It is really quite cool, but maybe for a more seasoned individual

What I mean is someone with more experience in electronics...

 

Yeah I have been drawing pictures all day trying to understand all these concepts. It is getting a little more complicated than I would like but I am still enjoying having to think really hard about all these things to make sure I understand how they work.

I have IR LED's and IR detector LED's. Which one would require more power? Also, wouldn't the IR solution not be good in well lit conditions (day time, indoor lights, etc.)?

The thing now is that I really want to understand how to use these ultrasonic transducers since it is becoming difficult to understand. I WILL NOT BE DEFEATED! The thing that bugs me is that there are circuits online (I believe someone posted one from that old magazine) that are not that complex. They only use transistors. How is it that these circuits work!? I think that now that we have traveled the "complex" path... lets try and head down a "simpler" path. With that said, let me start again:

So I have these ultrasonic transducers that I want to use to create an alarm. Anyone have a rough, very general idea of how I should go about doing this (no comparators, gates, or schmidtt stuff ).

 

You can still use your Usonic devices. Send carrier from TX to RX. If someone walks by RX level drops below a threshold and triggers a person walking by condition.
It would be something like ~~~~~~----~~~~ where the dashes are break in carrier.

It would not be a mere go/no go condition as the soundwaves would be bouncing around, so you would have to look for a drop in RX signal level, rather than 1 or 0.

Something like that. Get what I mean?

 

But will this work with a setup that has both usonic transducers on the same side? I do not want to have to put one pointing at the other. I want everything to be in one enclosure (one usonic transducer next to the other).

 

It could still work. You would have to shield tx from coupling to rx, then just detect reflected signal, and when it falls lower than static condition, someone has walked by.

Here is a basic functional block I came up with. it is by no means a design, just a concept drawing.

Attached Images

Sonicalrm.jpg (19.6 KB, 10 views)

 

I just noticed something. This circuit that I was referring to that only uses transistors is used in a different configuration than what I want. The transducers are pointed at each other and when someone steps inbetween, the signal is interrupted. This is not what I want so maybe what I want is too much

http://www.swtpc.com/mholley/Popular..._1966_pg42.jpg

 

Well, maybe my first image was not clear, and I have never built such a thing, but you should be able to keep TX and RX in one unit. You will just have to test for smaller RX changes.

Assuming Signal has a wall or some such to reflect. I dunno.

Attached Images

Sonicalrm1.gif (9.2 KB, 7 views)

 

That's why Doppler based detection fascinates me so much.

 

You might be right mneary. I was just looking at my concept and people may be sonic reflectors instead of absorbers in which case the circuit might have to detect an increase in RX power. Anyways, I think I am out of suggestions

 

Why not build one similar to an ultrasonic range finder?
The Tx unit sends a pulse which hits the opposite wall and the Rx unit receives the echo. You would sound the alarm if you didn't receive a return pulse, or the pulse came back too soon or the pulse came back too late.
If there is no wall to reflect off, then you would simply sound the alarm whenever you received a return echo from any distance. This would be easier to implement than the first example.

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Well there is a wall nearby (about 2-3ft from the circuit) but if a person crossed, the signal would not be absorbed but instead reflected. Therefore you cannot make a circuit that detects when the circuit does not receive a return pulse.

To detect if a pulse came back too soon or too late is essentially what we have been discussing (the doppler effect).

The best would be if there was no wall to reflect the signal. Then I could make the circuit just detect when a signal is reflected back to the circuit by a person passing by. However, this is not the case and there is a wall. Maybe I could fine tune the power so that the signal is not powerful enough to travel to the wall and back... however, the difference in distance from the wall to the circuit and a person to the circuit is so small that it is probably not possible to fine tune it to such a degree (especially when running off a battery that is not a stable voltage source since it will run low).

 

Yeah mike... the people will not absorb the signal, they will reflect it back to the circuit.

There HAS to be a way (simple way) to do this ...

 

A fat person wearing a thick winter coat won't reflect the ultrasonic beam. A naked person with "abs of steel" will.

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lol well there is no telling who will be passing by this alarm

 

Not exactly. Doppler measures frequency change, The method Kchriste is talking about measures time changes. Sorta like sonar. So a sonic device emits a pulse and expects a reflected return pulse in x amount of seconds. Any deviation from expected is considered a intrusion. One major difference is a doppler system can emit from TX continuously, where a system as Kchriste describes must be pulsed. In the latter case, you will use counters as your measurement device.
Simple in concept, not so simple to implement.