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diode logic Answered

I'm making a giant adding machine using only resistors(miscellaneous), switches SPST (for input) LEDs (for display) and diodes(for logic). NO TRANSISTORS I have it so that it can recognize 0,1,2,3,4,5,6,7,8,9, but if it recognizes 8, then it recognizes it as all the other numbers. If it recognizes 0, it recognize 1, and 7. If it recognizes 6 it recognizes 1, and 5. If it recognize 9 it also recognize 7. If it recognizes 3, it also recognizes 7. basically if you take a 7 segment display, any number on it, it'll recognize all the numbers in the number. I need help sorting it ou so that if it recognizes 8, it only recognizes 8. If it recognizes 3, it only recognizes 3. Etc...



7 years ago

cool idea!
id hate to burst your bubble but you cant replace transistors with diodes, because transistors can do alot more then you would think they can.

Actually you CAN do this, if you don't mind it taking up a LOT of space. Before transistors, they used vacuum tube diodes just for this purpose.

The first semiconductor diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals such as galena.  See my instructable on simple Radio construction.

A lot depends on the breakdown voltage of the diodes one wishes to use.  In the right combonation one could use jfets, tunnel, zener, schottkey, mosfet, or TVS diodes to achieve the desired effect.   Here is where a bread board would shine, as one would have to fiddle with the combonations for a bit to get it to work flawlessly.

accept you cant use diodes to amplify or oscillate current.

Actually, you CAN use them to make oscillators. You just need the right kind of diode.


amplification is actually very obtainable too, as this is how small voltages are turned into higher voltages- with diodes.

Not to divert from your subject, but I have been looking for a schematic of a simple diode circuit that uses, I believe, one or two Shottkey diodes or tunnel diodes or barrier diodes (my memory is fading I am afraid) and one LED to indicate leaks from a Microwave oven. I am at a total loss It was featured in the Nuts n Volts magazine many MANY moons ago.

sorry to ask/put it rudly but what is the relevance of that?

It isn't relevant (thus the apology straight off) :..-.( But I didn't want to clutter up instructables with another thread that asked a simple question ( I did not take offense ;-) ).

But I didn't want to clutter up instructables with another thread that asked a simple question

Stop doing that !!
Your questions deserves as much spaces than any one else questions.

Don't you think a forum full of interesting questions (and thus, of potential answers and solutions) would be more beneficial to the Instructable community (and to the rest of the world through search engines) than a forum full of "this or that" games or "k'nex SVR11 machine gun of the death" ?

Post your own thread !
(and I'm interested about the device you're talking about)

why are you intirested. microwave ovens are very well made angainst leakage, and if you are bombarded by microwaves, you will become hot, not irradiated.

why are you intirested
Because I want to know how this device is made, and because it could be a source of inspiration for something else.

Also, I'd like to see if it's possible to use it to measure others radiations like WIFI and GSM for instance.

I still haven't found this.....it consisted of a coffee can, a (Zener?) diode, an LED,  a bit of sheilded cable and a broom stick handle (to seperate me from the can/antenna).

Of course it is.  It is electromagnetic waves in some frequency range.  That is "radiation" by any technical definition.  What you're probably questioning is whether it is "harmful radiation" (ooooh, big scary atoms coming to get us!). 

For the politicians and fear mongers, the "jury is still out," but for reputable scientists, it's pretty clear that the energy scale is just wrong, unless you have the source unphysically close to the target, or power output comparable to a microwave oven (as opposed to a cell phone).

I really don't care if WiFi is harmful, I was just wondering if it's really a type of radiation. I wish I could remember two bytes about what I was taught concerning electro-magnetic waves and the frequency scale and whatnot.


.  I think the term you are looking for is "ionizing radiation". Visible light is radiation (but not ionizing). As kelseymh pointed out, radio waves are radiation (may be ionizing if energetic enough). Gamma rays are radiation (they are the ionizing kind). &c.

Don't forget that X-rays overlap with gamma-rays, it's just the definition that differs in that area.


They are, but leakage "normally" occurs to some extent after a period of time, as the door seals start to warp, crack, or otherwise not seal well. The microwave I tested this on (I can't even find the thing now) was old and someone else's and it showed some leakage (btw: it is not a device to show how much, it just shows "presence" of microwaves). It is literally only a coffee can, broom stick and the electronics ( specific length piece of wire, a diode (Schottky, Gunn, tunnel, I can't remember which) and an LED. It makes me crazy when I can't find my stuff grrrr

same here. but my stuff is usually fairy organised, making me even angrier when i cannot find it. (its usually in some forgotten junkpile)

Oh I have MY stuff organized, but what makes ME mad is that my wife has inundated the room with her junk and has completely burried my work station, tools, and even half a bookshelf. I am this close || to throwing it out the window and hauling it away *sigh*

oh yeah. for about a year, all the junk in the house ended up on my work bench.

I really want a filing cabinet and bindfers to put all of my not huge (everything but high watage resistors and big caps) in binders. I don't have 60 bucks that I would want to spend on a cabinet. I might make one...

An over hanging shelf of wood is handy, not only can you put things on top of them, but if you have lidded jars, like baby food jars, etc, you can nail the lid up to the underside of the shelf and use that as extra strorage (screw the jar up into the lid when you are finished with it). :-) Keeps small things off the desktop.

BTW: the device I mention at the start of this thread, is not really all that complicated....if I can find or remember which diode was used, I should be able to calculate the length of the one lead to use as an antenna and get a working "yes / no" detector put together again. It really isn't a complicated to make, just to figure out the specs.

You could even make and publish your first instructable ! ... and enter the current LED contest ! =o)

hang on. goodhart has yet to make an ible? wow. but hes always on the forums. sorta like me :-(

I access 90% of the time from work (where I have the MOST time to be online, in small spurts) and really can't "work on" anything there, but I can answer questions etc. :-)

Hmm, if I find the schematic or the directions or even just the bloody device *sigh*

it includes diodes for some sort of logic operation? my schematic is about 50% done, but I'm really buissy with school. You have to think about it and set your priorities straight, school first, then making stuff. GTG do homework now ;)

You'd need to make logical gates ... As far as I recall, only OR gates are possible with diodes. =o/

Really? I was actually planning on doing an instructable on using diodes in almost the exact same way...

I've been designing with and gates, but that still won't work, it doesn't discriminate against the different numbers. 8 is still recognized as 8 and all of the other numbers.

You need a NO gate to negate entries that must be low.

For instance :
8 = A and B and C and D and E and G
2 = A and B and D and E and G and NOT( C or F )
1 = B and C and NOT( A or D or E or F or G )

Well, I don't know how you officially call them in english lol
But yes, NO gate == NOT gate == logical inverter

Unfortunately, as Zach and Tech-King said, you'll need a transistor or an active device (like a relay).

Diodes setups on the page are meant to describe how the circuit work. But it need transistors ... =o/

i think relays would be okay though. they dont qualify as transistors.

This is not an attack of any sort - but what do you have against transistors? I'm curious.


i think so. my diagram here is so much simpler. you cannot really make a not gate from diodes though.

cue blue screen of death you could use one of the input switches or a relay as a not gate.

Here's a great point

"If we go one step further and connect the outputs of two or more of these structures to another AND gate, we will have lost all control over the output voltage; there will always be a reverse-biased diode somewhere blocking the input signals and preventing the circuit from operating correctly. This is why Diode Logic is used only for single gates, and only in specific circumstances."


I bet I could come up with a schematic that proves that wrong, I'll be back in a bit I have to go get dinner. (my parents are throwing a party to night or something)

Build it and see, a schematic can't prove anything.

it'll work, I know it'll work because it's the same principle as all and gates so why did the site say it can't be done?