ExpEYES Programmer`s Manual
Contents
1. and SQR1 to Al Run the following program from pylab import import expeyes eyes p expeyes eyes open p set_sqr1 100 t v tt vv p capture01 300 100 plot t v plot tt vv show 2 5 Capture modifiers The behavior of capture calls can be modified in several ways to enhance their flexibility They can be made to start only when the input is between some specified limits this feature is essential for getting a stable trace for CRO applications You can also synchronize the beginning of digitization process with some external logical signal Digitization is made to wait for specified level changes on a digital input This feature is useful for digitizing transient waveforms The synchronizing signal is derived from the waveform itself and applied to a digital input It is also possible to SET CLEAR or PULSE one of the digital outputs just before starting the digitization process The control functions only changes the settings at the micro controller end the actions are visible only during the subsequent capture calls 2 5 1 disable actions enable wait high low falling or rising Calling this function makes all the subsequent capture and capture01 calls to wait for the specified digital input socket to go HIGH LOW before starting digitization Tf that does not happen a timeout error will happen Connect SQR1 to both AO and IDO and run the following program from pylab import import expeyes eyes p expeyes e2. can vary from 7Hz to 90 kHz in four ranges Setting the desired frequency will automatically select that range Then you need to 11 adjust the external 22k0 potentiometer to get the desired frequency The actual value can be read through software p set_sqr2 10 print p get_sqr2 p set_sqr2 0 sets SQR2 to HIGH p set_sqr2 1 sets SQR2 to LOW will print anything between 7 to 25 depending on the position of the external potentiometer If no external resistor is connected result will be zero Setting 0 will make SQR2 HIGH and 1 will make it LOW 2 6 3 set pulse Sets the dutycycle of the 488 3 Hz pulse on the PULSE output from 0 to 100 Returns the actual value set print p set_pulse 30 duty cycle to 30 Even though the requested value is 30 the actual value set will be 29 8 since it is done in 255 steps 2 7 Frequency Counters 2 7 1 digin frequency Measure the frequency of a 0 to 5V square wave at IDO or ID1 Connect SQR1 to IDO and run the following code import expeyes eyes p expeyes eyes open p set_sqr1 500 print p digin_frequency 0 2 7 2 ampin frequency Measure the frequency of a bipolar signal amplitude gt 100 mV connected to Terminal 15 Connect SINE to T15 and run the following code import expeyes eyes p expeyes eyes open print p ampin_frequency The frequency of the sinewave will be printed 12 2 7 3 sensor frequency Measure the frequency of voltage fluc
3. e eyemath py data analysis using modules numpy and scipy They can be installed by using the tgz files or the deb packages provided on http expeyes in Chapter 2 Hardware Communication The module expeyes py contains all the functions required for communicating to the hardware in addition to some utility functions The functions are inside a class and the open function returns an object of this class if expEYES hardware is detected After that the function calls to access expEYES are done using this object as shown in the example below import expeyes eyes import the eyes library p expeyes eyes open returns an object if hardware is found print p get_voltage 0 print the voltage at input AO The hardware communication functions can be broadly grouped into analog inputs analog outputs digital inputs digital outputs time interval measurements waveform generation etc For making plots using the data from expEYES we will use the matplotlib package 2 1 Digital Inputs IDO and ID1 You can connect them externally to ground or 5 volts to make the voltage level HIGH or LOW The software can read the voltage level present the inputs A voltage less than 1 volt is taken as a LOW or 0 Anything greater than 2 volts is treated as a HIGH or 1 One of the powerful feature of digital inputs is the ability to measure the time between level transitions with microsecond resolution 2 1 1 read_ inputs Returns an intege
