TOD: Diode Matrix ROM Intro (7-segment Display)





A new series of instructables that will be using tons and tons of diodes. No IC's are aloud, the only semi conductors are diodes and transistors. The only passive components aloud are capacitors, resistors, switches, inductors, and potentiometers (variable resistors for those who don't know). Another rule is it must have more diodes then any other component. I made this all up, and I made up this group to see how creative people can be with electronics without resorting to IC's. My next one (this one is just a little wimpy intro) might use up to 2000 diodes.

This is an intro to Diode Matrix Roms, basically it takes a signal in (switch) and gives an output (number on the display)

NOTE: I couldn't complete a project designed by myself because my breadboard is way too small, but That'll be fixed in later instructables.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Parts

7x 68 ohm resistor or higher (I used somewhere 110 I think)

1x 7-segment display

1x 10dip switch (I could only find an 8, just less characters to display)

23x signal diodes (cheapest you can find), I had 23, but I could only fit 9 on my board

1x breadboard, preferably big (unlike mine)

Some jumper wire

some sort of power supply, like 2AA or AAA's

wire cutters help

Step 2: Put the 2 Main Components on the Board

insert the display and the dip switch (heheh dip switch) on the center of the board, ontop of the notch.

Step 3: Ground It

ground all of one side of the dip switch and ground the 2 ground pins of the display

Step 4: Save the LEDs!

Insert 7 resistors, one for each led and attach all of them to you power supply.

I later shortened the resistor leads to reduce clutter.

Step 5: Hook Up All the Diodes

Can't really help you here, just make sure they are all facing the right way and the leads arn't shorting out (especially the resistors, which could fry your display)

Step 6: Test It!

I could only fit so many diodes on my breadboard, so I could only make 5 numbers (well 6 if you include the default 8), only half that I could of done.

Congrats, you just made a Diode Matrix ROM

don't stop here, you could make lots of cool circuits. Later I'm going to make a big cube of weaving wire, with diodes connecting the weaving at certain spots driving an LED matrix.

Step 7: Schematc

here's the schematic I forgot to put in, sorry!

Edit: New, better setup by Fernbot

just put all of the diodes in the corresponding places. The diodes in the 2nd schematic (fernbot's) are just an example and have no particular output, it just is an example. Fernbot's schematic consumes less power, yet uses the same amount of components, just rearranged.

Be the First to Share


    • Assistive Tech Contest

      Assistive Tech Contest
    • Reuse Contest

      Reuse Contest
    • Made with Math Contest

      Made with Math Contest

    49 Discussions


    11 years ago on Introduction

    Holy power consumption!

    As it stands now, your circuit consumes more power when the LEDs are off than when they are on*. Looking at your schematic, what if you pushed the LEDs to the top (next to the resistors) and then disconnected the cathodes of the LEDs from ground? You could then use your diodes to ground the cathodes of the LEDs. Since the LED + diode is a larger voltage drop, you'll probably have to reduce the size of the resistors to keep the same LED brightness.

    It's fun to work with the basic components, isn't it? =D

    *Your diodes turn the LEDs off because they have a smaller voltage drop (~0.7v) than the LEDs (~1.3v), right? This creates a larger voltage drop across the resistor when the LED is off, which leads to a larger current, and therefore higher power consumption.

    7 replies

    Reply 11 years ago on Introduction

    you are right! I'm glad you pointed this out! I don't get exactly what you're describing, could you make a schematic?

    So true :). I just got done designing an ALU that can add, subtract, do all of the boolean logic operations, and now I'm working on bit-shifting. Once the design is done I'm going to hard-wire it all up.



    Reply 11 years ago on Introduction

    Ok, here is what I was thinking. Notice that now you put the diodes where you want the LED to be on instead of off. I just randomly put my diodes in the schematic, so the output would probably be meaningless, but hopefully it gives you the idea.


    Reply 11 years ago on Introduction

    ohhhhh so the switches are normally on, but when you flick the switch off so do the leds.. I'm going to post that schematic as a better way of doing it on my instructable

    Meran Eng.

    6 years ago on Introduction

    what you're doing with these instructables, is just awesome :)


    plz i need can i connect (9 digits)binary to seven segment? without decoder (9 -512)??????????plzzzzzzzzzzzzzzz help meeeee.thnx

    Okay, correct me if I'm wrong, but with diodes it's possible to make non-volatile (won't lose it when the power goes off completely) memory cells? Right?

    This is just what I need for my project. At first I thought about capacitors, but deemed it way too complicated. Also, where would I find a tutorial on doing this?

    (By the way, I love what you're doing with these instructables, and I hope you keep going. I prefer transistors to diodes, but still awesome).



    11 years ago on Introduction

    There's a PDF about DEC logic modules used in PDP computers. It's full of information about using DTL to make stuff, including adders, etc. The link is here

    I made a 2 bit plus carry adder out of DTL a few months ago, but I can't find any pictures of it. There were about 15 transistors and 28 diodes.

    3 replies

    Reply 11 years ago on Introduction

    thanks for the link! I'll look at it once it's done downloading (25 MB!)

    I'm making a 2 digit adder (xx + xx = xxx) only from diodes

    the schematic is a pain in the butt.


    Reply 11 years ago on Introduction

    I been working on DTL aswell. I have figured out every gate I could find info about. NOT, OR, AND, NOR, NAND, XOR, XNOR. Are there any that I have missed? When I have got a full set I'm goin to make an instructable on it.


    10 years ago on Introduction

    Perplexing question!


    Dr. asked me a question related to the university b Markp ROM on the design of the type of ROM through the Diode Matrix

    Q) Design an adoide matrix read only memory that stor the following 20 words:
    How to answer it and drawing with diode matrix read only memory??!!


    Is there a way to make this circuit to have a +5v input at each point instead of the switch? In other words input a +5 volt signal at any point and display the corresponding number on an LED 7 segment display. This would tell you which one has the +5v signal at its input.