[SOLVED] height using ultrasonic sensors

[mandar_mahajan]

I have implemented the circuitary & also getting the distance.
But the problem is, the ultrasonic is geeting reflected from hard objects at a good considerable distance But when it comes to reflecting from head , the distance is just around 40cms.
I don't know what is the problem? Whether its angle related or amplitude related.

Also want to make sure that whether the 40KHz ultrasonic is geeting absorbed & scattered by the hairs on head.

Attaching my schematic.
40KHz is generated from uc.
Plz need some suggestion. i am quite stuck up in it.

 

[keith1200rs]

I cannot see a schematic, but a human head is relatively soft & is convex which will are it a poor reflector compared to a hard, flat object.

Keith

 

[mandar_mahajan]

hi, kenith
Attaching the schematic. Is there any way to solve my problem.

 

[keith1200rs]

More gain on the receiving side probably. However, if you signal is weak you may also need some better filtering. Have you looked at the returned signal on an oscilloscope, before & after amplification?

Keith.

 

[mandar_mahajan]

My gain is of 1000. which is quite high.
All the observations/ debugging are done on oscilloscope only.
The returned echo from hard object is clearly seen on scope from long distance.
But when it comes to head, echo gets attenuated after say 40-45 cms from sensor.

 

[keith1200rs]

My gain is of 1000. which is quite high.

but it could be higher. However, without more/better filtering it may cause problems to increase the gain. I am sure the problem is simply due to the soft, curved nature of a head. A more focussed beam may help/

Keith.

 

[mandar_mahajan]

How to focus the beam, my asthetic design is in such a way that I can't use a cone for the sensors.
& about increasing the gain, if i increase it above 1000, it is creating problems.

 

[keith1200rs]

if i increase it above 1000, it is creating problems.

What problems? As I mentioned you may need to use some better filtering if you want to increase the gain. Try to split the gain equally between both amplifier stages, although it would probably be worthwhile having an extra stage. I have used gains up to 100,000 total with ultrasonics but that is with a lot of filtering.

Keith.