Wireless recievers, transmitters, for cheap!

[Mr. Ninja]

Hi,

   I am working on a project that involves LEDs, watches, and wireless recievers.

I was looking for any transmitters that can be activated by a button, set to a certain signature, and then sent to a reciever, which either opens up a current as long as the button is pressed, or records it to Arduino.

Thanks

[Physics Fu]

What kind of transmitters and receivers do you want? Infrared, radio frequency, etc? Infrared is dirt cheap but has its limitations, the line of sight requirement being the most restrictive. I haven't done much with IR, but Tayda Electronics ( http://www.taydaelectronics.com/sensors-transducer/optical-sensor.html ) has a good selection of dirt cheap IR components. Tayda is dirt-cheap in general for stuff were quality isn't paramount.
If IR isn't well-suited to your application, and you haven't provided much detail but it sounds like it probably isn't, RF is nice but a bit more work to set up and at least twice the price. SparkFun sells both receivers and transmitters (http://www.sparkfun.com/products/10534) for under 4USD each, and knowing SF they can probably be found elsewhere for half the price if you do some searching. If you would prefer transceivers (transmit and receive), Nordic makes nice ones (5.50USD, http://iteadstudio.com/store/index.php?main_page=product_info&cPath=7&products_id=53; also probably available elsewhere), and a great walk-through is available as well ( http://maniacbug.wordpress.com/2011/11/02/getting-started-rf24/ ).

There are other ways, too, of course (XBees, Bluetooth, etc), but they are costly and RF will probably do just fine instead. It depends on range and form factor. If you give more details about your application, I or someone else will be able to help you better.

[pterrus]

I'm using this right now and it's pretty sweet.  Incredibly easy to set up.

http://www.rentron.com/remote_control/TWS-8-bit-pack.htm

[Mr. Ninja]

Sorry about the limited information.

Since my mother is a teacher, she is always looking for ways to make the classroom more efficient. The idea she had was to have each child wear a wrist strap with some buttons on it. The child would press a button and a bell would ring, along with a LEDs with the childs name on it lighting up.. It would be controlled via netbook and would need something to send a signal to the netbook, and then the netbook would light the appropriate LEDs up, depending on the child.

We would like something that would not need a microcontroller to send the signal, but would have an individual ID.

(If we really need a microcontroller we could just outsource some PCB, as she has a limited budget)

[Soeren]

Hi,

Sorry about the limited information.

You still need to tell us about what range you require andwhether it has to work through walls etc.

Since my mother is a teacher, she is always looking for ways to make the classroom more efficient. The idea she had was to have each child wear a wrist strap with some buttons on it. The child would press a button and a bell would ring, along with a LEDs with the childs name on it lighting up..

So, she can sleep until required?

It would be controlled via netbook and would need something to send a signal to the netbook, and then the netbook would light the appropriate LEDs up, depending on the child.

I assume that's what you want the Arduino to do??

We would like something that would not need a microcontroller to send the signal, but would have an individual ID.

(If we really need a microcontroller we could just outsource some PCB, as she has a limited budget)

You could use encoders and a deoder from eg. Holtek, but a small microcontroller would be both cheaper (down to around 30 cents) and way more versatile.

Running the transmitter from eg. a CR2032 lithium coin cell, the cell will cost more than a controller.

For cheap transmitters (with less range than announced though), try the ISM transmitter/receiver pairs from Seed Studio:
http://www.seeedstudio.com/depot/wireless-rfism-c-139_140.html
(Perhaps ask them if they're willing to sell say 2 receivers and 30 transmitters (or whatever number you need.

One issue that you cannot escape easily, is the situation where two transmitters are on concurrently, but given the short time a transmission takes, it shouldn't be too bad (although an "acknowledged" LED or similar to tell the student that the keypress is received would be helpful).

[Mr. Ninja]

Hi,

Sorry about the limited information.

You still need to tell us about what range you require andwhether it has to work through walls etc.

It would need a range of somewhere between 20-30 feet, and it would not have to go through solid walls, but I'm not sure if It will need to go through a small whiteboard (on a metal trolley)

Since my mother is a teacher, she is always looking for ways to make the classroom more efficient. The idea she had was to have each child wear a wrist strap with some buttons on it. The child would press a button and a bell would ring, along with a LEDs with the childs name on it lighting up..

So, she can sleep until required?

It would be controlled via netbook and would need something to send a signal to the netbook, and then the netbook would light the appropriate LEDs up, depending on the child.

I assume that's what you want the Arduino to do??

Yes

We would like something that would not need a microcontroller to send the signal, but would have an individual ID.

(If we really need a microcontroller we could just outsource some PCB, as she has a limited budget)

You could use encoders and a deoder from eg. Holtek, but a small microcontroller would be both cheaper (down to around 30 cents) and way more versatile.

Running the transmitter from eg. a CR2032 lithium coin cell, the cell will cost more than a controller.

For cheap transmitters (with less range than announced though), try the ISM transmitter/receiver pairs from Seed Studio:
http://www.seeedstudio.com/depot/wireless-rfism-c-139_140.html
(Perhaps ask them if they're willing to sell say 2 receivers and 30 transmitters (or whatever number you need.

One issue that you cannot escape easily, is the situation where two transmitters are on concurrently, but given the short time a transmission takes, it shouldn't be too bad (although an "acknowledged" LED or similar to tell the student that the keypress is received would be helpful).

Which one are you talking about? I'm not sure

Edit: For the recievers transmitters you meant either of these two (http://www.seeedstudio.com/depot/315mhz-rf-link-kit-p-76.html?cPath=139_140 or http://www.seeedstudio.com/depot/433mhz-rf-link-kit-p-127.html?cPath=139_140) right?

[Soeren]

Hi,

Edit: For the recievers transmitters you meant either of these two [...] right?

Yes, which one depends on where in the world you are.
The 40m (roughly 120 feet) indoor is very optimistic, but they should be fine for a normal size classroom (a long as they're given the proper size antennas).
Start with a single transmitter and receiver before you cash out for a load of them though - hard to say how they behave when the antenna is coiled up in a bracelet.


If you use a protocol of short burts with the info coded into the inter-burst pauses, it can be quite efficient without draining too much on the battery. A short HF burst will enable the AGC of the receiver to adjust properly.

If you want to send eg. #26 (decimal = 00011010 binary) with a leading AGC burst, transmission could look like:

Code: [Select]

  ____
_|    |_|_|_|__|__|_|__|_|
  AGC  0 0 0  1  1 0  1 0

Sending the 8 bit word 2 or 3 times consecutive allows for comparing the received bytes to discard
any transmission where they don't add up. Repeating the byte 3 times would then look like this:

  ____                    0 0 0  1  1 0  1 0
_|    |_|_|_|__|__|_|__|_|_|_|_|__|__|_|__|_|_|_|_|__|__|_|__|_|
  AGC  0 0 0  1  1 0  1 0                    0 0 0  1  1 0  1 0

With an AGC burst of 5ms and eg. 200µs pulses with say 1ms and 2ms for "0" an "1" pauses respectively, the triple transmission would last less than 43ms (0.043s), so it should be easy to avoid collision.

This stuff is what you pay to not have to think about when you buy Holtek en-/decoders, but the bottom line is what happens to... the bottom line and since you're on a tight budget and have little room to spare, I'd stuff a PIC10Fxxxx on the transmitter and save both space and money.

Another way would be getting a single decoder for the receiver and just use the protocol that it expects (this will save you a lot of time on the decoding software).

[Mr. Ninja]

Thanks for all the help, I believe that will be all I need to complete this project.

Thanks again, and /thread .