blind proximity alert

[lilly2011]

I am in need of a simple circuit that can detect a small dog within about a one foot range that would set off a beep noise at 3-5 second interval as long as the dog was within range. I have a blind dog and want to set it up in various locations to alert her that she has found something or that there is danger ahead. It would need to be battery operated and have different tones (to denote differnt objects or danger). Any help would be greatly appreciated.

[pebe]

An interesting project.
Is the noise to be emitted from the object, or from something attached to the dog?

[lilly2011]

The beeping noise only has to be produced by the sensor so that she can orient herself to the room. Thank You in advance for any help you can give.

[pebe]

Hi Lilly2011,
An IR movement detector might do the job but I think that 1). It would not detect if the dog were coming straight toward it, and 2). It would be almost impossible to calibrate it for the 1ft in-range distance required.

So my first thoughts are for a short-range radio link. A transmitter could be made from a 4011 gate and a 455kHz ceramic resonator. Powered by button cells it could easily be attached to the dog’s collar. It would probably give enough radiation for a reasonably sensitive receiver a foot away, but if not a few inches of wire should do the trick. The spare gates in the 4011 could provide for an audio modulator if one fixed tone were enough.

For the receiver, the ZN414 single chip TRF receiver comes to mind. Its modern equivalent is the TA7642 readily available on Ebay for about £1 or from ‘Rapid Electronics’ in the UK for about £0.50. The chip will receive signals ranging from 150kHz to about 2 MHz. It has good sensitivity and may work satisfactorily with just a short length of wire connected to its input (untuned). If not then another 455kHz resonator may possibly be used as the tuning element, or an LC tuned circuit.

The output of the ZN414 can be used to drive a switch. It has a good AGC circuit that causes the DC level of the output voltage to fall with increasing signal. You could use an opamp as a comparator to sense the drop in output voltage. Its output would then switch the alarm on. Once you have got to that stage where the approach of the dog will operate a switch, then there is no limit to the types of alarm you can add on.

If you could manage with a single alarm sound then you could leave out the comparitor and simply follow the receiver with a small amplifier like an LM386 to amplify the modulating frequency and drive a sounder.

All this is just food for thought at this stage and, hopefully, other members will contribute to the discussion, either adding to this idea or trashing it and proposing a better one.

[lilly2011]

That sounds like it would work better than what i was thinking as the other dogs would not set off the alarm only the blind girl. Would be willing to compensate you for a wiring diagram i could use for assembly. my email is tbear@kci.net let me know if a collaberation would be possible.

[pebe]

Ok. I'll get the bits together and try some tests.

[lilly2011]

Sounds awesome look forward to hearing back from you.