as shown in fig1 - 5 , a mobile plethysmographic device is generally designated 20 . the mobile plethysmographic device 20 preferably includes an article 25 and an attachment band 26 having an exterior surface 26 a and interior surface 26 b . the mobile plethysmographic device 20 is preferably secured with velcro ® hook and loop material 31 a and 31 b . the article 25 preferably includes an optical sensor 30 , control components 43 a - 43 c and optionally a display member 40 . the mobile plethysmographic device 20 is preferably worn on a user &# 39 ; s wrist , arm 72 or ankle . the article 25 preferably has a usb port for a wired connection to a computer , tablet , video monitor or mobile communication device such as smartphone . it is desirous to adapt the mobile plethysmographic device 20 to the anatomy of the user &# 39 ; s arm 72 or even the user &# 39 ; s ankle . the band 26 is preferably composed of neoprene , leather , synthetic leather , lycra , another similar material , or a combination thereof . the article 25 is preferably composed of a semi - rigid or rigid plastic with a rubber - like or semi - flex plastic bottom layer for contact with the user &# 39 ; s body . the bottom layer of the article 25 may have a curved surface for contact with a user &# 39 ; s body . the article 25 preferably has a mass ranging from 5 grams to 50 grams . preferably , the lower the mass of the article 25 , the more comfort to the user . the article 25 preferably has a thickness ranging from 5 mm to 10 mm , and is most preferably 6 . 5 mm . although the mobile plethysmographic device 20 is described in reference to an article worn on a user &# 39 ; s arm , wrist or ankle , those skilled in the pertinent art will recognize that the mobile plethysmographic device 20 may take other forms such as eyewear disclosed in brady et al , u . s . pat . no . 7 , 648 , 463 , for a mobile plethysmographic device , method and system , which is hereby incorporated by reference in its entirety or a glove such as disclosed in rulkov et al ., u . s . pat . no . 7 , 887 , 492 , for a mobile plethysmographic device , method and system , which is hereby incorporated by reference in its entirety . fig6 - 8 illustrate the sensor 30 . the sensor 30 has a photodetector 36 , at least two leds 35 and an opaque light shield 57 . the leds 35 are preferably green light leds of the same wavelength . the sensor 30 preferably has a length , l , of 7 - 10 mm on each side , as shown in fig6 . the sensor 30 preferably has a height , h , of 1 - 1 . 5 mm , as shown in fig7 . the opaque light shield 57 blocks the direct light from the leds 35 to the photodetector 36 . only the green light diffused through the translucent media ( skin of the user ) 61 , as shown in fig8 , is allowed to enter the chamber of the photodetector 36 . this provides for a more accurate heart rate or vital sign signal . the use of two green leds form symmetric light diffusion volume around the sensor . the use of two green leds also mitigates mechanical noise . in a preferred design of the sensor 30 , the distance between the centers of active areas of leds 35 is preferably 5 - 6 mm . the active area ( photodetector 36 ) of a sensor 30 is placed in the middle of that distance . in the custom sensor , the distance of a custom sensor is preferably in the range of 3 - 4 mm ( which means the spacing between the centers of photodetector 36 and leds 35 is about 1 . 5 - 2 mm ). the distance is preferably sufficient for the placement of an opaque barrier between them . to control the amplitude of the led intensity pulse a sufficient current ( voltage ) range of intensity ramp is used to control the leds 35 and to achieve the same levels of intensity in both leds 35 within a given range . the electrical characteristics of 520 nm led in terms of voltage range for intensity ramp is sufficient . the top surface of the sensor 30 is preferably flat and in steady contact with the skin . under a strong motion condition , the skin moves at the border of the contact surface . the sizes of the sensor area and flat skin contact area are selected to reduce the boundary motion effects . if the distance between the leds and sensor is reduced , a lighted area of the skin is smaller , and the contact area is reduced ( 5 × 5 mm is acceptable ). a non allergenic epoxy is an easy way to seal the contact area from moisture . the preferred embodiment uses a fixed pulse width within the range of 125 to 250 microseconds ( μsec ) turning on leds periodically with period two msec and a tsl13t photodetector 36 . the output signal of the sensor 30 is monitored to ensure that it is not saturated . the use of short - term led pulses combined with a high pass filter to reduce ambient light effects . in the preferred embodiment , voltage is collected at the sensor output every two msec synchronously with the led pulse . the microprocessor , averages eight consecutive samples in order to improve the snr ( signal to noise ratio ) and then works with the averaged numbers . therefore the sampling rate for raw data is preferably two msec , however if eight - sample averaging is utilized in the integrated sensor the data output rate is reduced to sending a new averaged value every sixteen msec . an adc with at least 12 - bit resolution is used . the response of tsl13t photodiode ( from ams - taos usa inc ., of plano tex .) is acceptable . the detailed description of the sensor and front - end design along with signal processing method is disclosed in u . s . pat . no . 