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Semi Automatic water overflow controller

Prashant Zingade

Sep 7, 2016
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Hi All,

I created latch circuit to start water pump manually and stop Automatic, in that I'm facing issue when i touch probe of wire by hand circuit start Automatic. Im using 12v 1Amp SMPS power supply.

How to reduce sensitive ?

Please help.

Circuit diagram attached.
 

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Harald Kapp

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SW 1 is for manual start,
SW 2 is for automatic stop, right?
Try adding a capacitor from tha base of Q1 to ground (0 V) to reduce sensitivity to noise
 

Prashant Zingade

Sep 7, 2016
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Also I notice that when I use 9v 500ma power supply it work good. But when I use 12v / 1amp supply its become more sensitive.

What will be the value for capacitor to Q1 base and ground.?
 

Alec_t

Jul 7, 2015
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I would suggest adding a pull-down resistor of ~100k between Q1 base and ground to ensure the base is never 'floating' at an ill-defined voltage. Q2 could benefit from a ~100k pull-up resistor to the +ve supply to prevent possible leakage currents from causing spurious setting of the latch.
 

Prashant Zingade

Sep 7, 2016
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I would suggest adding a pull-down resistor of ~100k between Q1 base and ground to ensure the base is never 'floating' at an ill-defined voltage. Q2 could benefit from a ~100k pull-up resistor to the +ve supply to prevent possible leakage currents from causing spurious setting of the latch.
Ok thanks i will try it.
 

Prashant Zingade

Sep 7, 2016
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I would suggest adding a pull-down resistor of ~100k between Q1 base and ground to ensure the base is never 'floating' at an ill-defined voltage. Q2 could benefit from a ~100k pull-up resistor to the +ve supply to prevent possible leakage currents from causing spurious setting of the latch.
Capacitor is not required between Q1 base and ground ?
 

Harald Kapp

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I would suggest adding a pull-down resistor of ~100k between Q1 base and ground to ensure the base is never 'floating' at an ill-defined voltage.
Q1 is pulled down, weakly though, by R2 and RL1. An additional resistor of ~100 kΩ may decrease sensitivity.
A capacitor will reduce sensitivity to noise (AC).
You may have to add both. Give it a try and play around with values to optimize the result.
 

Prashant Zingade

Sep 7, 2016
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Added both 100k and 10uf/25v capacitor between base Q1 and ground. Circuit latch for 2 second and discount again.

Pl help.
 

Alec_t

Jul 7, 2015
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You could add a 'supply missing' switch in parallel with SW2.
 
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