Hi all,

I need to use the following water level switch .






Description:

• Product Name : Float Switch;Max Contact Rating : Max Contact Rating;10W : 10W;Max Switching Voltage : 100V DC
• Max Switching Current : 0.5A;Max Breakdown Voltage : 220V DC;Max Carry Current : 1.0A;Max Contact Resistance : 100mΩ
• Temperature Rating : -10 ~ +60 °C / +85 °C;Float Ball Material : PP;Float Body Material : PP;Float Ball Size(Approx) : 24 x 17mm /0.94" x 0.7"(L*D)
• Thread Dia(Approx) : 16mm/3/8" PT;Hex Nut Diameter : 23mm /0.9";Body Length : 90mm/3.5";Cable Length : 39cm / 15.3"
• Color : Black;Net Weight : 22g;

I want to use 10k pull up resistor with the switch to connect it with the microcontroller .

The distance between the tank(switch) and the microcontroller 15 m.

Should I modify the connection ?


Thank you .

 

That should work ok IMO, it may be wise to use a grounded shield for the switch conductors.
Also maybe debounce the input at the micro.
Max.

 

What microcontroller?
What power is powering the microcontroller?
How much voltage and current do you have available from the power supply that is supplying the microcontroller?

A 10kΩ pull-up might work but it will be susceptible to noise pickup.
A 220Ω ½W resistor would be a better choice.

And you may want to put a filter capacitor across the input of the microcontroller,

and maybe a MOV while you're at it.

Better yet, use an opto-coupler/isolator.

 

It appears to be a simple contact closure switch, what micro are you using?
I prefer schmitt trigger input for this application if it has one.
Max.

 

It appears to be a simple contact closure switch, what micro are you using?
Max.

TS is asking for 15m of cabling which I can only assume will be in an industrial environment.

 

TS is asking for 15m of cabling which I can only assume will be in an industrial environment.

Hence the grounded shielding suggestion.
Max.

 

I use pic16f877a ..
12v 1A power supply with step down buck converter

 

Hence my suggestion of 20mA current loop into an opto-isolator.

 

Use a 620Ω ½W resistor in series with an opto-isolator driven from the 12V line.
Then use a 2k-10k pullup on the receiver of the opto-isolator into the PIC input.

 

Personally I would test the simple input first, you can always go to plan B and add another option if needed.
Max.

 

Personally I would test the simple input first, you can always go to plan B and add another option if needed.
Max.

Oh, Max. Strange hearing that coming from an industrial CNC guy.
One power spike and he is going to fry his PIC.

 

You mean like this ..

 

Looks good. The switch should go on the GND leg for safety.

 

Like this ?

Why we used opto ?

Should the opto be close to pic or to the switch ?

Regards

 

The 620Ω value is not carved in stone. Anything from 470Ω to 1kΩ will work fine.

Why opto?
The objective is to keep EMI away from your PIC input. You want the opto close to the PIC.

Water switch = = = = 15m cable = = = = opto / / PIC

Any high voltage spike picked up on 15m cable does not jump across the opto-isolator.

 

Thank you

Should I denounce the switch or using the opto enough ?

if I use 9v ,7v or 15 v power supply instead of 12v should I modify the circuit ,)

 

Thank you

Should I denounce the switch or using the opto enough ?

If you just want to read the status of the water level then you don't need to debounce the switch.

 

And if I use 9v ,7v or 15 v power supply instead of 12v should I modify the circuit ,)

 

And if I use 9v ,7v or 15 v power supply instead of 12v should I modify the circuit ,)

When you select the opto-isolator, check the data sheet for the max current allowed on the LED. You don't want to exceed the max current.

With 15V supply , 680Ω series resistor would give about 20mA.
You have a lot of leeway with anything from 680Ω to 1000Ω for any supply voltage from 7V to 15V.

 

Thank you for your appreciated effort