555 timer circuit help

[Paul Proefrock]

I need to come up with a simple timer to prevent burn-out of a small pump. I
am using a float switch (spst) to sense water level in an aquarium. With the
switch closed, I trigger a small 12v pump to run and top-off.

My concern is if the reservoir runs dry. I want to come up with a timer that
will let the pump run for some adjustable amount of time (10-60 sec) then,
if the switch setting has not changed, it will trip a relay to lock out the
pump. The logic is if there isn't enough water to satisfy the requirement,
then shut off the circuit to keep the pump from burning up.

I've found a lot of 555 circuits but can't find any that will lock out.

Can anyone point me in the right direction or give any design tips.

Thanks

Paul P

 

[Joerg]

Hi Paul,

How about just another float switch for the reservoir?

Regards, Joerg

 

[WDino]

Instead of a 555, use a PIC or PICAXE. Much more versatile.

 

[Terry Pinnell]

I need to come up with a simple timer to prevent burn-out of a small pump. I
am using a float switch (spst) to sense water level in an aquarium. With the
switch closed, I trigger a small 12v pump to run and top-off.

My concern is if the reservoir runs dry. I want to come up with a timer that
will let the pump run for some adjustable amount of time (10-60 sec) then,
if the switch setting has not changed, it will trip a relay to lock out the
pump. The logic is if there isn't enough water to satisfy the requirement,
then shut off the circuit to keep the pump from burning up.

I've found a lot of 555 circuits but can't find any that will lock out.

Can anyone point me in the right direction or give any design tips.

A simple resettable timer (monostable) would do what you say. However,
some aspects of your spec are unclear to me.

1. How do you detect if the reservoir runs dry?

2. Must you use a 555? (Other obvious options for a resettable
monostable would use half a CMOS 4001 Quad NOR or 4011 Quad NAND, and
there are many more.)

3. I'm no aquarium expert, but it sounds odd to have one replenished
by a 'reservoir' which itself can apparently run dry. What replenishes
the reservoir? (Seems some risk of an infinite set of subcircuits here
<g>.)

4. Why use a timer to control the pump? You could for example instead
consider a latch (bistable) approach. That would avoid the issue that
prompted your post. The latch would be SET (pump started) by the
aquarium level switching the Low Aquarium float switch, and RESET by
*either* the High Aquarium float switch or the Low Reservoir float
switch. (That leaves aside the answer to Q3.)
A suggested circuit is shown here:
http://www.terrypin.dial.pipex.com/Images/AquariumPump.gif

 

[Terry Pinnell]

Instead of a 555, use a PIC or PICAXE. Much more versatile.

PICAXE? More like a sledgehammer to crack a nut. Even assuming the OP
has the PIC skills and resources.

See my simple suggested solution.

 

[Colin Dawson]

4. Why use a timer to control the pump? You could for example instead

consider a latch (bistable) approach. That would avoid the issue that
prompted your post. The latch would be SET (pump started) by the
aquarium level switching the Low Aquarium float switch, and RESET by
*either* the High Aquarium float switch or the Low Reservoir float
switch. (That leaves aside the answer to Q3.)
A suggested circuit is shown here:
http://www.terrypin.dial.pipex.com/Images/AquariumPump.gif

Low Reservoir float switch activates, you'll get an oscillation on the
circuit, meaning that the pump will still try to run, possibly causing the
same burn out problem. A possible solution could be... to place the
Aquerium Low, and Reservious low switchs in series - then the pump will
start ONLY with water is required and when there's water available to pump.

 

[Terry Pinnell]

Low Reservoir float switch activates, you'll get an oscillation on the
circuit...[etc]

Eh? No, you won't! The bistable is set when a +ve pulse triggers it
Set pin, and remains in that state until a +ve pulse triggers its
reset pin.

I'm guessing your circuits are designed as carefully as your
sentences:

"A possible solution could be... to place the Aquerium Low, and
^^^^^^^^
Reservious low switchs in series - then the pump will start ONLY with
^^^^^^^^^^ ^^^^^^^ ^^^^
water is required and when there's water available to pump."

That wouldn't work.

 

[Fred Bloggs]

I need to come up with a simple timer to prevent burn-out of a small pump. I
am using a float switch (spst) to sense water level in an aquarium. With the
switch closed, I trigger a small 12v pump to run and top-off.

