Let me start with I am a maintenance electrician not an engineer so go easy on me, I bought my daughter a maxitronix 500 in 1 electronic lab because she wanted to be a programmer and I thought she would need a solid base to build off of before jumping into programming. She has done many things out of the book but now she has begun improvising which I think is cool which is why I started looking for help and lead me to you, your site is the best I have found. Here is her new project she would like to build which is a combo lock which I have found some on your site but not quite what she is looking for, she is looking for one that fits the following criteria the combination consists of four binary numbers that must be entered in the correct sequence, each binary number is four bits it should have a reset button to initialize the circuit or clear an error.
A place (switches) to enter the binary value of the current combination digit on and some way to enter combo number to register the combination.
The combination numbers are compared as the combination is entered. If all four combination numbers are entered correctly, the unlock signal is set (GREEN LED) and remains set until the reset button is pushed. If you enter one incorrect digit in the combination, the warning signal (YELLOW LED) is turned on and the user is allowed to continue entering digits. If the user enters more than one incorrect digit, the fail signal (RED LED) is turned on and no new combinations can be entered for a period of one minute. Hopefully this is not impossible and easy enough for me to help her I do not want her to lose interest. I would like a schematic and parts list but any help you can give me would be much appreciated I did buy her a bigger bread board and switches that did not come with her kit and I will but whatever else she needs. The rest of her project I can do but I will tell you what it is, when the combo lock is opened it will trip a switch that turns on a motor which will wind up a string which when near the top will flip several rows of dominos knocking them over and doing what dominos do. The string will hit a kill switch before it is completely wound up. Kids got to love them. Thank you for your time.

 

So you are going to use 16 switches for the combination input? Do you want to power the electronics off of a battery or a wall wart?

 

The rest of her project I can do but I will tell you what it is, when the combo lock is opened it will trip a switch that turns on a motor which will wind up a string which when near the top will flip several rows of dominos knocking them over and doing what dominos do. The string will hit a kill switch before it is completely wound up. Kids got to love them. Thank you for your time.

Since you have a young daughter I'll assume that you're to young to know this, but there is a technical term for what you describe here....

It's called a "Rube Goldberg".... Really! You can Google it.

 

I have 2 switch block with 8 switches each but I will buy what every I can from radio shack , I have a dc power supply, I do not know what a wall wart is, I am sorry I am not really up on this type of stuff, I just want my daughter to have the best jump start she can. thanks again for all your help.

"Rube Goldberg" site, very cool I will show it to my daughter I can see her wheels turning already.

 

A wall wart is a slang term for an inexpensive wall outlet power pack, like battery chargers. They come in many flavors. Some can deliver filtered DC power.

 

Personally, I think this project is a perfect candidate for a microcontroller. A Picaxe 08M is less than $5.00, easy to program and it's well documented with copious amounts of sample circuits with included code. Since our youth are married to the PC your daughter will take to programming a uC easier than you!

 

I have 2 switch block with 8 switches each but I will buy what every I can from radio shack , I have a dc power supply, I do not know what a wall wart is, I am sorry I am not really up on this type of stuff, I just want my daughter to have the best jump start she can. thanks again for all your help.

"Rube Goldberg" site, very cool I will show it to my daughter I can see her wheels turning already.

Not bashing Radioshack, I too purchase things there on occasion, but you will save a ton of money if you by components through sites such as mouser.com and digi-key, just to name a few. So you are using 2 DIP switches it seems? Other components you will need are the LEDs and resistors. Then you will need some sort of electromechanical actuator for the output. The resistors you will need will depend on the specs of the LEDs. As far as the controller, someone else will have to point you in the right direction. I have messed around with Arduino (which would work in this situation) but Arduino might not be what you are looking for. What does your daughter have interest in programming? Once you figure out what you are going to use to control the circuit and get it programmed, the rest will be pretty simple.

 

How old is your daughter? That might help with figuring out what type of circuit to target.

If you go the microcontroller route, I would, especially since you mentioned your daughter wanted to get into programming, I would go with an Arduino as the learning curve for getting it working will be much less then buying a PIC. http://www.sparkfun.com/products/10175 I like to order parts, like switches from All Electronics or Electronics Goldmine. They're liquidators and usually much less expensive than Mouser, DigiKey or Radio Shack.

 

There is no... and I do mean no uC easier to learn and use or cheaper than a Picaxe. I don't think that this is a personal opinion. Just an obvious fact. Unlike all the uC families on the market, Picaxe was developed for the educational community. Enormous power in a little inexpensive chip.

 

I'm a big PIC fan myself. Honestly, I have not used the PICaxe but don't you need to provide power, filter caps and buy a programmer for it? It's the USB bootloader and software on the Arduino that make it so accessible. You'd learn more by doing all that yourself and not using the Arduino.

