Ac adapter for picaxe

I know the circuit diagram to power a picaxe from an ac supply in the getting started section, but just as a confirmation of that why can I not use a 5VDC output regulated power supply - why does the voltage have to regulated 2 times once at the 9 vdc stage and then at the 5vdc? Ok thanks


New Member
You can use a 5VDC regulated power supply. The section you are referring to assumes that most people will start with a commonly available wall wart power supply. I believe the lowest you can get is 9V. Thats why you have to bring it down to 5V and regulate it again.

Rev-ed just referenced a commonly available part(the 9V wall wart) that most beginners would use as a starting point.

If you have a regulated 5VDC power supply, by all means use it.


Senior Member
Once should be indeed enough! The point however (without checking the refs.) may relate to the need for squeaky clean DC, as Picaxes are extremely sensitive to supply line "noise". Naturally the use of batteries gets round this hassle,with the now near standard 3 x AA (~4½V)supply often lasting months as well- thanks to modest Picaxe current needs. Hence IMHO you are advised to tame initial designs with batteries & THEN work on the mains PSU. Stan
Thanks so much for the reply - I wanted to of use the model by CUI #FSK-S5-5U

input voltages : 85-264 Vac / 110-340 Vdc
wattage : 5W
output voltage : 5V
output current : 1000mA
dimensions (LxWxH) : 2.0x1.0x0.6
packaging : encapsulated PCB

sold by #102-1470-ND they list it as a "linear, regulated" do you think this will work? Thanks so much for your help


Senior Member
It is NOT a linear power supply, it is a 100KHz switching power supply, and you still have to deal with wiring it safely to a mains.

I am not sure how much of the switching noise will get into the output, you'd have to look at the spec sheet.

I would recommend you go to an online electronics surplus house and buy a 9~12vdc wall-wart for $5, then put a 5v regulator on your circuit near the picaxe. This way, there will be no messing with high voltages.

Digi-key has one of everything you could ever dream up, but their prices are higher and there is a minimum $25 order to avoid a surcharge. Mouser is more reasonable and has no minimum, and the surplus houses even more inexpensive:

All Electronics Corp
B.G. Micro
Electronic Goldmine
Jameco - not a surplus house, but good prices and good variety. Try here first.

Edited by - wapo54001 on 18/08/2007 23:50:51


Senior Member
All the more reason why it's recommended you START with AA cells! Here in NZ the switched battery pack shown =&gt;<A href='http:/// ' Target=_Blank>External Web Link</a> can be bought for ~US$1,&amp; 3 x AA alkalines for ~US50c each (with normal AAs ~25c each). Hence for just a couple of bucks you'll be cooking. Of course Picaxes handle supply voltages between 2&#189;-5&#189;V, meaning aging batteries can still cut the mustard.Unless you're driving motors, such a supply will last MONTHS-some of my 2003 packs are still up to the task in fact! Stan


Senior Member
Here's a supplier that I've dealt with for many years. No minimum order @ hobbyist prices.
BTW, for programming purposes, I don't see any benefits in using line power except for the fact that you can't beat the safety benefits of a 'Current Limiting supply when prototyping!




Senior Member
You should also be aware that many standard plug pack (or wall wart) type supplies are not that well regulated. They often supply significantly higher voltages than advertised when under little or no load - enough to over-voltage a PICAXE if using a 5V unit.

So I would concur with batteries, or, a cheap 7-9V plug pack and regulate with a MC or LM7805 Regulator for normal use and a LM2940 for automotive use - each with the relevant capacitors.

The regulators need a higher supply voltage than the output voltage to give them something to work with.

Have a fixed 9VDC 500ma supply here that delivers 11.35V while driving a PICAXE14M and 12 LEDS - the LM7805 delivers 5.05V rock solid.
Have another adjustable supply which delivers under no load;
<code><pre><font size=2 face='Courier'>set output
4.5v 5.15v
6v 6.71v
7.5v 8.35v
9v 10.37v </font></pre></code>


Edited by - BCJKiwi on 19/08/2007 01:38:31

Thanks for the catch sevs3, LM7508 corrected to LM7805

Edited by - BCJKiwi on 19/08/2007 04:52:09


*7805 BCJ :p

I have had many cicuits saved because of current limiting. Not a good idea to rely on it I know, but im learning.


Senior Member
BTW an inexpensive current limiter can be made with a LM317T and one resistor between regulator pin and output and then take output from the regulator pin [see LM317 data sheet]. You must have 1.2v to spare across the LM317T to have it work... and note that power dissipated in the 317 is I*V - may need heat sinking...


Senior Member
You should build or buy a bench top power supply with current limiting and a LCD display with volts and current draw read out . I built one as a kit from Altronics and it, along with a CRO, is the greatest thing since sliced bread.



