WO1995016308A1

WO1995016308A1 - Electronic touch switch and keyboard comprising such a switch

Info

Publication number: WO1995016308A1
Application number: PCT/GB1994/002530
Authority: WO
Inventors: Stamos Anastasios Dimitrios Fafalios
Original assignee: Fafalios Stamos Anastasios Dim
Priority date: 1993-12-08
Filing date: 1994-11-17
Publication date: 1995-06-15
Also published as: EP0729673A1

Abstract

The invention refers to a method and device for keying-in and switching, wherein the activation of the key or switch is achieved during the contact between part of the user's body (e.g. finger) with a metallic or other conductive surface which constitutes the outer sensor of the key or the switch and which method and device are characterised by the comparison of a reference wave form, unable to be influenced by user's presence in relation to the same wave form but distorted due to the influence exercised by the contact of user's body which is now acting as a conductor transferring part of the power (current) of the wave form down to the earth and distorting it relatively to the same reference wave form.

Description

Electron ic Touch Swi tch and Keyboard Compri si ng such a Swi tch

1. In general

2. State of the art

The standard mechanical switches, with movable parts, are mentioned to be the state of the art. With reference to switches or keys without movable parts, we may mention the standard switches or keys of two metallic conducts or conductive principle of operation, in which the contact of user's finger acts as a connecting conduct of two metallic contacts by causing a short-circuit. In this way, the inner circuit is distorted and the activation or keying-in etc. which are required may be caused. The use of a simple metallic contact as an outer sensor is used in conjunction with capacity proximity sensors to detect the approach of any kind of object e.g. non-metallic (i.e. user's body) or inductive proximity sensors to detect the approach of metallic objects which are however characterised by a bulky construction and high cost.

The disadvantages of the state of the art are mainly:

* wear problems (for the mechanic switches with movable parts),

* cost problems (when switches with multiple contacts are used and there is an effort for the outer sensor to be as small as possible like in the case of pocket calculators keyboards), * reliability problems (which are due to environmental factors such as humidity, extreme temperatures etc. or due to material being worn out),

* difficulty in increasing or reducing the sensitivity of the standard keys or switches and * limited life time (as in the case of switches with movable parts).

3. Disclosure of the invention

Referring to Figure 1, the invention operates as follows:

Through input unit (102) and oscillator (103), in the memory unit (104) a wave form is stored, unaffected by outer factors since the free contact (101) which controls the filter and the oscillator does not come in contact with the user's body. The said uninfluenced wave form is stored in the memory unit (104).

Following the same procedure and using an identical course and components, we may register in a registration unit (108) the wave form which is however influenced by the fact that the identical contact (106) (compared to the 101) comes in contact with the user's body (107). The comparison of the unaffected wave form registered in the memory unit (104) in relation to the affected wave form registered in the registration unit (108) determines whether there is a contact on (106) (that is if the key has been touched) or not, in which latter case the two wave forms (104 and 108) are identical.

If several contact keys are used, each time all keys are examined and the activated one, by means of touch, is determined.

4. Characteristics and advantages of the invention

The method has the following advantages:

1. Elimination of the possibility of erroneous readings caused by changes to the electronic data of the circuit.

- Changes in the environmental conditions (e.g. temperature, humidity etc.) do not affect the measurement.as in each measurement cycle the data is rectified based on the measurement of the reference contact. - The same applies on the wear of material and the changes of circuit characteristics used, since the reference measurement and the contact measurement pass through the same devices and circuits. Even better results may be taken if along with every measurement, a reference measurement is repeated.

- The only case of influencing the measurement is likely to be due to an instantaneous increase or lowering of the potential for a period less than the time required to take a full sample of the keyboard keys. This problem may be solved if a standard potential regulator is interfered.

2. Capability to increase or to reduce the circuit sensitivity by adjusting the comparison unit (105), so that for smaller or bigger differences between the reference wave form and the contact wave form, the contact readings to be verified.

3. Identification of the most probable key being touched in case that many keys have been accidentally pressed. If the measured magnitudes of a full sampling are registered in the memory, then their mutual comparison may give the prevailing key being touched.

4. All the advantages of a touch keyboard, such as unlimited life time due to absence of mechanical parts, minimal maintenance requirement, operation in adverse environments as long as it can be protected against dust etc.

5. Elimination of mechanical contacts with their resulting problems and significant reduction of the cost, since control logic, memory, counters etc. may be parts of a micro controller, keyboard. The remaining parts used such as the multiplexes, oscillators, filters etc. require low cost material.

6. Easy increase of the number of contacts so that keyboards with a large number of keys on a small surface can be produced. Extension may be achieved using the above method on:

- Keyboards with small dimensions for pocket calculators, palm computers etc.

- Devices tracing the passing of a finger ("grafo" devices).

- Mouse pads, joystick pads. - Graphic templates using both the finger movement and the identification of finger pressure on a surface containing a contact matrix.

- Standard switches to control conventional electro-mechanic constructions (e.g. elevators) and to replace the conventional mechanical switches or contact switches.

7. Capability to control the output characteristics of the switch (key), so that:

A. To control the switch output in order to be in the form of step function

0 - 1 or 1 - 0

B. To control the switch output in order to provide an linear signal during transition e.g. from the level 0 to the level 1, depending on the pressure applied on the contact surface. This is achieved by successive comparisons of the reference wave form in relation to the subsequent receptions of the contact wave form. When the finger pressure is increased, the yield current from user's body to the earth is increased and thus the distortion is escalated. Successive comparisons give an analogous signal depending on the estimated difference.

In this way:

C. The switch may be used to control undesired distortions to the circuit caused by instantaneous activation [Gibbs phenomena] (Bounce Control).

D. Similarly, the switch is adjusted in such a way that it requires a minimum pressure rate before it becomes activated or a maximum pressure rate before it becomes de-activated, This control is achieved, for example, by monitoring the sensitivity of the comparator (105) in order to display the minimum and maximum difference magnitude that corresponds to the given pressure rates of the finger.

E. The switch may be adjusted in such a way that it requires a minimum pressing time period for activation or a maximum one for de-activation to verify the contact or not. This may be adjusted by regulating the time required to register the data of the registration unit (108) in the comparison unit or in general by delaying of or extending one of the procedures required for the circuit control. Following the same regulation procedure, the time required for re- activation and pressure control is monitored.

5. Embodiment of the method

An embodiment of this method is presented in Figure 2. According to this embodiment, an oscillator of low frequencies (207) (equal or lower than lOOKHz) is used, the feedback circuit of which we may connect to the output of an analogue multiplexer (203) through a bandpass filter (206).

The multiplexer (203), according to the figure, disposes of as many inputs (201) as the number of keys to be traced (e.g. n). Each contact of the multiplexer (203) is connected with a touch key (201). The multiplexer (203) also disposes of another input (202) which is not connected with the contact key and is used to display the reference. The remaining parts of the embodiment circuit require standard parts of a micro controller unit (205) and are presented in the procedure of circuit operation. The whole procedure of tracing and registering the condition of keys is accomplished in three phases:

PHASE A: The circuit of logic control (204) transfers the multiplexer (203) to the unconnected input (202). Then, the counter (208) is set to zero and one period of the oscillator (207) is counted. The result of counting is transferred and registered to a memory (209). This phase is completed with the counter (208) set to zero.

PHASE B: The circuit of logic control (204) transfers the multiplexer (203) to the first measured input (201). The control circuit (204) also transfers the output of the oscillator (207 to the counter (208) for the duration of full period. Now the measurement of the period is taken.

PHASE C: The digital lines of the counter (208) lead a digital subtractor (210) which deducts the last measurement from the measurement registered in memory (209). The result of the subtraction is lead to a digital comparator (211) and the latter's input (217) is lead by a digital word chosen (212). The size of the digital word determines the sensitivity of the translator (211). If the size measured is larger than the digital word, then we decide that the key is pressed and the logic level is changed from 0 to 1 or vice versa.

The phases B and C are repeated as may times as the contacts we need to identify. The reading of the last contact flags the start of a new measurement cycle that is phases A, B, C etc. An extension of the method might be achieved with the use of a double multiplexer (203). The control of the pressure exercised is accomplished, in the same phase, by the gradual increase of the size of the digital word through the arithmetic controller (212) and the control unit (204), so that the sensitivity of the comparator (211) is gradually increased. For the same contact and the same phase, the size of the word determines the pressure exercised on the key. The control of the contact period etc. is determined by the control unit (204) when delaying or accelerating one of the procedures of phases B and C.

Claims

1. Method and device for keying-in and switching, wherein the activation of the key or switch is achieved during the contact between part of the user's body (e.g. finger) with a metallic or other conductive surface which constitutes the outer sensor of the key or the switch and which method and device are characterised by the comparison of a reference wave form, unable to be influenced by user's presence in relation to the same wave form but distorted due to the influence exercised by the contact of user's body which is now acting as a conductor transferring part of the power (current) of the wave form down to the earth and distorting it relatively to the same reference wave form.

2. Method and device, as in Claim 1, wherein an oscillator of low frequencies (207) is used, which has a feedback circuit connected with the output of an analogue multiplexer (203) through a bandpass filter (206) and every contact of the multiplexer, except one (202), is connected with a touch key (201) and is characterised by successive - in a tracing sequence - transfer of the multiplexer (203) through a circuit of logic control (204) to the unconnected input (202) and then to each of the contacts (201) while the measurements of one oscillator (208) period are simultaneously taken.

3. Method and device, as in Claim 1, consisting of parts described in Claim 2, wherein in a first phase the measurement result during the transfer of multiplexer (203) to the unconnected input (202) is transferred and registered to the memory unit (209), and the result of each measurement (208), during the transfer of multiplexer (203) to each input (201), leads to a digital subtractor (210), which successively subtracts each measurement from the one registered in the memory (209) and is characterised by the capability to delay and control the time of accomplishment if time control, required to activate the switch control circuit or not, is asked.

4. Method and device, as in Claim 1, with signal transfer procedure as in Claim 3, wherein the result of subtraction (210) is transferred to a digital comparator (211), the input (217) of which is lead by a digital word chosen by the user (212) so that the size of the digital word determines the sensitivity of the comparator (211) in order to change the logic output level from 0 to 1 or vice versa, and the whole procedure is repeated for each keyboard.

5. Method and device, as in Claim 1, wherein the extension of the method is achieved through the use of double multiplexer (203).