Building a Power Supply: Phase 1.5

Subtitled: On Hiatus

My new Weller WES-51 (from back in October) was finally used for the first time on Monday. It functioned for all of 2 hours or so. I believe a faulty transformer is to blame.

I followed the directions for troubleshooting the device up to the point where I sliced an inch-long gash in my thumb with a blunt screwdriver.

I no longer have a soldering iron and am not yet comfortable typing with my left thumb, let alone assembling circuitry.

It seems I should have taken Paul’s advice more closely to heart.

So I guess, stay tuned?

Building a Power Supply: Phase 1

Well, as alluded to in earlier posts, I have been working on a project over this winter break. I am designing and building a three-output adjustable linear bench power supply. I think that about 2 people who read this will have any idea what that means, so here’s the basic idea: If you want to skip all the back-story, please just take a look at the pictures instead. 🙂

Most engineers are engineers because they really like to tinker with things. Maybe that isn’t actually true of “most” engineers, but I think it’s true of all the cool engineers. 🙂 Anyway, electrical and computer engineers tend to like to tinker with electronics. For instance, this strange tinkering bug might possess them to build a cable to link their universal remotes to their computer for brain surgery. The end product of which, might, perhaps, allow the remote to display “MythTV” (why that?) on screen instead of “TV” or “VCR”…

…Not that anybody you know would do that…

Anyhow, in the course of messing with electronics, you need a fair number of tools. A digital multimeter to show you how many volts something is at, or how much resistance is in a given wire, is absolutely essential. So is a soldering iron to make changes to circuits. (mad scientist’s evil grin >:-D)

Another essential is some sort of power source. That’s where my project comes in. Most devices you buy (think digital camera, cell phone, remote control, answering machine, electric pencil sharpener) have either batteries, a wall plug, or a combination of both as a power source. Generally, devices which have a wall plug (such as your cellphone charger) convert the AC electricity in your house to DC electricity, like that which comes out of a battery. That’s all well and good, and every device is customized to use whatever precise form of DC voltage it needs, but what about building your own devices? Or powering up broken stuff? You (the electrical/computer engineer) would have to have one of every kind of power source, or at least the most common types, on hand.

Enter my adjustable bench power supply. (You knew that whole mess was going somewhere, right?) This is (/will be) a device that plugs into the wall, and converts the AC electricity available there into DC electricity at any voltage. Thus it can be made to work with any circuit’s needs. There are limits of course, though I haven’t completed enough of my construction to know the final specs yet. I expect to be able to provide about 1.0 amp at 1.5V to 30V from one output, and 1.0 amp on each end of a tracking ±1.5V to ±15V. Non-EE Translation: the supply will have three outputs. The first will be able to simulate anywhere from 1 to 20 AA batteries in a row, including “fractions” of batteries. The second output will be able to simulate from 1 to 10 AA batteries (adjustable separately of the first output). The third output will be adjusted simultaneously with the second, and will provide negative1 to 20 AA batteries, at the exact same voltage as the second output. I.e., if the second output is +9.5V, then the third will be -9.5V.

So enough nerd-babble. All anybody really cares about is pictures, right? Fine. Since I’ve only been prototyping for one day so far, I have only tested part of the final circuits. (For the electrically-inclined, I haven’t included the transformer or rectifier stages yet.) BUT, here is what I have so far:


This is the simplest adjustable voltage supply. The little blue box is the control (a potentiometer). Proof that it works [468K MPEG4]


This is the next iteration, with a digital circuit, a pushbutton switch, and three preset voltage levels. I’m rather pleased with how this turned out, though I still have some work to do on the switch, as it sometimes switches 6 or more times per button press (for the EEs: I tried using a RC debouncing circuit, until I realized that leaves the voltage level in the no-man’s zone around 1.2V for way too long. Oops. Now I just have a pull-down resistor, and the normally-open switch ties the clock pin on my CMOS 4017 to Vcc.)

Enough of that: I saved the best (IMHO) for last. Proof that this circuit actually does something [520K MPEG4]. In this clip I press the pushbutton several times. Note that the voltage switches from about 3.25V to 5V to 8V, then cycles around again. Also note the LEDs that track which voltage is currently selected 🙂

Alright, I’ve already wasted way more time on this blog post than I meant to. Back to the bench!

Howto: Resize Your Own Watch

I haven’t put too many posts up here that are actually helpful to anyone else in any way, so I thought I should start working on that. This may or may not be helpful to anyone either, but what the heck, I already had the pictures…

Disclaimer: I am not a jewelry / watch expert, and in fact know next to nothing about them. What I present here worked for me, but I make no claim that it will work for you and take no responsibility for your actions and any damage they may cause. 🙂

Back-Story

So why am I resizing a watch band, of all things? Well, my parents bought me a Seiko watch for Christmas during my senior year of high school, which I like very much. Unfortunately, wearing it for several years (and drumming with it on) popped one of the hands off one of the smaller dials, and that hand now rattles around freely under the crystal, frequently getting stuck under other dials and jamming the watch up:

Note the alarm dial (bottom) of the old watch is missing a minute hand, which is located upside down jamming its second hand (left dial).

