I have a shallow drain in my laundry room that is
shared by the kitchen.
A laundry tub somewhat regulates the flow from the washer
but periodically the drain gets jammed up with stuff from either the kitchen
disposal or laundry discharge ‘goop’.
Either way you know you’re in trouble when the
water backs up onto the laundry room floor.
While water monitors can be simple things I wanted to
be able to provide a bit more warning. Following a rather unpleasant laundry
room crisis, I wanted to build something that gave me a clue that the drain was
‘getting’ clogged, before I got to the ‘water all over the
place’ situation.
This application uses an inexpensive sensor and
minimal parts and footprint to provide a 2 point, settable, pressure alarm, at a total
cost of under 12$. In this application, a sensor tube would be inserted through
the floor drain plug and the trip settings to be set for ~1 and 5 inches of
water.
Referring to the schematic, the FreeScale,
MPCX2010 sensor, is a differential, ported, gauge sensor. The scaling
amplifiers use a LM324 quad op-amp and the detector is a LM1541. Although all the active parts, including
the regulator, are available in surface mount I have used socketed 8 and 14 pin
dual in-line ICs and the more traditional TO-92 parts. Assemblied
on a common .1” center perf with solder pads on
a single side passive resistors pots and caps are also through hole mounted.
Schematic Figure 1
In the past I had published an alarm controller, EDN,
Design Ideas, January 15, 1998, which modulated a pies-ceramic wafer.
I have modified it for this application to provide both
a periodic chirp for that first level, 1 inch, trip and a continuous warble for
a second, 5 inch, alarm trip. The newly coded alarm controller was then
re-compiled for Microchip’s 10F200 controller. Several Microchip
controllers can be used including the 10F204 and 12F508. These are small and
inexpensive controllers. The code, provided below, should run in any of these.
I have used a 1.45 psi sensor, scaled in half to
detect, full scale, 5 inches of water. Similarly packaged sensors, from
FreeScale, for this application include a 7.25, 14.5 and 29 pK sensor.
Conversion between pK, PSI and inches of water can be simply done, on-line
at:
http://www.sensotec.com/convert.shtml
Shown below, the circuit card was mounted in a small
plastic box.
The alarm and sensor were mounted on 1 side while the
socketed ICs and discrete parts were mounted on the other side.
Layout is not particularly critical. Referring to the
figures and schematic above, the assembled gadget uses 2 inexpensive PC mounted
pots to set both the first and second level trips.
Diodes D1 and D2 provide isolation and the battery,
B1, backup and a common 9 volt, wall based supply, PWin. The hardware consumes
~4ma.
As shown in the figure, I modified a drain plug to
accommodate a ¼” tube. The inside diameter had to be large enough
to prohibit a water-drop from sealing the tube. This tube is then routed to the
circuit and interfaced to the smaller tube which then fits over the pressure
sensor port. Shown the figure these interfaces must be air tight. In my
application I used a small 3/16th OD plastic tube at the sensor and
inserted that into about a 5 foot length of 1/4 OD plastic tube.
Sensor Alarm with Modified Drain Plug
The procedure, to set the alarm, begins by applying
power and inserting the open end of the tube into a jar or container with the
maximum depth of water to be alarmed. The 100 ohm pot, shown in the figure, is
then adjusted until it warbles. The tube is then completely pulled out of the
water and then returned to the level of water desired for the second alarm
trip. The 2nd pot, 10K ohms, is then adjusted until it chirps. The
trip repeatability is pretty good although I found that hot water with reduced
the trip depth about half an inch.
This works well for monitoring that laundry room
drain, although the same assembly could be used for other water related
applications, such as tub or hot tub level alarms.
Using a pressure based alarm allows the same gadget to
be used for other applications.
By tying off the end of the tube and setting the trips
to monitor to the pressure in this sealed tube, this application will alarm
when the tube is compressed, when stepped on or driven over, like might be used
for a garage parking or security sensor.
By connecting the open tube to a funnel I was also
able to alarm for air speed collected in the funnel’s open end.
Two point alarm of wind speed
The included controller code can be compiled into a
12F509 or 10F200, 10F 202, 10F 204 or 10F 206 controllers. These controllers
need their WDT disabled, operation for 4MHz, configured as an undedicated pin
and for internal reset.
; alarmT_pressure.asm
Gadget Freaks;
GPIO equ 6 ;
STATUS equ 3 ; Last mod 07-16-07 *
PC equ 2
#define ZERO STATUS,2
#define outa GPIO,0 ;
#define outb GPIO,1 ;
#define modea GPIO,2 ;
#define modeb GPIO,3 ; input only for F2xx
bits equ 12
temp equ 13
dwell equ 14 ; cycles
count equ 15 ; delay
steps equ 16 ; dwell
cnth equ 17
cntl equ 10
temp1 equ 11
#define timeout .50
#define flag bits,1
resetvec org 0
movlw 0D0 ; 1101 0000
OPTION
movlw 0xF7
movwf 7 ; compare disabled
movlw 0xC ; 1100
movwf GPIO ; set I/O direction
tris GPIO
; qualify enables and re-test mode inputs
top1
bcf flag
clrf cntl
clrf cnth
;
top
mode ; evaluate mode
rrf GPIO,w
movwf temp1
rrf temp1,w
andlw 3
addwf PC
goto mode3 ; siren
goto mode1 ; dual chirp
goto modeother ; disable via mode pins
;
; ******************** siren *****************
modeother
movlw 0xC
movwf GPIO
goto top
mode3 ; (init) siren
i1
movlw 37
movwf count
movlw 6
movwf steps
i2
movlw .64
movwf dwell
alarm1
call alarm1_set
call alarm1_clr
out1
decfsz dwell
goto alarm1
movlw .5
subwf count
decfsz steps
goto i2 ; reload dwell
movlw 0xFC
andwf GPIO
goto top1
; ************************ Duel chirp ***********
modeLh
decfsz temp
goto modeLh
modeLg
movlw timeout
movwf temp
decfsz cntl ; shooting for 7-10 seconds
goto modeLh
decfsz cnth
goto modeLh
bcf flag
goto top
;
mode1 ; init chirp *
btfsc flag
goto modeLh
clrf cnth ; init delay
clrf cntl
mode1e
movlw timeout
movwf temp
bsf flag
movlw 35 ; schedule 2 chirps
movwf count
movlw 1
movwf cnth
clrf cntl
mode1a
call alarm1_set ; set 1st pulse
call alarm1_clr
decfsz cntl
goto mode1a
decfsz cnth
goto mode1a
movlw .200 ; begin pause
movwf cnth ; ~6*199*255us
clrf cntl
mode1b
nop
nop
nop
decfsz cntl
goto mode1b
decfsz cnth
goto mode1b
movlw 1 ; set second pulse
movwf cnth
mode1c
call alarm1_set
call alarm1_clr
decfsz cntl
goto mode1c
decfsz cnth
goto mode1c
movlw 0xFC
andwf GPIO
goto top
; *******************************************
alarm1_set
movlw 0xE ; 1110
movwf GPIO
alarm1_clr
movfw count ; set for *4 to define pulse frequency
movwf temp
dec2 ; 4*temp*1us=240us or ~2Khz
nop
decfsz temp
goto dec2
movlw 0xD ; 1101
movwf GPIO
retlw 0
; **************************************
end