RF Module - Supply Voltage and circuit question

[n305er]

Hi,

I've just bought the 433MHz RF module for my F.Y. project and have a few questions regarding using the product.

First of all, a quick summary on my project might help to understand my requirements better...

My project consists of a host transmitter and slave receiver which switches a relay on/off based on the received signal.

Host - Using Labview, 8bit signal is generated using ascii symbols as labview can only send strings to serial ports.
[PC] -> [UC00A] -> [TX Module] --8 bit signal-->

Slave - PIC to compare 6 MSB bit pattern to DIP switch connected to portB and turn on/off relay based on the last 2 LSB if 6 bit address is matched.
--8 bit signal--> [RX Module] -> [PIC16F877A] -> [Relay circuit]

I've already done the code in the PIC and it works when UART pin is directly connected to it. My concern is on the RF module's capability and reliability of sending the signals far and accurate enough. According to the datasheet I've downloaded from Cytron, it supports Supply power of 3V to 12V. It states that voltage supply plays a role in improving the range of the transmitter... How reliable is the transmitter if I directly tap the 5V from the UC00A +V? Or does Cytron sell any good and simple DC-DC SMPS projects to step up the voltage?

Also, when I experimented the RX module with a multimeter, the Data pin has a small voltage (<0.5V) without signal and only slightly less then 2V with signal. Is the the correct spec for the RX module or was it supposed to be 5V when used correctly?

3rd, antenna is my worse subject. Do I really need to use an 18CM wire and straighten it out soldered onto the antenna port? Can the module work without an antenna? Can I coil the antenna and do I need to strip the insulation rubber off the wire first before using?

Finally, in the manual, the picture of the module has a BJT transistor on it. But my unit doesn't have any. Do I need to install one myself or does it actually do anything?

Thanks

-PS: I can't find a proper category to ask this:
Can anyone recommend any good and simple software to draw schematics like the one in your manuals?

[sich]

Wow...u got the clearest problem explanation in this forum so far. That really gave us a clear image on what you are doing. Thumbs up!

How reliable is the transmitter if I directly tap the 5V from the UC00A +V?

It should be fine. The reliability increases with the implementation of checksum, parity, and/or encode/decode algorithm like Manchester Encoding....etc. This's a project done by Cytron's engineer which also connects UC00A to RF-TX module directly. However, it doesn't implement any error detecting method. It's discussed in our Robot Head to Toe Magazine, Volume 4 too. http://www.robothead2toe.com.my/

Or does Cytron sell any good and simple DC-DC SMPS projects to step up the voltage?

No, Cytron doesn't have SMPS products at the moment. Sorry!

Also, when I experimented the RX module with a multimeter, the Data pin has a small voltage (<0.5V) without signal and only slightly less then 2V with signal. Is the the correct spec for the RX module or was it supposed to be 5V when used correctly?

This is because you're reading the average value of the data pin. When there's data transferring through the pin, it's not giving 'HIGH' only but a series of 'HIGH' and 'LOW', depending on your data. Since multimeter cant give you the visual implementation of the signal (data), It can only display the average value. If you're tapping the line using an oscilloscope, you'll see the actual signal which should be square wave of '1' and '0'. So i would say the value you get is normal.

3rd, antenna is my worse subject. Do I really need to use an 18CM wire and straighten it out soldered onto the antenna port? Can the module work without an antenna? Can I coil the antenna and do I need to strip the insulation rubber off the wire first before using?

From the user manual, it requires the antenna length to be 18 to 24cm depends on the frequency of your RF module. Just make it straight and no need to strip the insulator.

Finally, in the manual, the picture of the module has a BJT transistor on it. But my unit doesn't have any. Do I need to install one myself or does it actually do anything?

No need. Those are working units. No additional work is needed for the modules. Different batches of the module may have different design, pcb routing and component. Anyway, u should be able to find a SMD transistor somewhere at the bottom layer of the module.

[n305er]

Thanks for the answer! However, these answers gave me some more questions.

This is because you're reading the average value of the data pin. When there's data transferring through the pin, it's not giving 'HIGH' only but a series of 'HIGH' and 'LOW', depending on your data. Since multimeter cant give you the visual implementation of the signal (data), It can only display the average value. If you're tapping the line using an oscilloscope, you'll see the actual signal which should be square wave of '1' and '0'. So i would say the value you get is normal.

If the Data Pin is actually 101010 when receiving a data, wouldn't that affect the data I'm sending? Since I'm sending data using UART, wouldn't the UART signal become scrambled into something else?

From the user manual, it requires the antenna length to be 18 to 24cm depends on the frequency of your RF module. Just make it straight and no need to strip the insulator.

Will it be okay if I coil up the antenna as I need to hide it? I can't use a conventional straight antenna as it'll be a hassle for the people my project is targeted for to use. Which is elderly people and people on wheel chairs. Same as the receiver parts as the relays actually controls 3 pin power outlets so it's not right to have those things sticking out for people or geckos to touch.

Thanks

[sich]

This's a project done by Cytron's engineer which also connects UC00A to RF-TX module directly. However, it doesn't implement any error detecting method. It's discussed in our Robot Head to Toe Magazine, Volume 4 too.

First i want to correct my mistake about the mini balancing robot. Just read through the source code and found that it implements checksum error detect in the program. Sorry about that.

If the Data Pin is actually 101010 when receiving a data, wouldn't that affect the data I'm sending? Since I'm sending data using UART, wouldn't the UART signal become scrambled into something else?

I don't understand what you don't understand...

Will it be okay if I coil up the antenna as I need to hide it?

I'm not sure whether that'll affect the transmission of the RF modules. You may experiment it. This is very low cost RF transmitter and receiver pair so it has to be some inconvenience when using it. Normally better solution provides small chip antenna on board .