After sending it off to Seiko for a repair estimate ($162), we decided it wasn’t worth the money to repair, as it would be better spent toward the purchase of a new watch. Fast-forward several months, and I find my very same watch on Amazon.com for $105 (no longer available). I was pretty excited to have a chance to get it fixed, so I bought it. Fast-forward another week or so, and my new watch arrives. Three sizes too large for my wrist. Oops.

And so, here we are.

Goals

  • Resize a watch band of the “pin-and-link” type seen above.
  • Avoid fees to have it resized at the mall
  • Avoid damage by the inept worker at the Younkers jewelry department

Tools

  • Pentel 0.5mm mechanical pencil tips
  • Thumbtacks
  • 1″ Brad
  • Light hammer

Steps

  1. First, take a close look at your watch and determine how many links need to be removed, and from which sides of the clasp. Keep in mind that you should try to balance the removed links from both sides, or the clasp will end up on the edge of your wrist instead of the back.
    I had this step easy, as the old watch was fitted correctly to my wrist already as a model. In my case, I needed to remove 3 links total: 2 from one side of the clasp and 1 from the other.
  2. The next step is to determine exactly which links you will need to remove to accomplish this, and which pins hold them in place. Generally, you will need to remove 2 pins (one from each end of the link(s) you will remove), and then replace 1 to rejoin the watch band.
  3. Removing and inserting these pins without a commercial tool for doing so is the tricky part, and why I am writing this Howto. So, on to the pins:
  4. On my Seiko, I started by removing one of the pins on the links near the clasp, in the direction indicated by the small engraved arrow:
  5. One method to remove these pins uses the tip from a 0.5mm mechanical pencil. Remove the tip and place it point up on a solid surface. Then press the watch down, aligning the pin with the pencil tip’s metal shroud. Apply force as vertically and firmly as possible.
    This was the first method I tried, and though it worked for two of the pins I needed to remove, it destroyed 3 mechanical pencils by pushing the metal shroud into the tip. For this reason, I do not recommend this method.
  6. A second method is to use a thumbtack. Place the tack point-upward on a sold surface. Very carefully align the watch pin on the tip of the tack and press downward firmly. It is very important to keep the watch aligned so that you are always pushing directly into the pin, not at any angle. If you are not careful, the watch will slip off the pin, and if you’re like me, you’ll stab the pin a full quarter inch into the tip of your finger.
    Despite the increased danger in this method, I found it to be the most effective, and though I did destroy another few tacks in the process, I was able to remove the remainder of my pins relatively easily.
  7. Once all the pins are removed, you simply rejoin the remaining watch band pieces by reinserting pins as necessary. This is the second significant challenge.
  8. When reinserting the pins, it worked best for me to insert them in the opposite direction I had removed them in. I attempted to insert the pin in the direction of the arrow the first time around, pushing the “bulge” in the pin through first, with the result of destroying the pin:
  9. It is possible to push the pin nearly all the way back in just by hand and pressing the watch against a table, but replacing the pin the last 1/16″ proved trickier. You would like to reposition the pin as it originally was, to minimize the risk that it will fall out.
  10. The best method I found for recessing the pin back to its original position was to tap it lightly with a hammer, via a nail. Place the watch on a solid board or edge of a table so that the edge of the watchband rests solidly on the surface. Then align a small brad (I used a 1″) with the stub of the pin sticking out, and rap it lightly with a hammer as shown:
  11. Repeat for all pins that you need to remove and replace to adjust the watch size.
  12. And that’s it!

    Finished watch, down to size with minimal scratches.


    Total bill of materials:

    • 3 mechanical pencil tips
    • several thumbtacks
    • one watch pin
    • one stabbed finger

Stupidest Software Packaging Ever

I thought I was buying this brand-new for $0.01 back around Black Friday, until I realized (after I had submitted the order and they had billed my card, aka “too late”) that one $20 rebate was actually an upgrade rebate. Oops. So Fry’s got $20 for it instead of $0.01. Oh well.

None of that back-story can excuse this:

Yes. That’s a hinged computer software box. There is little more to say. I’m sad. : (

Playing catch-up

It seems that it has been a while since I’ve posted here. I’m going through a bunch of pictures from the past month at the moment, so I will start posting some things up as I encounter them.

Here’s a general summary of what I’ve been up to:

  • I finished my last final exam at about 8:30pm Friday, December 22nd, finally starting my winter break
  • My family picked me up in Madison on Saturday morning and we went out to South Dakota to visit my Grandma and my dad’s sister’s family. That’s the location of my previous post with the Christmas lunch
  • On the way home on the 26th, we stopped in Abbotsford, WI, to visit my other Grandma and one of my mom’s brothers’ family.
  • Back home, I finished Christmas shopping for my family on the 27th, (talk about last-minute shopping… actually, the sales are a really great way to shop. I’d strongly consider it next year.), and then later that day we had our family Christmas.
  • Thursday Jared, Scott, Ashley, Angela, and I went out to eat down at Hudson’s to catch up a bit, and then Friday Jared had a party with more high school friends, and Saturday Jared and Scott and I held a LAN party in my basement, complete with Figaro’s pizza
  • Since then I’ve pretty much just been hanging out. I spent a couple days designing a bench power supply and picking out all the parts for it. I’ll be sending in an order for those tomorrow, hopefully they’ll arrive in enough time for me to try it out before heading back down to Madison.

I think that’s it for this summary… as I sort my pictures, I’ll post some more.