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What plug should I choose for the light sensor and will a 4-pin JACK be good?

ziajek444 1710 7
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  • #1 16949324
    ziajek444
    Level 9  
    I am building a light sensor. The main components of my sensor are: Atmega8 (takes measurements and communicates over rs232), photoresistor (light sensitive element). With this sensor, the controller must communicate via rs232 but I want to power the sensor itself from the controller. In the skin, I want to transmit MASS, Rx, Tx, POWER over the cable connecting the controller and the sensor. Which connector should I choose? The expected length of the cable is between 2-30 metres. Because of the wide variation in length, this could be two different plug proposals (e.g. 2-5m and 5-30m). However, it would be more convenient to have one type of plug.

    I am currently considering a JAck 4 field plug and a standard width like the headphone input for a desktop computer.
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  • #2 16949338
    stonefree
    Level 27  
    If RS232, why not a DB-9 connector? And why two different plugs for two different cable lengths?
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  • Helpful post
    #3 16949359
    czareqpl
    Level 33  
    What about if someone puts in a 3 pole jack? Does he short the power to TX/RX or does he short the ground to TX/RX?

    I would recommend EDG connectors in a 3.5mm or similar raster. They go in tightly, hold firmly. You can also easily change the pin order.

    You can also use the softer connectors from the WS/HS family or the slightly larger connectors from the 402/403 family (molexes like in computer fans).

    How about using RJ11 connectors?
  • #4 16949391
    ziajek444
    Level 9  
    stonefree wrote:
    If RS232 then why not a DB-9 connector?
    .
    Because it's inconvenient to fit and it's expensive with sockets. Well, and I only need 4 wires so I feel it would be a bit of overkill to choose a plug with so many pins.

    stonefree wrote:
    And why two different plugs for two different cable lengths?
    .
    I don't know, it seemed to me that not every type of plug is suitable for every distance. My thinking was a consequence of reading about symmetrical cables.
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  • #5 16949763
    CYRUS2
    Level 43  
    ziajek444 wrote:
    I am building a light sensor. The main components of my sensor are: Atmega8 (takes measurements and communicates over rs232).
    .
    What is the purpose of the microprocessor there - what is the microprocessor supposed to do ?
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  • #6 16949950
    ziajek444
    Level 9  
    CYRUS2 wrote:
    What is the purpose of the microprocessor there - what is the microprocessor supposed to do ?
    .

    Buddy @CYRUS2 , The microprocessor analyses the analogue signal created by the current flowing through a voltage divider made of a photoresistor and a resistor. It converts such an analysed signal into a human-understandable value expressed in Lux.

    Anticipating further questions. When the sensor is queried for a value, it must provide this immediately so that the controller can react accordingly. The sensor is powered by a wire from the controller. Communication takes place via rs232.
  • #7 16951092
    CYRUS2
    Level 43  
    ziajek444 wrote:
    Kolego @CYRUS2 , The microprocessor analyses the analogue signal resulting from the current flowing through a voltage divider built from a photoresistor and a resistor. Such an analysed signal is converted into a human-understandable value expressed in Lux.
    This does not need to be explained to me.
    ziajek444 wrote:
    Preventing further questions. When the sensor is asked for a value, it has to give it immediately so that the controller can respond accordingly.
    The photoresistor is a rather slow sensor. It has its drawbacks.
    My advice is - have the colleague first check how the photoresistor - resistor measures the illumination,
    Whether the sensor circuit itself meets the colleague's measurement expectations.
  • #8 17018493
    ziajek444
    Level 9  
    Does it meet my expectations without any problems? In which plane would the problems manifest themselves?
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Topic summary

✨ A light sensor system using an Atmega8 microcontroller communicates via RS232 and is powered from the controller through a single cable carrying MASS (ground), Rx, Tx, and POWER lines. The user seeks advice on an appropriate connector type for cable lengths ranging from 2 to 30 meters, preferably a single plug type. Suggestions include using a DB-9 connector, commonly associated with RS232, or a 4-pin jack similar to headphone connectors. Concerns were raised about potential misconnection risks with 3-pole jacks shorting power or signal lines. Alternative connector recommendations include EDG connectors with 3.5mm pitch, WS/HS family connectors, Molex 402/403 series (used in computer fans), and RJ11 connectors. The user prefers a compact, cost-effective connector with only four wires, avoiding overkill from multi-pin connectors. The microcontroller processes analog signals from a photoresistor voltage divider to output lux values on demand. The photoresistor's slow response and measurement accuracy were noted as potential issues to verify before finalizing the sensor design.
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