Open Loop Demo: Stepping through LED Brightnesses¶

Import necessary Python modules¶

In [64]:

import numpy as np
import epics # 'epics' is part of pyepics
from time import sleep
import matplotlib.pyplot as plt

import numpy as np import epics # 'epics' is part of pyepics from time import sleep import matplotlib.pyplot as plt

Establish initial settings for LEDs, Shutter, and Photodetector¶

In [8]:

NLEDS = 6 # our sidekick system has six LEDs
for i in range(NLEDS): # for each of our six LEDs
    epics.caput('LEDS:CH' + str(i) + ':brig.VAL', 255) # Set LED brightness to 255 out of 255 (max brightness)
    epics.caput('LEDS:CH' + str(i) + ':dur.VAL', 500e3) # Set LED 'flash on' duration to 500 ms

epics.caput("SHUTTER:dur", 1.5e6) # Set shutter 'open' duration to 1.5 seconds (includes some time while opening)
epics.caput("PULSEGEN:reprate", 1/3.0) # Set systemwide repetition rate to once every three seconds

epics.caput("PULSEGEN:CH0:delay", 400.0e3) # Set LED trigger delay to 400 ms
epics.caput("PULSEGEN:CH1:delay", 0.0e3) # Set Shutter trigger delay to 0 ms
epics.caput("PULSEGEN:CH2:delay", 300.0e3) # Set Photodetector trigger delay to 300 ms

epics.caput("PHOTO:dur", 1000.0e3) # Set photodetector exposure length to one second

NLEDS = 6 # our sidekick system has six LEDs for i in range(NLEDS): # for each of our six LEDs epics.caput('LEDS:CH' + str(i) + ':brig.VAL', 255) # Set LED brightness to 255 out of 255 (max brightness) epics.caput('LEDS:CH' + str(i) + ':dur.VAL', 500e3) # Set LED 'flash on' duration to 500 ms epics.caput("SHUTTER:dur", 1.5e6) # Set shutter 'open' duration to 1.5 seconds (includes some time while opening) epics.caput("PULSEGEN:reprate", 1/3.0) # Set systemwide repetition rate to once every three seconds epics.caput("PULSEGEN:CH0:delay", 400.0e3) # Set LED trigger delay to 400 ms epics.caput("PULSEGEN:CH1:delay", 0.0e3) # Set Shutter trigger delay to 0 ms epics.caput("PULSEGEN:CH2:delay", 300.0e3) # Set Photodetector trigger delay to 300 ms epics.caput("PHOTO:dur", 1000.0e3) # Set photodetector exposure length to one second

Out[8]:

1

Write parser to interpret photodetector data string¶

In [63]:

epics.caget("PHOTO:data")

epics.caget("PHOTO:data")

cannot connect to PHOTO:data

In [62]:

def dataparse(datastr):
    """ Parse the photodetector data string, which comes in the format 'DATA: 0.02112776, TRIGCNT: 531' """
    [str1, str2] = datastr.split(',')
    data = np.float64(str1.split(': ')[1])
    trig = np.int64(str2.split(': ')[1])
    return data, trig

# Example usage:
dataparse("DATA: 0.02112776, TRIGCNT: 531")

def dataparse(datastr): """ Parse the photodetector data string, which comes in the format 'DATA: 0.02112776, TRIGCNT: 531' """ [str1, str2] = datastr.split(',') data = np.float64(str1.split(': ')[1]) trig = np.int64(str2.split(': ')[1]) return data, trig # Example usage: dataparse("DATA: 0.02112776, TRIGCNT: 531")

Out[62]:

(0.02112776, 531)

In [40]:

dataparse(epics.caget("PHOTO:data"))

dataparse(epics.caget("PHOTO:data"))

Out[40]:

(0.08680682, 91)

Record photodetector signal (to NumPy array) while stepping through LED brightnesses¶

In [57]:

