Were to start, designing circuits

Discussion in 'General Electronics Chat' started by Adamf001, Jul 20, 2012.

  1. Adamf001

    Thread Starter Active Member

    Sep 5, 2011
    hello AAC,
    I would like to design and build a 'Device' or protoboard that contains any manner of functions, like

    Function generator,
    power supply,
    speaker functions .... volume, change pitch,
    digital meter
    radio transmitter to control other circuits

    basically I would like to design something like arduino but bigger with more functions...

    The question is this: how would I go about designing something like this... how would you guys that have experience tackle a project like this?

    I'm thinking of having it so that each function is a separate module... ultimately I would like to build these for my school (me and my friend are making a howto blog thing for the younger years, to get them into electronics because our technology classes are not the best)

    also what should I make sure I have in the design, safety devices, surge protection ect...

    Thanks Guys
  2. panic mode

    Senior Member

    Oct 10, 2011
    start with something small, do one piece at a time, then do another one etc.
    while learning stay with low voltage and you are quite safe.
  3. Adamf001

    Thread Starter Active Member

    Sep 5, 2011
    ok I see what you mean, thanks.... say I want to build a amplifier from scratch how would I go about it...
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I always start like this... Google---> "amplifier schematic" or "DIY amplifier"
    and read and read and read till I know what I'm doing.. Then try/fail/try again..

    start really small.. Too complicated and you might get frustrated/loose interest.
    Like start with a LM317 based variable power supply. You can ALWAYS use that later. (See the completed projects forum of this site)

    oh and the first step should be reading all the ebook/volume learning tabs at the top of this site.. Read them all do all the experiments.. It WILL help a lot.
    anhnha and Adamf001 like this.
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    Where to start......at about the age of 8, building crystal radios!

    However, just in case you got a late start, building a crystal radio is STILL the best way to get the feel for any kind of electronics!

  6. Adamf001

    Thread Starter Active Member

    Sep 5, 2011
    Thanks for your responses,
    I was just wondering from a designing point of view how I would go about starting to design a circuit on paper,

    For product design I would start with a basic layout lets say a box.. then add a draw, some shelf's ect, building up a design adding new features,
    I assume this is not different for electronics??
  7. bretm


    Feb 6, 2012
    It's a highly creative process, and there's no formulaic answer. How do *you* learn the best? I tend to learn by doing, so I would start writing out the idea until it has enough depth that problems start presenting themselves, then you have something specific to work out.

    Your project description makes me imagine modular blocks that can connect together in any number of configurations. It raises questions in my mind about how they connect together, and what signals they need to transmit, receive, and share. Should it be a "bus" design, a daisy-chain, a grid, or something else? Should the size of each module be standardized? You mentioned Arduino, and its designers faced similar questions. You can study how they and others approached the problem.
    Adamf001 likes this.
  8. wmodavis

    Well-Known Member

    Oct 23, 2010
    A good place to start with any design is to define exactly what you want it to do. Too many 'designers' start out just trying something with no definition of the design goals. Start out with a piece of paper and a pencil and list everything you want the device to do. What are its "outputs". What "inputs" are needed to acomplish the design. Once you have those two defining portions in a list you can then and only then begin to design what is necessary to convert those inputs into the desired outputs. If you start somewhere in between those two items you will likely accomplish nothing.
    #12 likes this.
  9. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    Although out-dated and unsupported, Circuit Maker 2000 is pretty good for trying out circuits without actually building them. It has a reasonable library of components to choose from and will simulate the circuit showing waveforms, voltages, currents, etc. To me, it is a lot easier to use than LtSpice, but also not as flexible.
  10. WBahn


    Mar 31, 2012
    As others have said, start small and work your way up. Here are some other thoughts:

    Don't get lost in the forest -- be aware of the forest, but focus on the tree in front of you. You listed a number of things that you want to accomplish. Give some thought to the list as a whole and come up with some estimates of the features and specs that you think you will need to accomplish them. But then pick one module to start with and largely put the others out of your mind. Try to order the modules so that if Module C really can't be used except with Modules A and B, then do Modules A and B before you do Module C.

    Don't try to get it right the first time and don't try to have a finished product out of the box. For instance, in the end you are probably going to want a power supply module that is easy to use and has some bells and whistles. Forget about those at first and focus on getting a breadboarded power supply that more or less works, no matter how ugly or ungainly it is. For instance, you might want it to be a triple-output supply with adjustable voltages; well, just make a single fixed-voltage supply at first. Once you have it working, then refine the thing until it's working the way you want it to, including adjustability and limiting and whatever else you want. Then worry about the user interface, particularly how to deal with configuration and adjustment in a clean way. Then worry about packaging it nicely.

