Hello,

I am currently trying to build the 4-bit computer on a breadboard and am having trouble building the AND gates. I am using the BC547 transistors. At first I just tried to build one of the adders, but when I tried it out it would not work. I then decided to build it up gate by gate so I can troubleshoot as I build the adder. The problem is whenever I try to build an AND gate, I am able to light an LED with just one input into the gate. I am using a 9V battery and the 10k and 1k resistors from the circuit diagram. Also on the diagram it says the gates go to a +5V. Do you use something like a voltage regulator from the 9V battery to achieve this? I am completely amateur when it comes to electronics and thought this would be a fun project to try. I apologize in advance if there is something simple I am missing. Thanks for the great project! I have learned a lot about logic gates from this article.

Patrick

The '+5Vs' is a typo, the circuit was directly powered by a 9V battery.

When testing the circuit are you tying the inputs to both +9V (for a 1) and Ground (for a zero)? If an input is just disconnected to represent 0 it won't work. You have to connect the '0's to ground.

If you look at the 2nd circuit diagram on the project page you will see that the switches are connected via 10K pull-down resistors for this purpose.

I have a question about this project. The driver circuit...Was the same BC547 used for the transistors? The Rs are labelled, but not the Qs.

BC547 was used for the LED driver circuit too.