My concern is if the reservoir runs dry. I want to come up with a timer that
will let the pump run for some adjustable amount of time (10-60 sec) then,
if the switch setting has not changed, it will trip a relay to lock out the
pump. The logic is if there isn't enough water to satisfy the requirement,
then shut off the circuit to keep the pump from burning up.

I've found a lot of 555 circuits but can't find any that will lock out.

Can anyone point me in the right direction or give any design tips.

The main thing here is to keep the level switch in series with the pump
power control so that you retain the failsafe against flooding
regardless of what the electronics may do. The circuit shown below does
this by RESET-ing when the level switch opens, it uses the 555 in
parallel with pump and shuts it down at the sooner of level switch
opening or timing network charging to threshold. It is assumed that the
timing resistor RT is much larger than R1, a factor of 20 or more will
do, so that CT is discharged to GND for practical purposes when the
timer RESETS. For very long timing durations, the CMOS 555 would be
best, and tantalum or otherwise low leakage timing capacitors should be
used- RT will have to be a pot for adjustability.

View in a fixed-width font such as Courier.


..
..
.. LM555 TIMER PUMP LOCKOUT
..
.. PWR
.. GND 12VDC
.. | |
.. +----------------------------------------------+ |
.. | |
.. | |
.. | C1 1U |
.. +---------------------------||-------------------------+
.. | C2 + |
.. | +--------------------||--------------------+ |
.. | | 0.1U | |
.. | | | |
.. | | TIMEOUT=1.1 x RTxCT | |
.. | | | |
.. | | CT RT | |
.. +-----------------||-------------+-------/\/\----------+
.. | | | | |
.. | | D1 | | |
.. | | 1N914A | | |
.. | | +---|<|------+------+ | |
.. | | | | | | |
.. | | | +-------+------+------------+ | |
.. +------+----------|GND THR TRIG V+|---+----+
.. | | | | |
.. | | | | |
.. | | | LM555 | |
.. | | | | |
.. | | |DIS RST OUT | |
.. | | +-+-------------------------+ |
.. | | | | | |
.. | | / | | LEVEL| --+
.. | | 2.2K R1 | / SW o| |
.. | | / | 3.3K R3 |--<- +---
.. | | \ R2 D2 | / o|
.. | | | 1K 1N914A | \ | close
.. | +------+--/\/\---|<|---+ | | on fall
.. | | | D3 |
.. | 1K R4 | | 1N914A |
.. +------------------/\/\-------------+---------|<|------+
.. | | |
.. | 10K R5 | |
.. +----/\/\----+----------------------------+ |
.. | | D4 |
.. | | 1N914A |
.. | | +-----|>|-----+ |
.. | Q1 | 2N4403 | | |
.. | ----- +-------------------+ |
.. | / \ | | ----- | | |
.. +---------e c ----|--+--- UUUUU ---+--|------------+
.. | |
.. | |
.. | +--o o------|-----<PUMP PWR
.. | | NO COM |
.. | | |
.. | | |
.. +-------12V RELAY---+
.. |
.. +--------------> TO PUMP
..
..
..
..
..
..

 

[jtech]

The main thing here is to keep the level switch in series with the pump
power control so that you retain the failsafe against flooding
regardless of what the electronics may do. The circuit shown below does
this by RESET-ing when the level switch opens, it uses the 555 in
parallel with pump and shuts it down at the sooner of level switch
opening or timing network charging to threshold. It is assumed that the
timing resistor RT is much larger than R1, a factor of 20 or more will
do, so that CT is discharged to GND for practical purposes when the
timer RESETS. For very long timing durations, the CMOS 555 would be
best, and tantalum or otherwise low leakage timing capacitors should be
used- RT will have to be a pot for adjustability.

View in a fixed-width font such as Courier.


.

Terry's circuit has KISS. it is best for job in hand.

 

[Paul Proefrock]

Thanks to everyone for the input.

There is one detail that I left out that makes the solutions more difficult.
This is a "Nano" size saltwater aquarium and I don't have room for more than
one float switch.

I kept looking and I have finally found a circuit that uses a flip-flop to
sense presence of water. I can use this to verify presence of water in the
reservoir and shut down if necessary.

For those who are curious, the link is
http://www.uoguelph.ca/~antoon/circ/fishpond.html

again, thanks to everyone.

Paul

 

[jtech]

There is one detail that I left out that makes the solutions more
difficult.

This is a "Nano" size saltwater aquarium and I don't have room for more than
one float switch.

I kept looking and I have finally found a circuit that uses a flip-flop to
sense presence of water. I can use this to verify presence of water in the
reservoir and shut down if necessary.

