virtualwire vs wire

Projects Networking, Protocols, and Devices
1

Hello,

I'm trying to communicate between arduino uno and raspberry pi 2 through those cheap but apparantly not very reliable RF Rx and Tx 433 MHz

... and I get nothing. I'd like to make sure that at least the software part is not in fault...

So i tried to skip the RF by connecting directly through a wire my arduino Tx pin to my Rasp GPIO Rx pin (through a level converter 5V ==> 3.3V but is this actuallt needed? will it fry the Pi if i connect directly? ) , to test if the issue is related to RF or not , and i still receive nothing ....

Does this actually mean that there is an issue in the software ? e.g should i get something sending with vw_send( ... ) (arduino )and receiving with vw.rx(....) (python code in Pi) directly through a wire ?

2

The virtual wire library does NOT send data over the hardware serial pins, so directly connecting the hardware serial pins and using vw_send() is not going to result in data being transferred.

3

sorry but when i said arduino Tx pin i did not mean serial Tx ! its a regular digital Pin : D12 in my case which i use to transmit (but using the word Tx in this case is ambiguous , i admit)...

so the question is still the same

4

in other words, does Vw emitter introduce a header to encapsulate the data which would result in the vw receiver command inability to understand the message if the header is meant for the RF devices and supressed by them after their transmission ...

5

The answer is yes the correct software can be tested through a physical wire as i managed to make it work now ...

since the radio transmission still does not work, could someone say if those chips

need the instruction vw_set_ptt_inverted(true); ?

6

in other words, does Vw emitter introduce a header to encapsulate the data

You can look at the source code, to see what the functions do.

7

could someone say if those chips ... need the instruction vw_set_ptt_inverted(true); ?

That would be a 5 minute test.

8

What RF chips?
Normally you do not need the "ptt" option in VirtualWire.

How do you have the receiver/RPi wired? The typical 433 MHz receiver is intended for 5 V, and may not work on 3.3V.

9

PaulS:
That would be a 5 minute test.

When it does not work and you dont know why the number of combinations of errors that you could think about grows fast and the time to check them as well thus my question to hopefully eliminate one.

i'm led to the same conclusion as many others, those chips don't work

i tried feeding the receiver with 3.3V , then 5V

i directly connected the data pin to GPIO Pin as many tutorials do on the web

10

those chips don't work

I've been using the $1 433 MHz boards for around 10 years, and they work fine for me.

11

i used 17.2 cm soldered straight wire as antenna on both Rx and Tx ...

12

henryco:
i used 17.2 cm soldered straight wire as antenna on both Rx and Tx ...

Probably depends wher you buy them . For the ones i got, I should have noticed that half of the customers say they dont work on the Amazon site...

13

The 433 Mhz receiver wont work on 3.3V , needs 5V .
The Transmitters will work on 3.3 V , but with very poor range.
Im not that familiar with the Pi, but any multitasking OS is going to have trouble running a program like VW due to the time slicing causing jitter in the data sampling.
Try lowering the data rate, dont go below around 200 bps , and see if there is any improvement.

14

thank you, i'll retry...
I think i can exclude what you say about the timing issues as source of my inability to transmit on RF because the transmission is OK (still using Vw emission and reception commands) as soon as i replace the RF by a wire