RF and RFID design

[marvelous]

Hi again,

I have a couple of question if you'd please help me find out the answers:

1. Is it possible to build a nice RF receiver and an RF transmitter by using a PIC16f84 microcontroller? Is it sufficient for such a device or do i need more than 18 pins?

2. I would like to avoid interference between different RF devices. Assume i have a receiver and a transmitter device but there are many other RF devices in the place. What would i do to avoid interference? Do i need to use RFID tags? Is it the real purpose of RFID technology? What is the purpose of that technology then?

3. Assume there are more than one RF devices (transmitters) assigned to one (and only) specific RF receiver. What should i do to make that receiver to identify all of those different RF devices (transmitters) and memorize each of their identities one by one and seperately? Is it again an issue of RFID? or some other technology? ...and i guess the receiver would need a memory to keep the identities in mind...how would i embed a memory on the receiver?

Thanks a lot people.

Take care,
Marv.

 

[Russlk]

1. a PIC is not usually used for RF purposes. What frequency do you have in mind?

2. Radio and TV systems do that all the time. You need to be more specific in what you want to do.

3. I don't know what you are talking about.

 

[motion]

1. Is it possible to build a nice RF receiver and an RF transmitter by using a PIC16f84 microcontroller? Is it sufficient for such a device or do i need more than 18 pins?

I have seen an RFID card reader using a PIC16F84 chip. It uses the 125Khz carrier frequency and the 4Mhz crystal is divided down to produce the carrier. To receive the data from a demodulated RFID signal, you need just one pin. However, you can also use the PWM signal from a PIC16F627 chip to generate the 125Khz carrier.

RFID tags on the other hand are low power passive devices. It would be difficult to make one using PIC chips. There are off the shelf devices that are available like the MCRF200, MCRF250, etc.

2. I would like to avoid interference between different RF devices. Assume i have a receiver and a transmitter device but there are many other RF devices in the place. What would i do to avoid interference? Do i need to use RFID tags? Is it the real purpose of RFID technology? What is the purpose of that technology then?

There are RFID devices that have anti-collision feature. Search the Microchips site for the MCRF250 for 125Khz operation.

3. Assume there are more than one RF devices (transmitters) assigned to one (and only) specific RF receiver. What should i do to make that receiver to identify all of those different RF devices (transmitters) and memorize each of their identities one by one and seperately? Is it again an issue of RFID? or some other technology? ...and i guess the receiver would need a memory to keep the identities in mind...how would i embed a memory on the receiver?

There are design guides for 125Khz and 13.56Mhz RFID devices at the Microchip website. It would be a good starting point.

**broken link removed**

 

[marvelous]

1. a PIC is not usually used for RF purposes. What frequency do you have in mind?

Let's say my device would provide 315MHz or 433MHz or 900MHz or 2.4GHz. I think as the frequency increases, i can increase the distance between receiver and transmitter. Is this correct?

2. Radio and TV systems do that all the time. You need to be more specific in what you want to do.

Ok..more specifically: "I have an RF transmitting device and an RF receiver device. However, there are some other electronic RF devices in the medium that i use my own devices. Hence, it is possible that those other devices may interference with my own RF devices. How can i avoid it? By using RFID?"

Well..more specifically let's say my RF systems has 64 ID memories with transmission range up to 7m-10m to prevent interference among other RF devices in the place. For example, i have an RF sensor but there are also other RF devices (e.g. a radio) in the place.

3. I don't know what you are talking about.

I guess i could not tell it well. What i was trying to say is the following: "Assume i have more than one transmitters and only one receiver to receive all the signals coming from those transmitters. That device should identify all the signals separately and not mix them up. It should somehow memorize their IDs no to mix them up. Namely, a shared RF receiver with self-learning function to memorize and lock on specific RF devices.

Another question: How can i build a shared RF receiver using one I/O port for various RF devices. I also need help with this issue.


Thanks,
Marv.

 

[marvelous]

I have seen an RFID card reader using a PIC16F84 chip. It uses the 125Khz carrier frequency and the 4Mhz crystal is divided down to produce the carrier. To receive the data from a demodulated RFID signal, you need just one pin. However, you can also use the PWM signal from a PIC16F627 chip to generate the 125Khz carrier.

RFID tags on the other hand are low power passive devices. It would be difficult to make one using PIC chips. There are off the shelf devices that are available like the MCRF200, MCRF250, etc.

Ok..then i will start with PIC16F84 and see what will happen By the way, MCRF450 tag would also be a good choice right?

There are RFID devices that have anti-collision feature. Search the Microchips site for the MCRF250 for 125Khz operation.

When there are more than one product produced for the same purpose (let's say 10 RF sensors in the room that were manufactured by the same company), then each should have a different ID so as to avoid interference. Is this correct? Please correct me if i am wrong.


By the way, i'd be glad if you can also read other replies to my messages as well as my replies to those. There are some other specific explanation about "what i would like to do". I am an electronics newbie and having such a hard time learning things

Thanks a lot for the help in advance,
Marv.

 

[Nigel Goodwin]

When there are more than one product produced for the same purpose (let's say 10 RF sensors in the room that were manufactured by the same company), then each should have a different ID so as to avoid interference. Is this correct? Please correct me if i am wrong.

It doesn't prevent interference, two devices transmitting at the same time will interfere with each other. All the ID does is prevent it responding to the wrong signal - for interference you need some kind of anti-collision scheme, where data is resent if it doesn't get through first time (just as a network does).

