The electrostatic capacitance that causes between use human body and electrode undertakes capacitance type of the job feels switch, it is to be used at the smartphone at the beginning, be applied to machine of home appliance product, AV, car and industrial equipment widely again then. The composition that feels switch need not the reason of mechanical component, use so rise very agile, can install even go up in solid curved surface. The article feels technical foundation to go up in the electrostatic capacitance type of lucky Sa electron, the introduction feels the fundamental that switch detects and interference rejection technology to wait.

 

 

Switch of feeling of electrostatic capacitance mood is passed catch human body and electrode between electrostatic capacitance (1pF is the following) faint change, judge the ON/OFF condition of switch. A lot of kinds of methods can change DC capacitance the ON/OFF position that is switch. Among them the simplest method, it is to use electrostatic capacitance and resistor to form low connect filter (LPF) , charge through measuring / the change that the change of discharge constant judges electrostatic capacitance. This kind of means is called means of Zhang Chi oscillation. Because its circuit is simple, need not appropriative is electrostatic capacitance measures circuit, because this is applied extensively. But of this kind of method fight noise function to slant weak, can produce a miscarriage of justice as a result of the inversion noise of illumination luminaries or home appliance product sometimes.

 

The feeling of electrostatic capacitance mood that lucky Sa electron develops detects method, use switch capacitance filter (SCF) measure DC capacitance changeover for electric current, after undertaking magnify and be digitlizinged handling to this signal, decide according to it the ON/OFF condition of switch. This kind of method has sensitivity tall, fight the good point with noise strong performance. Detect specificly flow is shown 1 times like the graph. This chapter according to the graph the flow of 1, explain electrostatic capacitance type feels the ABC of switch.

 

Of switch of feeling of mood of graph.1 electrostatic capacitance detect flow (“ number. Digital ” shows paragraphic sign)

 

 

The mechanism that electrostatic capacitance produces is shown 2 times like the graph. Electrode and the electric system all round its (rim of ground wire, metal) between existence parasitism capacitance (Parasitic Capacity: Cp) . When human body when electrode of adjacent, feeling, the electrostatic capacitance that shows through the hand generation adds newly between human body and electrode (Finger Capacity: Cf) , join through OK and electric human body and earth (if pursue 2 in red line place is shown) .

 

The happening of graph.2 electrostatic capacitance (from capacitance means)

 

The total capacity of the electrostatic capacitance of the generation on electrode (Total Capacity) , following place show:

 

Electrostatic capacitance type feels switch to measure the DC capacitance of electrode circularly according to certain cycle, the addition of the electrostatic capacitance of the generation when be being contacted according to human body measures Cf, decide the ON that feels switch or OFF condition.

 

 

Be like [the happening of electrostatic capacitance] be narrated, the method that changes the DC capacitance that arises between human body and electrode the discharge that it is report used switch capacitance filter (Switched Capacitor Filter: SCF) . If the graph is shown 3 times, by 2 switch, control the control pulse of alternant ON/OFF movement, power source and capacitance comprise 2 switch SCF.

 

Graph.3 SCF forms those who reach electric capacity to fill discharge movement

 

SW1 and SW2 fall in the function that controls pulse, when ON of a switch, another switch OFF. If pursue,3 medium different pictures are shown, when SW1 = ON; When SW2 = OFF, capacitance charges. Subsequently, if pursue,3 medium right graphs are shown, switch arrives SW1 = OFF; After the condition of SW2 = ON, capacitance discharge. The relation between C of value of the switch frequency F of the voltaic I that sheds classics capacitance, switch, capacitance and V of voltage of circuit power supply, following type place show:

 

I = Fcv

 

If F and V are changeless, voltaic I and capacitance C become direct ratio. Accordingly, the change of the DC capacitance that can use the generation when SCF is close to human body changes the change that measures for electric current. Through adjusting switch frequency F and V of power supply voltage, can change the coefficient of proportionality between quantity of electrostatic capacitance change and voltaic change quantity.

 

 

After the capacity of capacitance is worth changeover to be proportionate cable flow, through change-over circuit of voltaic — frequency changeover is and electric current measures proportionate oscillation pulse. Next, tally is right oscillation pulse computation, it is voltaic changeover proportionate number to be worth then.

 

Voltaic numerical value changes technological process, if pursue,4 are shown. Carry out circularly to the capacitance of SCF when filling discharge to operate, the meeting in capacitance generates alternating current. Follow-up electric current is flowing after circuit is alternating current changeover dc electric current, electric current inputs voltaic oscillator, changeover is frequency and pulse of oscillation of proportionate of input electric current. Pulse tally is right the pulse computation inside proper time, save computation result.