    It's fine (and very, very good) to have a detailed goal upfront for how you want it to look and act when you are done, but don't be afraid to note TBD (to be determined) in lots of places. Then use that goal to guide your efforts through an iterative process and don't get too wedded to the specifics of that initial goal -- treat it as a game trail that can eventually lead almost anywhere and not a set of railroad tracks that can only lead you down a rigidly defined path. Some things you wanted may be too difficult to achieve, so be prepared to reevaluate the need for those things and, if necessary, make revisions to your entire game plan. Likewise, be open to possibilities that present themselves as you go and consider adopting them into your game plan.

    Get your hands dirty early and often.
    Adamf001 likes this.
  11. ramancini8

    Active Member

    Jul 18, 2012
    The design procedure most people use is to define the circuit requirements. Take an amplifier for example; input/output voltages/impedances, gain, output offset voltage, available power supplies, power consumption, size, bandwidth, phasing, and cost are critical design parameters. The newbie should consider the first 4 items adding other parameters to complicate the design as experience is gained.

    After the design parameters are nailed down the designer starts sketching a circuit that might fulfill the requirements. In this case a simple op amp will suffice with the only question being phasing (inverting or non-inverting). Adding other parameters complicate the schematic, and when cost/size is critical discrete transistors are usually an excellent choice.

    Now the designer writes the circuit equations to validate the circuit's ability to perform as expected. Error terms are considered in this phase. Often computers ore employed now to do the cumbersome calculations, but beware; computers can be the biggest liars around.

    Finally, the circuit is built and tested to determine if it meets the design requirements. Modifications often enter the design in this stage to correct designer oversights. Other tests like noise performance, static susceptability, etc. are performed to meet company requirements. See "Op Amps for Everyone" for a design example (chapter 12), free at the Texas Instruments web.

    For your breadboard kit; start with the power supplies using the LM317 for a positive adjustable regulator, and the LM337 for a negative adjustable regulator (National semiconductor app notes AN181, LB46 are a good starting place). About 25 to 50 mA should be enough current, and 0.5 to 30 Volts maximum is adequate. These power supplies will cover the majority of applications, furnish good experience, and don't neglect the negative supply.

    Next build an op amp amplifier and and a discrete transistor amplifier. Follow this with timer circuits (NE555), comparator circuits. interface circuits, and non-linear circuits. After this you are ready for the big time: ADC, DAC, opto, charge pumps, etc.

    Remember, have fun!!!!

  12. panic mode

    Senior Member

    Oct 10, 2011
    when i was starting, i made my own set of test tools:

    - fixed power supply 5 and 12V. they could supply up to 3A which is not much but was sufficient for testing tons of projects. today one can easily use old pc power supply and get couple of fixed voltages.

    - adjustable power supply. my first one was 1-18V, with current limit adjustable to 0.5A for anything fixed supplies didn't cover. also gave me chance to work with opamp circuits requiring dual supply (had to use it together with fixed 12V psu). that used LM723 and i didn't like the switching range at 7V. today one could do same thing with LM317 or similar.

    - small audio amp with speaker (today, that would be LM386 or just amplified pc speaker)

    - couple of oscilators, later on function generators (first with opamps then XR2206)

    - signal tracer/injector. was handy when fixin radios.

    - logic probe

    - digital counter

    - dip meter (hardly used it)

    other early projects included radios (rx and tx), audio amps, vu-meters, timers, chasing lights, dimmer, ttl clock, motor speed control, metal detector, mini tesla coil, bunch of FM transmitters etc.

    the idea is to learn and have fun. one pretty cool and very simple thing teasing many people was hangman (or 'hangbulb').

    instead of person, it was a small lightbulb hanging from infamous wooden structure. there was no switch so to turn it on, one would use match...
    to turn it off one would blow at it. trick was simple circuit with the positive feedback. light of flame would be detected by photo sensor. this would turn on the bulb and it's own light would keep the circuit in on state. blowing at bulb would make it swing out of position and it would turn off. no, using LED would not be good idea.
  13. WBahn


    Mar 31, 2012
    Why would using an LED be a bad idea?
  14. panic mode

    Senior Member

    Oct 10, 2011
    plastic does not handle flame very well, not as good as glass of the small bulb.
    but, everyone is welcome to try...:p
  15. WBahn


    Mar 31, 2012
    The how about your sensor?

    Why would you have to put the LED (or the bulb) in the flame? I guess it depends on how close the bulb has to be to the sensor for it to be enough brighter than the ambient light to be thresholded sufficiently. But I can see why you might choose to avoid plastic in any parts that will be close to the flame.

    Don't they make glass-encapsulated LEDs (just like they make glass-encapsulated diodes)?
  16. panic mode

    Senior Member

    Oct 10, 2011
    one should be able to do the same with LED and it could survive reasonably long, but it is a different story when puzzled crowd wants to give it a try... they tend to overdo things. :rolleyes: