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final year project: a blind stick that uses different sensors, help needed


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Hi everyone, this is my first topic....and yes i need help :)

I want to build a stick that can help the blind people while walking as my final year project.
the idea of the project is simple, im going to use a sensor (IR, sonar, prox....etc) to detect objects (walls, stones...etc) and also to detect fire.
so the sensor will detect an object, then it will send an amplified voltage to a microcontroller which will decide which sensor is active so it can send signal to the vibrator grabbed by the user.
will im facing some difficulties to understand some basic things....what is the best (easy to use) sensor that can be used in this kind of project...where i need a sensor that gives a proportional voltage value with the distance of the object faced. remember that im going to program a PIC and i will include the maximum distance by evaluating voltage values with its respective distance.
rang needed is around 1 to 2 meters only.

please advice me, and let me know if u need more info's

thank you for helping

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You can get pretty simple proximity sensors designed specifically for this type of thing - Google it.

There are different types of proximity sensors, it's up to you but I'd recommend ultrasonic because they have the greatest range and are pretty accurate.

Why use a PIC?

Heck, I'd do this the analogue way because it's easier and cheaper: a VCO connected to a speaker or piezo buzzer, could monitor the voltage and increase the frequency of the tone or pulsed tone as the object is approaching. Don't bother with an expensive VCO IC, it's easy to make one from a couple of op-amps.

A momentary switch could be placed in series with the whole circuit so it's only active when needed.

I know the analogue way isn't normally the cheapest but this is an exception, so unless you have to use an MCU then I'd recommend it.

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ok lets say im using an ultrasound sensor...and lets say im not going to use a PIC...is it possible to set a distance that when the device reaches the vibrators go on ? also note that im going to use a temperature sensor to sense any near fire from the device. btw...is the LM324 suitable for this kind of amplification ?

thank you for replying

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You can also buy ultrasonic proximity sensor modules which turn on an output when an object is placed within a certain distance.

For the thermistor circuit, you actually need two thermistors, one behind a parabolic reflector to sense radiant heat and the other sensing the air temperature, to compensate for ambient temperature changes.  A comparator could be used to activate an alarm when the thermistor behind the parabolic reflector senses a higher temperature than the compensator.

An LM324 could be used but the LM311, LM393 or LM339 are more suited to comparator applications.

What else do you want to do with this project?

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for the ultrasonic sensor...im thinking about using this one :
http://ssdl.stanford.edu/ssdl/images/stories/AA236/0708A/Lab/Rover/Parts/maxsonar-lvez1.pdf

and i might use another sensor beside the previous one to get a more accurate result, here is it:
http://www.robotokulu.com/ROBOTOKULU_dosyalar/GP2Y0A21YK-DATASHEET.pdf

sorry but i didnt understand the 2 thermistors idea, why cant i use 1, i mean what happens if i used only one (lets say LM35)  ?

if i have been able to finish this part early...im planing to make it possible to recognize holes and stairs using the Ultrasound sensor (which i think in this case i'll need a PIC )

:)

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for the ultrasonic sensor...im thinking about using this one :
http://ssdl.stanford.edu/ssdl/images/stories/AA236/0708A/Lab/Rover/Parts/maxsonar-lvez1.pdf

and i might use another sensor beside the previous one to get a more accurate result, here is it:
http://www.robotokulu.com/ROBOTOKULU_dosyalar/GP2Y0A21YK-DATASHEET.pdf

Either of those sensors will work, each has its advantages and disadvantages.

sorry but i didnt understand the 2 thermistors idea, why cant i use 1, i mean what happens if i used only one (lets say LM35)  ?

If you use only one temperature sensor and set it to sound an alarm only when it gets really hot (i.e. >50
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ok the temperature compensation is a must now...so you think 2 sensors in different places will do the job, like one sensor at the end and one at the middle of the stick  ???
what type of temp. sensor is more suitable for this application?

i think the plan of recognizing holes and stairs is no good, i was thinking about doing that by comparing the wavelengths received from the sonar, but that wont work at all :)
i'll think about another extra feature :)

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A very interesting task, indeed.