 

The technological process that numerical value of graph.4 electric current changes

 

 

Be like [the happening of electrostatic capacitance] be narrated, from capacitance means be through detecting the addition of DC capacitance judges human body to whether contact electrode. Of the DC capacitance that carries out carry on of 2.1~2.3 chapter intermediary circularly according to certain cycle measure, can decide according to the change of measured value whether does human body contact electrode.

 

When finger is close to and leaving electrode, the ON/OFF of switch decides flow is shown 5 times like the graph. The measurement of DC capacitance is carried out at regular intervals by the sequential that shows in the graph. Plan in if pursue,measuring a value, blue line place is shown, when finger is far from electrode, maintain the computation with be certain to be worth; When finger is close to electrode, DC capacitance and computation value increase gradually. Be far from again when finger when, computation value falls gradually and hold the numerical value with be fair. Regard fiducial value as the computation value when finger is far from electrode (dotted line of the green in the graph) . In the overlay on fiducial cost basis a threshold value, as critical value. When plan when measuring a value to exceed critical value, decide switch is ON. When plan measure a value under critical value when, decide switch is OFF. From this, can realize the ON/OFF switch of electrostatic feeling switch.

 

In addition, the size that changes threshold value can adjust the sensitivity that feels switch. Change plan measures cycle and computation the average that many computation are worth, can restrain the thrill of switch, adjust the response rate of switch.

 

The ON/OFF of graph.5 switch decides

 

Switch of feeling of electrostatic capacitance mood is the faint change that is based on DC capacitance and of the job. Accordingly, noise and the effect with fluctuant power source must avoid as far as possible when the design.

 

The Touch solution that lucky Sa electron offers, send feeling unit in capacitance feeling not only (abbreviation: CTSU) in inside buy a variety of noise restrain circuit, still offerred the software filter that is used at restraining noise at the same time. This chapter basically introduces the function of hardware interference rejection of CTSU module and software to refuse noise technology.

 

 

To restrain by radiation, conduct the noise that introduce, the buy inside CTSU a variety of noise restrain circuit, in order to stabilize the measurement of electrostatic capacitance. Show the composition of these circuit and function respectively below.

 

 

It is electric flow to use SCF to change DC capacitance, CTSU the ON/OFF condition according to switch of certain periodic switch SCF, implementation charges to exterior capacitance / the circular operation of discharge. Right now, if be on electrode,interfuse and SCF switch are the same as periodic noise, and the wave crest of noise / trough and charge / agree from beginning to end during discharge, so electric current can increase accordingly because of noise or decrease, may cause then measure cannot undertake correctly. As resolve the way to deal with a situation that is the same as cyclic noise, the buy inside CTSU the phase shift circuit of SCF drive pulse. What through inverting drive artery rushs is phasic, the wave crest that prevents drive pulse and noise / trough is inphase. Phase shift is decided by polynomial tally, 1 plan in measuring, the phase shift frequency of SCF pulse and number of 180° phase shift should agree.

 

The influence that is the same as cyclic noise and 180° phase shift are right the inhibition that is the same as cyclic noise, if pursue,6 are shown. If SCF drive artery is strong the wave crest with noise is inphase when charging, meeting overlay goes to the voltaic heft that noise produces of electric current fill discharge weaveform to go up. Right now, charging current can increase because of noise, cause plan measure a result to be more than actual size. If the capacity of noise generation is more than a hand to point to a contact,the capacitor that produces increases an amount, can produce the interference as a result of noise, although do not have feeling movement, decide the miscarriage of justice that is ON however as a result. Accordingly, need develops executive 180° phase shift to SCF drive arteries and veins according to certain regulation, through inverting the synchronism of drive pulse and noise concerns, the electric current that causes because of noise evenly estimates increase and decrease. The frequency of polynomial calculator and frequency, the register that can pass CTSU is adjusted.

 

In addition, displacement countermeasure can restrain the noise that is the same as frequency not only, to frequency the artery that it is drive develops the noise with times odder frequency likewise effective.

 

The balance of the influence that graph.6 is the same as cyclic noise and 180° phase shift to be the same as cyclic noise is changed

 

 

When noise frequency is frequency of SCF drive pulse is times more integral, the edge of drive pulse is met and noise is synchronous, cause an effect to the measurement of electrostatic capacitance. To be like the noise that the graph shows 7 times, can be used and the edge with the strong to SCF drive arteries and veins signal with drive asynchronous pulse does normalization to handle, patulous edge frequency. The place before be like is narrated, arise the voltaic input after modulation the pulse that normalization place uses to ICO For Spread Spectrum, can avoid SCF drive pulse and noise synchronism (referenced graph 8) .

