RF Transciever project help

Hello everybody,

Please i need your help in a project i'm working on, and here is the description of the project:
it's a transceiver module "Transmitter& Receiver", the transmitter to be installed in a key-chain like the car remote alarm one, with 4 buttons, to send four different signals to a Receiver which is the hard thing to be made in a very compact size PCB "3cm*1cm", to be installed in a bracelet in the hand of a child, with built in motor to make vibration when the signal is sent by the transmitter, so i need both the transmitter and the receiver to be included in a surface mount circuits.

so what the idea behind that project?, to do transmitter send four different signals to four receivers?, and how to do it?, would zigbee be a low cost way to use for the design?, or there is another way which is simple and lower cost than zigbee?, just need your help as i am not familiar with Communication engineering, but with some search and goggling i see that i can do the project, also with your help, so will appreciate your help a lot, as i'm in so much need to execute that project.
Thanks in advance.

Hi

what kind of signal will be sent to reciever? some control or configuration signal or something else?
why four receiver? are they installed at different places?
decision of realization technology will depend upon the range u want to cover and power of the transmitter and the data rate.

Anil

Thanks aniltunwal for your care to reply, and here are the answers for your questions:

- what kind of signal will be sent to receiver?
RF Signal to be sent.

- some control or configuration signal or something else?

yes, Four buttons to be used for activating motors which will be installed in a bracelet to make vibration in the arm of child with hearing disabilities for making attention to him, that's when button is pressed,
four buttons for doing that with four bracelets seperatly.

- why four receiver?

for four children, every child will have his/her own bracelet where the receiver is installed.

- are they installed at different places?
yes in different places, but in same circumstance.

- decision of realization technology will depend upon the range u want to cover and power of the transmitter and the data rate.
Power of the transmitter will be like the power of a car alarm remote control, in a volume of keychain with 4 buttons, so will be powered by 1.5 v battery, the data rate i think will be like the car alarm system data rate.

do you have an idea about how to do that?, recommend me a handbook, or a website with similar circuit diagrams?,Reliable circuit diagrams? the pcb of transceiver will be surface mounted, and the receiver circuit has to be in a volume of "3cm length*1cm width", to be fit in the bracelet,How can you help me with that?.
I'll appreciate anybody help here, as i need that project to be done as soon as possible,
Thanks in advance.

still waiting any reply to close my post, anybody willing to help me? .

It is no idea to reinvent the wheel for this kind of electronics.
Buy this one and adjust it to fit your idea:**broken link removed**
If you want to improve it or reduce size by developing something more integrated, is mostly a question what cost you can accept.
Also car remotes work in similar way at typical 433 MHz.
A bracelet is not best position for an antenna. Increasing frequency can help a bit as relative antenna size decreases proportionally. Drawback is reduced coverage, especially when out of optical coverage. Also current consumption increases with frequency in general.

That's not what i want, i need one transmitter works with four receivers, not one transmitter and one receiver, like the circuit you sent on ebay link, yes in a shape of the keychain car alarm system, the transmitter to be, but the four buttons would send signals to four receivers which will be installed in four bracelets, every bracelet with its own receiver.
Hope i expressed in a way let you understand what i wanna do for my project, so you an help me more.
waiting your reply,
Thanks.

You have to buy 4 sets of receiver and transmitters and then throw away 3 of the transmitters.
Now you have one transmitter and four receivers.

nice one E Kafeman,
an ideal solution for multiple receivers and you have some spare transmitters for when one gets wrecked and fails

BUT Gaber2611, you are going to have to reconsider the size of your receiver encapulation. cuz without some specialised hi tech design and manufacturing costing lots and lots of $$, you are not likely to make it as small as you hoped.

Dave

Thanks Davenn, :grin:
In this case do the Ebay seller sell both receivers and transmitters one by one. If Gaber2611 not did visit the seller Ebay-shop to find out that, can it be hard for him to find all other missing parts in his project. The simplest solution for him is to buy 4 TX/RX sets.
Besides that, same product or similar product is probably sold by 40 other shops at Ebay. I did select first one I did found. It is up to to Gaber if he wants to do some further digging to find better alternatives.
In a more general case, for prototyping and investigating if the circuit does work as expected, should it be enough to buy one receiver. If it not fulfill expectations are there a lot of alternative solutions both at Ebay and other places. If the circuit not is usable for Gaber2611's project, is it unnecessary to spend money on 4 identical circuits. For this RX circuit could it be seen at the Ebay-photo that RX IC is a DIL package which with some luck also exist in a smaller SMD size, probably better size for what Gaber want to build. To find out, is it more then enough to buy just one RX unit.

okay, Great, Thank you for your help, and for the laughing at me .

i am just wasn't sure that the module would be adjusted to my project, what if i use xbee?, would it be better solution, than buy four transmitters and throw away 3? .

Hi Gaber,
No I am not making fun of you. It was my way to tell you that you have to think your self and not expect me to give information about how to get correct number of units that you intend to develop.
There are many different RF communications systems and standards. All have different advantages and limitations. If it is a low budget project where you not want to do much more then solder together simple pieces and doing minor redesign, is the 315/433 MHz proposal as good as anything else.
If you want a better challenge, building a RF system requiring calculation and programming skills for both digital and RF, go ahead.
You maybe end with something like this: https://www.gizmag.com/go/1169/
It was compact technology then, for more then 12 years ago, and I had a tiny part of the development.
Guess what? Almost all kids hated it, and did throw it away, so it did also got a parental only locking function. If you not also includes a parental only locking function, can it be an reason for you to buy some spare receivers.

I think the size is not a big problem but it may be a big challenge to keep both transmitter and receiver in low power consuming. There are 2 schemes from google:
1. Based on wirelss remote control(such as used in a RC car toy): The transmitter sends out a coded FSK/ASK signal when buttons pressed. The receiver continuously receives signals on air under certain frequency which is controlled by a crystal or a SAW. When the receiver detects signal level above threshold, it will send out the code which is then decoded by an MCU or a decoder IC. The system is simple, fast in response and low cost. The receiver may consume 2~3 mA current and the transmitter has less power-consuming.
2. Use zigbee or other sub-1GHz wireless MCUs: The transmitter and the receiver will work in synchronized time slot mode with a duty cycle of such as 30ms/1 seconds. The system will be complex, powerful, security and slightly expensive compared with former scheme. Both receiver/transmitter consume 1~2mA current in average.

Thanks everybody for your help, i'll buy that kit and adjust it for my project, and let you know later.