detecting presence of palm or hand

[rajaram04]

Hello sir
i want to make a cicuit able to detect presence of human palm or hand without touching any part of the sensor , please help

 

[jpanhalt]

You mentioned earlier wanting to detect a hand, like is done in many commercial wash basins. That is done by detecting IR reflection. You can also use beam break to detect something.

Another, non-light approach is to use capacitance. This link describes one such detector for which the term, "capaciflector" was coined:
http://www-cdr.stanford.edu/touch/previous_projects/capaciflector/capaciflector.html

Finally, you might consider using sensitive heat detectors.

Of those three approaches, the first two are probably easier to implement, and the light-based methods are more common for detecting a hand in free air. Which way do you want to go?

John

Edit: I forgot to add that you can buy the light-based faucet sensors quite cheaply.

 

[rajaram04]

okk sir thanks a lot , i observed it needs relaxation oscillator , so i need too a compatible one.
Would you please let me have a relaxation oscilator's using simple 555 or 741 or 358 etc etc
thanks

 

[jpanhalt]

I have to leave very shortly and can't give a detailed response. This circuit works as a transmitter for 38 KHz IR detector modules. You may have to modify some component values. It can be used either for beam break or reflection.



JOhn

 

[rajaram04]

kkk sir john the info is enough to let me continue , ok you proceed & complete your task sir , we will discuss later on thanksssssssssssssssssssssssssssssss

 

[rajaram04]

sir a capacitor is labelled 01M1KV . . what does it mean please explain . . thanks

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sir is it possible for us to develop a frequency above 20 000 Hz using 555 or 741 or any other common ic ?

 

[jpanhalt]

[sir is it possible for us to develop a frequency above 20 000 Hz using 555 or 741 or any other common ic ?

The NE555 works well as an oscillator well above 20KHz as shown in the example I gave above. The NE555 datasheet/application notes state that operation up to 1 MHz may be obtained, but for conservative design, one should consider 500 KHz as the upper limit.

Why do you want to use an operational amplifier like the 741 as an oscillator? Its voltage gain drops off sharply above 10 KHz. For example, a gain of 1000 at 1 Hz drops to 100 at 10 KHz. Here is a good discussion. Pay particular attention to the last paragraph:

https://www.st-andrews.ac.uk/~jcgl/Scots_Guide/datasheets/Opamps/741.html

John

 

[RCinFLA]

Might look into Thereminophone. Russian inventor, Professor Léon Theremin, who patented the device in 1928.

Think he played it for Joseph Stalin. Beach Boys used one in 'Good Vibrations'.

 

[uglyduck]

@rajaram04: can you, please, share your experience with the hand detection device. I will be thankful.

I want to design similar device - I have built a relaxation oscillator using an inverter (7414), one cap. and a positive feedback resistor and have connected an antenna to the input of the inverter. When I move my hand around the antenna I was able to vary the frequency somewhere between 610kHz and 630kHz. The principle is pretty much like that of the theremin. Next I connected a frequency meter and was able to detect the presence of the hand. Now I have few problems that I need advise with:
1. Can I use a CPLD (CoolRunner II) instead of the inverter? I think I can and will try in a few days when I have the CPLD in hand. This should be possible as CoolRunnerII has Schmitt-enabled inputs and it is fast enough, so I can charge the external capacitor with a pulse and measure the frequency or simply implement a logic for one inverter and make it oscillate by itself - then do processing. What are your comments on this?
2. I am no good with antennas... it's kind of a black magic to me. Actually my antenna is some sort of about 10cm metallic rod. I want to increase the variation in frequency range so that it is more easy to discriminate frequencies - the problem is that this range of about 20kHz in my design seems to be error-prone. How can I extend the frequency variation and thus make my oscillator sufficiently sensitive and is there a way to vary that sensitivity?
Any suggestions, please...

P.S. forgot to mention the distance of the hand - roughly speeking it's something about: 5 - inf. cm = no presence; 0 - 5cm = presence

 

[rajaram04]

@rajaram04: can you, please, share your experience with the hand detection device. I will be thankful.

I want to design similar device - I have built a relaxation oscillator using an inverter (7414), one cap. and a positive feedback resistor and have connected an antenna to the input of the inverter. When I move my hand around the antenna I was able to vary the frequency somewhere between 610kHz and 630kHz. The principle is pretty much like that of the theremin. Next I connected a frequency meter and was able to detect the presence of the hand. Now I have few problems that I need advise with:
1. Can I use a CPLD (CoolRunner II) instead of the inverter? I think I can and will try in a few days when I have the CPLD in hand. This should be possible as CoolRunnerII has Schmitt-enabled inputs and it is fast enough, so I can charge the external capacitor with a pulse and measure the frequency or simply implement a logic for one inverter and make it oscillate by itself - then do processing. What are your comments on this?
2. I am no good with antennas... it's kind of a black magic to me. Actually my antenna is some sort of about 10cm metallic rod. I want to increase the variation in frequency range so that it is more easy to discriminate frequencies - the problem is that this range of about 20kHz in my design seems to be error-prone. How can I extend the frequency variation and thus make my oscillator sufficiently sensitive and is there a way to vary that sensitivity?
Any suggestions, please...

P.S. forgot to mention the distance of the hand - roughly speeking it's something about: 5 - inf. cm = no presence; 0 - 5cm = presence

ya bro actually you are doing diffrent way & i am finding out solution for budjets & practicing on infra red beams & ultra sonics , what you are using is increasing cost & i am using simple opamp but still have to work more coz my system is responcing to light or say photons are effecting it , vicinity is making an electrostatic shield like structure which too detects presence of human body part , you don't need to make your hand waving onto the IR beam & sensor area , but but but thats not my aim actually i have to remove this extra sensitive chapter from my experiment so i can explain my practice in that way & what you are asking in above explanations ? i don't know much but here are so many expert brilliant advicers in this forum , so ask them with about your issues , i can say you ll definitly find your solutions your way . . . . thanks for asking . . .

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ya bro actually you are doing diffrent way & i am finding out solution for budjets & practicing on infra red beams & ultra sonics , what you are using is increasing cost & i am using simple opamp but still have to work more coz my system is responcing to light or say photons are effecting it , vicinity is making an electrostatic shield like structure which too detects presence of human body part , you don't need to make your hand waving onto the IR beam & sensor area , but but but thats not my aim actually i have to remove this extra sensitive chapter from my experiment so i can explain my practice in that way & what you are asking in above explanations ? i don't know much but here are so many expert brilliant advicers in this forum , so ask them with about your issues , i can say you ll definitly find your solutions your way . . . . thanks for asking . . .

but ya later i ll refer your procedure when i find myself to that level but may be not now :razz: