 9, and each of the second and third 
light-emitting diode bars 3 and 4 consists of four light-emitting diode 
segments 9, i.e. a total of fourteen light-emitting diode segments 9 which 
are addressed by the control circuit 5. 
If each light-emitting diode segment 9 were to be addressed individually, 
14.times.14 lines would be required (FIG. 3 shows that one light-emitting 
diode segment 9 requires fourteen lines), i.e. 196 lines, 140 Y address 
lines and 56 X address lines. By having the same coordinates address a 
plurality of light-emitting diode segments 9, the number of lines can be 
reduced. With, for example, three groups of ten Y address coordinates 
(Y0-Y9, Y10-Y19, Y20-Y29) and five groups of four X address coordinates 
(X0-X3, X4-X7, X8-X11, X12-X15, X16-X18), fifteen unique sets of addresses 
can be combined by having each X address coordinate group constitute a 
part of the address in combination with each Y coordinate group. This is 
sufficient for addressing any individual light-emitting diode in one of 
fifteen light-emitting diode segments, each comprising forty 
light-emitting diodes. In this example, there are fifty lines from the 
control circuit 5, thus a 146-line reduction. 
FIG. 4 shows the front of a control unit 23 for the ventilator in which the 
device according to FIGS. 1-3 is installed. The control unit 23 is divided 
into different function fields 28 to 34 with setting knobs 24, 
light-emitting diode displays 25, setting indicators 26, alarm indicators 
27 and light-emitting diode bars 2, 3 and 4. The function of the various 
designated function fields 28 to 34 is as follows. The ventilator's 
operating mode is set in function field 28, the patient type, i.e. whether 
the patient is an adult, child or infant, is set in function field 29, 
oxygen concentration is set in function field 30, pressure is set in 
function field 31, flow rate is set in function field 32, volume is set in 
function field 33 and function field 34 indicates errors which can occur 
in the ventilator. Pressure is thus displayed by light-emitting diode bar 
2 in function field 31 and high and low resolution volumes are displayed 
by light-emitting diode bars 3 and 4 in function field 33, in the manner 
described above. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventors to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of their contribution to the art.