Voltage Regulators 101

Years ago I built a power supply with two adjustable outputs. It works for most of my needs, but it's still a work in progress. I built in an old digital multimeter with *incandescent display* (no, not LCD, not LED, not even vacuum fluorescent). Actually, that's the main reason I built the supply; I had to do *something* with that unusual display.

Functionally:

The two separate channels are completely independent. I could use it as a +/- supply by connecting CH1's positive output and CH2's negative output to GND. Or I could have two separate positive voltage supplies by connecting CH1 and CH2's negative terminals to GND.

The multimeter is connected internally to readout voltage or current from either channel and also has a third voltage measurement input (the middle terminals), the measurement can be selected via the pushbuttons between the voltage-setting dials.

Electrically:

It has two 24V 4A switching power supplies, on top. I think they were from a laptop. I used a simple adjustable-voltage-regulator circuit for the output; each output can vary roughly 2V-22V, and the regulators are rated to 5A.

The current-readout is a little bit flawed... I designed it to measure the voltage across a tiny-valued resistor in series with the output. I wanted the output voltage to be the least-affected over a wide range of loads. Unfortunately, that means the multimeter displays a fraction of the actual current (I think it's 1/100th) which is easy to deal with if you're using it all the time, but kinda confusing if you only turn it on once or twice a year.

So, one of the things I've been planning to do is add a simple op-amp circuit to amplify the voltage across the resistor to something more logical (1mA = 1mV would make sense!). This is more difficult than it sounds. For one thing, I'm not particularly good at op-amp circuits... It might well be because all the old op-amps I inherited from the 70's are burnt out, because I didn't have nearly as much trouble with those same circuits in school.

For another thing, I have to figure out which power source to run it off of! I might have to build two identical amplifier circuits, one for each channel, running off that channel's power supply. I'm not sure how well this will work if the voltages input into the op-amp are right near the rail. Or another option would be to run it off the multimeter's power supply. Either way, there're limitations. None of the internal supplies are bipolar. Also, I have no idea what would happen to the multimeter if it shared a voltage source with the measurement. It's circuitry is way beyond me (what's this piece of glass with wires coming out of it?! And this welded-shut-aluminum box?).

Tonight I had the brilliant idea that the circuit might work off a single-supply... how those single-supply op-amps work is magic to me... but they have example circuits in the datasheets. Anyways, I came to the conclusion it might be worthwhile to explore...

Part of that exploration came to checking whether there'd ever be a case where the output current would be negative. So I thought sure, what if I had one supply set to 12V and the other to 5V, sharing grounds, and I wanted to make use of the 7V in between...

Yeah, enter Voltage Regulator 101:

I hooked up a resistor inbetween 24V on one supply (long story, one of my regulators blew a long time ago and I don't have a replacement) and 20V on the other and was surprised to measure... no current. Zero (measured to .0001V). I measured the 20V output and saw it at 24V (higher than the regulator can output!). I tried a lower voltage setting, measuring it *with* the load resistor (connected at the other side to 24V)... set it to 20V and it looked like it was working. But when I removed the load, it dropped down to 8V!

Turns out, these adjustable voltage regulators *require* a minimum load. That's handled by the adjustment-circuitry, usually. But, by driving current *into* the regulator, that minimum load wasn't met. Sure enough, the datasheet says: "all quiescent operating current is returned to the output establishing a minimum load current requirement. If there is insufficient load on the output, the output will rise."


Anyways, this entire self-indulgent post to point out this little tidbit, because people use adjustable regulators for power-supplies all the time. They work great as long as your load *is positive*!


Realistically, there probably aren't many cases where this is a problem... Most circuitry returns the current back to ground, anyhow, as well it probably should. But part of the point of having an adjustable powersupply is for experimentation... And this is one thing that could be quite confusing. And, I have thought of a case where it might be handy to use the supplies as I just attempted... The minimum output is ~2V; if I needed 1V (and the regulators worked as I imagined before), I would have set one to 2V and the other to 3V and used the difference. But they don't work that way, so I need to put a note on my powersupply... maybe have a warning indicator if the regulators are dropping out.


In the meantime, I guess this makes my amplifier circuitry easier... I don't have to worry about negative-current cases. (Then again, it *did* work when I set the voltage *much* lower... I wonder if that's hard on the regulator circuitry).

catch-22: water filters which remove fluoride use oxidized aluminum... which is thought to cause alzheimers.

(yeh, I was a health-nut at one point).

Jury Duty and prosecutors

I did jury duty once.

Everyone it's come up with seems to have basically the exact same mentality: "only idiots get stuck with jury duty," IOW: if you're smart, you'll get out of it.

I did jury duty once. This is how it went:

Dude1 and Dude2 have known each other for quite some time and got into a fight and Dude1 ended up needing an ambulance. When asked why by 911, his girlfriend said that there was a fight. Because of this, the police were required to come. Because they were required to come, they were required to take Dude2 and they were required to file a report. Because they were required to file a report, it went to the prosecutor who was required to try to get some money for the county for making use of the police (who were required to be called). Because the prosecutor was involved, Dude1 thought he could make a buck suing Dude2.

That's it. Petty bullshit. Neither Dude1 nor Dude2 would have been in court if the prosecutor hadn't been required to at least ask Dude1 to be a witness for her case which wasn't really even about Dude1, it was about getting back some bucks for Dude2's police-involvement (which no one involved even asked for).

And I didn't even mention the pettiness the prosecutor showed in assuming we, the jury, wouldn't uphold *THE LAW* ("innocent until proven guilty, beyond a reasonable doubt") because "he seemed like a shady character who would do something like that" (actually, undoubtedly-so. Then again the prosecutor seemed to be just downright evil and good at hiding it behind legalese and professionalism).

It's a good thing all the smart folks avoid jury duty so all the dumb-folks can put each other away for petty personal-issues on a hunch... until there's not enough dumbfolks to be put away and they start putting away smartfolks for being unpatriotic.

And now my mom wants to work for the prosecutor "to give back to the community," because she's having a petty bickering-match with her boss.

I'm sure there are cases that are positive... hopefully most. Hopefully some against our country's own law-breaking. I just need to keep telling myself that, because mom's trying to work fo the po-po now.

I-Movie

BIG MISTAKE when trying to make a movie from footage that was originally on VHS:

thinking you can capture the *whole video* into a file on the computer then make clips and edit from there. 

After twenty minutes the audio sync is about twenty seconds off. Granted, I'm working with *old/expensive* and *new/cheap* equipment that really wasn't meant to work together... But I don't care enough about this project, at this point, to invest in both a new computer and a DV camera with firewire out and composite-in just so I can make a 3 minute collage from 4 hours of footage taken nearly a decade ago on an old-at-the-time camera that barely worked, and transferred to a worn-out old VHS tape. Presently, there's nothing really going on in my life to justify a DV camera, it's not really a path I'm interested in going down except for this project, and when/if that time comes the camera I get now will be outdated.

I could probably borrow one from a friend of a friend, or maybe the library...  Maybe I'll go that route some day...

"My education at insert tech-college here has given me a career where, above everything, I feel useful and that I'm making a difference."

Combine that with the guy who says "my education at insert tech-college here has given me a career where I can come home at the end of the day and spend more time with my family" and you've got one useful dude; he's on 24/7!

Besides doing something all day where he's making a difference, he's also looking out for the next generation by spending time with his children. On top of that, he gets the joy of being with them and his wife.

I've met him, he was a real go-getter, quite intelligent, a nice guy, and I'm sure a great father...

It was odd, though; at the time it seemed to me his need to feel useful didn't extend beyond *his* need to *feel* useful, as it seemed (at the time, to me) that he hadn't thought-through what *useful* meant in the grand scheme of things, nor the impact of the difference he was making. Otherwise, I was certain (at the time and for a while thereafter), he wouldn't have felt useful and that he was making a positive difference doing what he did.

Now? I have no idea what to think... Things aren't nearly as cut-and-dried as they had once been to me, which is odd considering how much thought and discussion went into coming to those original conclusions.

I wish I was capable of being in his shoes.

On Google+

Yeah, I've been posting a LOT in the past few days... I have a LOT of rants built-up. I'm sure this will slow soon... Especially considering I haven't even touched anything electronic in months prior to this latest burst.

When I thought about starting this blog, I contemplated looking into Google+. I have no idea what it does, I figured it's just Facebook-Google-style. Which wouldn't be so bad for a rant-column like this. But whatever.

