Cheap one way RF solution

Hi all,

I am looking for a CHEAP design for RF communication.

  1. The link has to be unidirectional from one microcontroller to another.
  2. The data rate requirement is not a consideration as it is very low.
  3. The communication range is between 20-30 meters with obstacles like walls in between.

I am new to RF so don't know which frequency has what advantages and which is cheaper and legal. I am in India. I believe I have 2 good options to work with.

  1. 433Mhz
  2. 2.4Ghz

Kindly suggest which would be cheaper and better suited to my needs.

Thanks, Rohan

Reply to
Rohan
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The Nordic nRF24L01 will do what you want (and a lot more besides) and is cheap.

Leon

Reply to
Leon

Thanks.. nRF24L01 is a Tranceiver. I believe they are more expensive than a reciever/transmitter pair? I am not sure. Just asking you guys. Since i want a Half Duplex path putting two tranceiver at both ends could be more expensive.

I infer that 2.4Ghz being the most common would be really cheap.

The data rate on this chip is for VOIP level and my requirement is a mere fraction of that. So again this chip seems a little high end for my needs.

Any ATMEL users around?

Reply to
Rohan

Thanks.. nRF24L01 is a Tranceiver. I believe they are more expensive than a reciever/transmitter pair? I am not sure. Just asking you guys. Since i want a Half Duplex path putting two tranceiver at both ends could be more expensive.

I infer that 2.4Ghz being the most common would be really cheap.

The data rate on this chip is for VOIP level and my requirement is a mere fraction of that. So again this chip seems a little high end for my needs.

Any ATMEL users around?

Reply to
Rohan

Hello Rohan,

What kind of controller are you using? I have some simplex/duplex code for a PCA equipped Atmel 8052 that works just as well in a simplex configuration. I used super cheap TWS-434A transmitter and RWS-434 receiver modules that operate in 1200 bps CW mode. Not too sure about the range, but you should get 20m with a brick wall in the way okay. Check my homepage listed below if you think that might help.

--
32°02'14.23"S 115°53'21.30"E
http://www.review-a-gadget.com/
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Reply to
Dhr de Luynes

Hi Rohan,

Atmel has series of Transmitters / Receivers for Automotive control i.e. Tire Pressure Monitoring System look at the following link

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Reply to
skr

You don't get receiver-only devices. There are transmitter-only, and transceiver types. Transmitter-only are now less common - they are not much cheaper than transceivers, and it's often nice to have a little feedback (blinking LED, for example).

Reply to
David Brown

On Mar 8, 7:27 am, David Brown

That isn't even vaguely true. RFMD, Philips, Melexis, Atmel, Microchip, ... all make receive-only devices. Not only are they cheaper, they're also cheaper to integrate due to fewer and simpler external components.

RKE applications, for instance, have absolutely no use for a transceiver.

Reply to
larwe

Fair enough - it looks like I've been over-generalising based on the manufacturers we have used. Nordic VLSI, for example, no longer appears to have anything other than transceivers. Chipcon (now part of TI) have transmitters, but no receiver-only devices. From the way these devices are designed, most of the hard work is on the receiving end - you save very little by making a receiver-only instead of a transceiver. If the quantities are high enough, then of course small savings turn into large ones.

Reply to
David Brown

Discussion so far...

  1. 2.4 Ghz vs 433 Mhz - 2.4Ghz is easier to impliment and cheaper but doesn't travel through walls well.

--This is a important consideration. Does anyone has any experience with the 2.4 Ghz range issues. Is it possible to increase the range to upto 50 meters with walls in between?

  1. Recieve only device is not much of a cost saving: fair enough and with rising sales of tranceivers the cost will eventually come below a recieve only device.

--So its better to base the design on a tranceiver device

Reply to
Rohan

Hardly! Where did you get this information?

Reply to
larwe
  1. Recieve only device is not much of a cost saving: fair enough and with rising sales of tranceivers the cost will eventually come below a recieve only device.

--So its better to base the design on a tranceiver device

----- Agree Receive functionality is difficult and consume most part of trans-receiver but not from marketing and selling point of view this is true from designing IC point of view.

You can go for receive only if you need only that

As Larwe specified RKE application is what your device looks like and you have IC available for that on Atmel or Maxwell

Reply to
skr

On Mar 9, 10:14 am, David Brown

This is not just a Tx/Rx or even a txvr/txvr pair, it is a complete network stack! Maybe this is where our logical disconnect is occurring.

If the goal is "transmit a few bytes from point A to point B cheaply" then an unlicensed transmitter in the 433MHz or 300-ish MHz (315MHz commonly in the USA) region is the cheapest solution. The transmitter can be little more than a couple of transistors, an xtal and a few matching passives (though it's easier to use an IC solution, which makes the BOM one IC, one xtal, half a dozen passives). The receiver can be any of several possibilities from Philips, Infineon, Melexis etc - Infineon probably one of the cheaper options. A comparator to slice the data, and a micro to decode it, and you're away.

