Multisim and Ultiboard

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how to use a 555 timer to trigger a 4-pin unlock code?


am new to NI multisim.
been trying to connect a keypad to a 555 timer.
then use a 4 digit pin code to Switch on a led at pin 3 of the far i managed to do it with just 1 push button. Please help .Screenshot (21).jpg

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Message 1 of 9

Hi there


Could you explain with more details what would you like to do?


I see that you want to connect a keypad to a 555 timer. Please take a look to this forum 



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Message 2 of 9

Actually am trying to design a circuit which works like an Electronic lock.
i need to connect a keypad from which i can input a 4 digit pin code e.g1234
When i press these 4 digits. A led should light up as output.
the thing is that i must use a 555-Timer which will register these input for a short delay of time and
then light up the led if pin code were correctly inserted.
1 constrain is that i cannot use any programmable IC except from the timer.

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Message 3 of 9

You might try something like shown on this website. Use the output to trigger your 555. Is this for homework?

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Message 4 of 9

Can you explain what the actual purpose of the 555 timer is?


If you need help prototyping a 555timer, it is fairly straight forward, I can help you with that. But I am not sure why you need it for a keypad? What functionality will it serve?


Also, if it is for homework then have you been specified any particular hardeware you need to use such as a microcontroller or FPGA?


Am I right in thinking this project will be used in a digital device such as an FPGA or EEPROM?

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Message 5 of 9

the timer will help me to store the pin code. so that when all the right input are set in a certain order.,the led lights up.
well i guess the guy above shared a pretty nice solution. i'll give it a try. 
i just need to get the LED on .
i'll keep u posted in case i need some help in enhancing the circuit .
thanks for helping  Smiley Happy

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Message 6 of 9

yes its for a homework . i guess your shared file, matches pretty well with the criteria. i'll give it a try . thank you

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Message 7 of 9

ok but 555-timers can't store information. They just send out a continuous on-off signal with a set time interval.


Good luck with your project

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Message 8 of 9

yes this is why i got wrong from the very start xD 

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Message 9 of 9