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Circuit review

Discussion in 'General Electronics Discussion' started by bobdxcool, Jun 16, 2020.

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  1. bobdxcool

    bobdxcool

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    Mar 9, 2012
    I built an automatic liquid dispenser using an arduino. Now I am planning to build one without an arduino. I am planning to use

    1.) IR sensor (https://www.amazon.com/DAOKI-Infrar...d=1&keywords=IR+Sensors&qid=1592302302&sr=8-6).
    This sensor outputs a low signal from out pin whenever an obstacle is detected.

    2.) Small submersible dc motor pump (3-6volts 200mA).
    (https://www.amazon.com/3V-6V-Submer...submersible+water+pump&qid=1592302828&sr=8-12)

    3.) 555 Timer IC

    4.) LM7805

    5.) 4 alkaline 1.5V batteries in series

    Please find attached circuit below.

    The values of R & C that I plan on using are 100k & 10uf for 1 second delay (or a potentiometer and 10uf capacitor).

    Also I plan on integrating a DC float switch (https://www.electronicscomp.com/water-level-sensor-float-switch-p43-india) in the tank. When the tank is empty, the motor should not run. When the tank is empty, there would be a connection between the two wires of the float switch. So I am thinking of connecting one end of the switch wire to positive terminal of motor (instead of +5v as seen in circuit below) and the other end of the wire to +5V.

    Also, I was thinking if it would be possible to directly connect sesnor output directly to trigger pin of 555 without any transistors or resistors.

    Request the people in this forum to let me know their opinions on this circuit.


    nocontroller.png
     
  2. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    The circuit will not work.
    Pin 2 is always connected to ground.
    To trigger the 555 you will need a low going signal:

    555 Astable circuit forest mim.png

    Bertus
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    This will turn-off the NPN transistor.
    Simply connect the output of the sensor by a series capacitor to the input (2) of the 555. The low going output will then trigger the 555.
     
  4. bobdxcool

    bobdxcool

    98
    0
    Mar 9, 2012
    Thank you. What value and type of capacitance should I use ? Is ceramic 0.1uf good enough ? So apart from removing the transistor and connecting a capacitor in between the sensor and 2nd pin of 555, does the rest of my circuit and float switch wiring seem correct ?
     
  5. bertus

    bertus Moderator

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    Nov 8, 2019
  6. bobdxcool

    bobdxcool

    98
    0
    Mar 9, 2012
    nocontroller2.png
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Looks (bobdx)COOL ;)
     
    bobdxcool likes this.
  8. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    I think that a LM7805 will not drop the voltage as wanted.
    It needs even 1 Volt difference at 0 mA and 1.5 Volts at 20 mA:

    LM78XX_voltage drop.png

    Better use a LD1117-50, that will have a voltage drop of 1 volt at 100 mA.

    Also put the motor direct on the battery.
    This will save you from a voltage drop when the motor is running.

    Bertus
     

    Attached Files:

    Harald Kapp likes this.
  9. bobdxcool

    bobdxcool

    98
    0
    Mar 9, 2012
    LM338 should also work right . This part is easily available near my place. Even if I connect 3 or 4 batteries (1.5*3 or 1.5*4) in series
    Capture1.PNG

    I am also considering trying without any regulator and using 3 batteries (4.5V) directly. Sensor should work between 3 and 5V. And maybe use a boost converter like this (https://sharvielectronics.com/product/sx1308-2a-dc-dc-high-current-adjustable-boost-module/).
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    What makes you think the LM338 will work? The graph you show is from the datasheet and clearly shows an input-output voltage differential of ~1.8 V at 25 ° C and 1 A current.
    You will need a low-drop regulator (Vin-Vout < 1 V) for your application as suggeste by @bertus .
    This possibly works perfect in this application. However, I suggest you add a filter between motor and battery tor protect the sensor and the 555 from noise produced by the motor. You can buy such a filter as "DC motor EMI filter" for exampel on ebay or any RD model accessory store.
    What for?
     
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