7v to 4.8v 08m

[davecarter]

Hi,
Its a simple question?
Can any one tell me how i am able to power a picaxe with alternative power supplies.
I want to ba able to use either or a 4 cell nicad at a nominal voltage of 4.8v or 5 cell at 6v.
I know that the 5 cell when fully charged can give 7v.

So its a question about regulation to bring the voltage to a safe level say 4.5v from an input ranging from 4.8 to 7v.

 

[manuka]

Good question. A normal 3 terminal 7805 of course would need several volts overhead. Exploit instead a working Si diode, which drops ~0.7V. Add as many in series with the supply as you need.

For larger drops, BUT AT MODEST CURRENTS (~20mA levels), maybe use a red LED. These drop ~1.8V when lit, & conveniently the passing current of course will be "visible".

The ever versatile LED can even be used as "poor mans zener" voltage reference.

 

[womai]

The professional version would be of course to use a suitable switching DC-DC converter to produce always the same output voltage (e.g. 5V) from a widely varying input voltage (e.g. 4.5 to 7V). Linear regulators like the 7805 can only reduce the voltage (and need sufficient overhead to produce a stable output), but depending on their design switching converters can have Vout<Vin, Vout>Vin, or even both.

Wolfgang

 

[Haku]

An expensive answer would be a DC-DC regulator such as the AnyVolt Micro, with it you could power the Picaxe & other components from 3 - 8 cells without fuss.

Bearing in mind that it has a lower efficiency at low current draw than a dirt cheap linear regulator, but powering a higher current draw it'll work more efficiently and without heating up like a linear regulator.

 

[Dippy]

Simple v-dropping is a bit clunky.
You need a regulator.
The 7805, as said, needs a bit of Volts headroom (i.e. a high 'dropout' voltage).
It's a very old design - in fact, quite a dinosaur really, but is cheap and cheerful.

DCDC (switched mode) can be very efficient unless , as said, the load is small. For small loads they can be really bad.
I've seen people, on this Forum, selecting DCDC devices without ANY consideration for this factor - indicating that reading past the Data Sheet headlines is jut far too difficult . And advice from Old Hacks is often ignored

A simple well-specced linear LDO regulator can be used for low current circuits.
That's why they exist.

If, for instance, your circuit is just the PICAXE and a few low power bits then something like the LM2936 5V regulator would be good.
It has a ~0.2V dropout at <50mA, so, in theory, will give 5V out for an input of 5.2 to Vmax.
For Vout behaviour below that then study the data sheet.
But a quick looksee shows it ain't bad.
Without more details of your Application the LM2936 would be my first choice.
The LP2950 would also be on my list for consideration.

You should note that around the lower voltages there is typically a slight rise in quiescent current - this is common to many, if not most, linear regulators.

 

[AndyGadget]

I've used this simple zener / transistor / resistor regulator a few times.

http://www.satcure-focus.com/tutor/page5.htm

You need a volt overhead for it to work so will work for 5 cell but not 4.

Andy.

 

[manuka]

Ok-I fired on the "simple", but certainly agree on the likes of offerings by Dippy,Haku & Womai. Keep in mind that most $ PICAXE applications may not justify professional $$($) PSUs of course. Many of us have ¢ budgets ...

Diverse IC approaches exist that can near suck every last electron out of just a few cells, although efficiency can suffer as a result. Hence SEPIC (Single Ended Primary Inductor Converter) convertors, such as those based on the Linear Technology LT1930 micropower switcher,can output 5V over an input range 3V-10V.

However the question arises as to why such a battery pack even would be needed, espeially since most of the PICAXE family happily run on as low as 3 V.

 

[Dippy]

Well I wouldn't really advocate a buck-boost design ("professional") in probably what will be a simple design - although no details have been forthcoming.

And anything with a significant V overhead isn't good. And if stability is required (e.g. for ADCing) then the simple Zener/tranny may not be good enough.

But, in a low power design, a simple well-specced linear LDO should suffice in most apps.
Even at farnell prices an LP2950 is 40p - is that cheap enough? Does it make cents?

But, hey, let's keep the thread going with different suggestions esp. as no specifc criteria have been provided.


Blimey, Stan has been Googling on DCDC

 

[davecarter]

The project is for RC model planes. My Friends either use 4 cell NMH of 5 cell NHM.

