problems with the Polaroid 6500 series sonar ranging module

[PauloMota]

polaroid 6500

Hi friends!

I've had some problems to interface the polaroid sonar with a PIC16F877. I send the INIT signal to sonar module but it doesn't send the ECHO signal back. When I use a function generator to send the INIT, the sonar works very well .
Anybody have any idea about the problem?

Thanks in advance.

Paulo.

 

[flatulent]

polaroid 6500 ranging module

Monitor the pulses with an oscilloscope. I suspect that it is a voltage or pulse width difference between the PIC and your lab generator. Or possibly not connecting the ground return of the module to the ground of the PIC.

 

[PauloMota]

polaroid 6500 sonar ranging module

Sorry flatulent, but I couldn't see your post last day.

I monitored the pulses with the oscilloscope and I didn't note difference between the signals and I think that all is ok about the ground. Could be a problem of insufficient current? I noted there is a lot of noise because I'm sending data to pc via PIC by MAX232 and appeared a lot of strange characters in PC (hyperterminal). When I moved away the sonar, the strange characters reduced but, again, the sonar didn't send the ECHO signal back (in my code, PIC send zero value (ascii) to PC when it don't receive the ECHO signal back).



Paulo.

 

[flatulent]

polaroid 6500 series sonar ranging module

To test for the irregular waveform (noise) from drive problems, try using a digital buffer like the 74hc4049 or 74hc4050. Put all gates in parallel. (One of these is inverting and the other is not. Pick the not inverting one.)

The other thing that you noticed is that there is interaction between the units. Try putting the sonar at the end of a m or two of twisted cable to get it far away from the logic. In fact you could go the doorway between two rooms and put the PIC on one room and the sonar in the other room on opposite sides of the common wall.

 

[robotman]

polaroid sonar

Weird.

I have used many different varients of this module before (Eval board, two different varients stripped from cameras). I have not seen the exact problem you are seeing.

A few things to check. Although there is a large cap on the input, you need a reasonable supply. What are you using. Alkaline batteries sometimes do not cut it (do to high internal R in the battery). You might want to add another big cap external.

Check the blanking control lines. Since I don't know which version you are using, make sure there are pull up/downs on the blank control.

Also, there is a power on init time. You must wait (I think I remember 50ms). If you are power switching via the micro., this could be an issue. It was for me.

Also for grins, I agree with flatulent. Check to make sure there are no ground loops. Try to always use star grounding at the supply side. Good design practice.

robotman

 

[PauloMota]

polaroid sonar ranging

Sorry flatulent, but I didn't understand what you wanted to say with "... putting the sonar at the end of a m". What is m...?
On Monday, I'll try putting the PIC in opposed sides of a common wall as your suggest. I'll try the buffer too.

Have anybody in this forum already worked with this sonar before?

thanks

Paulo.

 

[flatulent]

working of polaroid 6500 ranging module

m is the symbol for meters. The comment about the power supply dipping is good. I always do initial development with a lab supply so I can monitor the current and try the performance on the whole supply range. I also start out with big 1000 uF size bypasses everywhere and cut back at the end of development to whatever makes the supply glitches small or 22 uF several places which is greater.

 

[robotman]

polaroid 6500 range module board

PauloMota,
Are you using the 6500 eval board from polaroid? Describe the shape.

Yes, I have done designs with this board.

Thanks,
robotman

 

[PauloMota]

polaroid 6500 project

Thanks for the hints friends. I'll check all of attention.

Robotman, yes, I'm using the 6500 eval board from polaroid. The INIT signal that I'm sending from PIC to sonar stay 100ms in high and 100ms in low. The maximum range of the sonar is about 10m (equivalent to 38ms to receveid the ECHO signal back).

Sorry my lag to response, but my english is very bad and, sometimes I need a dictionary to help me


Robotman, Could you send me some project yours to me? I'm a begginer in electronics and this would help me a lot.



thanks all!

Paulo.