Superhack power supply



(click to enlarge)

I'm not going to count this in the April Maker challenge. I don't know why.

I hacked together a really hokey power supply for my tabletop foam cutter and as-yet-unbuilt acrylic bender (although strictly speaking, the portion of the foam cutter heating element that runs underneath the acrylic "table" has done a nice job of melting it). JTBarclay is using it for driving a 24V nigh-5W fan under a stir-plate, and Pat is building one for HIS foam cutter.

It does a fairly good job, although it has no check on the amount of current it draws from the unregulated DC supply, which is a MAJOR short coming. The IC is an 8-pin PIC that I've programmed with a PWM controller that reads a pot to determine the duty cycle (at least, in this configuration it does). Because of the way the design works, you can put a limit on the duty cycle by inserting a resistor between the potentiometer and the ground rail. Using a smaller potentiometer is wise if you were going to do that- you want to keep the overall resistance down. The larger the resistor, the lower the maximum duty cycle will be. If the resistor is equal to the value of the potentiometer, you'll be limited to a 50% duty cycle; if it is twice the pot's value, you'll be limited to 33%. The equation is Rpot / (Rpot + Rbias), where Rbias is the value of the added resistor.

Comments

  1. PatApril 16, 2009 at 8:04 PM

    Cool, thanks! I was getting almost there in KiCad. Does the minus terminal on the rectifier count as ground or should it be grounded another way?

    ReplyDelete

Post a Comment

Popular posts from this blog

18 Essential Skills for a Maker

@AntonOlsen recently posted an article on GeekDad enumerating 100 Essential Skills for Geeks. As he was inspired to do so by a list of "Essential Skills for Men", so I am inspired to make this list of essential skills for Makers. His list was a little long (100 items), terse (essentially one line per item, but with links), and slightly biased (heavier on computers than I might have liked, but to be fair, that is the most common geek fetish). I'm going to go for a shorter list, with slightly more verbose entries, and try to cast a wider net. If I get interest from this list, I'll follow up with an article on each point going into more detail. 1. Calculate power consumption and estimate battery life - Most electrical projects will involve batteries of some sort. Having an idea of how long your project will run on a battery can save you a lot of trouble later- that wireless garden soil moisture monitor is probably not going to run very long on a 9V battery. Mayb...
Read more

Breadboarding the Arduino- part 1

A few weeks ago, I purchased 10 Atmega328P's from Mouser , naively thinking it would be easy enough to get them working on a breadboard as an Arduino sans the fancy (expensive) board. I was planning to use an FTDI USB to TTL serial data cable to bootload (I bought a 5V one, then realized that the two 3.3V ones I already had would work fine- lesson one of this saga). I also bought a some 16MHz crystals and the appropriate capacitors. At this point, I want to extend my thanks to whomever it was that decided a 6-pin AVRISP compatible ICSP header would be a value-add to the Arduino. I know that 95% of the Arduino users out there will NEVER use it, but I am very grateful. So, first hurdle- I figure I'll take one of the 328s and upgrade my Arduino (it was one of the, what, six? Duemilanove's that shipped with a 168 from the factory). Supposedly, the Arduino IDE has the capability of loading the bootloader onto a blank chip through an AVRISP, but I'll be buggered if I co...
Read more

In Which I Create A Kerfuffle

Image
Caveat lector--this post has nothing  to do with making anything. Except the aforementioned kerfuffle. First things first--I am absolutely aware of my privilege. I'm a cis, hetero white man, of unexceptional girth and slightly more than average height. I have no scars, no birthmarks, no differences of ability which would draw the eye. In short, I'm playing the Game of Life on the lowest possible difficulty level, and damn lucky for it. So. A few months ago (right before Hogswatch  Christmas), I decided to start painting my fingernails. I've always wanted to--or, at least, since I was at least a preteen--but I've never had the courage to do it. I'm not prone to an action such as this simply for attention or to be "different". I simply realized that, for the first time in my life, I was comfortable enough with myself and my life to scratch a long-denied itch. My beautiful wife bought me many varieties of polish, and I've been painting my...
Read more