Regulated 9 Volt DC Power Supply

Hi, Dave. The easiest and safest way is to buy a wall wart. Hobbyists and other newbies probably shouldn't be experimenting with line voltage.

Mouser supplies a 9V 5 watt regulated DC output wall wart with a variety of snap-on outlet plugs which will operate with all international line voltages and frequencies for $12.82 ea. in single quantities. It's their part number 552-PSA-05R-090-R

Cheers Chris

I can buy a 9 v regulated wall wart, rated at 800 mA, but as I'm on a tight budget, I can't pay the $AU30 for it. I ALWAYS use extreme caution around high voltage. I've worked around high voltage in old valve radios, and learned to keep my hands away from energized equipment, I'm pretty comfortable working around mains voltage. If I build this PSU it will be in a plastic box.

OK, Dave. But if you're on a tight budget, you probably want to stay away from home brew power supplies, unless you've got most of the parts in your junkbox -- it'll still be more expensive to make it yourself.

Dick Smith Electronics has a new regulated 9VDC@600mA output wall wart for A$7.98 as their P/N M9560. I'm sure you could scrounge something at a local surplus outlet for less.

But if you're somewhat versed in electrical safety, and you've got enclosure, line cord with strain relief, fuse and fuseholder, DPST line voltage-capable switch, 12VAC secondary transformer that's good for at least an amp and a half, 6 amp bridge rectifier, 2200uF 25WV electrolytic cap and 10uF 16WV cap, you can buy an LM7809 from DSE for A$1.20 as their P/N Z6550 to make your regulated 9VDC supply. Oh, yes

-- you'll also need a 6 to 10 watt heat sink for the TO-220 package, as well as a bit of perfboard to mount the components. And mounting hardware. And bumper feet for your enclosure. And some kind of light to display that it's on.

Are you sure you want to go there?

Cheers Chris

Didn't think it would be that complicated. I'll have a look around to find the cheapest wall wart. Thanks for your help.

--
How much current?

I'm not exactly sure. The radio uses 6 "D" cells. I'm not sure of the current rating of "D" cells.

It's not hard to find wall warts that are being thrown away or sold for 50 cents or $1 at yard sales. I have about 25 in a box ranging from 3v to 24v, ac and dc. If you really want to build one on the cheap, start picking up discarded stereos, tv and microwaves, they have much of the hardware you need. Mike

regulated

when i need stuff like this... cheap ! there are several sources.

borrow one from stuff i have allready have, go to local salvage/second hand shop and buy it (usually small fraction of new cost), yard sales, flea markets any used stuff sale.

the electronics may be useless but you get the part you are wanting.

the second hand shops here usually have a 5 gallon (20 liter) (BIN/basket) full of wallwarts for 50 cents a piece and they get so many they dump the lot when the bin is full, hth robb

You pull a suitable transformer out of a piece of junked electronic equipment. Take a "computer power supply", they are certainly plentiful in North America, and strip it down, using the box for building the power supply. That first piece of equipment is likely to supply a suitable bridge rectifier, and electrolytic capacitors.

All that will really be needed is a 9volt regulator. An LM317 variable regulator may be easier to come by.

Michael

That's the way I go, but I just keep an eye out for them -- when I actually need something I don't have and need it now, it's not so easy to just find the right yard sale or junk bin, quickly.

For example, I found our local store "dumping" 18VAC@1.5A transformers at $1.50 each. I bought six, knowing that I'd use them for students wanting to learn, later on, where I'd give them away. Also, got a largish-looking (bigger than other wall warts I'd ever seen, frankly)

+5V@1A, -5V@1A, +15V@250mA, -15V@250mA wall wart power supply (bought 5) that cost me just a couple dollars each, in an electronics surplus outlet store. But if I needed something fast, I'm not sure I'd know where to go, right away.

Also, keep in mind the cost of gas, these days! One can "burn up" one's power supply budget just driving, looking around. UPS and FedEX have been recently raising their rates, as well.

If it weren't the case that so many things carry specialized ICs and parts, making junking them out for personal use less valuable than it once was, I'd begin to wonder if there might be a return to a practice of junking out TVs, radios, and so on.

I definitely used to do a lot of that, in my youth -- I lived poor, without access to medical care and in houses without walls for some time as a child and worked the berry and vegetable fields for money as soon as I could (age 11, I think), so what electronics I did I had to do without any cost to speak of. Which reminds me... used to be, kids were allowed to work the fields for money and I definitely needed to do that to survive -- I suppose this is a reason why welfare [which didn't exist for me] is needed, since there are laws preventing children from working the fields, now. By the way, when a bowling alley was demonlished by a freak tornado in our area, as a kid I actually got up the gumption to call up the owner and asked him for permission to rummage through it for parts... and got it! I got lots of good, long wire and relays from that. Boxes of stuff.

But things are different, today, in ways. I still do a cursory "go through" on TVs and so on before throwing them away, perhaps more out of old habit than anything. I make enough money today that I don't need to worry, but it still carries some fun for me so I do it and tuck away the parts in small drawers. Microwave units definitely get their power transformers pulled -- my daughter is profoundly autistic and has burned up perhaps 5 or 6 of them in the last few years, so I have a few sitting aside for some future use. Old habits die hard, I suppose.

But it would not be easy to set up a nice looking 9V power supply from that stuff. Modifying the transformers is often doable, of course, but would take some dedication to eventually get right for someone who hasn't done it before. And that is only one step along the way.

Jon

Maximum battery power doesn't come into play. It matters how much the RADIO draws. The power supply needs enough grunt to meet the radio's maximum current draw while still putting out 9 volts.

Now, old-fashioned wall warts, the kind with line frequency transformers in them, seldom have any sort of regulation circuitry. They come rated with a current. They will supply that current while still providing the nominal voltage. Heavier loads will drag the voltage down, and with lighter loads you will get a somewhat higher voltage. With such power supplies, voltage depends on how much power the device consumes, so you need to match the size of the power supply with the size of the device. An ordinary 9 volt wall wart, if it has enough heft, will run your radio. How big a wall wart you need depends on the size of the radio. A pocket transistor radio would run off the real small wall warts, like about one inch cube. A bigger radio would require bigger power supply. So grab a wall wart at a flea market or even out of the rubbish. See if it says 9 volts dc, weigh it in your hand, and take a guess at whether you think it has enough heft to run your radio. Then plug it in.

But you're suggesting that people only throw away recent stuff, when in reality there's still lots of older things that have yet to be discarded.

Yes, recent VCRs have switching supplies, which aren't too useful in themselves and certainly aren't a source of power transformers. But lots of VCRs have been sold over the decades, and they traditionally did have fancy transformers (full of multiple windings with a wide variety of voltages).

A lot of consumer electronics is out there waiting to donate a transformer. Admittedly in this case the transformer current rating may be higher than a lot of equipment will supply, but transformers (and casing) are often one of the biggest cost items when building things, and if you can pull that relatively low power transformer out of that clock radio, it will power that little project without costing you anything (or forcing you to use batteries).

And the older the equipment, the more likely you will find parts that can be reused. Those VCRs I keep bringing home are full of low power transistors that are fine for a lot of general purpose use.

If you're starting out, the lack of parts is often a liability, since you have to buy every single part and aren't likely to experiment as a result. But again, those VCRs (and other equipment) are a great source to build up a supply of ceramic capacitors and even resistors. Forget the cost of the parts, with the local electronic store often a thing of the past in many locations, being able to get that needed capacitor to finish a project can mean the difference between finishing it now, and having to order lots of other parts to fill an order and waiting.

Dot matrix printers can be a source of transformers too, though their time is enough in the past that the peak time for seeing them waiting for the garbage truck is mostly in the past.

Inkjets are what you see a lot of nowadays, and they can be a supply of many power transistors. They also tend to have switching supplies in standalone modules (if they don't use an external supply), which make them easy to extract. And unlike "computer power supplies" their current capacity is more appropriate for the experimenter, and even usually provide a higher voltage (ie up to around 24vdc).

I grab "computer power supplies" any time I see them, and I see them just lying by themselves often (no computer in sight). Like I said, the boxes are pretty useful for building things in.

I think it's a far better time to find scrap electronics than when I was a kid. 35 years ago, the average household had a tv set or two and a few radios, and not much else. Electronics was something you bought and kept and had repaired. If it was tossed, it was old tube stuff grungy with dust attracted by the heat and high voltage. Now there's a lot more variety of stuff, and even if you have to buy it at garage sales than wait for the garbage, it will cost next to nothing.

I think salvaging parts is as important for educational reasons than it is for saving money. Having parts around forces you to make a leap, instead of copying that project part by part and not understanding much, it requires you to know what the parts are doing and how tolerant each part is to variation. I also think it helps to demistify things; once you've taken things apart it's less of a mystery.

It's often worth just keeping a basic set of tools with you, so when you see some old junk, you can extract just the things you want, without having to haul the whole unit home. A little bit of knowledge helps. So if you see a radio, and are interested in radio projects, you know to grab the variable capacitor and loopstick if you see a radio, and maybe the whole circuit board. If you've got the tools, you can easily unscrew it and cut the wires to get the board out. Or just pull the power transformer, like I said those often cost more than the parts for a small project.

Michael

Yes, I suppose that is the case. However, just looking at me (and I've got a 1200 sq ft shed with "stuff" in it dating back a ways) and what I throw out these days, I can certainly see a lot less of easy use for a new hobbyist who is nearer the beginning than the end of their hobby.

I tend to "part out" the easy stuff in everything electronic we throw away -- which deeply bugs my wife, since she can't just get rid of things when she is busy and doesn't want to wait for my convenience. And of late, I am speaking of the recent 10 year period and comparing it with the decade of my early hobby years from '65 to '75. I have to say that I'm pulling out less and less I can later use for hobby things... by quite a stretch... and I know how to use a wider variety today than I could back then.

If you are talking about older, used VCRs, I don't have access to "VCRs I keep bringing home." Do you work somewhere in proximity to these things? I ask, because for the OP it may be nice to actually know where to go to get things with good stuff in them to extract. I was thinking about where to recommend, as a ready supply, and I'm not sure I have a good recommendation. Goodwill, perhaps. Or some place that scraps computers -- though I've actually volunteered at such a place a few months ago and helped out there and didn't find nearly as much as I'd imagined beforehand. Good motors in printers, yes. Heat sinks, yes. Some EEPROMs and FLASH memories, yes. I suppose the power supplies might have a few items. But nothing like the old Kaypro 286i, for example, which pre-dated the "chipset days" and had a board FULL of 7400 series SSI chips on them. And I'm not sure how easy it is to get them to let you rummage stuff -- the folks I worked with separated out the gold for extraction and sold other stuff, once sorted a bit, by the pound. But if I were to have asked to take stuff, I'd have had to "ask the boss" and I'm not sure how much they would have wanted to bother or worry about someone hauling out goodies while interfering with the sorting process.

I agree, conceptually, with you. The problem is in the details of actually knowing where to go for setting hands on good stuff to gut at low/zero cost.

This last one interests me. Where in the world can you hope to get a dot matrix printer, these days??? I just had someone ask me if I had any ideas at all where to get one. They wanted something that used a ribbon for the ink and supported _impact_ printing. I didn't have anything to offer, though I admit I assumed that he'd already searched on the web a bit before asking me. I could be wrong about that. But if you know of a source, I'll pass it on to him.

I haven't gutted a recent PC power supply. But they seem to be much smaller, from seeing them on the outside. Which makes me think they are line-powered, chopping and using high frequency inductors with opto feedback to operate them -- and if that is right, there won't be a nice transformer there for handy hobby use. But I admit not looking, yet. Can you say more about the recent supplies?

Well, I think there is a lot more "scrap electronics" around now -- admitted. But I'm thinking also of 35-40 years back, when I was needing these things and I feel this is all a bit of a mixed bag -- some good, some bad.

I used to find quite a few ready supplies of parts in the area. We had at least 4 or 5 BIG warehouse-style stores in the area -- Allied Elec, for example, operated a huge facility here that was open to the public. But there were four others here in the area and they competed heavily with each other. I used to take several days and walk through these places, over the flat tables of hand-bagged items or loose parts these places had collected up and offered for sale. NONE of these retail facilities exist, today. Not one. And I've lived here my entire life and watched the change. Radio Shack (and I remember the Tandy leathercraft stores here, too, before and after the merger) used to be, by and large, a parts store. No more.

On the other hand, I am greatly gratified by places like Mouser and Digikey, of course. And, except perhaps for Allied, I didn't have something like that as a kid -- though I probably couldn't have afforded it, either. But I did also have access to perhaps 20 or so suppliers of hobbyist quantities of glass of various types (a good two dozen types, at least, for lenses) and got copies of the five periodicals that used to exist for building your own telescopes -- all gone, now. Sky and Telescope still exists, but doesn't cater as it used to, of course, to that market. Of course, Heathkit is gone.

It's a mixed bag. I LOVE much of the change. I have ready access to microcontrollers of every ilk and because of that I can do things that would have been simply impossible, back then. I can buy demo boards for almost nothing (in today's terms) and, instead of having to wire wrap like a madman, I can get a nice FPGA board and program in VHDL to wire up all that logic for me. I don't even need to do the floor planning of it, if I am just experimenting around for play. I can't tell you how much of a boon that is. For example, I've designed a few CPUs of my own and was able to test out my own code, too. And it didn't take long, nor was it hard work. So, there are some big pluses today. For some of us.

But if I were starting out... well, ... okay, maybe you are right. Hard to say. But I do miss some things.

yes.

I enjoyed reading this and perhaps you are right about the times, as well. But I do wonder about someone starting out these days. There is so much available, for so little money to buy, that the motives needed to do the real digging are harder to come buy. "Back in the day," you didn't really have a choice. You either built it, or did without. When the Altair 8800 came out, I bought the kit and built it. In fact, that was the only way I could have afforded my own computer. I built my own telescopes, because back then there wasn't a ready market for a wide variety of them and where they did exist pre-made, they were WAY too expensive and there was a ready supply of cheap materials for making your own. In fact, I'd add to what you wrote above and say that you really cannot understand your telescopic instrument well, if you haven't been through all the trouble of actually constructing and testing your own to near perfection. The process of actually seeing what light does is very important and no "book learning" will quite do it for most of us. Setting up knife edge or Ronchi gratings and going through various repeated steps of correction and testing and trying out various light sources and so on is as much an important part as anything. I'm not sure that an amateur really can know what they are working with, if they have never been through that process at least once or twice.

Thanks, Jon

The Energizer E95 (D cell) datasheet uses 10 ohms as the load for a radio example. Assuming that is correct, you are talking about (6x1.5V/10) or almost an amp load. But I'm sure that volume affects this, too. Anyway, using that as a reference I guess that a solid 1A or 1.5A supply would probably cover the need. Of course, that could indeed vary a lot from radio to radio, so of course more is better.

Problem is, you can expect transformers delivering much more than an amp on their secondary, at voltages enough higher than 9V to be useful in linear circuits, to be expensive/big. You may be able to measure your current draw, with an ammeter if you have one. But my guess is that a largish wall wart supply should be okay for your use. I think you can get to around the 1A to 1.5A you are probably looking at.

By the way, D cells are rated to operate over a range of current loads. They are usually selected over C or AA, not quite so much because they last longer (they do) but more because they are capable of larger current draws without serious loss of lifetime. This suggests that your radio really does want access to something in the

100's of milliamps rather than something in the 10's. So you really do need to figure on estimating about .5-1A or so, simply because it uses D cells.

Jon

Thrift stores, yard sales, or even Ebay. 498 listings, right now:

Google has 2 million hits for dot matrix printer:

I have two sitting in the shop right now to test. I have about a dozen IEEE-488 Commodore 4032 printers in storage.

Banks and Credit Unions still use them to print multi-part forms. The OKI MICROLINE 320 is still a popular, new printer used in bamks.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

i use a standard euro voltage adapter to get 120vac, then use any number of off-the shelf 9v ac/dc supplys

Thanks, I'll let him know that folks on ebay seem to be willing to take money for them. ;)

Well, that might only be people _talking_ about them. I will not send him towards some 2M listing on google.

In fact, it was the Commodore printers that sprang to mind that I felt people might have sitting on closet shelves. I'll assume for now that you aren't offering, though.

hehe. Thanks. That's a pointer for him. I'll let him know.

Jon

Its *not* that complicated. If you've been fixing radios you probably have a couple of chassis hanging around you can gut for a n enclosure, mains lead switch etc. and a filament transformer good for 50% more than you want output current. You need 12V so 2 6.3V windings in series should do. If the current you want is under 1/2A use a 78M09. Should be able to scrounge equivalent diodes and caps out of your junk box.

78xx series regulators have Ov on the tab so you can use the chassis as a heatsink for moderate output currents. If you can find a 15-0-15 transformer build up a decent bench supply with 7805, 7809 and 7812 positive regulators and 7912 and 7909 negative regulators (not 0V on the tab) Then its time to think about a fully floating adjustable supply with variable current limit.

I hacked an old 8bit computer PSU to make a nice +5 & +/-12V psu (with power LED and a 4 pole isolating switch for the outputs so I can solder on my circuit board without blowing anything) many years ago and its still in regular use. Dont use 9V much but a 7809 with its caps soldered to its legs and wire leads with aterminal block all on an old heatsink hooks up to an old CB supply if I need it.

*collect* old good quality wallwarts. Always usefull for projects ;-)

--
Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL:

How many hours does it get out of a set of Alkalines?

Check the polarity first unless you *like* the smell of burning ICs. It can also be worth hooking up a 5 watt car bulb and seeing if the wallwart is good and can supply a bit over 300ma for an hour wihout burning up.

--
Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL: