RF modules testing

[poiuy]

I got an RF module and I suspect it is defective.

I connected the vcc and ground for the transmitter and receiver. Receiver
dataout does not go high when I set the transmitter datain high.

Does this mean the module is broken? I want to do serial communication between a pda and a PIC.

[Guest]

sometimes you can only transmit an AC signal with these modules... try putting a 1khz square wave with TTL level at the input and see it it shows at the output of the other module.

[rberek]

And some modules only want to see RS232 or other protocols. Read the manual and see what it says.

[poiuy2]

I hooked up my pda's tx pin to my transmitter datain and my receiver dataout to my computer. I sent ascii U from my pda but nothing shows up on my computer.

I haven't tried the 1khz signal input b/c I don't have an oscilloscope

I got the RF modules on ebay and have the datasheet for them but there aren't a lot of information on the modules.

[op]

they are ISM 315mhz modules.

[Guest]

probably they accept 5v ttl levels, not +-12V RS-232 levels. You need a couple of MAX232 or similar chips to put them working.

[Humberto]

[Guest]

is it possible that the receiver is not tuned? It has a variable capacitor on it.

How do I tune the receiver? I don't have any RF measurement tools btw.

[guest]

I was messing around with the tuning and I found a position on the variable cap that makes the receiver output = 0.4v when the trans input =5 and receiver output= 1.45v when trans input=0.

Kinda wierd how it is inverted and the voltage is not TTL

[Humberto]

[guest]

I hooked up the RF receiver to the scope and the output looks good. I transmitted a 1khz squarewave and the receiver got it. The weird thing is that sometime the output is inverted. If I shake or move the transmitter in a certain way, the output of the receiver would invert itself.

Also, when I stop transmitting, the RF receiver outputs some random signals.

[guest]

I use a transistor to amp. the 2.5v to around 3.5V which is enough i think for rs232. So now low=0v and high= 3.5v.

I tried sending UUUUU from my pda and I see it on the screen. The problem i'm having is garbage output. It is outputing a lot of garbage whenever I hook the transmitter Datain to my pda's TX pin. If i don't hook it up, then it is fine (Datain of transmitter is pulled up high) no garbage.

It seems like my pda outputs noise or some sort. I hooked up my pda to my computer directly and serial com works fine without garbage. Wierd.

Any advice?

[Humberto]

[treitmey]

Humberto: Do you have a suggestion for a more reliable RF module?
Any experience with one brand or another?

[Humberto]

treitmey,

The limitations of this kind of transmitters that operate in a free band, is that the regulations
itself do not allow that this devices irradiate more RF power.
Anyway I´m not involved in RF devices, I worked in a project with this kind of devices
(AM transmitters in 315/433Mhz) and tested a few of them but for sure, I do not remember
none of them who have been really superior.

Actually there are a new generation of devices with superb performance (according with
the manufacturer data sheet of course) that I didn´t play with them yet.

Just an example:
Key features of the EZRadio transceiver chipsets include:

"Highly programmable: Choice of unlicensed band (433, 868, 915MHz),
low noise amplifier (LNA) gain, baseband bandwidth (67kHz - 400kHz), data rate, automatic
frequency control, crystal load capacitance, output power level, FSK modulation deviation
- reducing production and customization costs.
Automatic Antenna Tuning (patent pending): Eliminates the need for production line
tuning costs and ensures optimal RF transmission throughout the product lifecycle.
Automatic Antenna Tuning takes the guesswork out of the design process, eliminates the need
for expensive RF engineering, and delivers an extremely robust wireless link.
Fully integrated on-chip RF features: Requires only two external components, a crystal
and a low-cost microcontroller, reducing the bill of materials and simplifying the design-in process.
Automatic Frequency Control (AFC): The receiver is automatically tuned to the incoming signal,
allowing the use of an inexpensive crystal without compromising the radio link.
Key radio management functions: EZRadio performs functions such as data recovery and
timing without a microcontroller, allowing the choice of a less expensive microcontroller.
Clock source available: Does not require a second crystal if a microcontroller is used.
Fast and reliable frequency hopping: Counter interference and multipath fading enable
over a hundred devices to be used in the same environment, without user issues.
High impedance loop antenna can be etched directly onto the circuit board:
Eliminates the need for more expensive external antenna designs. "

I want to state that I have not any kind of relationship nor comercial interest with EZRadio.


regards,

Humberto