help with AUTOMATIC WATER-LEVEL CONTROLLER project

[spidermanIIII]

i searched for AUTOMATIC WATER-LEVEL CONTROLLER project and i found this project but there are things i can't understand it first what is the usage of the capacitors 11 and 12 and how the ic 556 get triggered when the when the float interrupt IR sensor and how the output get high always


http://www.mediafire.com/view/tq14ek5vf69o45h/25.pdf

 

[KrisBlueNZ]

Hi there and welcome to Electronics Point

Here's the schematic you're referring to.



Both of your questions relate to detection of an interrupted infra-red light beam when the float in the capillary tube moves up or down far enough to block the relevant TSOP1738 infra-red receiver/demodulator.

When this happens, the TSOP1738 output changes from being pulled firmly low, to being pulled weakly high through a current source in the TSOP1738. (There are also two 1 MΩ resistors, R8 and R9, which are not needed.) C11 and C12 prevent the voltage from rising quickly; this is supposed to prevent the circuit from activating on brief interruptions of the modulated infra-red signal, which might happen due to an electrical disturbance.

When a modulated infra-red beam is interrupted, the C11 or C12 voltage rises. This is supposed to trigger one side of the dual monostable, producing a positive pulse at the output which is inverted by N3 or N4 and sets or resets the latch formed by N1 and N2, but it appears that the wrong polarity has been used - the trigger input on the 555/556 is active low.

I'm not sure what you mean about "output get high always".

This design has a number of problems and is unnecessarily complicated. Mistakes I've noticed so far are that the infra-red emitting LEDs should be connected in series instead of parallel; the wrong trigger polarity has been used with the monostables; there is no need for the monostables at all; there is no circuitry to ensure that the pump control latch powers up in the OFF state (as mentioned in the circuit description); there is probably no need to use modulated infra-red (it would be more reliable to have a steady IR light and a receiver with a set threshold); the latch output should be buffered or R7 should be increased. No doubt there are other errors; those are only the ones I've noticed.

 

[spidermanIIII]

Hi there and welcome to Electronics Point

Here's the schematic you're referring to.

View attachment 14198

Both of your questions relate to detection of an interrupted infra-red light beam when the float in the capillary tube moves up or down far enough to block the relevant TSOP1738 infra-red receiver/demodulator.

When this happens, the TSOP1738 output changes from being pulled firmly low, to being pulled weakly high through a current source in the TSOP1738. (There are also two 1 MΩ resistors, R8 and R9, which are not needed.) C11 and C12 prevent the voltage from rising quickly; this is supposed to prevent the circuit from activating on brief interruptions of the modulated infra-red signal, which might happen due to an electrical disturbance.

When a modulated infra-red beam is interrupted, the C11 or C12 voltage rises. This is supposed to trigger one side of the dual monostable, producing a positive pulse at the output which is inverted by N3 or N4 and sets or resets the latch formed by N1 and N2, but it appears that the wrong polarity has been used - the trigger input on the 555/556 is active low.

I'm not sure what you mean about "output get high always".

This design has a number of problems and is unnecessarily complicated. Mistakes I've noticed so far are that the infra-red emitting LEDs should be connected in series instead of parallel; the wrong trigger polarity has been used with the monostables; there is no need for the monostables at all; there is no circuitry to ensure that the pump control latch powers up in the OFF state (as mentioned in the circuit description); there is probably no need to use modulated infra-red (it would be more reliable to have a steady IR light and a receiver with a set threshold); the latch output should be buffered or R7 should be increased. No doubt there are other errors; those are only the ones I've noticed.

first i would thank you .the output of TSOP 1738 is high when ir is blocked i reed the datasheet of it

 

[KrisBlueNZ]

Right. When the light is blocked, the TSOP1738 output goes high. The trigger inputs on the 556 trigger when the pin is taken low. I believe that's an error in the design. But the 556 isn't needed at all. There's no need to set and reset the latch using pulses; it can be set and reset directly from the TSOP1738 outputs (after inversion, because a latch made from NAND gates has active low set and reset inputs).