Ultrasonic Project Crisis

[Hal9000]

Hey there folks,

I'm currently in the middle of a larg-ish project of 3D position location using ultrasonics and the principle of trilateration.

My transmitter has 4 ultrasonic transducers on it, and it sends a 40kHz burst for 0.1ms and then goes silent for 0.9ms. It uses Max232 chips to step up the voltage level to the transducers so that the range is further. This works fine.

I made some recievers each with a ultrasonic transducer, then an amplification stage with a single-rail op-amp and then a 567 tone decoder. These were all working before christmas, however, on my return to the lab all but one of them has stopped working.

What is supposed to happen, is that when the pulse is generated from the transmitter, the reciever then 'catches' it, this 40kHz is then amplified, then the tone decoder goes low (OV), (and when there is no 40kHz tone, it goes high (5V) ).

However, the tone decoder always seems to activate now, even without the transmitter switched on. I am using 0.1uF and 0.01uF decoupling capacitors and a regulated power supply, and obviously they were all working at some stage so I'm now wondering what went wrong. Could it be the power supply?

These are pretty much the circuit diagrams i'm using, except obviously the transmitter has max232s.

http://www.eetasia.com/ARTICLES/2002MAR/2002MAR08_RFD_DA_AN.PDF

Cheers for taking a look

[Admin]

quick stupid-check . . . did you check the voltages on all your pins with a multimeter? this will help you rule out components that fried . . . i am guessing the Max232 is giving you 20V? might possibly be exceeding/near maximum voltage on other components . . .

are all grounds still common?

if the tone decoder always goes high, yet you dont hear the ultrasonic pulses, then the tone decoder is the failure point . . . i suspect that it would be the problem.

[Hal9000]

Yeah, its going to be a weird one to sort out

Thanks for the suggestions, i'll take a look

[Hal9000]

Woop! It works now!

It was grounding faults and the references to ground that was the problem in the end. Thanks for your suggestions.

[santiagoe]

how do you program the basic stamp2 for using 2 or more ultrasonics ping sensors?

[Hal9000]

I haven't ever used the BS2 ones because they seem like a bit of a rip-off. You could try making your own with a 567 tone decoder, though

[Hal9000]

Actually, fairplay, the PDF document that I originally posted has the circuit diagram for that on.......so basically I am using it, but not for ping. Distance calculations are therefore very easy with this ping detection.

Like, switch on the transmitter and see how long (in clock cycles) it takes to reach the reciever, placed next to the transmitter. Relatively simple, no?