(A+B)(A+C)=A+BC circuit doest not work (protoboard)

[Noob of the Maths]

Homework Statement

Reproduce the boolean expresion: (A+B)(A+C)=A+BC (in protoboard)

Relevant Equations

Nothing

Hi guys :)!
I have a little problem with my homework protoboard circuit:

First, i try to connect the simplification (A+BC), the LED it doest not turn off and not response when i push the buttons.

All the components its ok, all its works. If the simplification works, the complete expression become easy to continue.

Thanks for read

 

[berkeman]

Please post your schematic. Also, you should be grounding all unused gate inputs (not outputs though, obviously).

 

[Noob of the Maths]

Please post your schematic. Also, you should be grounding all unused gate inputs (not outputs though, obviously).

I make the schematic in proteus and its works fine.

 

[Mark44]

If A is high (set) or if both B and C are high, the light should come on.

 

[berkeman]

Your schematic doesn't match either one of your equations in your first post, IMO. Also, where are the switches? What logic family are you using? What are the Vcc connections and ground connections? If you are using CMOS logic, the unused inputs of the other gates need to be grounded.

 

[Noob of the Maths]

If A is high (set) or if both B and C are high, the light should come on.

Yes, but in my case the LED is always turn ON and not responding to the buttons to take off ;(

 

[Noob of the Maths]

Your schematic doesn't match either one of your equations in your first post, IMO. Also, where are the switches? What logic family are you using? What are the Vcc connections and ground connections? If you are using CMOS logic, the unused inputs of the other gates need to be grounded.

The schematic corresponds to A+BC. I use logic probe like switches in the schematic, Vcc and ground are the blue connections in the first image.

 

[berkeman]

What logic family? 74HC? 74VHC? Vcc=5V or 3.3V? The switches are single pole double throw, break before make?

 

[Noob of the Maths]

What logic family? 74HC? 74VHC? Vcc=5V or 3.3V? The switches are single pole double throw, break before make?

74LS, Vcc= 5V. The switch are pushbuttons in the protoboard

 

[berkeman]

The switch are pushbuttons in the protoboard

What value of your resistor pullups or pulldowns (depending on which way the switches pull)?

Do you have a DVM where you can monitor the voltage at each gate input and output? That may help you figure out what is going on.

Also, 74LS is not very strong at driving a "high" output. It is better at driving a "low" output, so you may want to add an inverter (or a transistor) at your circuit's output so it can pull the cathode of the LED Low (rather than trying to drive the anode high). Check the datasheet for values of Voh, Vol, Ioh, Iol, etc. It may also help to use a high-efficiency Red LED, which can generally be driven with less current.