433mhz rf modules, without encoders and decoders?

[danrogers]

hi all, im using some 433mhz rf modules for a project. I’m not that experienced in electronics and I've never made anything around rf components.

Looking at the datasheets (attached) they both show a sample circuit with encoder and decoder chips connected. Do I have to use them or can I input directly to the input on the transmitter and use the output of the receiver to switch a transistor? I only need a simple 1 channel signal to be sent and received.

by the way the modules are

AM-HRR3-433 AND AM-RT4-433

Thanks in advance

 

[MikeMl]

I'm using a different brand, but similar modules. Here is what I learned. With no signal, the RX Data pin pulses randomly. It is a pretty good random bit stream. I did an Audio FFT on it, and is essentially uniformly distributed from 1Hz to 5KHz (the upper limit of my FFT). When a carrier appears, the Data Pin goes high and stays high as long as the carrier is present. If the carrier is interrupted (OOK), the data pin goes low. If the carrier is left off for more than ~1/2sec, the data pin begins pulsing randomly as described above. The transmitter OOKing rate should be somewhere between 10Hz and 4KHz; I used ~1KHz for my project. If you use a square wave to key the transmitter on/off at 1KHz, the recovered data signal is a 1KHz more or less square wave, where there is a lot of jitter on the edges with a weak RF signal, with the edges getting cleaner as the RF signal strength at the RX improves. I used a "tone-decoder" type of circuit to validate that it is my own transmitter I'm receiving...

Since the RX is a super-regen, it is quite broad (+-0/5MHz), so it will lock onto the strongest signal in the neighborhood, even if it is not your own transmitter. Sort of like the capture effect on an FM receiver. When hooked to an outside antenna at my house, I see a lot of ~300ms data bursts, probably from remote reading thermometers, door alarms, etc.

Remember that this is a shared band, and you are not allowed to transmit continuously...

 

[danrogers]

thanks for you reply Mike, I wont be continuosly transmitting, will be used for a short bursto to latch something on at the receiving end.

Alot of what you said does not mean much to me due to my lack of knowledge but I will do some research based on those search terms!

What do you think about using a encoder / decoder? could I avoid doing so?

cheers

 

[Nigel Goodwin]

If you don't use encoder/decoder chips then you need to program your own, check my PIC tutorials for one example.

If you're using commercial encoder/decoder chips ensure you buy the correct type, a simple remote control type may be all you require?, but those are no use for sending data.

 

[danrogers]

cheers Nigel. I've never done any programming unfortuniately. Your site looks usefull though and I will have a read later.

You are correct, I dont need to be sending any data with these modules, just simple 1 channel remote control functionality is all that is required. Could you point me in the direction of such a device?

I have been looking at these units.. **broken link removed** but im not sure if they are designed for data transfer or what really?

Thanks as allways for your help

 

[MikeMl]

That chip set looks like it is capable of sending four different commands, like a four button remote control. Should work for your application. Down load and read the data sheet.

 

[danrogers]

Thank you Mike. I've got the datasheet here but its a bit daunting! I notice that there are 4 o/p's from the decoder and also a serial data o/p. What would be sent out on that pin? I'm not really understanding the references to serial data on that datasheet.

Thanks all

 

[Nigel Goodwin]

Maplin do a range of ready made remote control kits, try these:

 

[danrogers]

Thanks for the link mate. I think I have seen those before. Look like a nice solution, however I already have the modules and I would like to learn how to make them work.

The transmitter will hopefully be triggerd by noise above a certain level picked up by a microphone should the whole project work!

Damn, just went to order the decoder and encoder direct from RF Solutions but they have a minimum order of £25 back to Maplin i go!