Trabajo de Dise;o de Circuito

7/28/2019 Trabajo de Dise;o de Circuito

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Description of requirements /thoughts of circuit design.

In brief: We will use 4 inputs to trigger an output of 24V DC. When any of the inputs are active,

output is active (a logical OR gate).

The

circuit

will

have

input

of

water

detection.

When

water

is

detected,

the

output

will

always

be

off.

In addition, and audible and visible alarm will be set. Audible alarm can be shut off when pressing a

button, but will re‐engage after 60 minutes or if the water sensor has been “low” in the meantime.

DETAILS:

In our opinion, a microcontroller is suitable for this purpose. Since the inputs must be electrical

isolated from the circuit, and the voltage that should be sensed varies, 4 opto‐couplers might be the

best solution. 2 of the inputs will be fed with 230V AC, and the remaining two must be able to handle

both 12 and 24 V. In the drawing we have 2 resistors for each input, giving us the possibility to

connect the inputs to either 12 or 24 V. None of the inputs needs to be secured via fuse. All inputs

have a small

led

to

give

visible

control

that

power

is

going

into

the

opto

‐coupler.

By using Google, we have found a schematic for a water detector that uses a PIC microcontroller, but

has no knowledge about it’s functionality. If it can reliable be used as drawn than this is an option,

but possibly an amplification with suitable transistors is necessary.

The output of 24 V DC must be able to deliver 0.5A. Can a Mosfet be used for this? And, since the

load is inductive, suitable protection against back‐EMF must be provided, and also a fuse.

Indication of water detected, should be short beeps with 5 – 10 seconds interval, and a blinking LED.

By

pressing

a

“quiet‐

button”

the

audible

alarm

will

shut

off,

but

visible

remains.

The

audible

alarm

shall reactivate after 60 minutes, or if the water detector had been low and then high again (ie: no

water sensed, and then water sensed again).

When designing the PCB, than power to the circuit and output can be external. Connections for input

can be via screw‐terminal on the pcb, this also includes water probes, and output. Adequate distance

between 230V and low voltage as required by European safety standards. Quiet‐switch must be

accessible via enclosure, but the switch itself can be on the pcb, but with enough distance to 230V

connections.

For the 12/24 volt input, a tree‐way terminal is ideal. Note that in use, there will only be either 12 or

24 volt

on

one

input,

never

both

at

the

same

time.

Despite

that

the

input

will

be

by

technician,

maybe a protection against wrong polarity is necessary.

On the drawing:

1 & 2: Optocouplers for 230V input.

3 & 4: Optocouplers for 12/24 V input

5: Microcontroller

6 & 7: Current limiting resistor, led and diode for the 230V AC input

8 & 9: Current limiting resistors for both 12 and 24 input, with led.

10: Water probe (water sensing electronics not drawn)

11: Quiet‐button



12: Buzzer

13: Water alarm LED

14: Output circuit. 24 V DC 0.5A output into inductive load. Fused and protected against back emf.

15: Power supply for circuit. Input 24 V DC regulated from external power supply.

NOTE: No

ground

connections

are

shown

in

the

drawing.



5

IN/OUT

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1

2

3

4

15

6 7

8

9

10

11

12

13

14

Untested water detection drawing for use on PIC

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Trabajo de Dise;o de Circuito