4. for one cycle and the second one returns the time for 10 cycles 9 rising edges in between skipped This call can be used for frequency measurement The accuracy can be improved by measuring larges number of cycles 2 9 Active Time Interval Measurements During some experiments we need to initiate some action and measure the time interval to the result of it The actions are initiated by setting clearing or by sending pulses on the Digital Outputs The results will generate voltage transitions on Digital Inputs 2 9 0 1 set2rtime set2ftime clr2rtime clr2ftime int set2rtime out in remaining functions have similar prototypes These functions SET CLEAR a digital output socket specified by out and wait for the digital input specified by in to go HIGH LOW USAGE p set2rtime 0 1 2 9 0 2 pulse2rtime pulse2ftime int pulse2rtime int out in int pulse2rtime int out in Sends out a single pulse on out ODO or OD1 and waits for a rising falling edge on in IDO or ID1 The duration and the polarity of the pulse is set by set _ pulsewidth and set_ pulsepol functions On powerup the width is 13 microseconds and polarity is positive voltage goes from OV to 5V and comes back to 0V The initial level of out should be set according to the polarity setting If the polarity is LOW TRUE the level must be set high beforehand and it should be set low for HIGH TRUE pulse p set_pulse_width 1 p set_pulsepol 1 print p pulse2rti
5. ExpEYES Programmer s Manual Ajith Kumar B P Inter University Accelerator Centre New Delhi 110 067 Version 1 May 2011 http expeyes in Contents 1 Introduction 4 Lbs Software t s Ore be Give ois ad wes A A one Ge oe ee ed 5 2 Hardware Communication 6 2 1 Digital Inputs IDO and ID1 Sal ee oes ee al et ae ee al ot ae o cae 6 Dell read Inputs aren ar ae op eee ae Ae og arte gp Al at atte tp VE co oe Ue ME ce ee Se Bes pte 6 2 2 Digital Outputs ODO and OM o tik eck ae teat he ey oti Ee ate eR ate ct 7 2 LES OI US e ga e p o e e AB ee eee a She A T7 Zar Analog US a a e oe A oe eat a ene aj T Pee SOL AR T 2 ABOT CUTTERE do e o a ae th ee eh ee ee S a e Se atl EN 7 Zoe SEL DOV 6p amp hace ahh Bo doe ta Se ee Spine BG ae ga ae a 8 2A Analog PUTS ste ton Gots Shoe rena an Wee aOR a ee ee is N 8 24 1 g t Voltage s i e rd tad Rye Bed Atk Ob hee ah hole Bek ee ee hd 8 2A SEA ii a E ey ae Wat 8 2 4 3 captureQl A e BSG Brae bom aa alo les pd fae co da fe 2 de 9 2 0 Capture modifiers cool son eh A ee Rea pil Soe Wee 9 2 5 1 disable actions enable_wait_ high low falling or rising 10 2 5 2 enable set high enable set low 10 2 5 3 enable pulse high enable pulse_low 10 2 6 Waveform Generation iS A DRA E e AA VEA 11 26l a A A A aaah athe ee teed ee 2 11 202a SRO DS SOTZ eee a e AAS as de An MA 11 2 0 3 SCL pulse 2 A AAN A E OAR AA e aa 12 27 Frequeney Counter
6. l in milliseconds is the second argument Returns the frequency spectrum ie the relative strength of each frequency component Connect SINE to AO and run the following code from pylab import import expeyes eyes expeyes eyemath as em ns 1000 number of points to be captured tg 100 time between reads in usecs p expeyes eyes open t v capture 0 ns tg x y em fft t tg 0 001 tg in millisecs plot t v The raw data plot x y data calculated from par show Modify this program to show the frequency spectrum of a square wave 17 Chapter 4 Experiments Most of the experiments described in the user manual can be done by writing few lines of Python code 4 1 IV curve of a resistor cs 28 GND 27 Make an array of current values and another one with same size filled with zeros The voltage at the CS terminal returned by set_current is filled in to the second array Both are from pylab import import expeyes eyes expeyes eyemath as em p expeyes eyes open NP 20 current linspace 1 2 0 NP voltage zeros NP for k in range NP voltagelk p set_current current k plot current voltage x vf par em fit_line current voltage plot current vf print R 5 3f kOhm par 0 show 18 4 2 Transient response of RC circuits opi a 1K COIL uF GND Ao 26 We need to apply a voltage step at OD1 and immediately start capturing the vol
