BCD to 7 segment display decoder using diode logic

Introduction

In my previous blog I explain about the discrete transistor BCD counter.  After that project I decided to  make a project which count numbers and display it in decimal numbers. For it we need a 7 segment display and some hardware to display the numbers. So I decided to connect a BCD to 7 segment decoder after the previously designed counter.  So here I explain how it make. All the components are used here is discrete transistors, resistors and diodes.

What is 7 segment display ?

It is a small display unit which is given in the figure. It contain 8 individual leds. It has a common leg which is connect as a common supply point. That is, it is available in common anode and common cathode type. Here I use a common cathode type. These led are individually controlled to show the numbers. It is shown in the given image, also the pin out is in it. OK. 

Deign

Here the BCD output is a 4 wire out. But the 7 segment has 7 inputs. So we need a decoder circuit for working the display. First we make a table which show which individual leds are ON for each BCD code.  From this we find the leds which are ON in each code. Now we use some mathematical procedure to find the Boolean equation of each led. From the equation we realize the circuit. The K-map method is used for circuit solving. It is given in the figures. But before it we use some techniques for reduce the hardware.

Optimization techniques

• From the K-map it is get that number of zero is greater than  number of one in almost all the K-maps. So interchange one with zero and zero with one and group the ones. (output inverting is required)
• Write ones in all the blank boxes. 

circuit realization using basic gates

Here I don't explain more about K-map and its reduction. Because it is just a mathematical operation. It is not electronics. The circuit is also designed by using thinking instead above mathematics. OK. The mathematics reduce the solving time. That's all. OK. 

Circuit design

The final equations are given below. These are used to design the circuit. The designed circuit for each led is given below. Here I made AND and OR gate by using diodes only. Because it reduce the number of transistors.  The circuits are simple. So I not explain more about it. 

Output

The video shows the working model of 7 segment display. 

Please support me. For more details please visit my instructable page.