8 , 460 , 199b2 , which is hereby incorporated by reference in its entirety . the optical sensor 30 of the mobile plethysmographic device 20 is preferably worn on the user &# 39 ; s arm 72 , wrist or ankle . however , those skilled in the pertinent art will recognize that the plethysmographic optical sensor may be placed elsewhere on the body of the user without departing from the scope and spirit of the present invention . in a preferred embodiment , the optical sensor 30 is a plurality of light emitting diodes (“ led ”) 35 , as shown in fig6 - 8 , based on green light ( wavelength of 500 - 570 nm ), wherein the leds 35 generate green light , preferrably at wavelength of 520 nm , and a photodetector 36 detects the green light . yet in an alternative embodiment , the optical sensor 30 is a photodetector 36 and a single led 35 transmitting light at a wavelength of approximately 900 nanometers as a pulsed infrared led . as the heart pumps blood through the arteries in the user &# 39 ; s arm , ankle or wrist , the photodetector 36 , which is typically a photodiode , detects reflectance / transmission at the wavelengths ( green , red or infrared ), and in response generates a radiation - induced signal . a preferred optical sensor 30 utilizing green light is a tsl13t light to voltage converter sensor from ams - taos usa inc ., of plano tex . output voltage is linear with light intensity ( irradiance ) incident . fig9 shows a system 100 for detecting pac events utilizing a mobile plethysmographic device . the mobile plethysmographic device 20 comprises an optical sensor 30 , bluetooth 29 or wireless radio , an application 28 , and memory or a database 27 . using bluetooth or a wireless network 70 , the mobile plethysmographic device 20 sends data to output devices 45 such as a mobile smartphone 50 or an interactive gaming device 55 . the data is then sent to a secondary communication node 80 , such as to a data analysis center 90 or to a doctor &# 39 ; s office 85 , via a private cloud ( server ) 65 or through a dedicated medical communication network 60 . if the mobile plethysmographic device 20 is equipped with a transceiver then data can be sent directly through a cellular network 75 to a secondary communication node 80 . in one embodiment , discussed below , the display member 40 is removed and the signal is sent to an output device 45 such as a personal digital assistant , laptop computer , mobile telephone 50 , exercise equipment , gaming device 55 , or the like for display and even processing of the user &# 39 ; s real - time vital signs information , as shown in fig9 . alternatively , the circuitry assembly includes a flexible microprocessor board which is a low power , micro - size easily integrated board which provides blood oxygenation level , pulse rate ( heart rate ), signal strength bar graph , plethysmogram and status bits data . the microprocessor can also store data . the microprocessor processes the data to display pulse rate , blood oxygenation levels , calories expended by the user of a pre - set time period , target zone activity and time . the display member 40 is preferably an organic light emitting diode ( oled ) array . alternatively , the display member 40 is a liquid crystal display (“ lcd ”) or other similar display device or a light emitting diode ( led ). a microprocessor processes the signal generated from the optical sensor 30 to generate the pleth waveform for the user , which is displayed on the display member 40 . the control components 43 a - c are connected to the processor to control the input of information and the output of information displayed on the display member 40 . the mobile plethysmographic device 20 is preferably powered by a power source positioned on the article 25 . preferably the power source is a battery . the power source is preferably a lithium ion rechargeable battery such as available from nec - tokin . the power source preferably has an accessible port for recharging . the circuit assembly of the mobile plethysmographic device preferably operates in a range of 3 . 5 - 5 volts and draws a current of 20 - to 40 milliamps . an alternative power source is an aa or aaa disposable or rechargeable battery . the power source preferably provides at least 900 milliamp hours of power to the mobile plethysmographic device 20 . the mobile plethysmographic device 20 alternatively has a short - range wireless transceiver 29 , which is preferably a transmitter operating on a wireless protocol , e . g . bluetooth , part - 15 , or 802 . 11 . “ part - 15 ” refers to a conventional low - power , short - range wireless protocol , such as that used in cordless telephones . other communication protocols include a part 15 low power short - range radio , standard bluetooth or bluetooth low energy ( to conserve power ) or other low power short range communications means . the short - range wireless transmitter 29 ( e . g ., a bluetooth transmitter ) receives information from the microprocessor and transmits this information in the form of a packet through an antenna . an external laptop computer or hand - held device 45 features a similar antenna coupled to a matched wireless , short - range receiver that receives the packet . in certain embodiments , the hand - held device is a cellular telephone 50 with a bluetooth circuit integrated directly into a chipset used in the cellular telephone . in this case , the cellular telephone may include a software application that receives , processes , and displays the information . the secondary wireless component may also include a long - range wireless transmitter that transmits information over a terrestrial , satellite , or 802 . 11 - based wireless network 70 . suitable networks include those operating at least one of the following protocols : cdma , gsm , gprs , mobitex , datatac , iden , and analogs and derivatives thereof . alternatively , the handheld device is a pager or pda . a general method is as follows . the light source 35 transmits light through the skin of the user . the photo - detector 36 detects the light . the pulse rate is determined by the signals received by the photo - detector 36 . this information is sent to the microprocessor for creation of user &# 39 ; s pleth waveform . the microprocessor further processes the information to display the pleth waveform . the information is displayed on a display member or an electro - optical display . a plurality of premature atrial contraction events are preferably recorded in a memory of the mobile plethysmographic device 20 and accumulated for statistical purposes for display on the mobile device or on a remote device transmitted via a transceiver of the mobile plethysmographic device 20 . the mobile plethysmographic device 20 alternatively downloads the information to a remote computer for further processing and storage of information . the download may be wireless 70 or through a cable connection . fig1 illustrates a graph 105 of a ppg 110 and ecg 115 . a portion of the ppg 110 is further shown in fig1 . the ppg is generated by the mobile plethysmographic device 20 . fig1 a illustrates a graph 120 of motion detected by an x 121 , y 122 , and z 123 accelerometer . a motion sensor is included to assist in identifying motion noise and filtering the noise from the signal sent by the sensor 30 . the motion sensor , such as an accelerometer , is integrated into the circuitry and software of the mobile plethysmographic device 20 . as the motion sensor detects an arm swinging , the noise component is utilized with the signal processing noise filtering techniques to provide additional filtering to remove the noise element and improve the accuracy of the mobile plethysmographic device 20 . more specifically , the signal from the optical sensor 30 is transmitted to a custom adaptive filter before being sent to a heart beat tracking system and then transmitted to a heart rate beat output . the heart rate beat output provides feedback to the custom adaptive filter , which also receives input from the motion sensor . in one embodiment , a first systolic pulse peak and a second systolic pulse peak has a first time interval . the amplitude of the first waveform is a measurement from a first valley to the first peak . the amplitude of the second waveform is the measurement from the first valley to the first peak . fig1 illustrates a graph 150 of an example pac event as a ppg waveform . as illustrated , a pac event 155 occurs when time interval between peak p3 and previous peak is shorter than previous time interval and followed by a longer time interval , measured between peaks p3 and p4 . fig1 illustrates a plot 160 of an example pac event as it occurs in the sequence of time intervals between the nearby peaks . as illustrated , a pac event occurs when a short time interval is followed by a longer time interval , both outside the thresholds . fig1 a illustrates the maximum threshold and minimum threshold for the time intervals , and illustrates the pac event , which is a short time interval that occurs outside of the minimum threshold followed immediately by a longer time interval that occurs outside of the maximum threshold . when light is applied to a body part , such as the arm 72 , a ppg waveform , as shown in fig1 , is obtained through reflection of the applied light , the leds 35 of the mobile plethysmographic device 20 . photoplethysmographic signals given by the intensity of the led light received by the photo sensor after it is attenuated in the skin . total attenuation of the light is composed of a pulsatile component ( ac ) 141 and nonpulsatile component ( dc ) 142 , as shown in fig1 . ac 141 is a change in blood flow , which reflects a change in a blood stream due to heartbeat and related to arterial pulsation , while dc is related to light absorption in the tissue , vein , and diastolic arterial blood volume . the ppg waveform is obtained by measuring intensity of light after it has been attenuated in the skin . this intensity has an ac compliment that is inverse to the ac attenuation that occurred due to the heartbeat . the method for determining a premature atrial contraction event for a patient using the mobile plethysmographic device 20 begins with generating a plethysmographic signal . the plethysmographic signal 110 , as shown in fig1 , for a patient is generated from an optical signal generated by an optical sensor 30 and digitized and processed by a processor , which is then measured . the optical sensor 30 and the processor are on the mobile plethysmographic device 20 . the plethysmographic signal 110 comprises multiple pulse waves . a maximum peak value for each pulse wave of the multiple pulse waves of the plethysmographic signal is identified at the processor to generate maximum values of the plethysmographic signal . time intervals between adjacent maximum values of the plethysmographic signal are calculated at the processor . as shown in fig1 a , a threshold minimum time interval and a threshold maximum time interval for the time intervals are established at the processor . as shown in fig1 , a premature atrial contraction event for the patient is determined at the processor based on an identification of a time interval that is below the threshold minimum time interval followed immediately by a time interval that is above the threshold maximum time interval . the system and method described herein may be used with the mobile plethysmographic device comprising an accelerometer disclosed in rulkov et al ., u . s . pat . no . 8 , 579 , 827 for a mobile plethysmographic device with an accelerometer , method and system , which is hereby incorporated by reference in its entirety . from the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof , and other embodiments illustrated in the accompanying drawings , numerous changes modification and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claim . therefore , the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims .