SentiLux
Latin for: Light sense

Range Finder Assistance
 

Content

• Background
• Description of function
• Program modes
• Practical examples
• Parts
• Menu and settings
• Calculating the laser power
• Laser Safety
• Calculating the power consumption
• Lenses and focal length
• Schematic

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

• 2 point touch technique

Swinging the cane from side to side and tapping the edges of one’s walking path on either side in an arc slightly wider than one’s shoulder
 
• Constant Contact Technique

Sweeping the cane from side to side and keeping the cane tip in contact with the surface at all times

Categories of performance when using a cane

• Object preview
  is related to the reliable detection of obstacles on one’s walking path,
   
• Surface preview
  refers to the detection of changes in elevation and texture of one’s walking surface.
  Drop-off detection is a key component of surface preview and is crucial for the safety of blind travelers,
  since missing drop-offs, such as curbs, may cause cane users to fall or stumble into the path of approaching vehicles.
  
• Foot-placement preview
  pertains to whether the cane tip has touched the surface area where the cane user’s foot will be placed 

Description of function

• SentiLux is a replacement for the traditional white cane. It has the same function and length as the regular white cane but includes some extra smart features:
  
*    Increase length (up to 10m)
*    Surface roughness feedback
*    Light and heat feedback
• 5 vibrating micro motors are used as a distance feedback.
• The distance is measured at a high sampling rate, 100 times/s, which will result in a very rapid and sensitive feedback.
• The range finder comprise of a laser, photodiode and a TOF (Time Of Flight) counter.
• It uses the Time Of Flight technique to calculate the time it takes for a laser pulse to travel from the device to the target and back again.
  The distance is calculated by the formula: Distance = 0.5 * Time Of Flight * Speed of light
  
• There are 5 different modes to choose from.
   

  Mode (Switch)	Function	Distance in meters
  		Vibrator 1	Vibrator 2	Vibrator 3	Vibrator 4	Vibrator 5
  1	2 point touch	0.25 - 0.5	0.5 - 0.75 0	0.75 - 1	1 - 1.3	1.3 - 1.75
  2	Constant contact	0.25 - 0.5	0.5 - 0.75 0	0.75 - 1	1 - 1.3	1.3 - 2
  3	Light feedback	Hot & Bright				Cool & dark
  4	Max 5m	1	2	3	4	5
  5	Max 10m	2	4	6	8	10

• Mode 1 is used to simulate a white cane with 2 point touch technique. With this method it is possible to feel when the distance reach the tip of a virtual cane at 1.3m. If the distance is shorter then 1.75m, vibrator 5 starts to vibrate at a minimum amplitude that will increase as the distance decreases. All vibrators will vibrate when the distance passes below 1.3m to indicate the tip of the virtual cane...
• Mode 2 is used as Constant Contact Technique. The only difference from Mode 1 is that there is no vibration feedback at 1.3m, the length of the "tip" is increased and the surface roughness feedback is more aggressive.
• Mode 3 is for light feedback. It is actually a combination of both light and temperature making it feel difference between for snow, asphalt/pavement, skin, fire etc.
• Mode 4 & 5 is the far sighted mode . It is used to feel house endings, trees, cars or people in crowded places.

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

• Mode 1
  Below is an illustration how the vibrators works during a linear movement from 2.1m to 10cm.
  All the vibrators oscillate at maximum for 40ms when the distance passes 1.3m. This mode is used to simulate the 2 point touch technique.
  

• Mode 2
  This mode is very similar to Mode 1, the only difference is that the feedback pulse at 1.3m is removed, the length of the "tip"
  is increased and the surface roughness feedback is more aggressive. This mode is used to simulate the Constant Contact Technique.
  
• Mode 3
  Mode 3 is a combination of both light and temperature feedback. It feels difference between snow, asphalt/pavement, skin or fire.
  
• Mode 4 & 5
  Below is an illustration how the vibrators works at mode 4 and 5. This mode is used to get a quick view of the surroundings,
  for example cars when crossing the road, a house ending near a crossroad, a door opening or the incline or decline of a pathway.
  

Practical examples

• Walk in the park
  Below is a typical example on how the range finder works. In the example the SentiLux scans the surroundings from left to right at mode 4.
  
   
• Sensing the decline of a pathway
  The range finder is set to mode 4 and moved from 1m to 5m.
  
• Update frequency and beam angle
  Below is a visual view on how the update frequency and beam angle covers the field of view.
  The picture illustrate a fast walking, 0.5s between sweeps and a 2 point touch technique.
     

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)

Lens material
Price example: ø 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

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.

• Class 1:
  Laser products which are safe un-der reasonably foreseeable conditions either inherently or by virtue of their engineering design.
• Class 1M:
  Laser products which are eye safe without optical instruments but potentially hazardous when viewed using optical instruments such as eye loupes.
  The AEL values for Class 1 and Class 1M are the same but the measurement criteria differ.

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

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

Lenses and focal length

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

Schematic:

    >Property of Swetronic<