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Wireless receiver and transmitter

Design requirement: A child monitor control is to be designed. Parent will hold a receiver and there are 2 children holding the transmitter. When one of the kids go beyond 3m, the receiver of the parent will beep and showing which kid is going too far away from him/her. Besides, the receiver still need to indicate the battery level.

Design concept: I am about to use FM transmitter and receiver for this project. For transmitter, I am planning to use NE555 to transmit the frequency. For the receiver, I will use the receiver of a radio. I will use PIC to control the LCD as well.

Doubts:

1) Since there are 2 children (transmitter) with only 1 receiver, will it be a problem for the transmitters to transmit same frequency? Will the frequency 'step' each other and cause the frequency distorted?

If ya, how should I overcome this matter? By modulating the signal into different frequency for each kid before transmitting it out?

Or by using a receiver with 2 channel and 2 transmitter with different frequency transmitted?

2) How am I going to track for the kid to go out of the range (3m), since those waves are propagating with light of speed and PIC is not compatible to track that. So, I am thinking of using RSSI to track the strength of the signal, and from that I track whether the kid falls out of the range or not.

Will 1m, 2m and 3m make a significant difference in term of the strength of signal?

Do u all have any other better idea in building this wireless device? If I am wrong in design concept, please correct me, I am really green horn in this field. Your help will save my day. Thank you very much

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Reply to
sushi
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On a sunny day (Wed, 19 Jan 2011 09:05:34 -0600) it happened "sushi" wrote in :

Here are 2 ways for position:

1) Use GPS 2) Send a signal and measure how long it takes before you receive a reply.

It is possible to use 1 frequency if you use a packet like system, where each transciever waites for a free channel, or any other system where the remote side is sequenctially polled by the main transceiver.

There are other more complicated systems too.

3 meter is not much, way in visual range. Piece of rope, like a dog, much cheaper.
Reply to
Jan Panteltje

Here's a gps based child-tether...

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Two 10 foot cords would do just as well.

--
-Scott
Reply to
Lab1

Better, and much more cost effective and better: a piece of string or cord, tied to the child's belt or belt loop, held by the parent, which is about 3 meters long. Child wanders more than 3 meter... Oh, wait with this they *can't* wander away.

System has worked for many, many years. I'm a really old guy, and my mother 'confessed' she used one on me when I was a toddler. (I don't remember it...)

Why make a complicated, easy to fail system, when a simple one works well?

Reply to
PeterD

When we were of child-rearing age there was a harness and _leash_ for kids ;-)

Never needed one... we tended to be near "tiger mother" parents, except we stressed independent thinking.

Even the grandchildren understand. Had _one_ (out of eight) open a car door while I had stopped to get gas... swoop up kid and spank... never happens again ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

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hello,

Using RSSI will not provide you a solution given your proposed system, as the 1/r^2 relation does not hold.

You don't know the orientation of the transmitter (it will not be an isotropic radiator), the child may shield the antenna. Propagation is also height dependent.

Do some experiments with a commercial receiver with RSSI and you will convince yourself.

Best regards,

Wim PA3DJS

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without abc, PM will reach me very likely

Reply to
Wimpie

Jim, I'm with you. 5c, 12gc 8ggcs. The only one that did anything real dangerous was to climb on the rail of an ocean liner when she was about 4 years old.

48 years later and NOBODY has forgoteen it. PS she did not get as far as going over the side. 
--
John G
Reply to
John G

Wow! You're way ahead of me. Only one of our grandchildren is of marriageable age, she just turned 21 and graduated from U of A in December ;-) I was in McKale Center December 18... where the Loughner "Memorial" was just held :-( ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Jim Thompson laid this down on his screen :

I meant to add above... By the general tenor of the original question, he is way out of his depth to build such a thing. No harm in asking but I think the correct answer is buy something ready made.

--
John G
Reply to
John G

PeterD wrote: ...

Man, that's an awfully long parent! ;-P

Cheers! Rich

Reply to
Rich Grise

My parents never needed to put a _leash_ on me or any of my siblings - probably because they knew how to raise children properly.

Cheers! Rich

Reply to
Rich Grise

sushi schrieb:

Hello,

wrong concept, a FM transmitter ist not useful to measure the distance between transmitter an receiver, especially for so small distances of some meters.

Bye

Reply to
Uwe Hercksen

you mean something like this?

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Reply to
David Eather

On a sunny day (Thu, 20 Jan 2011 19:06:47 +1000) it happened David Eather wrote in :

Cannot beat that price :-)

Reply to
Jan Panteltje

Try this about to the bottom of the page "Follow Me"

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this is even better

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Reply to
Herman

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One wonders how it works. (Or even if it does work.) I wouldn't think you could do GPS or nano second timing for that price.

George H.

Reply to
George Herold

You should have seen my mom's reach!

True story:

When we moved to a new house when we were young, my mom saw the boy who was to become one of my best friends... Being marched down the street, by his mom, who had hold of his ear to guide him along. That woman was feared more than anything else by her kids--even their friends steered well clear of her whenever possible.

Reply to
PeterD

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