How can I make a combination of the 7 Transistor Logic Gate and putting those gate in only one breadboard.? I've seen the combination on this Topic: How to combine multiple transistor logic gates without gigantic voltage-drop? I am very much interested to do try on how it was built in only one breadboard... strong text


If you just want to make your own logic gates to see them work, then RTL (resistor-transistor logic) is probably the easiest for you to implement.

The basic gate output is a pullup resistor to the supply with a NPN transistor connected between it and ground. When the transistor is on, the output is actively driven low. When the transistor is off, the output is passively pulled high.

Use about 5 V for the power supply and 2 kΩ for the pullup resistors. These logic gates will be very slow and power hungry by today's standards, but that is of no consequence when experimenting with a few of them on a breadboard. You wouldn't want to build a CPU out of such gates because the power dissipation would be enormous, but you're not trying to do that so don't worry about it. Note that each output that is low will draw 2.5 mA from the power supply, which is 12.5 mW. There is no problem with this with a few gates on a breadboard.

Here is a simple inverter:

To make a NOR gate, put a diode feeding IN from each of the NOR inputs. Note that this is a good example of NOR being simpler than OR with inverter on the output.

Get a 100 each of signal NPN transistors, 10 kΩ and 2 kΩ resistors, and small signal diodes, then start experimenting.

  • \$\begingroup\$ If you're willing to work with FETs, NMOS is arguably even easier. \$\endgroup\$ – duskwuff Aug 30 '15 at 20:11

Perhaps I am way off base here, but interpreting the OPs questions, there are a few, I think he is trying to build a "demo" of all of the logic working off 2 switches. See below.

Top Level Diagram:


simulate this circuit – Schematic created using CircuitLab

After adding the remaining gates to the circuit, the OP would need to realize the gates at transistor level, as other have pointed out, there are some issues at the transistor level.

  • \$\begingroup\$ Why is it that sometimes, AND gate works well, sometimes not. This happens to me when I connect the 7 Logic gates just the same on what you've done in above.. I mean it works fine using multisim but when performed on the breadboard, I come up with a problem on that gate.. On the first attempt, it works fine.. Then I add and add and add another gate.. then for the 2nd attempt, it just blinks, then totally lights off.. Whats the problem? \$\endgroup\$ – Rimar Obias Virtus Aug 30 '15 at 14:48
  • \$\begingroup\$ It is hard to tell without a proper schematic perhaps you can upload one, showing how everything is connected. Possibly your power supply is being dragged down, is it a battery or bench top? Double / Triple check wiring. Make sure your bread board jumpers are in correctly (connecting each bank)... \$\endgroup\$ – Tyler Aug 30 '15 at 15:28
  • \$\begingroup\$ I use one 9V battery to operate as a source.. Is it on the battery? So better to use voltage regulator? \$\endgroup\$ – Rimar Obias Virtus Aug 30 '15 at 23:32

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