Transmit data via RF

@davee 

Hello Dave 

I found this information 

Signal compatible with RS232C interface , serial , no handshake operation 

2400 Baud

1 Startbit

8 Data ASC11-Bit

1 Stopbit

no Paritybit 

Was away on some treatment but back again 

• @will 

• I found this information 

   

  Signal compatible with RS232C interface , serial , no handshake operation 

  2400 Baud

  1 Startbit

  8 Data ASC11-Bit

  1 Stopbit

  no Paritybit 

Hi @zaeng,

  Good to see you back ... hope you are fit and well.

  The information is indeed a helpful start. I don't have any direct experience of the modules, but the format looks hopeful, in that the 2400 Baud Rate is within the specified range.

There may be some practical problems to overcome. Possible concerns include:

1. It looks probable that data only travels in direction, as it says 'no handshake'. However, some systems transmit in both directions. This is obviously more complex. Recommend testing this at an early stage - I never believe anything I haven't seen personally .. and even then I am not sure!
2. The 433MHz band is restricted to low power. This limits the maximum range and implies transmitter and receiver may need to be in 'line of sight'. I have seen maximum useful range of 30 metres mentioned, but this will depend on many factors. Again some simple experiments, see below.
3. The limited power, etc. might result in data corruption problems. Adding Arduinos at both ends could enable a more complex protocol with error correction. I would see this as 'a later enhancement' if the basic system without Arduinos works 'most of the time'. I haven't discussed it here.

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In principle, you should not need Arduino processors in the path, but a pair of Arduinos could be useful as a temporary 'halfway house' for test purposes. That is, repeat Bill's video experimental transmitter and receiver set up to get the 'radio' side problems sorted, then replace the Arduinos with the your timing device and display board. Use this test system to ensure the system has sufficient range. Be prepared to 'optimise' the antenna arrangement -- the spring ones are reported to have a very short range. To minimise problems, use 5V Arduinos, not 3.3V ones.

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Note that 'true' RS232 voltages are higher and more varied (+/- 13V) than those normally found on an Arduino or the 433 MHz Rx/Tx. I am assuming your timing device and display board are 'true' RS232 and not the 'processor friendly' logic voltage levels normally asssociated with Arduinos and Raspberry Pi, which are sometimes still referred to as RS232.This implies you will need a converter at each end.

I haven't used them, but something like https://www.banggood.com/3pcs-RS232-to-TTL-Serial-Port-Converter-Module-DB9-Connector-MAX3232-Serial-Module-p-1527334.html   might be worth considering. This example has a handy 15-pin connector for the RS232 side ... other boards with similar electronics, usually a MAX3232 or similar chip ... with just pin connections are available if you prefer.

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To test the voltage converters and prove only 1 direction data flow is required, the following test set could be rigged up:

Timing_Device --> RS232 to TTL convert --> (2 wire connection Tx->Rx + return) ...

                                                           ... TTL to RS232 convert --> Display device

The converters will (probably) need to be powered for the test.

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Hence, I suspect you will need voltage converters for both ends. Assuming data traffic is only in 1 direction, the chain could be:

Timing_Device --> RS232 to TTL convert -->  433 Tx -->  ......air space ...

                                .......      433 Rx -->  TTL to RS232 convert --> Display device

Note: Commercial RS232 to/from TTL converters usually convert both directions. Using only 'half' the capability should not be a problem. When choosing a device, make sure the power supply arrangements are convenient to your system design.

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It appears the transmitter power voltage can be up to 12V with some modules, which should give more range. The RS232 to TTL converters will probably be 3.3V to 5V. If Tx power voltage is above the voltage supplied to converter, make sure the TX data pin voltage does not  exceed the converter supply voltage. (In Bill's video, and the Arduino examples I found, both have 5V supply, so this problem does not arise.) I haven't found a data sheet that addresses this question.

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Hope this helps ... sorry it is not as simple as I would like. Good Luck!

@davee 

Hi Dave 

Thank you for the advice , I will follow the steps and test as suggested

regards