555 ic to switch a relay with a catch

Thread Starter

trevor lloyd

Joined Jun 30, 2015
3
hi guys

really in need of some help i am completley new to 555 timers and electronics in general actualy

i am trying to find out how to make a simple project that i was told can be done with a 555 ic so let me start :)

i am trying to switch a pump on as soon as i open a tap rather simple idea but a bit harder then i thought...

so what i have got is a flow control device like bellow:
https://www.robotics.org.za/index.php?route=product/product&path=57_134&product_id=411

so now what i want to do is as soon as the flow controller tells me that the tap is open it will switch a relay on thus turning on the pump then as soon as i close the tap it will turn off the pump...

is this possible and can some one help me do it

thanks so much everyone
 

#12

Joined Nov 30, 2010
18,224
If the pump is not on until water flows, what makes the water start flowing?
You must have a way to maintain pressure (a pressure tank of some sort and a check valve) or this won't work at all.
If you have a pressure tank, you can use a pressure switch to control the pump.
That's the, "old school" way.

The, "flow control" device you pointed to doesn't control flow, it measures flow and outputs electrical pulses.
If you can get the flow meter to output a pulse, you can trigger a 555 timer.
A retriggerable monostable holds its output high for a fixed amount of time after it has a pulse at its input.
If the pulses are often enough, the monostable circuit will pretty much stay on until the pulses stop...and then some. One time constant of the monostable timer.

So, what's your goal? To get a pump to work or to build some electronic stuff?
I mean, old school is dead simple.
Still, you're free to try a different way.
 

Thread Starter

trevor lloyd

Joined Jun 30, 2015
3
thanks for the info

sorry i did not give much of the story.

i have a low presure solar geyser in my house so as a result the water pressure from them is never the best so what i want to do is just put a small pump in line so that when i turn on the shower it will turn on the pump so i get better flow....

sorry for my stupidity here but can you give me a basic easy words on what or how this "retriggerable 555 monostable" is

thanks again guys
 

GopherT

Joined Nov 23, 2012
8,009
And 'astable' 555 circuit just keeps clicking on/off forever at a specific frequency.

A 'monostable' 555 circuit will trigger one time for a set period of time.
 

ericgibbs

Joined Jan 29, 2010
18,766
sorry for my stupidity here but can you give me a basic easy words on what or how this "retriggerable 555 monostable"
hi tevor,
A retrig monostable output will be set High while the stream of pulses from the flow meter keep coming.
When the pulses cease, the monostable output will go Low.

The output of the 555 via a transistor can be used to operate a relay, which will be used to switch the pump On/Off
 

tracecom

Joined Apr 16, 2010
3,944
thanks for the info

sorry i did not give much of the story.

i have a low presure solar geyser in my house so as a result the water pressure from them is never the best so what i want to do is just put a small pump in line so that when i turn on the shower it will turn on the pump so i get better flow....

sorry for my stupidity here but can you give me a basic easy words on what or how this "retriggerable 555 monostable" is

thanks again guys
From looking at the product in your link, I think what you can do is use the pulses out of the liquid flow meter to retrigger a 555 monostable. A monostable is also called a "one-shot" because when it receives a trigger pulse, it activates for a period of time that is determined by a resistor and capacitor. At the end of that time period, the 555 releases. A retriggerable version allows the activation period to be restarted each time a trigger pulse is received. Thus, you need to be sure that the trigger pulses from the flow meter recur in less time than the 555's activation period. Fortunately, the trigger pulses from the flow meter seem to be "low going," which is what the 555 requires.

What is the power source you plan to use for your circuit?
 

Thread Starter

trevor lloyd

Joined Jun 30, 2015
3
WOW guys thats all i can say this is an amazing community !!!! thanks so much for all the info i am going to do a bit of digging into this and il get back to you tomorrow but this does look very promising
 

AnalogKid

Joined Aug 1, 2013
10,987
Three questions:

1. What power is available for the sensor and the control circuit? For example, if the pump runs on 110 VAC and you have no other power supply, then you'll need a small battery charger wall wart that comes with cell phones and cameras to power the sensor and control circuit, and a solid-state relay to control the pump. If it is a DC pump, say 12V or 24V, and you have a power supply for it already, then the control circuit can run directly off of that.

2. What does the pump need to run? 110 VAC, 24 VDC, etc.? Also, what is the current or power rating for the pump? These will determine what is needed to take the control signal and use it to turn the pump on and off.

3. What is the water flow rate when the pump is running (gallons per minute)? The sensor is a water wheel, and makes a short pulse with each revolution of the wheel. The faster the water is flowing, the faster the wheel turns and the faster the pulses occur. The retriggerable monostable fills in the gaps between the pulses so the relay controlling the pump sees a continuous signal. A 555 can do this, but so can other circuits. If you have some guess as to the pump flow rate, it can be used to calculate the slowest sensor pulse rate as a starting point for the controller circuit design. For example, one gallon-per-minute (gpm) flow rate is approx. 26 Hz out of the sensor.

ak
 
Last edited:
Top