Interesting… Very Interesting.

Posted at 3:14 pm on Nov 1st, 2009 by Magnavoid

ah finally the oddity i have been looking for =P

Posted at 3:15 pm on Nov 1st, 2009 by protozo

Bah, got my hopes up with the intro, was hoping there was finally a hack for that college/no career bs.

Posted at 3:38 pm on Nov 1st, 2009 by Skitchin

I’m actually more intrigued by the form factor than the circuit itself. (both are cool imo)

I haven’t run across any hacks utilizing custom keyfobs before. I looked over his part list and see the fob is a part available from digikey. I hadn’t realized they carried such things :)

Now I’ve got ideas running through my head for home / car automation ran from these sort of things.

Posted at 4:00 pm on Nov 1st, 2009 by smilr

It reminds me of the book, The Traveler (some characters used a random number generator to keep decisions truly random)

Posted at 4:24 pm on Nov 1st, 2009 by Tuckie

coin toss v2.0 :P
great!

Posted at 4:52 pm on Nov 1st, 2009 by Zake

And for those who just cant make a decision on there own there’s this complex device.

Or you could just carry around a coin/dice or my favorite the Magic 8 Ball = )

Posted at 5:09 pm on Nov 1st, 2009 by VIPER!

it’s good to see some proper randomness in a small project :)

Posted at 5:16 pm on Nov 1st, 2009 by nave.notnilc

@smilr

I was surprised to find how many different key fobs are easily available — just google “key fob enclosure”. Some, manufactures will even sell any quantity directly (polycase) or give you some samples. That Serpac case fit my requirements (2 buttons, room for a display, location of buttons, overall size), but it might not fit yours, so look around to find a best match (or just make a random choice…)

Posted at 5:30 pm on Nov 1st, 2009 by Leon

Instead of trying to force a digital bit and then forming the number in software wouldn’t it be just easier to use and ADC and read out the voltage ?.

Posted at 6:13 pm on Nov 1st, 2009 by Franklyn

@Franklyn

I looked in to it but decided that wasn’t the way to go. I’d probably need the op-amp for amplification anyway — the signal right out of the transistor is only a couple mV, and the maximum resolution of the 10 bit ADC would be 3/2^10~=3mV (assuming that the ADC is really that good).

Since the op-amp chip had two op-amps on it, using the second one to make the signal digital seemed like the way to go.

Moreover, even if I did use the ADC directly, I’d still need to do work in software to take in the one or two useful bits per reading, debias them, make sure the number is in the right range, etc.

If there’s a version two, I may well look in to a controller with a better ADC for this purpose, since getting rid of the op-amp would keep the part count down (although I seem to recall that AVRs with 10 bit ADCs were my only options due to size constraints… although I might be misremembering.)

Posted at 7:05 pm on Nov 1st, 2009 by Leon

Thanks for clearing that up. I actually found the design quite interesting it’s definitely not something i’d think up on my own. Thanks for posting the writeup.

Posted at 7:30 pm on Nov 1st, 2009 by Franklyn

Nice little project, well written up. The bound setting is a nice embelshment. Hat tip to Leon {and thanks for the Pad2Pad link}.

I’ve actually done a fair bit with practical randomisation problems, so if anyone is inspired by this hack, a few protips;

* A pseudo-random number (PRN) generator, such as the CRC16 polynomial, either based in hard or software, isn’t *actually* random. It’s simply a count in an odd order, but *repeating*, and the first and second half of the count are mirror-images offset by one.

For most applications a PRN is quite random enough, but in some applications a basic rule asserts itself, a digital computer cannot *alone* produce a truly random (“Stochastic”) number (i.e. where the next state cannot be determined from the current state).
{Windoze is an exception}

In fact it is exactly this predictability in PRN generators that is exploited in Spread Spectrum radio techniques to get the receiver PRN to slide into lock with the transmitter PRN.

* A flicked coin toss is not truly random unless the coin is flicked strongly enough to make it rise at least a foot (30cm), it *rings* {and you quickly get a sore thumb}.

* A simple but very effective way of generating a truly random number is to put a human in the loop. We ended up running an overflowing s/w counter flat out while waiting for button presses, rediscovering the old Apple-II trick. You could build a simple decision-maker just using a 4060 running fast, but here the microcontroller is justified by the hex range, and ease of bound setting {I really like the human>pot>micro}.

* Multiplying random numbers together does not make them more random.

It’s a very inviting idea that if you have a random number routine, the more often you call it, the more random it will be. Sounds logical.

But it isn’t so.

a) If you are using a PRN and you call it repeatedly it becomes *LESS* random, rather like the moiré effect with “watered silk”, due to self-correlation. (One odd outcome of this was a routine that never once produced the two of clubs over 30,000 deals)

b) With stochastic noise sources (mostly analogue) multiple readings make no difference at all, the first reading of the noise diode voltage is as random as any other.

A variation of (a) is to get a random number, then get random numbers that number of times (rand x rand), grabbing the last. As above.

But In Real Life tossing a coin, rattling dice, or shuffling cards, it is surprising how much tossing, rattling, or shuffling is required to *actually* (not just apparently) randomise the process. {Solitaire on W95 plays quite differently to a real deck and I am very sus of their dealing routine}

HTHH :)

Posted at 8:58 pm on Nov 1st, 2009 by Roly

awe, I was hoping this hack actually involved french fries. :(

Posted at 10:20 pm on Nov 1st, 2009 by luigi517

We should all make one to evade our Tabula Rasa overloads through unpredictable action.

Posted at 10:32 pm on Nov 1st, 2009 by Kit

This would be great for Mr. Monk :-)

Posted at 12:24 am on Nov 2nd, 2009 by markii

leon-
You mentioned that you moved away from the PIC line because there was no free C compiler for linux and OSX. The PIC16F support looks recent but you may be interested in SDCC – sdcc.sourceforge.net .

Posted at 12:25 am on Nov 2nd, 2009 by jimmys

Or you could study in a country where a degree doesn’t cost you an arm and a leg. I payed $10k for four years of full time studies :)

Posted at 1:23 am on Nov 2nd, 2009 by lexi

I got a scholarship for all my studies :)
Didn’t pay a cent and now I’m debt free.

Posted at 1:58 am on Nov 2nd, 2009 by Hackius

Aha! This is just the thing for me! Up until now, I had always used the clock trick for making random decisions (and wear an analogue watch just for this reason).

Posted at 2:39 am on Nov 2nd, 2009 by Taehl

I just masturbate all day, it saves needing to make decisions, nor do I need to fool myself into thinking I am being random.

Posted at 2:52 am on Nov 2nd, 2009 by babble

Lol, keychain random number generator is random.

Posted at 5:12 am on Nov 2nd, 2009 by M4CGYV3R

…I swear this intro was used an an article just a week and a half a go… maybe 2.

Posted at 6:33 am on Nov 2nd, 2009 by Louis II

I can see it now. 2 D&D geeks are standing on a sidewalk some ware, one says something worthy of being flogged, the other reaches into his pocked dials up a key-chain to 6 (representing d6×1) and says “Roll you charisma!”

Posted at 6:41 am on Nov 2nd, 2009 by DeathsPal

@jimmys

That’s good to know. I made the PIC/AVR decision some time ago. I seem to recall the PIC compiler existed, but was at an early stage.

Posted at 9:06 am on Nov 2nd, 2009 by Leon

@lexi
You spent $10k and didn’t even learn how to spell “paid?”

Posted at 10:50 am on Nov 2nd, 2009 by Killerabbit

@ Killerabbit

Perhaps it’s not an english speaking country lexi’s talking about. And what does it matter anyway?

Posted at 4:17 pm on Nov 2nd, 2009 by Jikki

fjdkalfjdklajfdaflj
Lazy? Funny? or just Random, heh heh

Posted at 7:19 pm on Nov 2nd, 2009 by GenesisOfMoY

Useful for new age dice living :)

If you havent read it read “The dice man” from 1971 by Luke Rhinehart (George Cockcroft) it’s awesome!

Posted at 6:27 am on Nov 3rd, 2009 by Jonas

Looks well done but not all that useful. A portable stick on combo lock cracker… leave it there see what happens.

Posted at 9:26 am on Nov 3rd, 2009 by mic

People complain they need to pay for studying but meanwhile once they have a degree they are assured a high income forever basically, get over yourself eh, you can only complain if you were actually prevented by the cost, not if you could make it but just don’t like to pay.

Posted at 11:27 am on Nov 5th, 2009 by Wwhat

Now the hard question… Do I use the generator or not? Got a hack for that?

Posted at 9:37 pm on Nov 6th, 2009 by Tod