For those who are curious, the link is
http://www.uoguelph.ca/~antoon/circ/fishpond.html

again, thanks to everyone.

Paul

Hmm, use COPPER in a fish tank - especially salt. The sensor wire will also
have a small current on them , which will cause it to oxidize more copper
into your water - which will kill your fish.
Find a way to make a sensor switch. Maybe with a small tube with a foam
float inside to push a microswitch. ?maybe?

 

[Peter H Anderson]

I need to come up with a simple timer to prevent burn-out of a small pump. I
am using a float switch (spst) to sense water level in an aquarium. With the
switch closed, I trigger a small 12v pump to run and top-off.

My concern is if the reservoir runs dry. I want to come up with a timer that
will let the pump run for some adjustable amount of time (10-60 sec) then,
if the switch setting has not changed, it will trip a relay to lock out the
pump. The logic is if there isn't enough water to satisfy the requirement,
then shut off the circuit to keep the pump from burning up.

I've found a lot of 555 circuits but can't find any that will lock out.

Can anyone point me in the right direction or give any design tips.

Thanks

Paul P

Paul,

The PICAXE-08 costs about $2.00. The software is free from
http://www.picaxe.com and this is a very simple task.

I have sketched out some code. This could be improved to read a pot
so as to vary the timeout between 10 and 60 secs.

Top:

If Pin0 = 0 Then PumpOn
' else
Count = 0
Low PumpOut ' turn pump off
Pause 1000 ' pause for a second
GoTo Top

PumpOn
High PumpOut
Pause 1000
Count = Count + 1
If Count > = 60 Then LockOut
GoTo TOP

LockOut:
Low PumpOut
Goto LockOut

If you need help on this, send me e-mail at pha(at)phanderson.com

http://www.phanderson.com/picaxe/picaxe.html

 

[Fred Bloggs]

[...snip...]

The original request was specifically for a 555 timer that will trip a
relay and cut power to the pump, and that is exactly what he got. If
you have previous ( and more importantly successful ) experince in
dealing with this particular problem with nano-sized salt water tanks,
then feel free to share- but tell it to the OP and not me- otherwise
GFOAD.

 

[petrus bitbyter]

I need to come up with a simple timer to prevent burn-out of a small pump. I
am using a float switch (spst) to sense water level in an aquarium. With the
switch closed, I trigger a small 12v pump to run and top-off.

My concern is if the reservoir runs dry. I want to come up with a timer that
will let the pump run for some adjustable amount of time (10-60 sec) then,
if the switch setting has not changed, it will trip a relay to lock out the
pump. The logic is if there isn't enough water to satisfy the requirement,
then shut off the circuit to keep the pump from burning up.

I've found a lot of 555 circuits but can't find any that will lock out.

Can anyone point me in the right direction or give any design tips.

Thanks

Paul P

Paul,

As too often it can be done but you experienced the problems you run into
already. The most simple solution I'm aware of is an extra floating switch
(or other sensor) that detects the empty reservoir. It has to activate a
normaly closed switch that opens when the liquid level in the reservoir runs
too low. Just put the switch in series with the motor circuit and the motor
will never run dry. The aquarium floater requires a switch that closes when
the level in the aquarium runs too low. It also has to be put in series with
the motor circuit. AFAIK these floater switches always has some build in
hysteresis due to the nature of the momentary switching technic used. I ever
heard about switches with deliberately extra hysteresis build in but I could
not get a confirmation at the time. Nevertheless, when the waterlevel in
your aqarium becomes too low AND the reservoir contains water your pump will
run untill the aquarium level is high enough OR the reservoir runs empty.

petrus bitbyter

 

[John Fields]

Thanks to everyone for the input.

There is one detail that I left out that makes the solutions more difficult.
This is a "Nano" size saltwater aquarium and I don't have room for more than
one float switch.

I kept looking and I have finally found a circuit that uses a flip-flop to
sense presence of water. I can use this to verify presence of water in the
reservoir and shut down if necessary.

For those who are curious, the link is
http://www.uoguelph.ca/~antoon/circ/fishpond.html

---
If you'd like to get rid of the switches and the possibility of
dissolving metals from submerged metallic sensors into your tank(s),
you could use a couple of self-heated thermistors to do the level
sensing. You can get them sealed in epoxy or glass so they would be
impervious to salt water intrusion and wouldn't contaminate the tank,
either. If you're interested I'll post a schematic for you.