SentiLux
Latin for: Light sense

Range Finder Assistance
 




 

Content



Background

Blind people have used canes as mobility tools for centuries. Other techniques have been developed over many years to try to
replace the White Cane but up to now, no one have been successful. There are at least 29 million blind peoples in the world.
The most common reason for blindness is Cataract (clouding of the lens), it's responsible for more than 22 million cases of blindness,
Glaucoma (raised intraocular pressure) is responsible for 6 million cases, and Leprosy and Onchocerciasis each blinds
approximately 1 million individuals worldwide.


There are two different techniques on how to use a white cane

Categories of performance when using a cane

Description of function

Surface roughness feedback
    Mode 1 & 2 uses a derivatives formula to enhance the feeling of the surface roughness. Below is a example of the
    Constant contact mode. Constant contact mode has a more aggressive surface feedback settings.
       

Constant contact (Mode 2)                     Intensity = Distance derivative * Surface_Gain


Program modes

 


Practical examples

 


Parts

Partlist for prototype 1

 

Qty Part Sample Price pcs Price  1k  
1 Laser: OSRAM SPL LL90 Pulsed 25W Yes $23.43  
1  Laser Power Mosfet Driver EL7104C  Yes $7.42 $2.18
1 LDO Adj. LM2931 Yes $0.6 $0.22
1 OPAMP OPA2170A Yes $1.7  $0.7
1 PCB Adapter SO8 Yes $0.15  
1 Photodiode BPV10 Digi-Key: 751-1001-ND  Yes $0.96 $0.44
1 Transimpedance Amplifier MAX3654ETE+ Yes $13,1 $5.5
1 PCB Adapter for QFN16 or LGA16 Yes $0.8  
1 Acam TDC Time-to-Digital Converter TDC-GP2 Yes  $18.00  
1 PCB Adapter for QFP32 or QFN32 Yes $4.47  
5 Haptic Driver DRV2603 Yes  $2.01  
5 SMD Adapter QFN14 Yes $3  
5 Linear Resonant Actuator: LRA C10-100
Immersion TS3000 LRA
Yes $1 $0.7
1 IC REG BOST 0.85A SOT23-6 LTC3400 Yes  $4.84  
  SMD Adapter SOT23-6 Yes  $1.92  
1 INDUCTOR 4.7uH Yes  $0.34  
1 IC REG BOST 40mA SOT23-6 MAX5025E Yes $4.84  
2 INDUCTOR 47uH Yes $0.34  
1 INDUCTOR 4.7uH  Yes $0.34  
      $89.26    

 

Partlist Box / Opto+

Pos Part Sample Price pcs Price 1k  
1 Microcontroller: ARDUINO MINI 05 LIGHT Yes $15.5  
1 Photodiode Lens: F12mm Qioptiq. Part.no:      
1 Laser diode Lens 5mm      
1 Bandpass filter 12mm x 1mm 905nm Yes $46 $8,2
1 Optical Bandpass filter 12mm 808nm-1064nm Yes $4  
1 Rod Box   ?  
1 Flex Circuit board: 1 layer      
1 Battery: Rechargeable AAA      

 


 



Menu and settings


    Top                         Side                     Bottom

Menu position

Press

Button Result Feedback
Operating / Run      Vibration corresponding to measured value
-"- Press A Mode - Vibration: Mode x = vibrator x
-"- Press B Mode + Vibration: Mode x = vibrator x
-"- Press & hold A Settings Vibration on all vibrators
-"- Press & hold B On Sequence: Vibrator 5,4,3,2,1
-"- Press & hold B Off Sequence: Vibrator 1,2,3,4,5
Choose settings Press A Mode - 2Hz Vibration on corresponding vibrator
-"- Press B Mode + 2Hz Vibration on corresponding vibrator
-"- Press & hold A Enter Sequence: Vibrator 5,4,3,2,1 (fast)
-"- Press & hold B Exit Sequence: Vibrator 1,2,3,4,5 (fast)
Edit settings Press A Decrease 4Hz Vibration on selected value
-"- Press B Increase 4Hz Vibration on selected value
-"- Press & hold B Exit Sequence: Vibrator 1,2,3,4,5 (fast)

 

Choose settings Edit settings
1 2 point touch Surface roughness attenuationon
2 Constant contact Surface roughness attenuation
3 Light feedback Light attenuation
4 Max 5m Surface roughness attenuation
5 Max 10m Surface roughness attenuation

 

Lens material
Price example: 12,7 mm F 25 mm plano-convex

Material Price % @ 905nm Optical Properties
Barium Fluoride BaF2 130 90%
BK7 Glass 8 90%
Silica Glass SiO2 15 93%
FS Glass 48 91%
Calcium Fluoride CaF2 89 92%
Lithium Fluoride LiF 69 93%
Quartz Crystal 27 90%
Sapphire 40 83%

 


 

Calculating the laser power

Material Reflectivity [%]
White paper ~100
Dimension lumber(pine,clean,dry) 94
Snow 80-90
Newspaper with print 60
Beach sand ~50
Concrete 24
Asphalt 17
Black rubber 2
Opaque white plastic 110 (max.)
Reflecting foil 3M2000X 1250 (max.)


Facts Result
Sun power @ 250-2250nm 1004W/m
Sun power @ 250-2250nm & 0.07 m 70W
Sun power @ 900nm (/m/nm) 0.75 W
Sun Power @ 900nm 10nm & 0.07m 1.5W
Laser power @ 0.07m 15W
Area of Half sphere @ 10m dist. 628m
PD power @ 628m with 15W from the laser (SPL_LL90) 0.024uW/mm
PD power with 314mm Lens 7.5uW
PD current @ 7.5uW (BPV10) 1uA
Voltage @ stop1 with 62dB gain & 1k 1.25V (ideal circumstances)

 




Laser safety
The range finder must be safe to use. The goal is to keep the radiation within the limits of a class1 or
class 1M laser.


Requirements according to IEC 60825-1: (international standard for laser safety)

  1. The exposure from any single pulse within a pulse train shall not exceed the AEL* for a single pulse.
  2. The average power for a pulse train of emission duration T (applicable time base) shall not exceed the power corresponding to the AELAV...for a single pulse of emission duration T.
  3. The average pulse energy from pulses within a pulse train shall not exceed the AEL for a single pulse multiplied by the correction factor C5.
    If pulses of variable amplitude are used, the assessment is made for pulses of each amplitude separately, and for the whole train of pulses.
    * AEL = Accessible Emission Limits

 


Figur 7

Figur 4



Figur 6

Figur 11b


Figur 10b
 

 

Feature

Value

 

Laser radiation angle

30 mrad (1.72)

30mrad is too small!

 

90 mrad (5.16)

 

Aperture size

7mm

 

Aperture distance

100mm

 

Aperture angle

2 x tan-1 (3.5/100)=4

 

Laser wavelength

905nm

 

Laser pulse with

20ns

 

Laser pulse train

100 pulses/s

 

Time base

100s

 

αmax

100mrad

 

αmin

1.5mrad

 

sa

?

 

N (100s x 100Hz)

10 000

 

λ

905nm

 


Applies for 905nm

 

 

IEC 60825-1

T2 = 10 10[(α αmin)/98,5] s

T2 = 10 10(90 1.5)/98,5= 79.15s

 

Table 1-4 Note 2 fig. 4

C4 = 100,002(λ 700)

100,002(905700) = 2.57

 

Table 1-4 Note 2 fig. 6

C5 = N1/4

100001/4 = 0.1

 

Table 1-4 Note 2 fig. 7

C6 = α/αmin  for αmin <α ≤ αmax

30mrad/1.5mrad = 20

30mrad is too narrow

Table 1-4 Note 2

"-"

90mrad/1.5mrad = 60

 

Table 1-4 Note 2

Class 1 & 1M (single pulse)

Calculated limits

Laser output

IEC 60825-1

2 10-7 C4 C6 J

210-7x 2.57 x 20 = 10uJ

15W x 20ns = 30uJ

Table 1

2 10-7 C4 C6 J

210-7x 2.57 x 60 = 30.8uJ

15W x 20ns = 30uJ

Table 1

MPE cornea (single pulse)

Calculated limit

Laser output

IEC 60825-1

5 103 C4 C6 J/m

510-3x 2.57 x 60 = 0.257J/m

15 x 20n/0.07 = 43uJ/m

Table 6

MPE cornea (pulse train)

Calculated limit

Laser output

IEC 60825-1

AELtrain = AELsingle x C5 

0.257x(79.1x100Hz)1/4= 106mJ/m

43uJ/m

8.4 f) (13.3)

MPE = AELtrain/tp

0.0257/20x10-9= 1.28x106 W/m

2150W/m

 

Conclusion
The laser radiation angle have to be increased from 1.72 to at least 5.16 to comply with the
IEC 60825-1 with a 100Hz and 15W output laser power.



Calculating power consumption

Power consumption @ 100Hz & 2 Point touch

IC

Power @ 100%

Active % of time

Resulting Power

MAX3654

136mA

5% (0.5 of 10ms)

6.8mA

EL7104CS

4.5mA

100%

4.5mA

OPA2170

220uA

100%

220uA

LM50BIM3

130uA

100%

130uA

TDC-GP2

260uA

100%

260uA

MAX202CPE

8mA

0%

0mA

74AC273

3 x 4uA

100%

3 x 4uA

DRV2603

0.3uA

100%

0.3uA

LRA (vibrators)

50mA

27.5%

13.75mA

5V_Off

0mA

5%

250uA (Due to Cap.)

15V_Off

??? mA

5%

2.25mA (Due to Cap.)

Result

 

 

28.4mA

 

Runtime with 9V battery

Type

mAh

Runtime

9V Alkaline

500mAh

31h

8.4V NiMH

250mA

14.8h

 

 



Lenses and focal length

Photo diode active area: 0.88 x 0.88mm
Laser diode aperture size: 0.2 x 0.002mm

Focal  length

Lens

Dia. at far

Distance

Diameter at diode

Magnification

Focal length

Photo diode

300mm

9990mm

√(2x0.88) = 1.1mm

300/1.1 = 272 ggr

9990/272 = 36.7 mm

Laser diode

300mm

10000mm

√(0.2+0.002) = 0.2mm

300/0.2 = 1500 ggr

10k/1k5 = 6.7 mm

 


 


Schematic:

    >Property of Swetronic<