 

[marvelous]

A little long but please read

Dear All,

First of all i'd like to thank you so much for providing me with all the information and help. Now, i am at the stage of reviewing and aggregating those things you told me. So, i thought a last review and confirmation would be good for a double check and better understanding.

As you remember my project is as follows (or have i ever told about it?):

Two keypads having a couple of buttons on them to control two remote devices/machines (an agitator and an analyzer) by means of RF signals in "two" closed areas (mixing room and laboratory) of a waste treatment facility. I am responsible to develop the keypads (simple looking ones) and the receivers having interface with the controllers (industrial PCs embedded into the machines). ***I am just a chemical engineer with a very few knowledge about electronics ***
So, the followings are what i understood from your advices:

1. I'd need two microcontrollers. One is for transmitting device (i.e. keypad) and one is for receiving device (receiver).

2. I'd need a flexible PCB for keypad so that i can solder/mount all the components and buttons including PIC16F84.

3. I'd need a normal PCB for the receiver so as to mount the components.

4. I'd also need RF components with "anti-collision tags" so that other RF devices (such as a radio etc.) would not interfere with my keypad and distort the signals. There should not be any interference among my keypads as well. A reminder: i will make two keypad since i have two rooms in the facility.

5. I do not need an RFID because i do not need a barcode or a telemetry kind of thing. I will not trace anything or i will not assign more than one transmitting device to one single receiver. (and that's why i do not need RFID...is it reasonable?)

6. If i use "higher" frequency RF, then my receiver can sense the signal coming from "longer" distance. (Is this correct?)

Now, here are my questions:

1. One of you told me that "All the ID does is to prevent the receiver from responding to the wrong signal coming from a wrong transmitter."

This sounded interesting to me. Because i will make two transmitters with the same exact frequencies. I will also make two receivers for those two transmitters. I mean all the two transmitters and two receivers will be same with same features. One receiver will be attached to an agitator in one room (mixing room) and the other receiver will be attached to an analyzer in another room (laboratory room). However, while i am using my transmitter for the agitator (in the mixing room of the facility), i do not want other guy comes from the lab. room with that other transmitter (the one which is used for analyzer and remember it has the same features of my transmitter) and use the device. I mean it would be so bad if he uses his keypad (transmitter) and send wrong orders to the receiver on the agitator while i am using my transmitter to send some signals (orders) to the same receiver. (He can manage his analyzer but he can not manage the agitator and if he gives wrong signals in the room in presence of me or while i am out. In the same manner, i can manage my agitator but i do not know how to manage the analyzer. So, it could be so devastating if somehow i use my transmitter in lab. room unintentionally to send signals to the analyzer.) How should i prevent this? By anti-collision? or by an RF ID?

2. Think of two cars of "same" brand and "same" model. Say, two Mercedes SLK200 cars with RF carkeys to open the doors. And assume one of them is mine (ah i wish ) How come my RF key does open the doors of my Mercedes SLK200 but can not open my friend's Mercedes SLK200? Is it because of RFID? is it because of what? I mean how come the receiver on the car identifies that the signal is coming from the right (correct) transmitter?

3. On some printed manuals, i read the following statements: "Independent product ID for each product. 256 ID and RF-technique to prevent interference" or the statements like: "32 ID memories with transmission range up to 5 meters to prevent interference among RF devices." or statements like: "Shared RF receiver using one I/O port for various RF devices" or statements like: "Shared RF receiver with self-learning function to memorize and lock on specific RF devices" What does all the jambo-mambo mean? I am CONFUSED

I would be really very very happy if you can give answers to my questions, correct my mistakes and pray for me

Thanks a lot. Take care all.

Marv.

ps: Please do not ask me to make my transmitter with different frequencies so as to avoid collision etc. because i should use the same frequency for both of the transmitter. There is a reason behind it.

 

[Nigel Goodwin]

I've only read your post fairly quickly, but it seems to describe a totally different requirement to that originally suggested.

If I now understand you correctly, you have two pieces of equipment, and you want two seperate remote controls to turn them on - but you don't want them to affect each other.

Is that what you require?.

If you look at my IR PIC tutorials at http://www.winpicprog.co.uk I describe the Sony SIRC's IR remote control system. As is common amongst remote controls it sends two pieces of information - an actual command (on, off, volume etc.), and also a device ID (TV, VCR, Stereo etc.). For your application all you need is a remote system with different device ID's.

 

[Russlk]

Perhaps you could use a TV/VCR remote control, disconnect the IR LED output and connect it to the modulator of your transmitter. The demodulator output of the receiver would be connected to the IR receiver from the TV or VCR. This would save a lot of work and cost, and the chance of sucess would be better. This answers 1, 2, & 3.
4. I don't know about "anti-collision tags", but two transmitters on the same frequency at the same time will interfere and cause distortion. It cannot be helped.
5. The data has to be coded such that the receiver knows which to respond to. This will be taken care of by use of the TV remote.
6. Higher frequency does not go farther, quite the opposite.

In order to prevent the person in the laboratory room from controlling the agitator in the mixing room, remove the button in the remote control that addresses the agitator.

 

[prunzi]

RF Receiver, Transmitter

check Cypress semiconductors, they have very nice ICx CYWUSB6934 and 33 for doing wireless transceiver, receiver and transmitter, with comprehensive how to instructions.