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

Picture of 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.

Step 1: Parts

Picture of 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

Picture of 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

Picture of 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!

Picture of 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

Picture of 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!

Picture of 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

Picture of 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.


Fernbot (author)2008-01-26

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.

tuck9117 (author)Fernbot2014-08-05

i know they should just have a normal off switch lol

guyfrom7up (author)Fernbot2008-01-26

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

guyfrom7up (author)guyfrom7up2008-01-26

btw it is fun to work with basic components ;)

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.


Fernbot (author)guyfrom7up2008-01-28

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.

guyfrom7up (author)Fernbot2008-01-29

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

guyfrom7up (author)Fernbot2008-01-26

you make a good point, I'll check with my multimeter, be back in a jiffy!

Ehsan Al Aani (author)2013-05-01

thank you very mach

Meran Eng. (author)2013-01-12

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

timitrisanto (author)2012-04-09

May I have a layout for printed circuit board?

ashraf sallah (author)2010-06-21

sry 9 bits

ashraf sallah (author)2010-06-21

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

dungeon runner (author)2010-04-27

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).


thrashbarg (author)2008-01-26

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.

guyfrom7up (author)thrashbarg2008-01-27

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.

microman171 (author)guyfrom7up2008-01-27

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.

Nope. That's all of 'em.

asa-tech (author)2009-02-12

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??!!

hotwaterwizard (author)2008-12-13

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.

Will this one work? it only puts power to the circuit when needed.

Llamarama (author)2008-10-09

Nice one! How refreshing is is to see some real (!) electronics! Funnily enough im working on a diode matrix ROM to form a BCD to HEX decoder.

AzN1337c0d3r (author)2008-10-07

Good luck building anything more complicated than a 7 segment display, you make EEs and electrical technicians everywhere cringe with that mess. Also you use way too many diodes where they are not needed.

engmohammed (author)2008-09-11

plz show where intersections are.....

engmohammed (author)2008-09-11

it will be much easier by using the sn74ls47 ic(only 4 inputs)

GorillazMiko (author)2008-04-24

1 question- how do you know this stuff?!

guyfrom7up (author)GorillazMiko2008-05-09

books, and thinking, then researching to see if there's something similar to my original intentions

guyfrom7up (author)guyfrom7up2008-05-09

oh, and of couse, asking on forums ;)

GorillazMiko (author)2008-02-09

Kind of a retarded question, because I don't know much about schematics and stuff, but what do diodes do? :P

guyfrom7up (author)GorillazMiko2008-02-10

diodes only let electricity pass one way, likea one way valve for water. I use diodes here so that the signal doesn't backtrack.

GorillazMiko (author)guyfrom7up2008-02-10

Oh. Wait up! Aren't you supposed to be taking a break from Instructables? :-O

guyfrom7up (author)GorillazMiko2008-02-14

I'm taking a break from taking a break, lol. I pretty much accomplished everything I wanted to do in my break, so I'm back.

GorillazMiko (author)guyfrom7up2008-02-14

Welcome back. :P

rmd6502 (author)2008-01-25

How many diodes would be needed to make an adder? Could it even be done without transistors, or would the losses add up too quickly? I suppose with schottky barrier diodes with very low Vf it could be done...

guyfrom7up (author)rmd65022008-01-25

That's actually going to my big cube machine, so you might have to wait on it for a bit. I came up with this design during school, drew all of the character (numbers) I wanted, took note of all of the diodes were off. I made a grid, similar to the schematic, labled the columns 1 through 7, labled the 7 segment display 1 through 7, and I just placed diodes on the grid in the appropriat places. For example, for 0 (row 1) the middle (I called it 4) had to be off, so i put a diode there. I just told you incase you want to design your own. when I came back home I discovered it's called a Diode Matrix ROM. I think it's neat.

guyfrom7up (author)guyfrom7up2008-01-25

here's the original sheet with closeups I was originally going to do one with a 5x4 led display with letters. But it couldn't display 5 (i think) characters and it took 196 diodes, which I didn't have. I thought this demonstration was sufficient for now.

BigRich (author)guyfrom7up2008-02-12

Quick question. The 2nd picture shows making the 1 and using 6 diodes, am I incorrect in thinking only 5 would be needed? I dont want to sound rude or anything and I have not used diodes in anything either.

BigRich (author)BigRich2008-02-12

Haha forget that comment above, just saw picture 3

guyfrom7up (author)rmd65022008-01-25

the losses won't really add up, the diodes are only used for shorting the led so it doesn't light up, for an adder that I'm desgining it'll only drop about 2 volts, and won't be a problem at all if I use a 9 volt battery.

Einsteins Circuitry (author)2008-01-26

I guess you like doing things the hard way right? Fun at first but it would probably get boring after a couple thousand diodes. :p

thats what she said probably, but it'll be like a piece of art!

GorillazMiko (author)2008-01-26

Dang, nice job 7up man! Haha, so this was the Instructable you were working on when Instructables crashed, eh?

guyfrom7up (author)GorillazMiko2008-01-27


guyfrom7up (author)2008-01-26

the schematic should be the 2nd step, but whenever I try to reorder them I get a NULL error. Just if you're wondering.

chooseausername (author)2008-01-26

Nice work !
You should add schematics into the instructable too.

oops, my bad, forgot to add it in, I'll fix it. This is my second draft of this instructable, I must have forgotten to put it in my bad

guyfrom7up (author)2008-01-25

sweet, I'm on make blog, it hasn't even been an hour, and where I am it's midnight!

nebula (author)2008-01-25

awesome! I had wondered how the logic in chips did things like this...

guyfrom7up (author)nebula2008-01-25

me too, then one day I just came up witht this design, but I later found there was actually a name for it, lol. People always say that you shouldn't care about what's going on inside of an ic, but expanding an IC into it's basic parts is always so much cooler! I'm going to try and tackle the max1709, 1112 transistor count lol jk

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