I'm missing an important point. How will the user determine the relative direction of an obstacle?

Telling me he will by using the stick you might as well forget about it. Many blinds have used a stick (and a specially trained dog) - consequently there is no advantage to your intended design.

To hero999,

I had expected a more qualified reply concerning fire detection. Where do you suggest to put the "hot" sensor in relation to the environmental sensor? A parabolic "antenna" is a great idea, but works only in one direction.

I'd dislike the idea to warn a blind of fire in front of him while the flames burn him up from the rear.

To the OP: Do a bit more brainstorming and you'll come up with a two dimensional warning system at least.

Concentrate on weight problems which might arise if the sensor array on the stick gets too heavy for the user.

Regards to both of you

HtG

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ok the temperature compensation is a must now...so you think 2 sensors in different places will do the job, like one sensor at the end and one at the middle of the stick  ???

Use a parabolic reflector as I said above. You can take the reflector from a torch and replace the bulb with the temperature sensor. The compensator should be near the sensor but not enclosed within the reflector.

what type of temp. sensor is more suitable for this application?

It doesn't matter what type of sensors you have as long as they are as identical as possible.

I'd probably use precision thermistors but a temperature sensor IC will do.

I got the idea from a book: Forrest Mims Sensor Projects, page 42 & 43.  I wouldn't recommend using the exact circuit in the book, rather than the 741,  I'd use an LM311, LM393, LM339 etc. and probably make a few tweaks to the circuit such as adding hysteresis.


A very interesting task, indeed.

I'm missing an important point. How will the user determine the relative direction of an obstacle?

If the sensor is designed to very directional, then simply sweeping the sensor from side to side will give the user an indication of where the obstacle is.

I had expected a more qualified reply concerning fire detection. Where do you suggest to put the "hot" sensor in relation to the environmental sensor? A parabolic "antenna" is a great idea, but works only in one direction.

I'd dislike the idea to warn a blind of fire in front of him while the flames burn him up from the rear.

Well if the fire is behind them, then at least they're already walking in the right direction. ;D

To be honest, I don't see much point in a fire detector.

How many times does one go walking and encounter a fire?

If the user is at a bonfire party then the fire will be so fierce they'll be able to smell the smoke and feel the heat on their skin.

And as I said before, a fire detector will be activated by sunshine and other heat sources such as incandescent lighting. This could be partly solved using a blue light sensor to disable the heat sensor in sunshine but then it will become unable to detect fire.
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well...im kind of disappointed now :(
the reason why i want to add the fire detection is to make the project more interesting... so if you have good ideas that will be helpful...i dont want to make a stick that detects obstacles only !
thats very disappointing...do you think i should look for other topic ? 

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well ya i guess i'll add it, but im still considering the PIC, just in case i found another feature.
hey...how about controlling the ultrasonic sensor distance...is that possible...i mean like a toggle switch that changes the desired range of detection ??

hey thank you for everything...you really helped me out :)

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It depends on they type of sensor you use.

A cheap proximity switch will just output a high when the object gets within a certain distance of the sensor; most are adjustable but you need to use a small terminal screwdriver.

A more expensive proximity switch will output a current, voltage or digital signal which varies depending on the distance of the object so you can use a comparator with an adjustable threshold to alter the trigger distance.

Then you can get plain ultrasonic transducers which need to have a driver circuit which you design. If you want to use a PIC, then you might as well use transducers. I've nver done this my self but it shouldn't be too hard to send the transmitter a 40kHz signal, and time how long it takes for the echo to be received. The speed of sound varies with the air temperature so if you already have a temperature sensor it shouldn't be hard to compensate for it.

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  • 2 weeks later...

ok...i'll start working on the amplification circuit soon...and i'll upload a picture of circuit im constructing...note that i need the output of the amp ( the input is connected to the ultrasonic sensor) to be giving a variable voltage starting from 0 to 5 or 7 volt depending on the distance of the obstacle.
hope to get advices and help from everyone who read this topic.

thank you

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You'll probably find that just sending a 40kHz sound out through one transducer and monitoring the intensity of the reflected pulse, will give unpredictable results. The intensity of the refection will depend as much on the shape object and its composition than its distance. For example you have two objects, one made of foam and the other from steel: the steel object is reflects sound and the foam object absorbs sound. If you placed both objects the same distance away from the amplifier proximity sensor, the absorbent object will appear to be a much further away than the reflective object.

