Good day!

I'm doing a simple project using a bcd counter and bcd to decade decoder..

if you push the correct button the LED connected to the output of the decoder will light on...


my goal is to put a buzzer in the circuit for it to sound when you push the wrong button...

i tried to attach one side of the buzzer parallel to the LED and the other to ground but the LED stays on..even the buzzer...

when i push the correct button the LED takes all the current and lights fully..and if i push the wrong one the buzzer experiences the same thing..

I think because the Vcc is parallel with the ground that's why the current is divided to the LED and the buzzer.

I would really appreciate any help regarding this matter...


Thank you very much!

 

please...lend me a little hand..

 

Hang on dude ....you have to give 24hrs before regular members log in due to time zone

 

oh yeah right! i'm sorry....

 

oh yeah right! i'm sorry....

You are new here, right?
where are you from mate?

 

I have looked at ur diagram....
I think I might be missing something but did you debounce the Pb switches

 

yup! from the Philippines...but now am studying in South Korea...
~I've been working on this circuit for 3 days...and can't find a solution...
the deadline is this Thursday though...

 

OK..cud u explain a bit in detail what you want the circuit to do and what kinda problem you are having

 

ok...i'm reading something about "debouncing" switches now...


the 555 sends the pulse to the 7490 BCD-decade counter..

then i connected the outputs of the counter to the inputs of

the 7442 bcd to decade decoder.... and i just connected each of the 7442's outputs to one side of pb switches...

i believe that u know how does 7442 works that's why i connected all of the other side of the pb switches to the negative pin of an LED and Vcc(5V) to the positive side.


this is a number guessing game... if you press the button of the correct number (number of pulses given by the 555) the LED will turn on, if not then it won't.
... i also connected a 7 segment display to check the right number...

i wanted to improve it so... what i would like to do is to put a buzzer when you press the wrong button..

turning on the LED and the buzzer simultaneously when you press the correct button is easy... but i can't find a solution to what i'm planning to do right now...

thanks in advance!

 

This is examples of debouncing.

How about a block diagram? Doesn't have to be pretty, hand drawn and scanned is fine.

Never mind, just looked again at the first post.

You need a resistor going from pin 4 to ground of the 555. When the switch is open the input is floating, always a bad condition for any logic. 1KΩ would do it. The resistor will give the 555 reset pin a logic zero.

 

Hello,

I also noticed the wrong connections of the red and green led at the bottom.

BTW what are all the gray blocks doing in the schematic?

Bertus

 

I think they are resistor arrays.

 

What about the 270Ω at the other end of the LED?

 

thanks for the examples about debouncing....but may i know what does debouncing do?

yeah....at i though there wasn't any difference if you put a resistor or not..so i just took it out...better put another one...

how about the buzzer? any ideas where and how can i put it to achieve my goal? thanks again

 

You can XOR the high level from the button output with the "Correct" LED, if they don't match (LED Doesn't light), the output of the XOR will be high (while the button is held down, anyway).

 

Mechanical switch always bounce before they come to rest.

If you use Pb as digital inputs you cannot tell how many transitions it will make when you press it before coming to rest.

That is why Pb's always debouced before they are fed into any digital circuitry