AUTO-FLOW:

DIY WATER Sprinkler

System

Mikel Emmanuel De Crus

Copyright © 2013 Mikel Emmanuel De Crus

All rights reserved

Do not reproduce the material in this book by any means whatsoever without written permission from the author.

Mikel Emmanuel De Crus

Via Mezana 21,Varese,Italy

E-mail: emmanuelde.cruz@gmail.com

Chapter 1: Introduction

1.1 Problem statement

The plants in a garden need to be taken care often. In order to ensure that the plants in the common household is always in a healthy condition daily watering is needed. Plants need the water to sustain natural processes such as photosynthesis (sunlight energy is absorbed to synthesize energy) in order to survive. People nowadays have very little time to water the plants in their common household garden. Left unattended these plants could just wither away if not watered regularly, especially when the owner is away for long periods of time. The motivation of designing and building the “Auto-Flow” system is to eradicate this problem as it automates the watering of the plants in the common household.

1.2 The “Auto-Flow” system.

The Auto-flow system is an automated water sprinkler system is a system that designed to automatically water plants in a garden in the common household. The development involves designing an automated control valve that is directly connected to the water supply (in this case the common household faucet or tap).The control system will have an electronic circuitry attached to water inlets pipes to perform the timing control. The system design is designed to water the plants at designated intervals thus allowing the occupants of the household to maintain their garden even when not at home. This domestic product features a timing circuitry connected to a valve that allows the flow of water from a faucet to water the plants through a tube. The automated water sprinkler system in this project was termed “Auto-Flow” as its name represents that the system is fully automated to allow the to water plants in his or her garden at the users discretion

1.3 Scope of the “Auto-Flow” Project

The scope of this project is to design the hardware and necessary circuit to a 555 timer system to give a control output that will the set the ac valve open in order to allow the watering of plants through tubing system, every 1 hour and for each duration the water must be allowed to water the plant for a minimum of 5, 10 or 15 minutes.

1.4 How the “Auto-Flow” system works.

The Auto-Flow system utilizes a timing circuitry that uses IC timers to control a valve that lets the water flow through a tube that is connected to the common faucet in the household. The user is allowed to choose when to water the plants, for example, after one hour. For each interval the user is allowed to choose how long the system will water the plants, for example 15 minutes. The system will automatically stop watering the plants after fifteen minutes. This cycle will continue repetitively unless the user turns off the power to the system which will permanently shut the system down .The cycle could be  also be interrupted if the user decides to reset the system for which the system will begin a new count regardless of previous settings.

1.5 Benefits of “Auto-Flow”

The gained benefits of “Auto-Flow” system are as the following:

         A water sprinkler system for the common household garden that is fully automated and easy to use.

         Provides the user a sense of security and assurance that the plants in the garden will be automatically watered even if the user forgot to water his plants or what’s even worse; the user is away from the household for long periods of time.

         Reduces dependency on the occupants of the household to water the plants. Thus, the user of “Auto-Flow” will be able to save time, money and energy.

         Introduces a smart electronic household appliance with commercial value.

CHAPTER 2: Review of Literature

2.1 The 555 timer

Figure 2.1: General Block Diagram of 555 IC

The 555 timer was first introduced in 1971 by the Signetics Cooperation as the NE555/SE555.It was one the first timers invented and still very much popular today. Because it is cheap, stable and user friendly it has provided circuit designers and hobbyist the chance of building reliable and quality circuits and products. The common 555 timer utilizes a maze of 20 transistors, 15 resistors and 2 diodes depending on the design by the manufacturers. The equivalent circuit in the general block diagram shown above provides the functions of control, triggering, level sensing or comparison, discharge and power output. The 555 timers are available in two versions namely the 8-pin T packet which will not be discussed here [2]. The model IC discussed here is the 8-pin V-packet as shown in the following figure.

Figure 2.2: 8-pin V-packet 555 timer

The 555 timer uses the supply voltage of 4.5 to 18 volt and supply current of 3 to 6 mA. The timer also has a rise and fall time of 100 nanoseconds. The 555 timer relies on an external capacitor to determine the on-off time intervals of the output pulses as it takes a finite period of time for a capacitor to discharge or charge through a resistor. The time the capacitor takes to charge or discharge through a capacitor is clearly defined and can be calculated. To further explain this let us assume that the capacitor is initially discharged. When the switch is closed the capacitor is charged through the resistor and voltage rises up to the DC value applied form zero volts because of the RC design. [6] 

Figure 2.3: Graph of charging voltage versus time

The curve shown in the figure above clearly explains this phenomenon. The charge after a time constant of 63.2 % is considered to be its maximum charge. The time which it takes to charge can be calculated with the following expression:

T= R x C, where

T=charging time of capacitor,

R= value of resistor through which capacitor   charges (Ω)

C= value of external capacitor that is charging (F).

