Matrix clock is a breadboarding win

Normally when we feature a clock made with a 32×8 LED matrix we’d load up an image of the display for the banner photo. But this time around we were so impressed by [JB's] breadboard work we had to use this image. We see an ATmega168, three buttons, three LEDs, a piezo buzzer, 32.768 kHz crystal, smoothing capacitor, and a few resistors; everything he needed to keep time and display it on the matrix module. If this is just going to sit on your bookshelf for a while it’s a great alternative to point-to-point soldering on a protoboard. Nice work fitting it all on there [JB].

Comments

  1. Luke says:

    Damn. That’s packed in there pretty good.

  2. svofski says:

    A clock crystal is typically 32768 Hz.

  3. mowcius says:

    Well the website says it’s 32678Hz :p

  4. jh says:

    it is 32k…
    “RTC timer interrupt triggered via external crystal at 32.678kHz.”

    typo there Mike

  5. steaky says:

    Surprised to see that the crystal doesnt need any caps – might just be a feature of atmel chips tho (I am more of a PIC man myself).

    Also was going to point out the 32768hz typo, but everyone else has it covered

  6. naturetm says:

    Sure looks a lot nicer than any breadboard I’ve made. Looking at those switches, he must be setting the pins next to the switch input pins high or low, and using internal pull-ups or pull-downs on the inputs since I see no connections on the switches other than the chip. New idea to me, clever.

  7. Brennan says:

    Good job with the breadboard, I always like it when jumper wires are sized correctly and used so that they are straight and not looped or tangled. It makes the whole thing so much more tidy. In one of my circuits classes at the Uni we were actually graded on neatness of our breadboards and our prof was really picky about stuff like that.

  8. Eric says:

    Where’d he get those nifty breadboard jumper wires with the attached ends?

  9. Scott says:

    @steaky – while the datasheet likely suggests crystals are required to be capacitively coupled to ground, in my experience it’s not needed for the oscillator to function. Note that I say “function”, not “function well”. In theory, those capacitors ensure that the oscillator begins, keeps oscillating, and oscillates stably. Since this is a clock, stable clock is important, so there probably should be capacitors. HOWEVER, this is breadboarded, and those parallel rails have their own capacitance and even inductance approaching higher frequencies. Always remember this about breadboards!

  10. naturetm says:

    @Eric

    Sparkfun has those jumpers. If you have an option between regular and premium, get premium. I had the regular ones, and there have been several occasions where I spent a lot of time debugging, and once even junking a piece of hardware, only to find that the problem was a broken (but visually ok) jumper wire. I personally just use solid core wire and strip the ends. Much cheaper and not too big of a hassle.

  11. KC8RWR says:

    This is very pretty but don’t trimmed leads on a breadboard kind of defeat the purpose? I know when I build on a breadboard it’s because it’s meant to be temporary. After using a breadboard I either move the components to a PC or perf board where I may need different lead lengths or they go back to the bins for re-use.

    I use my breadboard jumpers only on breadboards so those are always for re-use. I do hate curving them around though. I’ve thought of cutting some of the ones in my collection just to have a greater variety of lengths but I can’t imagine actually cutting them to fit specific projects. I would think that would reduce one’s stock of jumpers to a random collection of small wire bits.

    I’m not trying to be critical, I’m actually interested in hearing other’s opinions on this.

  12. Mike Szczys says:

    @Svofski, Mowcius, and JH: Yep, slip of the finger, fixed.

  13. Addidis says:

    It took me a minute to figure out how he had those switches on there. I think any one can look at that for a minute and find something to admire.

    I am also (usually) totally OCD about my breadboards being neat. Unless im low on jumpers.

    Im actually trying new jumpers from ebay. 500 jumpers 5 breadboards for 20$. Kinda unsure how I will like the giant loopy wire method. Ive always been really partial to the little bent wires.

  14. JB says:

    Thanks for posting this! I was surprised to see it here so fast.

    Yup, it’s 32.768kHz. I haven’t added caps yet, but still looking at how the time is deviating against my benchmark clock (linux server w/ NTP). It seemed to be accurate enough for now, but I might be adding 35-60pF’s later on.. (not quite sure what the value should be).

    @naturetm
    Yep, the interrupt pins are on high’s and the adjacent pins are pulled low to provide the “drain” when the buttons are pushed.

    Thanks all for the feedback

  15. Brennan says:

    @KC8RWR
    Every jumper wire kit I know of has a variety of different sized wires (color-coded). So you simply have to spend a little bit of time using the right size of jumper wire to get from point A to point B, no cutting necessary in most cases.

    @Eric
    The technical name for those is simply “reinforced jumper wires” and most electronics hobby shops will have them. They are usually much more expensive but pretty handy for prototyping. I have never had a problem with a bad jumper wire like the other poster did.

  16. svofski says:

    @JB: the capacitance of the wires and breadboard busses is probably much higher than recommended load capacitance of your crystal :)

  17. simpleavr says:

    I love seeing mini-breadboard projects.

    if you enjoy complete projects on a mini breadboard, take a look on one of my creation. One 8×8 matrix clock on top of a tiny2313 (3 or 4 components only), just trying to show the possibilities.

    http://www.simpleavr.com/_/rsrc/1283282408157/AVR/avr_mclock.jpg

    I have not finish the project documentation yet, but intended to do so.

  18. Tim says:

    No decoupling caps on the regulator? I always thought they were a must – nice to know one can do without these in a pinch.

  19. gyro_john says:

    @KC8RWR:

    When I’m breadboarding something, it’s all about hook it up fast, with some attention to grouping components reasonably, keeping noisy signals away from one another and zero attention paid to making the wires look pretty. That’s for if I go on to make a circuit board.

    In fact I try to keep them all loopy 3-dimensionally far away from each other to reduce capacitive coupling.

    What I like to use for breadboarding wire is a scrap of garbaged multi-line phone telephone cable. I strip it out and have a variety of different coloured solid copper wires which I can then cut to any length. I collect a few which I’ve pre-bent to .1″ apart, .2, .3, .4 and after that I pretty much go into airborne loops.

  20. simpleavr says:

    @KC8RWR i use cat5 network cables to breadboard, a segment from a dollar shop last for a year. also as they are thinner (like phone cables) and u can fit two in a single tie point.

    usually i would breadboard before drawing the schematic and will code the MCU around the layout. fritzing is the ideal software to do this. http://fritzing.org/

    @tim i tend to neglect the 0.1uF when the project is pure digital and battery powered. when adc is needed, i would put more than one.

  21. JB says:

    Pretty tight proto-board.

    (no, I’m not the author :P )

  22. juice says:

    Using breadboard for a microcontroller project is asking for trouble.

  23. fluidic says:

    Win, or fail?

    It works, but normally you don’t want to get any more compact on a breadboard than you’re forced to. Space optimization is for PCBs. On a breadboard, the priority is being able to make changes with a minimum of fuss. The scope of this circuit isn’t large enough to have this bloom into a major problem, but this is not a good practice to get in to.

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