pic: Custom Built Stopwatch
 

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Thats pretty cool, what kind of chips did you use and how long did that take you?

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Nice. I've recently been wanting to build a small clock out of breadboards and other various electronics, but haven't got the time due to learning programming and other stuff.

Do you have the schematic for it?

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there ya go

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The main counting feature is done by the Motorola 4553, which is counter that counts up to 10 (0-9). It was a pain to figure out how to use, but once we got it working it was pretty straightforward.
The cool thing about this is that it doesn't use any flip-flops, we can make the 4553 do the counting from 0 to 9 and then 0-5. Basically this how it works, the first counter is the least significant number or in this case milliseconds, it is run off a 555 timer that goes into a 4520 counter. However we use the 4520 as the clock signal, and not the counter. The clock signal come out of the 4520 goes into the clock signal of the first 4553 which 0-9 milliseconds, when that count reaches 10 we use combinational logic to detect it (using AND Gates and inverters) to send a send a signal to reset it self, and also to send a signal to other counter in line to count. This logic can be directly applied to all the other digits. For our project we only went up to 60 minutes .

If you want to learn more about this, I have a whole PowerPoint presentation I can send you.

Re: pic: Custom Built Stopwatch
 

I did this last year in my digitial electronics class. We did the schematic on the computer but only implemented the seconds counter due to time constraints.

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Ahh thats the answer I was looking for ...

That would be excellent, i think it would be better if you just uploaded it here so anyone who wanted to see it could get a hold of it.


Nice job

-D.J.

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Great!

I have played with clocks and such before in high school. Digital was the best class out of the four electronics classes I had in high school.

Now all you have to do is make i fit on your wrist.

Just one question why did you use LED's over LCD's?

LCD's are much funner to play with! :)

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Before my former-english-teacher-grandmother turns purple and jumps in, it's:

"LCD's are much funner more fun with which to play with!"

-dave

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Well my group and I only had CC (Common Cathode) or CA (Common Anode) LEDs available to us at our labs. The LEDs are easy to work with, and they require no multiplexing. You can directly take the outputs of 4511 CMOS (BCD to Seven Segment Display) into the inputs (a through g) of the LED. We originally were going to have a 4 seven segment display but that required multiplexing, and a couple of other things we couldn't get working before the end of the semester.

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Was it required for your project that it be 60 minutes? It seems like once it gets beyond seconds, it becomes a project of managing wires, rather designing a stopwatch circuit.

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There were no requirements on the stopwatch per se, we just decided to go to 60 minutes, because most commercial stopwatches are only 60 minutes.

For the massive amount of wires, well that is the price you pay for using breadboards. While it is easy to connect wires and other stuff to breadboards, it gets messy pretty quick, there is no avoiding it.

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Cool project! I always liked those types of projects in college, though figuring out why it is broken quickly becomes a challenge with so many wires!

If you (or anyone else reading, for that matter) are interested in experimenting more with digital logic design, you should think about getting an FPGA development board. For those who don't know, an FPGA is a chip that you can download a digital circuit into. You draw a schematic using a program on your computer and then you can download that schematic into the FPGA. It's very cool since you get all the fun of designing a circuit without the hassle of dealing with stripping wires, breadboards, etc. Anyway if anyone is interested in this, check out https://digilent.us/sales/Product.cfm?Prod=pegasus. It's a nice little FPGA development board that has a nice set of IO devices onboard to play with. It's only $89 (I know, I know - that's a lot of $$$ for a high school or college student, but it's worth it if you're thinking about a computer engineering career) and it comes with the programming cable & power supply. All you need to do to get it going is download the software for free from Xilinx.

Re: pic: Custom Built Stopwatch
 

I got one of those electronics project kits when I was six, and there was a model that told you how to build a single digit stopwatch (that was all that was included in the kit). I tried to build it when I was 8, but by then (you know how 6-yr olds are), I lost most of the resistors and broke the pins off the provided IC chips.

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Yes I agree, in my digital design class we were all given these FPGA boards and had the experience of using Xilinx. Xilinx was alot of trouble in the beginning being that it would always crash (We use one of the older verisons for some reason...apparently the new one is VHDL only??) In any case the program is pretty good and you can get pretty complicated very quickly (The last lab we had to do took over 25 hours!!) If I still had my board I would take a pic and upload.

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It defaults to VHDL, but you can still do schematic design if you want. I've done it with the board I mentioned above. I haven't taken the time to learn VHDL yet and really I prefer the schematic at this point as it feels like I have a little more control over it. Of course, once you start to get really complicated designs then designing a schematic starts to become cumbersome or even impossible.

Check out http://home.freeuk.com/fpgaarcade/games.htm for an interesting application of FPGAs - these guys have recreated various old-school arcade hardware inside an FPGA. Pretty neat.

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One question. Are those things re-usable (meaning you can program over and over again) or are they just a one time thing, like a PLA

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They're definitely reusable. The FPGA itself is RAM-based, so you can download to it over and over as much as you want. The only problem with RAM is that when you power off your design is gone :(. Luckily, the prototype board that I mentioned (and most others, I believe) include a flash chip which you can download your design into. Then when power is turned on, the FPGA will automatically boot itself from the flash chip. This happens so fast that it appears instant.

One of the applications of FPGAs is to allow designs to be updated or changed in the field (after a product has shipped). (FYI, FPGA stands for Field Programmable Gate Array).

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That sounds similar to my final project for my design of digital systems (senior level) course. It was a simple pong like game on an Altera development board. It used a standard monitor (640x480 and 8 colors), and a ps2 keyboard.

For the freshman level digital course, we did a counter/stopwatch on the same board.