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power supply?

Marky-MarkMarky-Mark Posts: 26
edited 2007-10-04 23:50 in General Discussion
Hi all,
I am just getting into electronics, but one of the things I still need is a power supply.· Can one be made or should I just get a prefabed?· What are some of the features to look for?· Voltage range?· Current Capacity? Gages?· Multiple voltage outputs?· Cost?
Sorry to ask such a basic question, but this place has a lot of experiance that I would love to draw upon.

Mark.

P.S.· If Parallax could set up a section on their site for "getting started in electronics" that would help out a lot!!!
(hint, hint, hint)

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-04 16:10
    Buy a ready made power supply. Working with 120VAC is dangerous.

    The kind of power supply you might want depends on the kind of projects you plan to do. If it's all computer / logic related, get something that has a 7.5V output with a current rating of 1 to 2 Amps like the "wall-wart"s sold by Parallax. This will give you enough voltage to run small motors or servos, yet can be run through a 5V regulator for 5V logic without producing too much needless heat. The 5V can be similarly regulated to 3.3V for stuff like the Propeller or other 3.3V logic circuits. Rather than get built-in gauges, I'll just buy a decent digital volt/ohm/milliamp meter. RadioShack sells several in the $20-$30 range. Any of them will work fine.

    If you're going to run several small motors (like 3 to 4 servos) at the same time, a 1A supply may not be enough. You can always run the logic off one wall-wart and the servos off a second one (rather than buying a larger supply to begin with). There are advantages to using separate supplies (like not introducing noise from the motors into the logic circuitry).
  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-04 16:19
    Parallax is really in the market of supplying educational materials and supplies for the use of microcontrollers rather than electronics in general. There's clearly a lot of overlap, but they don't really provide for "getting started in electronics". The ARRL (American Radio Relay League) still publishes some excellent books on basic electronics. There's an "Electronics for Dummies" that will get you started on basic concepts.

    The ARRL Handbook is a "classic" introduction to electronics, particularly communications: www.arrl.org/catalog/?category=&words=arrl+handbook&SearchWords.x=0&SearchWords.y=0.

    Post Edited (Mike Green) : 10/4/2007 4:25:01 PM GMT
  • MinimumWageMinimumWage Posts: 72
    edited 2007-10-04 16:23
    If you just need a 5VDC power supply for your breadboard, check out the sparkfun website. They have a nice web tutorial on how to build a 7805-based circuit that fits right in the corner of the breadboard. That would be perfect for getting started with any 5V logic based project (like a Basic Stamp).
  • Marky-MarkMarky-Mark Posts: 26
    edited 2007-10-04 16:28
    Hi Mike,
    I am reading through The Art of Electronics for learning the electronics side of it.· The basics like what breadboards to get, basic parts, power supplies, etc.·is what I don't want to mess up.· There is basic stuff that you will need through out, that you don't want to buy twice, but you don't need certain features utill you are a hobbyst pro.· (I have many "must haves" from other hobbies that are gathering dust while the basics are still in use. smile.gif ) I know Parallax is selling their wares, but it would be nice to help out the public by letting them know:· "you might need this too, and this you got to have, but this you don't need."
  • Mike GreenMike Green Posts: 23,101
    edited 2007-10-04 16:52
    Marky-Mark,
    The difficulty is that what you might need depends on what your intentions are. Again, if you plan to do just microcontroller / logic / robotics stuff, then you need power supply stuff and instrumentation stuff to support logic circuitry. These days, that's just a +5V regulated supply and general purpose multimeter. If you want to do other things, then the list gets much bigger and very much more variable. I think Parallax does a good job for their market. Beyond that, the needs of an experimenter are just too hard to define.

    The ARRL Handbook used to have a whole chapter on what sort of tools you might need ... It included even tools for building your own enclosures back when most high powered amplifiers were all vacuum tube and the power supplies provided high voltage (1-2KV). These days, when most enclosures are prefab or partially so and most high power amplifiers are multiple paralleled MOSFETs with moderate voltage (like 50-150V) and high current (20-30A), everything is different.
  • David BDavid B Posts: 592
    edited 2007-10-04 21:56
    If you want to start using digital electronics, you'll need a regulated power supply, probably either 3.3 or 5 volts or both. You could connect a wall wart to your own discrete regulator, but even that simple circuit has plenty of ways to go wrong - regulator oscillating, pulling the supply voltage too low and regulator overheating if you draw much current... So I'd recommend that you use a power supply that is already regulated, or else use a pre-wired regulator. I did a search for breadboards that include power supplies, but the prices knocked my socks off - $169? Sparkfun sells a $10 regulator kit that has a wallwart input and 3.3 and 5 volt outputs that would probably be just fine for getting started.

    If you want to do analog breadboarding, you might want plus and minus 15 volts as well as maybe 5 volts and maybe also a variable voltage supply. But you could get by with a few hundred milliamps if you're just doing low-level signal projects. Plenty of analog circuits run just fine on nothing but a pair of 9 volt batteries, but you'll have to solder up 9V connectors to breadboard wires to use them.

    If you plan to jump right into microcontroller breadboarding, you could buy a Parallax Tech board that includes an SX, a regulator and a breadboard all on a small unit. Add a wallwart and you've got a complete experimentation board.

    There's no way you can anticipate now what you'll want in the future, so just go ahead and buy enough now to get started, and as you progress from project to project, follow your interests and buy more specialized tools and parts as you need them. Everyone I know who has done this sort of project work for any length of time is continuously getting new and different tools, breadboards, power supplies and stuff. And everyone I know messes up from time to time in some way, wasting money on poor quality tools or parts, so don't hold back too much for that reason.
  • RDL2004RDL2004 Posts: 2,554
    edited 2007-10-04 23:50
    A decent variable voltage supply can get you through many years of electronic experimenting. The first electronic device I ever built was an LM317 based power supply right out of "Getting Started in Electronics" by Forrest Mims (all parts bought at Radio Shack). It worked great for many years.

    A good place to find ready-made power supplies at very economical prices is eBay, look under: Business and Industrial > Industrial Electrical and Test > Test Equipment > Power Supplies.

    For microcontrollers and digital, 5 volts regulated with 1 amp capability will cover almost everything (though 3.3 volts is getting more common). For analog mostly what you need is the 9 to 15 volt range, though if you want to work with op amps, you may need a dual polarity supply (positive and negative).

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    - Rick
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