Plenty of people sell canned solutions for this sort of thing, e.g. is a rather cute- looking option.

The FHSS and DSSS 2.4GHz solutions are _very_ complicated to deal with (compared with the simple Manchester-on-a-wet-string ASK techniques) unless you buy everything canned, in which case they are expensive.

Reply to
larwe

The price and complexity depends on your application type. I have mostly required two way communication with various types of data, networks of several radio nodes, automatically finding and identifying new nodes, retries on errors, and that sort of thing. I've therefore been using more integrated devices (which is why I never even knew about receive-only devices). There is little doubt that the more advanced devices make this easier, as they handle the low-level telegram transfers themselves (think of them as somewhat like a CAN controller, rather than a UART). These devices first appeared, to my knowledge, with 2.4 GHz chips - but there are certainly 433 and 900 MHz devices with this sort of functionality.

If you mean easier from the regulations viewpoint, then you are right (as long as you stick to low power) - at 2.4 GHz, you can pick frequencies that are available almost all over the world.

If you are looking for something really simple, then as others have suggested, a transmit-only and receive-only pair will be the lowest cost for high volumes. Atmel have some 4-bit microcontrollers with transmitters for very low prices.

Reply to
David Brown

Something that I've been noticing lately is that 2.4 GHz devices are becoming so popular that there is an incredible amout of congestion on that band. You didn't mention whether your indoor environment is office or home or industrial but if you do decide to go with this band you may have all sorts of other devices causing interference like WiFi, Bluetooth, microwave ovens, cordless phones, wireless video cameras, just to name a few.

We recently got a 2.4 GHz cordless phone for the office. Completely useless. In a large office building there are so many other phones and WiFi devices that this phone would start dropping out as soon as you got more than 2m away from the base station. We replaced it with a 900 MHz phone and it's crystal clear even at the far end of the office which is about 20 m away.

The other ISM bands like 433 MHz or 27 MHz have very few devices on them so the chance of interference is very low. Probably the biggest users on 433 are keyless entry devices and wireless thermometers, while 27 MHz is popular for cordless mice and remote control toys.

In terms of transmit-only and receive-only devices, there are single chip modules like these:

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and there are also CPUs with built-in transmitters like the rfPIC12F675 and the standalone receiver rfRXD0420. The prices are around $2 - $3 in quantities of 100. The transmitter can be made for well under $1 if you're willing to invest in some RF design. Take a look at how a typical keyless entry transmitter is built. The entire RF section consists of one large PCB trace that acts as an antenna, one UHF transistor and a few passives.

---Tom.

Reply to
Tom

so

are

Not to mention radio amateurs that are allowed to produce 400 Watts in the entire 430 to 440MHz range. If I would go to a gas station and talk to a fellow ham on 433,920MHz, which is a perfectly legal thing to do, no one at that gas station would be able to unlock his car with his keyfob....

Meindert

Reply to
Meindert Sprang

Otherwise OK, but the international amateur power limit on the 430 MHz band is 1 kW.

The frequency division plan states clearly that these low- power devices have no interference protection from the legal higher-power services on the same band.

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Tauno Voipio, OH2UG
tauno voipio (at) iki fi
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Reply to
Tauno Voipio

On Mar 9, 1:19 pm, "Meindert Sprang"

Worse, in the US it is a fairly common thing that military/police installations will expand their spectrum usage to cover unlicensed low- priority-user bands, and suddenly in an entire neighborhood people cannot open their garage doors remotely.

Reply to
larwe

Hi Rohan -

I guess I'll add a couple of comments here...

You might also check into Linx components. Their we address is

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and they carry very small, inexpensive transmitter-only and receiver-only modules. The interface is simple. The range (from experience) with the 433MHz varieties is over 300 feet (over 90 meters) line-of-sight. The power requirements are also very small.

The range will be less with walls in the way but may still be in the range you're looking for. They also carry a line of 315MHz devices.

I hope this helps.

Dave

Reply to
Dave

It is indeed where our logical disconnect occurred - my last post was trying to explain where I had been coming from, and thus why I'd never really looked at the low-end parts, and also why 2.4 GHz integrated transceivers can be easier and cheaper - if your application requires such features. Perhaps I didn't make it very clear that I *do* see the difference between what *I* needed, and what the cheapest solutions offer.

I have also used "Manchester-on-a-wet-string" solutions (transceivers), and implemented networking stacks on top of them - I am glad to have moved on to more advanced devices, as they are much easier to work with and therefore far cheaper (for our volumes, and our requirements).

Reply to
David Brown

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