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I have a question

NormaRobinson

New Member
Hi,

I am planning a project that includes a circuit (to say safely) but don't know where to start.

I want a code of about six numbers with two tries to get the code correctly. If the code is incorrect, an alert is turned off with audio output.

If the code is correct, it will turn off an electromagnet and open the safe but only after a delay of 3 minutes

i don't know how to approach this so any help with links or schematic is appreciated

Thanks
 

AnalogKid

Well-Known Member
Most Helpful Member
What you describe can be done with all discrete logic components, but it will take a lot of chips. If you already have programming and microcontroller experience, this will be much easier in a PIC or Arduino.

ak
 

Nigel Goodwin

Super Moderator
Most Helpful Member
What you describe can be done with all discrete logic components, but it will take a lot of chips. If you already have programming and microcontroller experience, this will be much easier in a PIC or Arduino.
And even if you don't, it will be MUCH easier, cheaper and faster to get that experience than to try and do it in hardware - and you can give it much more functionality with little effort.
 

gophert

Well-Known Member
Most Helpful Member
Hi,

I am planning a project that includes a circuit (to say safely) but don't know where to start.

I want a code of about six numbers with two tries to get the code correctly. If the code is incorrect, an alert is turned off with audio output.

If the code is correct, it will turn off an electromagnet and open the safe but only after a delay of 3 minutes

i don't know how to approach this so any help with links or schematic is appreciated

Thanks
do you want to hardwire the 6 numbers into the circuit or do you expect to be able to change the code as you wish after the circuit is built?

also, I assume you mean a six digits 2, 5, 7, 0, 8, 6
Not six numbers 24, 92, 33, ...

six digits that are hardwired into the lock is doable with discrete logic chips (one chip per 4-bit digit plus two more chips. A transistor to power the latch opening and an SCR for the buzzer.

if you want reprogrammable values with dip switches, that's not too bad and doable.

if you want multi-digit numbers and software controlled combination so users cannot probe the PCB to determine the combination, you'll need a microcontroller.
 
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gophert

Well-Known Member
Most Helpful Member
Here's a mock-up of a 4-digit combination with hardware determined digits that must match the value of a 4-bit rotary encoder value (encoders far right. Forgive the right-to-left layout flow of the schematic - the pinout of the chips makes it flow better that way.

. Once the digits are set to desired value, the push button is pressed to test the correctness of all encoders. The counter (7469) is cleared if a good combination is entered, otherwise the counter increments. The counter triggers the SCR if two bad combos are hit - the SCR turns on the buzzer until the power is turned off.

the LED on the 7485 chips would be removed for the real circuit - also, the unused inputs would have to be properly connected to ground or positive rail. Capacitors added for decoupling, etc.

FE626486-660F-46EC-AA95-15688554DBD3.jpeg
 
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