 

Drive artery of graph.7 SCF develops the give typical examples with times frequency noise

 

Graph.8 passes patulous clock to develop normalization to SCF drive arteries and veins

 

 

The anti-noise circuit of the buy inside CTSU cannot eliminate the low frequency noise under several KHz. The low frequency noise of several KHz frequency domain needs to be eliminated through software method. The following illustrate restrains the software countermeasure of low frequency noise.

 

 

The influence that the result that feeling detects can be changed by the environment such as ageing of temperature, humidity, material. The slow change under these frequency number KHz, pass hardware very hard to handle. Accordingly, need restrains the interference of these low frequency noise through the method of software integral.

 

The working principle with corrective drift is shown 9 times like the graph. The place before be like is narrated, fiducial value and the ON/OFF threshold value that create on its foundation are by software computation is generated. Plan measure value and generated threshold value successive to compare, decide then feeling or blame feeling (ON/OFF) . Plan the result after operation of the integral that measure a value takes average to serve as fiducial value, change of OK and gently environment is right plan those who measure a value to cause is fluctuant. Change integral operation place to use plan a number that measures a value, can adjust the adaptability that changes to the environment.

 

In addition, should decide when eventuate ON, suspensive drift is corrective processing; Should decide follow-uply when result occurrence OFF, restart again drift is corrective processing. If decide,carry out drift to continue when ON corrective processing, long feeling movement can cause fiducial value to be close to gradually plan measure a value, be equal to finally plan measure a value. At this moment, the miscarriage of justice of OFF of meeting occurrence eventuate. Accordingly, should decide when eventuate ON, should suspend drift corrective processing, prevent result miscarriage of justice.

 

Graph.9 drift is corrective processing

 

 

Be opposite to restrain random noise plan the interference that measures a value, increased to be opposite in software plan the software filter that measures a value to undertake flowing processing. Undertake demonstrative to software filter through example below.

 

 

The example of flowing filter, if pursue,10 are shown. In this exemple, use this second plan before measuring a value to reach 3 plan measure a value (add up to 4 times) average serves as this second detect plan measure a value. Through adjusting calculation average place uses plan a number that measures a value, can restrain the noise of different frequency. For example, plan when measuring periodic = 20ms, the noise to restrain 10Hz (noise cycle = 100ms) , those who need to use 5 above plan measure a value to calculate average. Those who need an attention is, those who be used at computational average plan measure a value number is more, the response rate that feels key is slower.

 

The give typical examples of graph.10 flowing filter

 

 

Upper limit filter is compared above all this second plan measure before the value is mixed second plan measure a value. If the poor value of both is more than beforehand the upper limit needing a value of set, criterion will before second plan measure the sum of value and poor value upper limit to regard as this second plan measure a value. Should appear in the system erupt when type noise, plan the conference that measure a value appears to change acutenessly. Filter of use upper limit, can come true smooth plan the effect that measures a value. Pass limitative plan to measure the sharp increase and decrease of the value, the feeling that because noise is caused,restrains / the miscarriage of justice that is not feeling. Because upper limit filter reduced the peak value of noise, because this is controlling noise aspect, than in front flowing filter of the introduction is more effective. But what need an attention likewise is, the upper limit that narrow difference is worth when set / floor level, can increase the time that feeling detects, lower the response rate that feels key thereby.

 

 

With mechanical contact switch identical, use feeling key also needs to eliminate thrill sometimes. The following specification eliminates the countermeasure of thrill.

 

 

When the condition that judges feeling key ON→OFF, OFF→ON changes, if successive N second judgement all agrees as a result, namely N second when judgement all is ON as a result or all be OFF, decide for ON or OFF. Increase the frequency N that agrees continuously, but the effect that aggrandizement restrains thrill, but the response rate that can lower feeling to bolt.

 

 

Accumulative total is certain the ON inside time or the frequency of OFF, the frequency much person as this second judge an outcome. With afore-mentioned N second uniform standard photograph is compared, the judgement rate of most and uniform standard is rapidder, but go thrill ability is relatively inferior.

 

 

Use feeling of electrostatic capacitance mood to detect technology, can reduce the use of mechanical component, reduce cost, can apply on all sorts of face plate neatly. Technology of capacitance mood feeling needs special attention when use the processing of interference rejection. Disturb frequency in the light of different noise respectively paragraph, union uses hardware and measure of software interference rejection, can raise electrostatic capacitance type effectively to feel the dependability of testing system.