proximity obstacle detection sensors problems

[Shahar Levi]

Hi,
I am trying to built a presence detection device with a small microcontroller and sensors which is located on the ceiling and could alert on whether an object (non moving) is present within the radius of 1 meter in all directions. It should be very small and cheap (less than 5$) so any solutions like radar or laser scanning is out of the question, so I have left with the ultrasonic and infrared possibilities, but due to budget and size limitations i need to use as few sensors as possible.
I have tried to make some measurements with infrared transmitter and receiver in the same housing but so far I've been able to detect only objects in the range of about 20 cm, and pretty much only if it is perpendicular to the sensor. I have used TSOP1838 as a receiver and TSHF5210 as an emitter and supplied it with different current values but I could not significantly increase the range and the beam detection angle
1)

how could I increase the range and angle? I check the IR detector with a normal TV remote control and i see that the range could reach up to 5 meters and the detection angle is very large. is the IR transmitter in the remote control is amplified? and if so, how? with optical lenses or with electronic components?​

2)

I understood that the carrier frequency of the receiver is 38kHz. Then how come when I operated the emitter with 38kHz there was no detection at all? actually the detection was the strongest at around 50Hz and when I applied it with steady DC there was again no detection. what should I calculate to find the optimal frequency?​

3)

how can I increase the detection angle and save the use of multiple sensors? I thought of using metal reflectors to bounce the beam in all directions. would that work?​

4)

I have not tested it yet with ultrasonic sensors because they are a bit more expensive but if the IR fails I will have to try it. could you recommend on a ultrasonic sensor which is cheap and small and can do the job?​

Thank you very much in advance 
Shahar

 

[HTA]

Hi Shahar, I think everything depends on the size of the object and what the background is reflecting to create a meaningful signal to noise ration. For low cost application your can check-out also LED-triangulation like it is used to detect a person in front of an elevator or automatic door. How triangulation work you can check-out here: https://www.ichaus.de/FB5_en . By using HB-LEDs distance can be easy extended.

Enjoy your design work!

 

[Shahar Levi]

Thanks HTA for your reply. I am checking your suggestions.
The purpose of this is to serve as an add-on to a smoke detector and alert when large objects as a wardrobe for example is located near the detector and could undesirably affect the detectors sensitivity. Small objects would not simnifically affect the detectors sensitivity and therefore, the objects to be detected are rather large, but should be detected at any direction under the detector at about 1 meter radius.

 

[Shahar Levi]

what I don't get is how a normal tv remote control, which for my understanding does not use some high power or high brightness IR led emitter, but rather a normal 960nm one, is bale to transmit to a range of about 10 meters and with such high angle. why can't i get more than 40 cm detection? what am I missing here?

 

[HTA]

Hi Shahar, the optical design of the sensor is key to spread the beam. Example for automatic door opener: **broken link removed** . In 3D monitoring systems for elevators a time of flight approach is also used(see: **broken link removed** ).

Enjoy your design work!