water level indicator 7 segment display and LED problem

[david0802]

hello everyone,i have face a problem which is when i no connect the wire together,the 7-segment displays also show me '4'

after i connect the 1st wire ,the 7 segment displays also show '4'. What is the problem?

In addition,the LED also dont work well, I want my LED 1 light up, when the wire 1 connect, and wire 2 connected,the LED 2 will light up. However now the 3 LED also light up

Thank you so much !

[aa232004]

Hello. I love your schematic, it is great.

but lets get serios -

a few problems -

transistors - you connected them all wrong way - collector and emitter should be swopted

resistors R11,12,13 - are to big - let say LED's  direct current is 10 mA, voltage across LED is 2.0 v, and transistor's Vceo is close to 0, so resistance should be (5-2)\0.01 = 300 Ohm

resistors R14.15.16  - there is no need for them actually,

resistors R17.18.19 should be much higher - arounf 2..10 k

fix all that and try again

good luck

Michael

[david0802]

hi,Michael

my 7 segment displays still can not function as well

and my LED is some problem again.When my level 1 connected,my led 1 is off,another 2 is ON.

May i ask you why the voltage go through the Led is 2V?

thanks again!

[Buechsenschuetz]

Again, this forum is NOT dedicated to solve circuit design problems. 

However, it is very normal that there is a voltage drop across a LED of approx. 2V. There is current flowing through the LED and the output power (converted to light) must have an origin, so there must be a voltage difference between the two terminals of a LED. The approx. 2V are due to the properties of the internal junction of a LED. 

[aa232004]

Hello,

look, in order to answer you I have to understand what task you are trying to acomlosh, and I do not.

please describe how that module shuld work.

 In the meantime I do not understand, why you connected U1-11 to the GRND constantly.

I 'd recomend  - when you are getting  description of what that module should do, build to your selt true table of all input and output conditions .

it 'll make  much easier to build and to troubleshoot.

2 V it is avarage direct drop voltage for most LEDs. that number is good for draft calculations.

exact voltage could be found in specific LED data .

thanks

Michael

[david0802]

Sorry,may i know what forum can i ask this kind of question?thanks

[david0802]

Thank you!

now i trying connect to breadboard