Activating a pump based on water flow

[Paulo Borges]

Hi, thanks, I will change my test circuit with your suggestion.
I had this problem with my test circuit, the one I mention at the first post.
I had a the sensor connected via a 1K resistor to pin 2.
I added a 0.1uF capacitor in series and it looks like it solved the problem.
Will work on the changes.
Thanks
Paulo

 

[Paulo Borges]

Ak, I have combined my circuit (positive trigger) with the given circuit proposed above.
I will still use a led for now and migrate to the relay next.
Can you please take a look and see if you agree?
Thanks
Paulo

 

[Alec_t]

Assuming you can get at least one pulse per second from the flow sensor, and that the default sensor output is 0V in the absence of flow, something like this should do the trick :

 

[AnalogKid]

and that the default sensor output is 0V in the absence of flow,

Not always true. The sensor is a magnet and a hall effect device. I can stop in either state.

ak

 

[AnalogKid]

Ak, I have combined my circuit (positive trigger) with the

Reduce R2 to 10K
Increase R1 to 10K
Add a 100K resistor from the base of Q1 to GND.

ak

 

[Alec_t]

It can stop in either state.

Then, as proposed earlier, capacitive input coupling is called for.

 

[AnalogKid]

Whoever proposed that was a smart guy.

 

[Paulo Borges]

People, thanks for your assistance, I tried both circuits and both work OK, just added a 220uF/16v capacitor at I had in my toolbox at the very entrance of the signal coming from the flux sensor and it works great with a led. I would probably have taken ages to figure it out by myself, I am just a hobbyist.
Thanks Ak and Alec_t for your time.
Keep well
Paulo.

 

[Alec_t]

Good to hear you have it working.

 

[Paulo Borges]

Hi people.
At the end of the day the circuit I am using is the one shown at the attached picture. (some components replaced as per availability).
I do have a minor problem though:
When I apply power the relay is immediately activated, likely as a result of charging capacitors.
This is not a serious problem as the pump is activated by just a couple of seconds but is an imperfection that bothers me a little bit.
Have you got any suggestion?
Thanks in advance.

 

[Alec_t]

You could try a standard 'power-on reset' arrangement. Connect pin 4 of the 555 via a high value resistor to the +ve rail and via a fat cap to ground.

 

[Paulo Borges]

Thanks