On Google: Back in the day there was AltaVista, Yahoo, and AOL... if you used something else, you were outside the realm of normalcy. I had a friend who told me about Google... This dude was into OpenSource... ran Linux and all that. Listened to indie music before indie music had a nickname... believed in online privacy... Yahknow, a real outsider. So, he told me about Google, and I looked at it, and I thought "wow, here's a great search engine that doesn't give you all the garbage, and is a friend of the OpenSource community..." HAH! I won't even go into what it's become. Oh, and then I read an article about their Beowulf clusters (yahknow, thousands of linux machines... COOL!) And then they stood up when the DOJ tried to subpoena search records from them... I actually respected them for that move! Then I found out that they actually have a *censored* version of Google in China... And it makes you wonder... Their algorithms are pretty good at censoring information already, by burying things that
the mainstream isn't looking for under thousands of pages of pop-culture... But who knows what censoring they're *intentionally* doing here already. I remember when searching google meant actually *knowing what you're looking for* and *knowing how to locate it.* Now, if I do a search for "EDID" I get top results for "Edit" and no info on how to correct the search. I miss my raw-text search engines... yahknow 'EDID monitors OR monitor OR vga -edit AND OSX OR "OS X"' if anyone knows of a better one, or a way to convince Google to work the way I remember... please let me know.

Anyways, Google+ is kinda creepy right off the bat. I tried to create an account using a nickname for trial-purposes and here's what I got:

It's not enough that I submitted to their rigorous Gmail sign-up procedure?!
I don't even want to go into the details of *everything that's wrong* with this... It reminds me of a quote, I'm sure I heard it was a literal quote from someone high-up at Google... basically said something like "when your kids turn 18, they should seriously consider changing their names because of the online profiles they had as kids." Google's scary, sorry. Yeah, blogger's via Google... I know. And it's still my only search engine... And, maybe one day if someone actually bothers to read this blog, I could make some money through their targetted advertising... can always hope :)

Here're some fine examples from the Google+ "Name Policy:"

There's more!

Violations!

Nah... we're not talking "recommendations" here, we're talking flat-out "violations." I won't bother to paste all the BS they claim they can and will do if you violate their policies... let's just say it's ugly.

Appeals! This is the best part, seriously... They have this down to a friggin' science... It's more complicated to appeal your name on Google+ than it is to get a replacement Social Security Card (I've had to do it). And you have to give them more *personal* information!

And name-changes... again with the more complicated and rigorously-enforced than Social Security:

I like this part at the bottom of the sign-up page:

HAHAHAHA "and almost nothing with your boss." Why? Because all the people who'd be willing to submit to these terms-of-service either are too young to have a boss, or never aspire to working for a place like Google? 'Cause, seriously... I'm starting to think the Google services are nothing more than weed-out processes for (or great means for spying on) potential employees.

Oh good god, I really worry what tinted-window-vans will be parked outside my apartment after posting this.

RED = POSITIVE, BLACK = COMMON

It's simple... Everything electronic as far back as I can remember (and I've been taking apart electronics since I was 6) has had this scheme. RED is connected to the positive terminal, and BLACK is connected to the common (usually "GROUND", "COMMON", or "RETURN") terminal. We're talking 5V systems, we're talking PCs, we're talking remote control cars, TV remotes, VCRs, CD players... When you enter college for EE you're provided two wires with clips for your power supplies... a black one and a red one. The labels on the power supplies are Red and Black. Guess which terminals they are... For your signal generators you've got a red connector which is the signal and a black wire which is the ground... It may not be rocket-science, it may not even make 100% sense, but it's pretty simple and it's damn-near universal.

So why is it that two devices I've worked on in the past few days have EVADED this scheme?!

Example 1: PowerBook G4: has a connector with three wires; Red, Black, White running to the hall-effect switch used for putting the system in standby. As I recall (I've since closed it, and have no intention of opening it again) RED was the signal back from the hall-effect. WHITE was GROUND, and BLACK was +3.3V.

Example 2: USB mouse. My stupid mouse, the cheapest you can buy, has a break in the cord near the connector... had to cut it apart to resolder... Wait, something's wrong... what's this red wire doing on GND and this yellow wire doing on 5V?! I musta twisted something when I cut the cables... I checked my logic numerous times... opened up the mouse itself... sure enough, the PCB's labelled with the USB connections, and sure enough they're wired in that weird scheme. (Gray and Black are apparently the USB data signals).

I'm just saying...

Example 1A is a little less exemplary: multiple iBooks: have a four-wire connector leading to the LCD backlight inverter. It's handy to have a 1+kV voltage source around... if not to light up LCD backlights, then just to give yourself a good zap every once in a while. (Seriously, it's a health-thing... kinda like accupuncture). Not *certain* they didn't use the regular scheme, but after Example 1, I'm no longer convinced the reason it wouldn't light-up when connected to 5V or 12V was due to one of the other wires being an "enable." (I still have 'em sitting around for later electropuncture experiments, maybe I'll look at the circuitry next time).

Anyways, it's just stupid. Plain and simple. I have a hard time believing it's not intentional... some Chinese kid is laughing his ass off right now because a repair job on a mouse that wasn't even worth the five minutes it woulda taken to repair turned into twenty minutes... Forty, if you count the ranting here. Meh, I guess it's kinda fun to be frustrated sometimes over stupid stuff with no real victims. (Sorry chinese kids).

(And, if you want some other ranting, this German freak I worked for for way too long insisted that Europeans use Blue for positive and Green for ground, and insisted I follow the same scheme, like I never worked with electronics before I worked for him... goddamned German freak... I love him like an uncle, but I'm still not on speaking terms with him... certainly it's because of the Blue/Green thing. And another thing, Blue and Green?! Seriously!? What about people who're colorblind?! What about low-lighting conditions? I'm pretty sure he just made that shit up so he could use two wires next to each other on rainbow ribbon-cables.)

Time Wasted: Dynex Mini-DVI to Composite (TV) adaptor

I bought this thing on ebay for a few bux. Was so ready to use my TV for movies instead of the tiny LCD on my PowerBook G4 (yep, I'm running an OLD system).

Got the thing and was immediately having trouble. I'm sure you can find out all about its incompatibility with my computer online. But I was so sure it was just a timing issue. I discovered the device actually reports itself to the computer as something like "fake device." So, that's it! All I had to do was manually configure the display parameters...

Yeah, manual display configuration... strangely reminiscent of my old XFree86 days with a fixed-frequency monitor. No biggie, I've done this before. Found a couple utilities on the 'net that actually allow you to manually tune those parameters in OSX (holy crap).

I fought those params for HOURS... looked into the NTSC specification, figured out numerous methods for calculating proper values that would work with a TV that ALSO were outputtable by my vidcard...

First of all, I could never get a timing value that synced with the TV. Either I had multiple pictures, or the picture would scroll... Yeah, it's just a timing thing, I'll figure it out, right? Found a bunch of timing-parameters for NTSC that people have used to drive a TV straight from their VGA port... yeah, that's basically what this cheap adaptor is doing...

But there was something else... it was only in black and white.

Boiled down to one thing I hadn't considered... It may well be possible to use a simple circuit (like the one in this adaptor) to merge the timing signals with the video signals... but there's no way feasible to take three separate color signals and merge them into a single composite output.

Basically, it was a tremendous waste of time. I learned a bit, I suppose... but I spent at least two days fighting with that. There's a lesson here, somewhere... I need to learn to not fight to make a $3 adaptor do something it wasn't designed to do. This adaptor was NOT designed to work with this laptop... it was designed to work with ones that have that circuitry already built-in (probably in the GPU itself)... which is why the Apple adaptor that's made for this computer costs upwards of $40.

This was never an issue of "well, if Apple can do it with their adaptor, then this adaptor just needs some timing parameters, or the mac just needs to be convinced this is an Apple adaptor" it was an issue of this is a simple pass-through adaptor and the Apple one has active circuitry inside... I've run into these things plenty of times, I should have known better.

What did I learn? I don't know, actually... I guess I learned that it's possible to change timing parameters manually on MacOS just like can be done for X... that's kinda nice to know... not that I've needed to mess with that stuff for nearly a decade. I guess I learned a little bit about NTSC and composite signals... I could do to learn a little more... (how do they merge that color info, anyways?)

Actually, after writing this, there's one other possibility I hadn't thought of... I was messing with timing parameters, assuming the device was merely passively merging the colors and timing from the VGA output into a single composite output... There is a small possibility that active-circuitry I was talking about is in fact inside the mac, and all I have to do is fake the EDID information so instead of reporting "fake device" to the system, it reports the same info as the Apple adaptor would... then the drivers would recognize it and activate that circuitry. It's plausible... (Though, the driver loaded by the system *was* the TVOut driver... I dunno.)

I am sure this isn't worth all this trouble... but these sorts of challenges seem to be the only types capable of keeping my mind at bay these days. What kinds of challenges? I guess (though I'm not sure) small-scale ones that are easily shoved to the side when they don't work... can be picked up months later when I get a tiny bit of inspiration like this and need something to drown out my thoughts... This is the dilemma of the year, if not longer... what can I do with the brain I've got, the way it's been working lately? Sleep...

Oh the plasma...

Did some more hacking at it... had it running for a whole movie and noticed something disillusioning... There's a very distinctly-shaped blob that never lights up in the upper right corner, and a smaller one in the upper-left corner. I'm pretty sure that means there's a gas-leak which is unrepairable.

I'm glad I didn't invest $150 in driver boards to find this out.

Looking for ideas of what to do with this blasted thing. I remembered that Tesla had a means for lighting a light-bulb (fluorescent?) wirelessly, and thought that might be a cool thing to try. With all those multicolored pixels, it could be pretty cool.

I found *one* video on youtube where a person tried it... and, frankly, it's kinda boring... a spark jumps from a tesla coil and where it hits the screen the screen lights up, white. It seems it shorted a few things out internally, so there're a few blobs that light repeatedly and there are a few horizontal and vertical lines that do as well.
"Plasma vs Tesla"

I guess I was hoping for something less obvious... maybe no sparks, just a wand that lights up pixels as you wave it in front. But, even then, I don't know what would be so cool about it.

Here's a dude who actually connected a neon transformer to the signal lines... The effect is quite awesome, and becomes pretty after about 5 minutes:
Plasma vs Neon transformer

Some awesome images of it here. Like this one:

There's another dude who wields the output of a microwave transformer... it's crazy in that "with my hands I control shittons of electricity" sort of way, but the visual from the screen is less interesting... basically like the tesla coil experiments. Actually, it's better the second time around.

I think I might try the neon transformer... I've got to do *something* to justify and finally lay to rest all the effort I put into this damn thing over the past couple years. And, I've a friend with a neon transformer, so yay!

Plasma TV... and flaming art!

I've been working on this Plasma TV for at least two years now... I get these short bursts of inspiration, but usually end up at the same point I reached from the start. I did make progress in the beginning, pinpointed a couple shorted components which were redundant anyhow, removed them and got this fiery blob. felt pretty proud. Then blew a couple more and had to buy new ones and lost hope for a while. Anyways, here's the progress so far. Running to stand still.

Actually, it's kinda cool if you think about it... it looks like fire, which is kinda ironic for a plasma display. And to take it a step further, to think that it's being raster-scanned and looks like fire... whoa, it boggles my mind.

We'll See...

We'll see where this goes.

Background:
I'm a former-geek/nerd. Or something. I've always straddled the lines of almost everything, never fitting in to anything... not even being an outsider. If you look at my resume, you might think I'm a classic nerd... but it's not quite the whole story.

I was/am(?), according to others:

• Hella-Smart (at least, according to my non-geek-friends)... 
• "The next Bill Gates" according to my family, as I brought them into the computer-era.
• A Nerd(?) in college. I was really good at what I was good at, if not one of the best. But pretty bad, and getting increasingly worse at the others, including those that were *significantly related* to the things I was good at. (Digital Electronics: top-notch. Analog Electronics: bleh.)
• "Socialite/Bad-boy, bordering on danger and insanity" amongst my nerd-friends.
• "Loner, nerd trying to recover, bordering on sociopath, possibly unibomber material if we don't set him straight" amongst my social friends.
• Worldly/Experienced compared to most, been everywhere, tried everything, though most don't bother to ask about it. If you're interested, please ask! (See Below).
• "Cliff" (From Cheers, though I'd prefer to think of myself as and aspire to be Norm) amongst my bar-fly friends
• Looking, desperately, for my soul-mate (the characteristics of whom I cannot even begin to describe here)... or at least someone who knows how to not let me go before we even get started.
• ...

Conversation Starters/Asking Points:

Here are some topics... Past experiences that define me. (Again, always straddling lines, so expect my experiences below to be somewhat outside your expectations).

