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
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cstudyhelp7 days ago

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Fernbot7 years ago
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.

i know they should just have a normal off switch lol

guyfrom7up (author)  Fernbot7 years ago
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)  guyfrom7up7 years ago
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.

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)  Fernbot7 years ago
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)  Fernbot7 years ago
you make a good point, I'll check with my multimeter, be back in a jiffy!
thank you very mach
Meran Eng.2 years ago
what you're doing with these instructables, is just awesome :)
May I have a layout for printed circuit board?
sry 9 bits
plz i need help.......how 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).

thrashbarg7 years ago
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)  thrashbarg7 years ago
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.
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-tech6 years ago
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.
Will this one work? it only puts power to the circuit when needed.
Push to digit Com Cathode.GIF
Llamarama6 years ago
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.
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.
engmohammed6 years ago
plz show where intersections are.....
engmohammed6 years ago
it will be much easier by using the sn74ls47 ic(only 4 inputs)
1 question- how do you know this stuff?!
guyfrom7up (author)  GorillazMiko7 years ago
books, and thinking, then researching to see if there's something similar to my original intentions
guyfrom7up (author)  guyfrom7up7 years ago
oh, and of couse, asking on forums ;)
Kind of a retarded question, because I don't know much about schematics and stuff, but what do diodes do? :P
guyfrom7up (author)  GorillazMiko7 years ago
diodes only let electricity pass one way, likea one way valve for water. I use diodes here so that the signal doesn't backtrack.
Oh. Wait up! Aren't you supposed to be taking a break from Instructables? :-O
guyfrom7up (author)  GorillazMiko7 years ago
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.
Welcome back. :P
rmd65027 years ago
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)  rmd65027 years ago
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)  guyfrom7up7 years ago
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.
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 BigRich7 years ago
Haha forget that comment above, just saw picture 3
guyfrom7up (author)  rmd65027 years ago
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.
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