2.2 Definition of pin functions:

Pin 1 (Ground):

The common or ground pin is the most negative–supply potential of the device. This is pin is normally connected to the common ground of the circuit.

Pin 2 (Trigger):

This is the input pin to the lower comparator (labeled D) in the block diagram. It is used to set the latch will cause the output to go high. Triggering is accomplish by taking the pin from above to a voltage level of 1/3 V + which allows input levels that are sensitive ,slow-rate changing waveforms as well as pulses to be used as trigger sources. Thus, the triggering is always achieved by setting a low input voltage pulse or state. The minimum allowable pulse width for triggering depends on the pulse level but generally it must be greater than 1us for the triggering to be reliable. The current is typically 500nA and will define the upper limit resistance allowable from pin 2 to the ground. 

Pin 3 (Output):

The output of 555 timers comes from a combination of transistors. Their Darlington connection provides a high state output voltage of 1.7 V which is less than the V+ level used. The output saturation voltage varies with supply voltage for both high and low states. For example, at +5 V, the low state Vce is typically at 0.25 volts at 5 mA but operating at +15 V it can be 200 mA if an output voltage of 2 V is available. The high state level is normally at 3.3 V at V+ = 5V: 13.3 V at V+=15V. The rise and fall time of the output pulses are about 100 ns. The output state will always be an inverse of the of the logic state at latch (input) as shown in Figure 8 in the following page.

                    (a)                                                                      (b)

                       Figure 2.4: Low input and high input of timer

The triggering of the output to a high condition, the trigger input is momentarily taken from a high level to a low level as shown in figure 9. This causes the latch to be set (done by a transistor in timer) and the output to go high. Actuation of the lower comparator (labeled D in block diagram) is the only way in which the output can achieve a high state. The output can be returned to a low state by causing the threshold (pin 6) to go from lower to a higher state. The output can also be made low by taking the reset to a low state near ground.

Figure 2.5: Input pulse and output pulse are inverted

Pin 4 (Reset):

This pin is used to return the output to a low state and it is also used to reset the latch. The reset voltage level threshold is 0.7 volt and a sink current of 0.1 mA is required to allow reset. The reset input is compatible for any supply voltage and are independent of the relative V+ operating level. The reset level is an overriding function that will force the output to a low state regardless of the other input states into the timer. Thus it can be used to terminate an output pulse prematurely or to gate oscillations from on to off state immediately. The delay time from reset to output is normally 0.5 us. The minimum reset pulse width is 0.5 us and may vary from one manufacturer to another. The reset pin, in other words is used to reset the flip-flop that controls the state of output pin 3. The reset pin is activated when the output voltage is between 0 and 0.4 volt. The reset pin will force the output to go low no matter what the other flip-flop for the inputs are in. When not in used the reset input should be as close as possible to V+ to avoid false resetting.

Pin 5 (Voltage Control):

The control voltage pin allows direct access the 2/3 voltage divider point in the timer for the reference level of the upper comparator (labeled C in the block diagram). It also allows indirect access to the lower comparator. The use of this terminal is an option to the user but the pin allows modification of timing period and resetting of the comparator. When the timer is used in a voltage controlled mode, the voltage controlled operation ranges from about 1 volt less than V+ down to within 2 volts the ground voltage. Voltages applied here should be confined within the limits of V+ and ground for reliability, however, voltages outside these limits can be safely applied too. Applying voltage to this pin, it is possible to vary the timing of this device regardless of the external resistor and capacitor setting. When the timer is used in the astable mode which will be discussed later, the control voltage can be varied from 1.7 volts to the full Vcc voltage which will produce a frequency modulated (FM) output. If this pin is not used, then it should be bypass to ground with a capacitor of about 0.01 uF for immunity to noise. [2]

Pin 6 (Threshold):

This pin is connected to the input of the upper comparator (labeled C) and is used to reset the latch which causes the output to go low. Resetting through this terminal is done by taking  the terminal from below to a voltage above 2/3 V+ ( normal voltage level on pin 5).The threshold pin is level sensitive which allows slow rate of change of the waveforms. The safest voltage range that can be applied to this pin is between V+ and ground. A DC current must also flow through the terminal from an external circuit. This is the threshold current and is typically 0.1 micro amperes and will define the upper limit of the resistance allowable from pin 6 to V+. For operating voltage of +5V, the resistance is 16 MΩ and for +15V operation the maximum resistance is 20 MΩ.

Pin 7 (Discharge):

This pin is connected to an npn transistor in the timer ,the emitter of the transistor to be precise, which is then grounded .When the transistor is turned on the pin 7 is effectively shorted to the ground. The timing capacitance is usually connected to the pin 7 and ground and is discharged when the transistor turns on. The output stage is identical in timing to the conduction state of this transistor. The transistor is on when the output is low (low resistance to ground) and off (high resistance to ground) when the output is high. The saturation voltage is typically below 100 mV for currents of 5 mA or less. Maximum collector current is internally limited by design. Thus, this removes restriction on capacitor size due to peak pulse-current discharge.

Pin 8 (V+): 

The V+ pin or Vcc pin is the positive supply voltage of 555 timers. The supply voltage operating range for the timer is between 4.5V (minimum requirement) and +16 V (maximum voltage) and will operate over these range of voltages without changing the timing period. The most significant difference in operation is the output drive capability, which increases for both current and voltage range as the supply voltage is increased. Sensitivity of the time interval to supply voltage is low (0.1% per volt)

2.3 Features of the 555 timer:

Table 1.1: Features of the 555 timer Table 1

 Features |  Maximum rating (NE/SA/SE type)
 Supply voltage |  4.5 to 18 volts
 Supply current |  3 to 16 mA
Rise / fall time |  100 ns
 Total resistance |  20 M ohm (for 15 volt operation)
 Output current |  225 mA (approximately)
 Input Voltage(CONT, TRIG, RESET, and THRES): |  Vcc or V + (supply voltage)
 Operating temperature (free-air): | NE 555 (0 -70 Celsius or -273 to -203 Kelvin) SA 555 (-40 to 85 Celsius or -313 to -188 Kelvin)  SE 555 (-55 to 125 Celsius or -328 to -148 Kelvin)
 Storage Temperature |  -65 to 125 Celsius or -338 to -148 Kelvin
 Casing Temperature | 260 Celsius or -13 Kelvin (this for 60 seconds exposure)

CHAPTER 3: Design Methodology

3.1 The design of “Auto-flow” system.

The general block diagram of the “Auto-Flow” system is shown below:                           

Figure 3.1: General Block Diagram

The block diagram shows how the automated water sprinkler system “Auto-Flow” works generally .Water flows through the tubing system to water the plants from the source (the common household tap or faucet) .The tubing system has a valve connected to it to let the water pass through at certain intervals in time which is controlled by the timing circuitry .This timing circuitry uses a 555 timer as will be explained in the following page. The valve will be timed to open at designated intervals. The tubing system will be approximately 6- 8 meters in length will be shown in the following pages which will be fitted with plastic inlets to allow water to sip through and water the plants.

3.2 General visualization of “Auto-Flow”:

There was a number of visualization for this product implementing various design using mechanical valves schemes in its infancy stages but the finalized scheme which uses an electromagnetic valve is as follows:

Figure 3.2: Visualization of “Auto-Flow”

3.3 Tubing System

The tubing system will be fitted with small plastic inlets to allow water to drop on plants. The flexibility of the tubing system allows versatile watering. It can water plants along uneven grounds and different heights.

Figure 3.3: Tube used for system

3.4 Valve

The AC valve is connected to the timing circuitry that uses 555 timers. [1]

Figure 3.4: Front view of the FVS-65V ac valve

(200-240V- 50/60 Hz)

3.5 Timing Circuitry

Figure 3.5: Schematics of timing circuitry.

The circuitry has an astable timing circuitry that is connected to a monostable timing circuitry which utilizes two 555 timers. The use of this timers and how they operate will be explain in the following section. [4]

Among the other components used for this circuit are as following:

DC/AC Solid state relay
S1: On/Off
S3: Range
B1: 9V or DC adapter
Capacitor: 33uF, 2200uF, 100nF (electrolytic capacitor)

AC valve- FVS-65V (model number) 200-240 Volts and operates on 50/60 hertz.