7. list 4 f 0 C Connect SINE to AO and run the following code from pylab import import expeyes eyes expeyes eyemath as em p expeyes eyes open t v p capture 0 400 100 vfit par em fit_sine t v print par A f 0 C plot t v The raw data plot t vfit data calculated from par show par 1 is frequency in kHz since the time is given in milliseconds 3 0 3 fit dsine Accepts two vectors x and y and tries to do a least square fitting of the data with the equation A Apsin 27 ft 0 x exp dt C Returns the fitted data and the parameter list A f 0 C d par 1 is frequency in kHz since the time is given in milliseconds and d is the damping factor 16 3 0 4 fit exp Accepts two vectors x and y and tries to do a least square fitting of the data with the equation A Agexp kt C Returns the fitted data and the parameter list 4 k C Connect a 1uF capacitor from AO to GND 1k resistor from OD1 to AO and run the following code from pylab import import expeyes eyes expeyes eyemath as em p expeyes eyes open p write_outputs 2 Take OD1 HIGH p enable_set_low 1 OD1 go LOW before capture t v p capture 0 200 20 plot t v vfit par em fit_exp t v print par plot t v The raw data plot t vfit data calculated from par show par 1 is the time constant RC in milliseconds 3 0 4 1 fft Does a Fourier transform of a given data set The sampling interva
8. me 0 1 measures the time from a pulse on ODO to a rising edge on ID1 2 9 0 3 set pulse width Sets the pulse width in microseconds to be used by the pulse2ftime and pulse2rtime func tions p set_pulse_width 10 14 2 9 0 4 set pulsepol Sets the pulse polarity to be used by the pulse2ftime and pulse2rtime functions pol 0 means a HIGH TRUE pulse and pol 1 means a LOW TRUE pulse p set_pulsepol 1 2 10 Disk Writing 2 10 1 save data Input data is of the form x1 y1 x2 y2 where x and y are vectors are save to a text file Save the data returned by the capture functions into a text file Default filename is plot dat that can be overriden by the second argument Connect SINE to AO and run the following code import expeyes eyes p expeyes eyes open t v p capture 0 200 100 p save t v sine dat open the file using the command xmerace sine dat 15 Chapter 3 Data processing The data acquired from expEYES hardware is analyzed using various mathematical techniques like least square fitting Fourier transform etc The module named eyemath py does this with the help of functions from the scipy package Most of the functions accepts the data format returned by capture functions 3 0 2 fit sine Accepts two vectors x and y and tries to do a least square fitting of the data with the equation Asin 27 ft 8 C Returns the fitted data and the parameter
9. nction The calling program should make sure that the socket is set to LOW before calling capture else a HIGH to LOW transition will result instead of a pulse The enable_pulse_low takes the output LOW and then HIGH after some duration This function can be used to capture a waveform that is triggered by an input signal For example connect the digital output OD1 to the input of a C555 mono shot circuit and connect the 555 output to AO Set the mono shot delay to around a millisecond and run the following code from pylab import import expeyes eyes p write_outputs 2 OD1 to HIGH p set_pulse_width 1 p enable_pulse_low 1 LOW TRUE pulse t v p capture 0 300 10 plot t v show 2 6 Waveform Generation ExpEYES can generate square waves on SQR1 and SQR2 Variable duty cycle pulse of 488 Hz can be generated on the PULSE output The output SQR2 require an external variable resistor for its operation 2 6 1 set sqrl Generates a square waveform having 50 duty cycle on SQR1 The frequency can vary from 15Hz to 4MHz but all intermediate values are not possible The function returns the actual frequency set import expeyes eyes p expeyes eyes open print p set_sqr1 1000 print p set_sqr1 1005 The first line will print 1000 0 but the second line will print 1008 06 that is the possible frequency just above the requested one 2 6 2 set sqr2 Generates a square waveform on SQR2 The frequency