NSTEPS = 30 # We will explore brightness level in 30 distinct steps

brigs = np.linspace(0, 255, NSTEPS).astype('int') # Create a list NSTEPS long, that spans 0 to 255
data = np.zeros(NSTEPS) # allocate array to hold photodetector value for each brightness step
trigs = np.zeros(NSTEPS) # allocate array to hold trigger count corresponding to each photodetector value

for i in range(NSTEPS):
    print("Brightness: ", brigs[i])
    for j in range(NLEDS):
        epics.caput('LEDS:CH' + str(j) + ':brig.VAL', brigs[i])
    sleep(5)
    datastr = epics.caget("PHOTO:data")
    data[i], trigs[i] = dataparse(datastr)
    print(datastr)

NSTEPS = 30 # We will explore brightness level in 30 distinct steps brigs = np.linspace(0, 255, NSTEPS).astype('int') # Create a list NSTEPS long, that spans 0 to 255 data = np.zeros(NSTEPS) # allocate array to hold photodetector value for each brightness step trigs = np.zeros(NSTEPS) # allocate array to hold trigger count corresponding to each photodetector value for i in range(NSTEPS): print("Brightness: ", brigs[i]) for j in range(NLEDS): epics.caput('LEDS:CH' + str(j) + ':brig.VAL', brigs[i]) sleep(5) datastr = epics.caget("PHOTO:data") data[i], trigs[i] = dataparse(datastr) print(datastr)

Brightness:  0
DATA: 0.00000000, TRIGCNT: 323
Brightness:  8
DATA: 0.00000000, TRIGCNT: 325
Brightness:  17
DATA: 0.00010094, TRIGCNT: 327
Brightness:  26
DATA: 0.00034941, TRIGCNT: 328
Brightness:  35
DATA: 0.00106118, TRIGCNT: 330
Brightness:  43
DATA: 0.00363388, TRIGCNT: 332
Brightness:  52
DATA: 0.00584165, TRIGCNT: 333
Brightness:  61
DATA: 0.00752141, TRIGCNT: 335
Brightness:  70
DATA: 0.01316894, TRIGCNT: 337
Brightness:  79
DATA: 0.01664235, TRIGCNT: 339
Brightness:  87
DATA: 0.02094400, TRIGCNT: 340
Brightness:  96
DATA: 0.02456753, TRIGCNT: 342
Brightness:  105
DATA: 0.02807200, TRIGCNT: 344
Brightness:  114
DATA: 0.03156094, TRIGCNT: 345
Brightness:  123
DATA: 0.03594800, TRIGCNT: 347
Brightness:  131
DATA: 0.03982517, TRIGCNT: 349
Brightness:  140
DATA: 0.04201741, TRIGCNT: 350
Brightness:  149
DATA: 0.04661153, TRIGCNT: 352
Brightness:  158
DATA: 0.04646917, TRIGCNT: 354
Brightness:  167
DATA: 0.04995294, TRIGCNT: 355
Brightness:  175
DATA: 0.05335388, TRIGCNT: 357
Brightness:  184
DATA: 0.05667976, TRIGCNT: 359
Brightness:  193
DATA: 0.06146282, TRIGCNT: 360
Brightness:  202
DATA: 0.06619929, TRIGCNT: 362
Brightness:  211
DATA: 0.06718541, TRIGCNT: 364
Brightness:  219
DATA: 0.07447129, TRIGCNT: 365
Brightness:  228
DATA: 0.07525035, TRIGCNT: 367
Brightness:  237
DATA: 0.07820352, TRIGCNT: 369
Brightness:  246
DATA: 0.07980047, TRIGCNT: 371
Brightness:  255
DATA: 0.08152941, TRIGCNT: 372

Plot recorded data to identify trend¶

In [58]:

fig, ax = plt.subplots()
ax.plot(brigs, data, 'x')
ax.set_xlabel("LED Brightness (in range of 255)")
ax.set_ylabel("Photodetector Integrated")
ax.set_title("Impact of LED Brightness on Photodetector Signal")
plt.show()

fig, ax = plt.subplots() ax.plot(brigs, data, 'x') ax.set_xlabel("LED Brightness (in range of 255)") ax.set_ylabel("Photodetector Integrated") ax.set_title("Impact of LED Brightness on Photodetector Signal") plt.show()