LASER detection circuit

[nips]

laser detection circuit

I want to build a laser transmitter and receiver for use in my robot's positional system.
Anyone with info, links,circuit ideas ?
Do i need to use modulated laser to avoid interference from ambient light.
I intend to use the laser in laser-pointers as they are cheap.
Will normal photodiodes work ? How do i build them so that they receive only the modulated beam rejecting other frequencies.


Here's how the positional system would work:
The laser is mounted on a rotating motor.The co-ordinates of 3 detectors are known and the angle subtended by the detectors can be found when the laser hits the targets(detectors).Using triangulation, the position can be calculated.

 

[Igor_S]

laser pointer circuit

Hi,
First, the modulated light is certainly better than constant one. But, if you use the laser pointer, it is difficult to provide modulation. You should use the separate laser diode and laser diode controller ( look at **broken link removed** , for example). Or use the above pointer as is, adding elektroabsorbtion modulator on beam path.
Second, it is unclear how you will define the angle under which the beam hits detector. If the detector is just a photodiode, it most often covered with lense, focusing the beam on silicon pad. You should use something more complicated, as position sensitive detectors ( HAMAMATSU makes such)

I suggest to use the opposite - few lunidirectional light sources with known coordinates, and roytating detector onboard robot.

Assuming above mentioned, it looks to be non-trivial task.

Why you do not want to consider something may be more complicated in principe, but ready-made?

For example, you can consider GPS module, providing the RS232 stream with coordinates? You just need to transmit this stream to main computer, or process it onboard.

Or, just use TV camera,( CCD or CMOS module) and some processing software?

Best Regards,

 

[Serge57]

laserpointer circuit

Sure, that is simplest way to use the direct measurement of diffusion reflection light. And modulation of source light need for this.

In lab. experiments I used the laser pointer, directly modulated from uC. Life time of the laser pointer decreese, but not signifacant for me.
May be more good solution for you is to use power infrared LED.
There are two reasons for this - 1. you don't need reflection from the narrow area 2. max of sensitivity the Si-photodiodes in IR (~1000nm) , that corresponding with the emmitted IR LED's light (~800-950nm). In other words, to use the red laser pointer with ~650nm (were the sensitivity of the Si-photodiodes aproxim. 1/2 max), not effective.

To avoid influence from ambient light, you need good photo-recieve-system with big dinamic range. This is possible, if used ph-diodes or optoreceivers like OPT101, OPT201. To avoid saturation of optoreceiver fix small gain for direct current ( constant light ) in stage convertion photocurrent-voltage. For example, set external resistor for OPT101 less then 50k ( although native 1M for this chip), use capasitor an output. You need post-amplificaition with high gain only for AC component in narrow band of you's modulation frequency.
Very best for detection signal is to use a synchronous detection.

For additional, it is very good idea to use optical filtr before optorecievers.
In case IR light system you can use the filtr from TV remote control .

It's usefull for you, that fluorescent lighting give very big disturbance. It have 100% modulation of light, in comparison with 20-30% incandescent lamp. One more reason to use IR light.

good luck!

PS: sorry for my English.

 

[nips]

laser detactions circuits

Hi,
thanks for replying.

Wouldn't it be an overkill using GPS and cam for this purpose ?
If everything else fails i will have to fall back on expensive ready-made solutions.
Anyway using unidirectional light sources means the detector has to be in the path of beam to detect the source's angle.Whereas the requirement is to detect the angle from any point in the workplace.

Serge, it would be great if you could post here the schematic of your modulated laser-pointer circuit and the receiver using opt101.

Thanks a lot !

 

[Igor_S]

laser detector circuit

Hello,
Sorry - I meant "omnidirectional" light source, thus the detector onboard robot is always capable to detect it. The angle value you can get from detector's rotation encoder. Thus, three angle values of maximum dtetcted light give you the position. By modulating the light sources, you can differ among them, thus knowing under which angle each source is seen.

Best Regards, and all the best in New Year!

 

[maxer]

laser pointer circuit schematic

use sharp sensors

maXer

Added after 10 minutes:

or have a look at optek's devices.

maXer