10. nt p get_voltage 0 prints the voltage at A0 print p get_voltage 2 prints the voltage at A2 Connect BPV to AO using a piece of wire and run the following program several times import expeyes eyes P v input Enter V 5 to 5 expeyes eyes open p set_bpv v print p get_voltage 0 2 4 2 capture t v capture ch NP tg where ch is the input channel number NP is the number of measurements and tg is the time between two measurements in microseconds Two lists containing the time milliseconds and voltage volts coordinates are returned by this function Connect SINE to AO and run the following program from pylab import import expeyes eyes p expeyes eyes open t v p capture 0 300 100 plot t v from pylab show from pylab Terminal Channel Range V AO 0 5 to 5 At 1 5 to 5 A2 2 0 to 5 SEN 4 0 to 5 CS 6 0 to 5 If the voltage to be measured is in the 0 to 5V range use A2 that will give a better resolution than AO or Al The SEN input is capable of measuring the value of a resistance connected from it to GND 2 4 3 capture0l This function captures AO and A1 together with timing correlation t v tt vv capture01 NP tg NP is the number of measurements and tg is the time between two measurements in microsec onds Four lists containing the two pairs of time milliseconds and voltage volts coordinates are returned Connect SINE to AO
11. r whose 2 LSBs represents the voltage level present at the Digital Inputs IDO amp ID1 print p read_inputs amp 3 print only the 2 LSBs will print the number 3 11 in if nothing is connected to the sockets they are all internally pulled up to 5 volts With only IDO grounded the result will be 2 10pin TYou can learn more about this package from http matplotlib sourceforge net The python book at http expeyes in sites default files mapy pdf gives an introduction to matplotlib 2 2 Digital Outputs ODO and OD1 You can set the voltage level on them to LOW or HIGH volts using software The first Digital Output ODO is transistor buffered and capable of driving up to 100 mA current but OD1 can drive only 5 mA If you connect LEDs to them use a 1K 2 series resistor for current limiting 2 2 1 write outputs The function takes an integer as argument whose 2 LSBs are used for setting the voltage level on the four Digital Output sockets p write_outputs 1 Sets ODO HIGH p write_outputs 2 Sets OD1 HIGH p write_outputs 3 sets both HIGH Measure the outputs with a voltmeter or by connecting an LED from the terminal to ground with a 1kQ resistor in series 2 3 Analog Outputs ExpEYES has two Programmable Voltage Sources the Unipolar Programmable Voltage UPV and the Bipolar Programmable Voltage BPV The voltage level on UPV can be set from 0 to 5V The resolution is 12 bits means the minimum step is aro
12. s iay e A A EAS E RA 12 Dovel o ic ao AAN 12 Qed SAMA ATEQUENCY ote Uae he oe ii A A a den 12 2 7 3 sensor_ frequency Ls EA a 13 2 8 Passive Time Interval Measurements Laa Oe A oy 13 2 8 1 r2ftime f2rtime r2rtime f2ftime o a 13 2 8 2 m AA A eae 13 2 9 Active Time Interval Measurements a a 14 2 9 0 1 2 9 0 2 2 9 0 3 2 9 0 4 2 10 Disk Writing 2 10 1 save_data 3 Data processing 3 0 2 3 0 3 3 0 4 4 Experiments 4 1 4 2 Transient response of RC circuits IV curve of a resistor set2rtime set2ftime clr2rtime pulse2rtime pulse2ftime set pulse width set_pulsepol clr2ftime Chapter 1 Introduction The design of expEYES is shown schematically in the block diagram below Python functions are available for accessing every feature of the expEYES hardware like measuring a voltage or frequency setting a voltage or frequency measuring time intervals etc Data analysis and graphics functions are given in two separate modules Application programs are developed using these modules USB link The top panel showing the 32 Input Output connectors Experiments for Young EXP E YE S Engineers amp Scientists gt PHOENIX Project www expeyes in Developed by IUAC New Delhi 67 www iuac res in 1 1 Software There are mainly three modules under the expeyes package e eyes py hardware communication e eyeplot py Graphics using using Tkinter module
13. tage at AO NP 200 number of readings tg 10 time gap between them keep NP tg around 3 RC from pylab import import expeyes eyes expeyes eyemath as em p expeyes eyes open p write_outputs 2 p enable_set_low 1 OD1 go LOW before capture t v p capture 0 NP tg choose NP tg according to RC plot t v vf par em fit_exp t v exponential fit plot by wiser print abs 1 par 1 print RC value show 19
14. tuations at SEN input Connect SQR1 to SEN and run the following code import expeyes eyes p expeyes eyes open p set_sqr1 100 print p sensor_frequency 2 8 Passive Time Interval Measurements Digital Inputs can be used for measuring time intervals between level transitions on the digital inputs with microsecond resolution The transitions defining the start and finish could be on the same terminal or on different ones 2 8 1 r2ftime f2rtime r2rtime f2ftime r2ftime ini in2 r2ftime returns delay in microseconds from a rising edge on in1 to a falling edge on in2 The arguments 0 or 1 indicate digital inputs IDO and ID1 Similarly f2rtime measures time from a falling edge to a riding edge Connect SQR1 to IDO and run the following code should print around 500 usecs import expeyes eyes p expeyes eyes open p set_sqr1 1000 half period 500 usecs print p r2ftime 0 0 2 8 2 multi r2rtime Measures time interval between two rising edges of a waveform applied to a digital input The second argument is the number of rising edges to be skipped between the two measured rising edges This way we can decide the number of cycles to be measured Connect SQ1to IDO and run the following code import expeyes eyes p expeyes eyes open p set_sqr1 1000 a p multi_r2rtime 0 9 time for 10 cycles in usecs print 10 0e6 a frequency in Hz 13 For a periodic waveform input the first line returns the time
15. und 1 25 mV The voltage at BPV can be set from 5 volts to 5 volts UPV is the direct output of a DAC BPV is made from a unipolar signal using summing circuits that may give some offset If the requirement is only from 0 to 5 volts use UPV 2 3 1 set upv Set the output voltage of the UPV The value of V should be from 0 to 5 volts p set_upv 2 5 Sets 2 5 volts on UPV 2 3 2 set current Set the output current at CS between 0 05 mA to 1 mA This function returns the voltage at the current source output that will be decided by the value of the external load resistor connected For example setting 1 mA and connecting a 1kQ resistor from CS to Ground the voltage read will be 1 volt 0 001A x 1000Q The load and the current should be chosen such that the product is less than 2 volts print p set_current 1 0 prints the IR drop across the load Note You can use either UPV ot CS at a time since they share the same DAC output 7 2 3 3 set bpv Set the output voltage of the BPV The value of V should between 5 and 5 volts p set_bpv 2 5 Sets 2 5 volts on BPV 2 4 Analog Inputs There are four analog input channels AO A1 A2 and the SENsor input We can read the voltage level at any of this inputs either as single reads or multiple reads in a single function call normally to capture a waveform The time gap between consecutive reads inside a capture can be set with microsecond resolution 2 4 1 get voltage pri
16. yes open p set_sqr1 100 p enable_wait_rising 0 wait for a LOW on IDO t v p capture 0 200 100 start at a rising edge plot t v p disable_actions removes all modifiers t v p capture 0 200 100 can start from anywhere plot t v show 2 5 2 enable set high enable set _ low In some applications it would be necessary to make a digital output socket go high low before digitization starts This function when called with a digital output socket number as argument makes the subsequent capture function set clear ODO or OD1 before it begins the capture process Action can be defined on only one digital output at a time Capturing the voltage across a capacitor while charging discharging is a typical application of this feature Connect a luF capacitor between AO and GND Connect a 1KQ resistor from OD1 to AO and run the following code from pylab import import expeyes eyes p expeyes eyes open p write_outputs 2 Take OD1 HIGH p enable_set_low 1 OD1 go LOW before capture t v p capture 0 200 20 plot t v show The enable_set_low 2 makes OD1 to be taken HIGH just before digitizing the voltage on AO 2 5 3 enable pulse high enable pulse low In some applications it would be useful to send a PULSE on a digital output before digitization starts The enable _ pulse_high makes the specified output HIGH for some duration and then 10 makes it LOW The duration is set by the set_ pulsewidth fu
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