• sailboat live-aboard
• sharing shots with iguanas (Mexico... oh oh Mexico.)
• backpacking Europe
• homelessness, living in a tunnel
• San Francisco
• Buddhism vs. Lutheranism vs. Agnosticism vs. FuckedUptism
• Vegetarianism, my long-past (and yet still evolving) experience
• Living in a small village, cut off from society (No TV, phone, radio, internet)
• An avid non-smoker who's now smoking a pack a day.
• 420-friendly, but 420 doesn't consider me a friend.
• Fetishes -- yep, I've got 'em, and I don't *want to* share with just anyone. If you've somehow found out, feel free to *ask me about them.* But, until we've talked please just forget it, and don't share with my friends!
• Artistic endeavors
• ...

I'll leave it at that, for now. 

Geek Resume (justifying this blog):

• 6-10y/o: Took *everything* apart, and saved all the pieces. Built a train from a block of wood, lantern batteries, and a car light. Exit-sign. Spotlight with a speaker-switch... got-zapped in the rain. Was convinced all it took to make a wired remote-control car wireless is to cut the cord and tie all the wires together in an antenna-shape... and was sad to find out the truth. Built "EPOL" (Eric's Power Outage Light) using a relay, wall-wart, and a flashlight for family/friends. Built a remote-control for my favorite car which leaked battery-acid. Built a "robot" whose head spun and eyes lit-up from VCR parts and a bucket. Favorite store: Cascade Electronics, favorite item: LED display grab-bag. Dreamt about finding Blue(!!!) LEDs at Cascade for $60 apiece, and felt like I'd won the lottery. Took apart a laser-contraption with my best friend Rickey.
• Pre-teens: head computer assistant, set up all my school's computers, network, and lab: Mac (OS 7), ethernet, Apple IIe, DEC Alpha (NT3.5.1), more. Got my first computer, a Mac 68k with a 486 daughter-card. Got my second-computer a 486SX25, loaded Slackware linux from a book of distributions. Got my third computer, an 8088 IBM/AT (was my favorite for some time). Found and repaired a 486/DX2-66 at the recycle-plant. Wasn't smart enough to figure out the mini-fridge-sized Unix-server a friend gave me (with no password, no documentation, and no monitor!)... so took it apart. Got a few surplus items from a friend at HP, including a couple pen-plotters. Watching that thing draw was amazingly inspirational.
• Early-Teens: built PCs and did tech-support/training for my family, their co-workers, friends... introduced countless people (including my 80+y/o great-grandmother) to computers. Every dollar I made went to keeping up with computers... Cyrix 5x86-133
• Teens: worked for the school district IT department, "Student Technician" with "Network Analyst" privs; Active Directory, Networking, Windows2k, deployments, Ghost, scripting, everything. Ran Linux almost exclusively at home, and multiple computers, a personal webserver/site... Bought a surplus DUAL(!!!) Pentium-60 (size of a mini-fridge) and learned NT4 and to love EISA. Also claimed replacement on the processors due to FPU bug.... Developed a graphical LCD controller using TTL chips for timing, an 8051, and an SRAM chip from my old 486
• Late teens: Shifted focus back to electronics: Microcontroller coding 
• .... (Getting tired)
• College: Interned at an established 7-person business designing embedded stuff, Interned at a Fortune-500 corporation designing a radar system, Worked for an artist designing custom electronics/code, Worked in a research lab, Worked on a fast-paced robotics team, came up with an absurd mechanical design which was built but never tested. Worked for a start-up. Started a business with a friend doing military-funded research. Got promptly burnt-out on designing things for killing-purposes... and, unfortunately, can't see now how anything electronic isn't ultimately a detriment to society.

Shit, I've done a lot. Again, that's the "Geek Resume." I had *plenty* going on during that time, including multiple trips to Europe, Mexico, and Hawaii, Moving from my mom's to my Dad's, Moving Numerous times, living on a sailboat, living in a tiny village... this is just the tip of the iceburg... and the point isn't that I moved a lot, because I've lived here since I was ten. But that I have a LOT of experiences...

I have an online-presence, mostly in the past... Maybe I'll allow that to merge with this... But, for now, this blog was intended to document some of my recent attempts at Geekery, and how they fit in with my limitations, and experience.