 

This daughter is 10, I think she is more into programing video games, but want her to have the basics of or and nand nor, not, xor and the algerbra to go with it, I do have plc's for her to play with, I also have a peco controller. my power supply is a Hewett Packard 6202B, the switches are ALCO ADE 08 some of the chips I have so far are SN74LS47N, 7442N 7938,HD74lS08P, SN74LS04N, MC74F32N, 74HC00, 324, 74HC76, 546, 555, 74HC4511, 74HC402874HC0274HC191 I also have a variety of caps and resistors that came with her kit. As I mentioned before I will buy whatever else you tell me I need within reason. I would like the circuit built out of the basic gates, even the timer. that way when I show her the timer chip she will appreciate it more and have a full under standing where it came from. the great thing about this is I learn right along with her while we spend quality time together I am truly and thankful for your help.
Thanks for the shopping tip too because it does seem to get expensive fast, I also scrounge old machine boards for chips and such from the shop so I do have a wide variety of stuff to hunt through for parts but some of those are soldered in.
I will look into the other controllesr too, thanks again have a good day

 

I'm a big PIC fan myself. Honestly, I have not used the PICaxe but don't you need to provide power, filter caps and buy a programmer for it? It's the USB bootloader and software on the Arduino that make it so accessible. You'd learn more by doing all that yourself and not using the Arduino.

The Picaxe also uses a bootloader and that's what enables it to use a natural (Picaxe Basic) language. The programming Editor is very well designed, will simulate your code without even having the uC. It's loaded with neat testing features and is FREE. The programming board can be purchased as a kit cheaply or you can build your own from minimal components. A coworker brought in an expensive Ardino project for me and RFactor to look at. We both agreed that we're sticking with Picaxe. Cost, programming ease, you name it.

 

I would like the circuit built out of the basic gates, even the timer. that way when I show her the timer chip she will appreciate it more and have a full under standing where it came from.

If you're referring to the 555 Timer chip, those TTL logic chips have little in common with it. The 555 is a analog device. It wasn't born from any of them.

We have plenty of members that can help you if you want to go the logic block rout but that's not me. To many years have passed since I spent quality time with them. On the other hand, if you decide to go the Picaxe rout I'll be here.

 

Just some random thoughts: You may need an additional set of switches to input & store combination or use one set to load a register, then use it as the key. A 7485 [ or 74L85 different pin out at least in 1973 was ] is a digital 4 bit comparator, but if comparison has to be bit by bit, then a exclusiveOR or 2 ANDs, 2 invertors, & a OR. How do we know when a bit has been entered, if we start with all 0's & enter a 0, no action takes place- OK to add an enter push button? Help!

 

thaks CDRIVE I will keep you in mind when we get that far, thanks again for your help.
Bernard, I will buy what we need, I just don't know what that is yet, that is why I am here seeking all of your help. I think an enter button would be fine I would have to get one, I did get some more switches. Thanks for your time and help.

 

When you think she's ready here's some Picaxe links. Lots of small inexpensive kits, software and pdf manuals. Software and manuals are free for download. Your daughter can learn to program the chips with absolutely nothing but the software and the pdf's. All my Picaxe projects are written and tested with the built in PC simulator long before I ever put a uC chip on the programming board or connect a single wire. Do your daughter a favor and download the free Programming Editor and let her play with it. I think the pdf's are included. If not, down load them seperately. Microcontrollers are not the future, they're now!
http://www.rev-ed.co.uk/picaxe/

This is a relatively expensive kit but it's full blown and tricked out. I don't think she needs to start this high end though. It's a heck of a lot cheaper for you than her wedding will be though!
http://www.sparkfun.com/products/9439

 

Don't forget to check out the TI LaunchPad microcontroller kit for $4.30. It comes with two CPU chips, an assembled board and the cable to hook it up to a USB port on your PC. Tons of programming software can be downloaded for it for free. I got mine from Mouser along with some other stuff I needed to order, shipping on just the TI product would probably only be $2.50 Parcel Post or $4 UPS

http://processors.wiki.ti.com/index...G2)?DCMP=launchpad&HQS=Other+OT+launchpadwiki

 

Personally I don't think the distinction between analog and digital is as severe as has been implied. A 555 (a type of integrated circuit) is routinely used in digital circuits to make them clock, think of it as a type of generator. Alternately, digital signals are also routinely used to create analog effects. The line blurs in many cases.

For now a simple 300 in one is a good way to go. Let her have fun, play with her while she is using it. The quickest way I can think of turning her off of it is pushing her (but play time with dad, with her picking the projects and doing the work) is a really good incentive. I love that age in both boys and girls, they are full of questions and still think we are smart.

 

More thoughts: If a reset is desired for individual numbers, with out resetting manually individually dip-SWs, then it seems that NO push-buttons with a storage register would be needed for the key. CD74HCT85E $ .60 ea. SWs PB-NO 4/$1.00. I think it can be laid out with all ICs and some Rs & Cs.

 

I'm afraid I can't help you with your circuits, but as a 16 year old who's 'back in the game' four years after trying to get some simple circuits to work and failing, I can offer you this advice:

If she is 10 and understands logic circuits, she's way ahead of where I was! I spent too much time reading about theory and not enough time implementing — so you've gone down the right track getting her a breadboard. Does she have a multimeter? They are imperative for understanding what's happening in a circuit.

Get her to research things herself, maybe guide her through buying parts online. Encourage her to TAKE THINGS SLOWLY (I tried to do too much too fast and gave up because nothing worked and I didn't understand any of it) and see what's happening.

If you go down the microcontroller route… I cannot tell you which system will be easiest, but I can tell you which one is the hardest to understand, especially at 10. PICs programmed in assembly!

Thanks, good luck to you both,
Barnaby