555 Sanitizer Dispenser (With cut-Off)

Simple analog Sanitiser Dispenser (No-Contact) using 555 timer IC with auto cut-off timer (even with trigger).
Cheap and No-Coding Solution.

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There are many Arduino / Microcontroller based no-contact Sanitizer dispensers, the only problem with them is that they are expensive and require coding.

Some of The Analog Solutions Available on the internet work, but doesn't have any mechanism to auto cut off the dispensing system when a trigger is detected. They just don't stop pouring sanitizer if a person doesn't remove his hand away from the dispenser, Hence wasting the sanitizer.

Desired Features:
1. No-Contact Sensing (IR, PIR)
2. Dispenser Timer (Adjustable) dispense only required amount of sanitizer.
3. Auto Cut-Off even if Trigger is present / Hand not removed
4. Require Fresh Trigger to restart Dispensing Sanitizer
5. Simple and Cost-Effective
6. Able to drive micro-pump or solenoid
7. Liquid Level-Indication
8. Adjustable liquid dispensing time.

In this design, i will be using a 555 timer IC in monostable configuration to achieve no-contact automatic sanitiser dispenser.

When trigger is connected to a sensor, the monostable circuit itself can start pump.

but we encounter a problem with the standard monostable circuit, where the output stays high as long as the trigger pin is held LOW / Triggered.

But that is a problem in our application, as the liquid overflows the pams and starts to drip to ground, hence wasting the liquid.

so, by adding an RC (resistor, capacitor) in between trigger pin and trigger source, with +ve of capacitor to trigger source and -ve of capacitor to 555 trigger pin, we can make this circuit auto cut-off after the monostable pulse time set by (Rv and Cv) at 555 IC.

The RC couple in between the trigger circuit acts as trigger pulse, where, even if sensor is countinuously triggering, only a single pulse is sent to the 555 IC trigger pin.

This happens because, when the trigger is detected, the pulse is sent to 555 trigger pin only till capacitor is fully charged, after that the capacitor blocks the trigger signal.

on removal of trigger signal from sensor, the capacitor gets discharged by the resistor in parallel to it, resetting the RC pair, ready to accept new sensor trigger / signal.

Hence, for each time hand detected by sensor, liquid is only dispensed for only the set amount of time even if hand is placed below the sensor indefinitely, and it only re-dispenses liquid on removal of hand and placing it again.

by using this circuit, we can limit liquid usage and also avoid wastage.


Circuit of the design

Portable Network Graphics (PNG) - 175.91 kB - 07/20/2020 at 21:58


  • 1 × NE 555 main controller of our circuit 555 timer IC
  • 1 × Micro-Pump / Solenoid to pump / dispense the sanitizer
  • 2 × 22k resistor
  • 2 × 1k resisstor
  • 1 × 470k resistor

View all 14 components

  • Scrapping of Old Circuit for New One

    vybhav-nag10/13/2020 at 04:35 0 comments

    The old circuit v1 is based on 555 IC, for which needs more discrete components and can't connect the IR diode / photo diode directly without an amplifier.

    So, if an amplifier is used cheapest one available is an LM325, which is a dual OpAmp package, so instead of using a 555 to create a single pulse / one shot / monostable circuit. The same can be achieved using an OpAmp.

    OPAMP 1 : Sensor / Signal amplifier.

    OPAMP 2 : Monostable / One Shot circuit.

    So, whoever wanting to create a project using these circuits, please wait for V2 of circuit, which will b cheaper and more reliable.

  • Sensor test and modifications

    vybhav-nag08/31/2020 at 18:28 6 comments

    IR sensor modifications : When white paper is placed at about 0.5cm, transistor gets 0.56v just enough to trigger it.

    but when a human hand is placed at same distance or even near, the photodiode output voltage doesn't rise above 0.42v as shown in pic.

    the 222n transistor used requires min 0.55 / 0.6v at base to switch it ON.

    * run the circuit at higher voltage (currently testing at 5v)
    * search for alternate transistor with lower min base voltage ( should be cheap and widely available)
    * try adding more IR emmiters / LED around the photo diode, possibly increasing photodiode output.

    will further test with given solutions.

  • IR sensor testing and modifications

    vybhav-nag08/31/2020 at 18:08 0 comments

    working for white objects, but doesn't work for hands (IR sensor)

  • Circuit design and simulation

    vybhav-nag07/21/2020 at 07:24 0 comments

    Designing the final circuit for simulation and layout.1. adding auto put-off timer using RC pair in series with trigger input.2. modifying circuit to use any generic IC pair as proximity sensorwill soon upload LTspice simulation and KiCad design files.

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