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Tag: example circuit

Building a Full Adder Using NPN Transistors

Building upon the last two posts where I showed how to build NAND, NOR, AND, OR, NOT and XOR gates using NPN transistors, this post will show how these gates can be used to build a full adder. A full adder is one of the circuits used in an Arithmetic and Logic Unit (ALU) which a central component in a microprocessor. The screenshot below shows the full adder circuit using combinational logic running in Circuit Simulator.

Full Adder Circuit Using Combinational Logic

The next screen shot shows the same full adder circuit built using NPN transistors.

Full Adder Circuit Using NPN Transistors

As always, the code for the circuit can be found here. Just copy and import the code into the free Java Circuit Simulator to get a feeling for the circuit.

Building a 4bit Counter Using JK Flip-Flops

This weekend’s electronics project with my son was to build a 4bit counter using JK flip-flops. Before implementing the circuit in hardware, I first explained the binary system and we then designed the counter using the free Circuit Simulator which I described in a previous post. Interestingly, he was amazed by the fact that adding just one more bit doubles the size of the counter – exponential growth is not intuitive ;-). The counter circuit, which chains together the flip-flops can be seen below: 

4bit Counter Using JK Flip-Flops

One important feature of the design is that we tie both J and K to +5v which turns the JK flip-flop into a T or Toggle flip-flop. Below is the code for the circuit. Copy and import the code into Circuit Simulator to get a better feeling of how the counter works – just press the switch to activate the next “tick” of the counter. 

$ 1 5.0E-6 10.20027730826997 50 5.0 50
162 496 272 496 208 1 2.1024259 1.0 0.0 0.0
g 320 208 320 176 0
w 320 208 496 208 0
r 496 272 496 352 0 330.0
r 544 272 544 352 0 330.0
162 544 272 544 208 1 2.1024259 1.0 0.0 0.0
r 592 272 592 352 0 330.0
162 592 272 592 208 1 2.1024259 1.0 0.0 0.0
r 640 272 640 352 0 330.0
162 640 272 640 208 1 2.1024259 1.0 0.0 0.0
w 496 208 544 208 0
w 544 208 592 208 0
w 592 208 640 208 0
156 368 464 432 464 0 5.0
R 288 432 256 432 0 0 40.0 5.0 0.0 0.0 0.5
w 288 432 288 464 0
w 288 464 368 464 0
w 288 464 288 528 0
w 288 528 368 528 0
s 288 432 352 432 0 1 true
w 368 496 352 496 0
w 352 496 352 432 0
156 528 464 560 464 0 0.0
w 528 464 512 464 0
w 512 464 512 528 0
w 512 528 528 528 0
w 512 528 512 576 0
w 512 576 288 576 0
w 288 576 288 528 0
w 464 464 480 464 0
w 480 496 528 496 0
w 640 352 640 416 0
w 640 416 464 416 0
w 624 464 624 384 0
w 624 384 624 352 0
w 624 352 592 352 0
156 704 464 736 464 0 5.0
w 512 576 672 576 0
w 688 528 688 576 0
w 672 576 688 576 0
w 688 528 704 528 0
w 704 464 688 464 0
w 688 464 688 528 0
w 624 464 640 464 0
w 640 464 640 496 0
w 640 496 704 496 0
w 800 464 800 368 0
w 800 368 544 368 0
w 544 368 544 352 0
156 864 464 896 464 0 5.0
w 688 576 864 576 0
w 864 576 864 528 0
w 864 528 848 528 0
w 848 528 848 480 0
w 848 480 848 464 0
w 848 464 864 464 0
w 800 464 816 464 0
w 816 464 816 496 0
w 816 496 864 496 0
w 496 352 496 384 0
w 496 384 960 384 0
w 960 464 960 384 0
w 464 416 464 464 0
w 480 464 480 496 0

The next step was to build the circuit using real JK flip-flops. We used dual HEF 4027BP JK flip-flops from NXP Semiconductors, 4 LEDs, 4 330 ohm resistors, a 10k resistor and a push button. Please note that these flip-flops are triggered on the rising edge and therefore, we chained them together via NOT Q and used Q to power the LEDs. As we used a push button to activate the clock on the first flip-flop, we pulled the clock pin down to 0v using a 10k resistor connected to ground. One last detail is that the Set and Reset pins for each flip-flop are connected to 0v. Below is the finished result built by Luke. 

4bit Counter

Amazing Java Circuit Simulation

Circuit Simulator is an amazing piece of free software. If you are in any way interested in electronics, download it from here and play around with it for an hour or so. I’m going to be using this application to publish the layouts for the cicuits we are working on in my future electronics related posts.

Circuit Simulator

If you want to see how the blinking LED circuit shown in the previous post works, paste the following into program using the import feature.

$ 1 5.0E-6 382.76258214399064 99 5.0 43
v 352 672 352 400 0 0 40.0 5.0 0.0 0.0 0.5
w 352 400 352 288 0
w 352 288 608 288 0
w 608 288 880 288 0
162 880 288 1008 288 1 2.1024259 1.0 0.0 0.0
r 1008 288 1008 320 0 500.0
w 1008 320 1008 336 0
w 1008 336 1120 336 0
w 1120 336 1120 832 0
w 1120 832 1104 832 0
r 1104 832 992 832 0 10000.0
w 992 832 816 832 0
t 528 400 608 400 0 1 -0.12632236495348304 0.5010407108474094 100.0
w 528 400 528 832 0
w 528 832 736 832 0
w 528 400 528 352 0
t 944 400 1008 400 0 1 0.5847909946260287 0.6273630758008925 100.0
w 1008 336 1008 352 0
w 1008 352 1008 384 0
w 1008 416 1008 672 0
w 800 352 800 400 0
w 800 400 944 400 0
w 1008 672 672 672 0
w 672 672 352 672 0
w 608 416 608 560 0
w 608 560 656 560 0
w 656 560 656 608 0
w 656 608 672 608 0
w 672 608 672 624 0
w 672 624 672 672 0
r 608 288 608 352 0 5000.0
w 608 352 608 384 0
r 608 352 528 352 0 5000.0
w 800 352 608 352 0
c 736 832 816 832 0 1.0E-5 0.21083170251411693

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