Resistors: 8.2 MΩ, 1.5 MΩ (variable) (resistor R6=4.7 kΩ is used to make sure input is always low when entering the transistor)
Q1: BC109C NPN

The transistor used is a BJT transistor which the common base configuration is used to perform small signal amplification for the relay network. [3]
D1: 1N4004 DIODE

The diode in this circuit serves as protection device for the transistor.

3.6 The design circuit using the 555 timer.

The section before this explain how the 555 timer works. The circuitry was designed by manipulating the characteristics of the 555 timer. By utilizing the 555 timer to build an astable circuit to serve as input signal or timing circuit to a monostable timing circuit which also utilizes the 555 timer, a complete and working model of the timing circuit was designed and built. Thus, before proceeding to explain to circuitry in detail, an understanding of the astable and monostable circuit is needed as the following section explains.

3.6.1The Astable Circuit

Figure 3.6: Astable circuit

The versatile features of the 555 timer allow a number of very useful circuits to be designed. One of those circuits, the astable circuitry, has been used to designed part of the circuitry to realize this project. The astable circuitry used in this project design is the heart of the “Auto-Flow” system as it used to time the exact interval for watering the plants. The output of the astable circuitry is connected to input of the monostable circuitry which will be discussed later. The astable circuitry is used to time the monostable circuitry which tells the system how long to water the plants. [5]

Astable means “no stable state” and the astable circuitry producers an output that continually switches between high and low output pulse. This thus produces a square wave output as shown the figure below.

Figure 3.7: Astable pulse

Form the figure 3.6, it can be seen that the value of the resistor, R1 and R2 and the capacitor value is unspecified. It is because the values of these components determine the length of the output state and they are calculated using the equation below. This is possible as to the operations of the 555 timer. (Refer to the operations of pin 2 and 3.)

For the high output:

T = 0.7 x R t x C,

where

R t = value of external resistors (R1 + R2),

C = value of external capacitor.

For the low output:

T = 0.7 x R 1 x C, where

R ₁ = value of external resistor,

      C= value of external capacitor.

The value of the capacitor is set first in order to determine the value of the resistor. The calculations involved and the results obtained will be shown in the following pages. The low output pulse of this circuit is used as the input to the monostable circuit to trigger it. The termination of this setting, the reset button could be activated which will result in pin 4 being invoked (refer to pin 4 functions).

3.6.2 The monostable circuit

Figure 3.8: Monostable circuit.

Utilizing the salient features of the 555 timer, a monostable circuit was built was use the drive the solid state relay to open the ac valve at timed intervals. An example of the circuit used is shown above in figure 13. Monostable means one stable state. A monostable circuitry produces one pulse that is in one stable state, or in other words, in produces a pulse of set length in response to a trigger input which in this case is supplied by the a low input pulse from the astable circuit discussed earlier as shown in figure below. The output current from pin 3 of the timer, is amplified by Q1 and used to drive a solid state relay. The output of this circuit stays in the low state until

it receives the trigger input from the astable circuitry. [5]

Figure 3.9: Monostable (a) input and (b) output wave form.

Form the figure 3.8, it can be seen that the value of the resistor and capacitor value is unspecified. It is because the values of these components determine the length of the output state and they are calculated using the equation below. (Refer to the operations of pin 2 and 3.)

For the high output:

     T = 1.1 x R x C, where

      R = value of external resistor,

C= value of external capacitor.

The value of the capacitor is set first in order to determine the value of the resistor. The calculations involved and the results obtained will be shown in the following pages. The trigger input to this circuit which is the output of the astable circuit which must be low. The termination of this setting the reset button could be activated which will result in pin 4 being invoked (refer to pin 4 functions).

CHAPTER 4: Presentation of Data and Discussion

4.1 The Control Algorithm for the Time Setting:

Whenever a trigger pulse is applied to the input the 555 timer will generate its single duration output pulse for the monostable circuit and for the astable circuit it will continue pulsing until the cycle is interrupted. Depending on the values of the external resistance and capacitance used the output timing pulse may be adjusted from approximately one millisecond to hundred of seconds .In the Auto-Flow system, the intended setting for the timer to switch on the valve is about approximately 5, 10 and 15 minutes using the monostable circuit and for the astable circuitry the intended setting is for 1 hr or in seconds is equivalent to 3600 seconds. Therefore, using the relations obtained from the monostable and astable circuit, the suggested algorithm for this project is calculated as follows:

4.1.1 For the monostable circuit:

Using the known relation,

T= 1.1 x R x C (in seconds)

Since it is known that the first intended setting is for 5 minutes or 300s, and choosing the R value as constant (in this case 8.2 MΩ) the capacitance required is:

C= T / 1.1 R

= 300/ 1.1 (8.2 x 106 )  

  = 3.6585 x 10⁵ F

≈ 36.58 μF (capacitor value used is close to value)

Now using C = 36.58 μF for a time of ten minutes or 600s,

R= T/1.1C

  = 600/1.1 (36.58 μF)

  = 14.91 MΩ

  (Approximately twice the value of 8.2 MΩ)

Using the same value of C for 15 minutes or 900s,

R= T/1.1C

  = 900/1.1 (36.58 μF)

  = 22.36 M Ω

  (Approximately three times the value of 8.2 M Ω)

Figure 4.1: T mark of Monostable

The time T= 300s, 600s and 900s is the high output pulse represented by T mark.

Thus for the monostable circuit which controls the ac valve, the resistors are connected in series with a switch that increments the resistance in multiples of 8.2 M Ω and setting the capacitance as close as 36.58 μF (in this case 33 μF as available) to give the user a choice of selecting an approximate of 5, 10 or 15 minutes to water his or her plants.                             

4.2.2 For the astable circuit:

In the “Auto-Flow” system the target for astable circuit is to pulse for 1 second

(T space ) which is the input trigger and this trigger input is set to pulse every 1 hour or 3600 seconds (T mark) .

Figure 4.2: T mark and T space for astable

Thus the High Output is represented by T mark = 3600s (1 hour) .By the following known relation,

T mark = 0.7 x (R1+ R2) x C

And setting the capacitor value for value of 3300μF (as available),

                                                  R t = T mark / 0.7 C

                                                       = 3600/ 0.7 (3300μF)

                                                       = 1.558 MΩ

                                                       ≈ 1.5 MΩ

where R t = R1 + R2.

The Low Output represented by T space= 1 s, which is used to trigger the monostable circuit and is given by the following relation. .

T space = 0.7 x (R2) x C

                                                         R2= T space / 0.7 C

                                                              = 1/0.7(3300μF)

                                                               = 432 Ω

                                                                ≈ 500 Ω

So since,

                                                      R t = R1 + R2, thus

                                                      R1=   R t - R2

                                                      R1 = 1.5 MΩ - 500 Ω

                                                            =1.499MΩ  

                                                            ≈ 1.5MΩ (value of R2 is negligible)

The astable circuit is used to trigger the monostable circuit that switches on the motor for a designated time period of 5, 10 and 15 minutes as discussed earlier.

The prototype of the model built is shown in the following diagrams.

Figure 4.3: The “Auto-Flow” prototype

Figure 4.4: Inside the “Auto-Flow”

Figure 4.5: First prototype built compared to the final prototype

CHAPTER 5: CONCLUSIONS

5.1 Summary of the work

In this project, a number of basic 555 timer circuits design was used to build an automated timing circuitry, thus making the “Auto-Flow” a value added product as the features added are those that would appeal to most household users. The user can water the plants in his garden just a touch of a button up and continue doing other household chores. The system can water the plants for a few weeks or even months. The “Auto-Flow” system also benefits the user as the user is able to save time, money and energy and the water sprinkler system for the common household garden is fully automated and easy to use. It provides the user a sense of security and assurance that the plants in the garden will be automatically watered even if the user forgot to water his plants or what’s even worse; the user is away from the household for long periods thus reduces dependency on the occupants of the household to water the plants.

5.2 Recommendations for future work.

Although the prototype model built does meet the requirements of the project, the model could be further improved, for example the model built here utilizes two separate power supply, the valve uses an ac power supply but the timing circuitry is biased by the dc power supply. The circuitry can be improved by tapping the power from the ac power supply and converting it with an ac to dc converter to bias the timing circuitry which uses dc current. This will eliminate the need of having two power supplies to power up the product as the model featured uses two different current source. This will make it more user-friendly for user of the product.  

Disclaimer:

This is a DIY hobby kit for personal use. It uses basic electronics and it is not approved for commercial use. Please practice safety at all times as the project involves tinkering with high voltage and current sources. Water is an excellent conductor of electricity hence do not test product without proper and adequate supervision. The author will not be held responsible for any lives lost, damages incurred or injuries sustained.

Table of Contents

Copyright

Chapter 1: Introduction

CHAPTER 2: Review of Literature

CHAPTER 3: Design Methodology

CHAPTER 4: Presentation of Data and Discussion

CHAPTER 5: CONCLUSIONS