Senior Member
What! You've not heard of &quot;Swan's Law&quot;, which states <b>&quot; You can never have too many power supplies&quot; </b> ? At last count I'm well into double digits,BUT still maintain 3xAAs are best for numerous Picaxe circuits. Naturally they falter under arc welder type loads,but maybe 90% of Picaxers are just tinkering with a few mA! Hence AAs win on portability, versatility,low cost,compactness &amp; of course dead smooth output. Stan


Senior Member
Another good option, if you happen to be a R/C hobbiest, is the rechargeable 4.8V RX packs. I happen to have several, and just keep a couple charged up and ready to go in my box. Of course, I wouldn't go to the expense of buying them for this alone (as you also have to have a proper charger, etc.), but if you already have dozens lying about and use/charge them regularly....

Likewise a BEC (Battery Elimination Circuit) for RC delivers 4.8, 5.0 or 6.0V depending on the model from larger voltage (7.2v, 9.6v, even 12v batteries). I have also used these.

However, there is much to be said for 3 AA alkalines. And, as indicated above, if you do not have a surplus of RC stuff, are the way to go.




Senior Member
Yes if ADC is used and an accurate voltage measurement is required the Vcc has to be stable and known!...

For 3.3v or 5v the LM317 can be adjusted wherever you want with a pot... for low dropout high [3amp] current the Micrel MIC29302 is a very good unit [some models with shutdown pin on 'em as well as 3 pin type]. The power supply is always fundamental and a good bench supply is a tech's best friend... Stan, who can't have too many thermometers or power supplies, must have a thermomter monitoring each PS :)


Senior Member
Some years ago, I buy one big box of wall warts &amp; plug packs from one &quot;garage sale&quot; for
only 20$ (41 adaptors), only 2 refuse to work, the rest (3.3~15v) still works.

Mostly part of them, are old Phone chargers for cellulars, anothers are home appliances
power packs ( razors, wireless devices, desk lamps, etc) no matter what, I always put
some linear regulator (78xx) to avoid complications, on PCB.

And buy another box of old rechargeable cell packs from cellPhones &amp; notebooks, dismantle
some and rescue several still useable cells (Ni-Cd or Ni-Mh).

Mouser is one of my hobbys, it's more like therapy (and no Shrink doc to pay)



Senior Member
Power $ factoid - at 11.4 cents per KWH
One watt 24/7 for a year costs $1.

Often old wall transformers dissipate more than a watt... doing nothing. Newer standards have been implemented on the switching type units. Anyhow the bottom line is unplug what you aren't using... [when you consider the millions of wall transformers in use one watt implies megawatts...]


Senior Member

I put in my workshop all individual switched wallsockets, so switch-off anything not
indispensable, one by one.
multisocket =&gt;<A href='' Target=_Blank>External Web Link</a>
singlesocket =&gt;=&gt;<A href='' Target=_Blank>External Web Link</a>



Even though Francis' question has been answered I'll just mention a couple of things just in case he has a quick look.

1. Sometimes you may need a 'dual' supply, for example 12V or 9V to power a peripheral and obv the 5V for PICAXE. Hence one example for 2 regulators.

2. For experimental work may I suggest saving up the pocket money and buying a proper Bench power supply which has current limit control. This WILL save you money when used correctly by preventing the Multiple Magic Smoke (MMS in the trade). For older hobbyists it may save grey hair, bald patches and the cost of incontinence pads.

Buy a TTI or other top brand which does NOT have Made in China written on it. I know Thurlby Thandar (TTI) is a funny sounding name but it is superb gear. I bought unbranded 'Made In PRC' PSU to compliment my second hand 15 year old TTI. It lasted 17 days. It went back and I bought a TTI off Ebay - parfait!


Senior Member
Better to have a decent bench supply to swear by than to have an overly-powered and inadequately filtered substitute to swear at ;-)

My bench supply is an ancient Heathkit (anyone remember *real* kits?) that has a single output with adjustable voltage (30 volts or so) and current limiting (up to 1.5 amps). When not running my latest PICAXE work-in-progress, it also serves as a substitute charger for a wide range of batteries.

For higher current needs, I have a couple of 6Volt SLA batteries from a UPS - no longer capable of running the UPS for an hour, but OK for short-term testing.



Senior Member
I use an even more ancient Heathkit 50v 1.5a current limited and so forth. The one gotcha is the large output capacitor pulse _before_ the current limiting takes effect :)


Searching I found this <A href='' Target=_Blank>External Web Link</a>

may help you



There are several ways to do this and NONE are safe for newbies.
For your safty and the safety of your PICAXE I strongly suggest that you don't use this kind of thing unless experienced.
Your Doctor and Insurance Company will hate you.

Anyone fiddling with mains-to-DC power supplies should really by ready-made items. Be aware that come wall PSUs made in you-know-where had illegal CE markings. This only came to light after some caught fire.
Put your tight-fistedness to one side when choosing. &quot;But I can get one for 2 cents...&quot; - pah!


Yeah...Dippy sounds right, but maybe you can tell me where I can BUY experience...
I probabily NEED 200 pints of that...

If one's don't DO experiments, NEVER will be &quot;experienced&quot; (Not Kamikaze stuff, but you STILL need DO somethings...)

Explanations helps a lot, so, read and learn, later do experiments in the best way... SAFETY (with caution)

Edited by - rookie on 22/08/2007 22:48:44


Senior Member
i wouldn't be building that ciruit,
by the time you purchase all the parts you may as well have bought a cheap wall wart

it's almost the kind of thing that'll get ya in to the darwin awards

Edited by - demonicpicaxeguy on 22/08/2007 23:27:10


New Member
Re Rookie &quot;Where do I buy experience?&quot;, I'd suggest start with simple things and work up, and stay curious. Eg finding picaxe and finding the Basic instruction code might need some guidance, but once you have found the instruction you are looking for, read through the others as well just to see what they do.

Get an electronics kit and build it, but then spend some time studying the circuit diagram to work out how it really works.

I wouldn't build that transformerless power supply though. Wallwart plugpacks are so cheap and are far safer.


Dracula, you say exactly what I want hear.
<i><b>...and work up, and stay curious. </b> </i>
I'm a curious kind of people, I want to learn, to do what I want do.
Only for the worst and common wish in the history of humankind
&quot;because I can, and want do&quot;

I'm only another stupid human over the face of the earth.

Certainly i'm not build that TPS if I can grab one wallpack cheap and &quot;ready-to-use&quot;
But I'm feel idiot only doing or building stuff that other people already do and
sale as &quot;electronic Kit&quot;... is limited thing... like &quot;monkey see, monkey do&quot; stuff.
I have tons of things used but working (mostly) to learn about, and hack to improve it
or recycle some parts to build some new stuff, this is my &quot;source kit&quot;, everybody i
know, and friends of them, give me things before drop to rubbish, or for repairs
than &quot;service can't do&quot; or to find &quot;unique solution&quot; to bring it &quot;back to life&quot; of work.
That is a real challenge, NOT legoland crap!.

I really admires some &quot;brains&quot; around here... like manuka, Dippy, Hippy, Premelec or
you often make best advices &amp; suggestions than Technical, and more fast.
I read every thread I see of this guys, only to learn (and wonder How they can think
that so fast) but I think that clarity of mind only come with years of dedication.
So I promise stay curious and Do things for the rest of my life.
But if someone can give me The cristall ball or the magic wand... that helps a lot.

Keep in touch pal's.


Senior Member
those small kits interestingly enough can actaully be quite useful and it's incredible the wealth of knowledge thats just in the paperwork that can come with them,

we used to have a kit series down here called the &quot;funway&quot; there were 3 levels to it and through each project it had in each book (there 20 odd per book) it would go into very intimate detail on how the circuit worked,
when i went to tafe(an aussie educational thing run by the government) one of the teachers there used to recommend that every night download a datasheet for any little electronic device you're interested in and read it top to bottom because they are even filled with hundreds of little hints and tricks you can apply to other circuits


Rookie, I admire your spirit and desire to experiment. The trick to a long life is to know what and what not to experiment with.
When it comes to working with mains voltages, the simple rule is that if you need to ask, you probably shouldn't be doing it.
But don't let that put you off. Build and try out similar circuits that work at low voltages. All the theories, equations and pain are the same but not life threatening when it goes wrong. Once you are 100% confident about the circuit and how it works, then redesign it for high voltage with 100% confidence that you have done everything correctly.

Edited by - beaniebots on 23/08/2007 08:09:13


Thanks BeanieBots.
<i><b>&quot;...The trick to a long life is to know what and what not to experiment with. &quot; </b> </i>
As I say before, Kamikaze stuff are out of my mind.
I see what the mains voltages do to the people (A very close view, front row)
Always double check the entire stuff, and make my own test-bench workshop.
Install one special switchboard with termic and differential switch, after that
one special made transformer 240v to 120+120v 10A to isolate the power source, after
that, one fuse box (automated microcontrolled multifuse device) Two analogic modules
one ammeter &amp; one voltmeter, and later individually switched wall sockets.
So then I can cut off any part or whole thing.
Allways work with Multimeter, fast fuses, rubber shoes, and someone looking at me
(just in case), that make my workshop looks like Frankenstein's lab.



Rookie, I'm all for experimenting.
The reason I made my comments is that some of the younger readers (and also some of the older tight-fists) may just think that 'any old' component can be used.

Projects such as the transformerless mains-5V can explode if the wrong components are used. And projects such as this can kill/injure/catch fire if done in a slap dash way. Stuffing some dusty components nicked from Grandad's 1956 radiogramme onto veroboard is asking for trouble.

Personally, I prefer the capacitor method for doing this but it's still potentially just as dangerous. And judging by some questions posted here it shows that some people are on the first rung of the knowledge ladder .

So where the knowledge ladder is concerned; walk before you rung (geddit?). Ha, not bad for 9 in the morning.

Get a Bench Power supply with variable V &amp; I. Even a Chinese made one is better than nothing.


Senior Member
&quot;where the knowledge ladder is concerned; walk before you rung&quot;

And my (adult) kids complain about the PUNishment I give them..