This is why you need to measure the amount of time it takes for a pulse to be reflected off an object to gauge its distance, simply measuring the intensity of the reflection won't work. As I said earlier, if you want accuracy you'll need temperature compensation and for real accuracy air pressure compensation, although this is probably overkill for what you want.

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  • 1 month later...

What have you been doing for the last month?

When is the deadline?

Here's a comparator tutorial.
http://home.cogeco.ca/~rpaisley4/Comparators.html

Here's a couple of sites to help you with the potential divider.
http://en.wikipedia.org/wiki/Voltage_divider
http://www.technologystudent.com/elec1/resist2.htm

If the supply voltage isn't well-regulated you can use a voltage reference such as a zener diode or the LM431, the calculations are on the datasheet.

Please read through all the pages linked above before asking any more questions.

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thank you
well the deadline for the whole project is after 4 months, plus i have other subjects and projects so i cant concentrate on this one alone although its the most important.
i found my circuit in one of ur links...calculating the resistances values right now.

thank you again

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alright...i went through all websites.

ok lets say i choose this simple comparator :
comaparator1.gif

and lets say i want the comparator to trigger ON when the input reaches almost 2V.
the equation used is Vref = (R2 /R1+R2) * Vcc
substitute Vref=2V , Vcc=5V
R1=3R2/7,  lets say R1= 10K R2≈4.7k
am i still on the safe side ?
RL i couldnt find the way to get its value, same as Rv.
my main question...if i have a lets say IR sensor connected directly to this comparator, and i want it to trigger when i have 2V coming from it, where it should be connected exactly, cuz from the graph above the Vin is pointing to the Rv.

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The calculation for R2 doesn't look right to me, the correct calculation can be found in the Wikipedia article I linked above.

With R1 = 10k and R2 = 4k7 the trigger voltage will be 1.6V.

As for RV and RL: I don't think you've given this enough thought, you're not supposed to copy the schematic parrot fashion but understand it and apply it what you've learnt to the problem.

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for R2...i did get 1.6V from this equation...but the thing is the nearest resistance value that can be found in market is 4k7 (i guess) thats why i wrote  R4.7k.
regarding RL...well i think its the load thats going to b connected (i.e. motor)
Rv is represents that input device. rit ?

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for R2...i did get 1.6V from this equation...but the thing is the nearest resistance value that can be found in market is 4k7 (i guess) thats why i wrote  R4.7k.

That's pretty far out.

What value did you calculate?


regarding RL...well i think its the load thats going to b connected (i.e. motor)

Look at the datasheet for a comparator IC such as the LM393, do you really think it can directly control a motor?

Rv is represents that input device. rit ?
Yes.
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im very sorry..i think i used the wrong equation...ok R1= 3.3k R2= 2.2k

i went through the datasheet...well im not that good at reading datasheets...i get really confused. but i guess ur point is the motor can't be connected directly to LM393 without motor drive. rit ?
i hope you dont get angry or bored of me, im under real stress these days.
thank you

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  • 1 month later...

hello again

recently im facing s problem in the Ultrasonic sensor that im using,
the ultrasonic im using is LV-Maxsonar-EZ1, its a great sensor that can give different types of outputs like Analog and digital outputs. here's the datasheet of the sensor:
http://www.wrighthobbies.net/datasheets/MaxSonar-EZ1-Datasheet.pdf

the problem that im facing is that the analog output of this sensor is proportional to the distance of obstacle detected...which means when the object is at 3m distance the value (lets say) 3V, and at 0.5m the value is 0.4V.
i want it to be inversely proportional to the distance, in order for the vibrator (which is connected to the output of the sensor) vibrates strongly when an abject comes near by instead of the opposite.
any idea how to overcome this problem ?

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