The PIC will be used for either sequenced switching of lights though, a Mosfet/relay or sequenced control of servos.
I am wanting to make sure that if a 5 cell NMH is used then it wont blow the PIC.

Thank you all so much for your input. I read with interest about the low drop out voltage regulators, and all the other suggestions.

 

[manuka]

Dippy: First round to you. I'm presently a "5 minute expert" on DC2DC,due most recently to work with a boost PSU intended for a 5V @ ~2-5mA circuit. You'll be pleased to know that a ZE002/ANA608 is strutting it's stuff nicely for this.

Your turn to Google. Stan.

 

[fernando_g]

I'm going to add my two yen on the subject.

Since the 08M runs quite happily on 3 volts, please google "3.3 volt LDO regulators" and you'll find dozens of options from the major semi vendors.

That way you have a single circuit that will work well with either 4 or 5 cells, and will continue to regulate even when the batteries are completely flat.

The LP2950 mentioned below is a good choice and is available in 3.3 volt versions, and can be had very cheaply (US$ 0.50) from the following site:

http://www.westfloridacomponents.com/T160/LP2950L-3.3+LP2950+3.3V+Voltage+Regulator+LDO.html

 

[Dippy]

Haha. I don't know what an ANA608 is.
An Ebay special?
Yes, I did Google. But gave up looking through crap links after 5 min

 

[boriz]

@Dippy.

With respect. Please stop digging people who, like me, use search engines / Wikipedia to fill-in or update their knowledge. It’s how the modern world works. Get used to it. (And it’s how I personally learned much of what I know about electronics, microcontrollers and various programming languages). And now the can is open, you have frequently made snide remarks about Ebay purchases and ‘Chinese specials’. How do you think that makes us poor impecunious types feel, who often don’t have the choice of something better branded that would meet with your approval?

 

[BeanieBots]

@Boriz,
The issue is that people buy 'cheapskate' after reading some poor advice given on an unprofessional web-page by someone who got it off another page without reading everything and then wonder why it doesn't work as expected. They then get all in tizz and EXPECT people on forums such as this one to save the day for them when extra few pence would have prevented all the issues. Only the EXPERINCED should make such purchases because they KNOW the consequences and also accept that it's always a gamble.

How often have we seen posts like "I've found this really cheap gizmo with no data available, will it work"?

As for the isssue in hand.
I've found that a well charged pack of 4 AA NiCd/NiMh works very well over nearly the full working range of the pack with a LDO 5v regulator. Even when flat, the extra loss of the LDO is insignificant.

 

[manuka]

Boriz: Having evolved from such stock myself,I sense Dippy's style is part of traditional British mocking humour that may take others aback. Google the likes of Blackadder for insights.

"Give in equal measure" is the answer- tease him about the UK weather/ale/economy/traffic/parking/accents addling the brain !

Stan.- in the balmy South Seas

 

[Dippy]

Oh Boriz, let it out... release that anger .... now breathe deeply and slowly,,, better now? .

Oh Stan, why delete. I liked it


When have I ever had a real dig about Google other than the truth?
I use it (and Alta-Vista) a lot and it's a fanatstic and frustrating tool that's a bit wonky.

Ebay, I tease 99%. But some things are a little serious.

Putting jokes to one side for a second, you opened the can, so let's give it a squeeeeze :-
I have seen on various Forums quite a number of occasions of people having problems only to find that the product has been of very poor quality.
With my other hat on I get flabbergasted having to give technical assistance only to find the the third-party 'product' is of poor quality, often (not always) because the product has been bought on the cheap.
Amazingly, when a 'proper' replacement device has been bought then the 'problem' goes away ... just like magic. That extra quid did the trick.

Ebay is synonymous with "cheap" and all the unfortunate connotations.

There is good and bad made all over the world... it's just funny that most issues I see are because of anonymous products usually bought on... [ ________ ] Fill in the blank.


Therfore, on these (albeit rare) occasions, someone has saved 50p and then others have to spend hours/days fixing it.


I realise that you meant it sarcarstically (touchee Boriz - and it made me laugh), but it's not a question of my "Approval" it's simply just having a think before purchasing ... pennypinching is not always sensible even if you are impecunious. To drive 50 miles to save 50p.
And if I was that broke I'd get a paper round
(That was a joke by the way. I'm not suggesting you should become a paper boy or get any other job).

 

[Haku]

I happen to really like eBay, been using it for over 10 years now and have gotten a lot of good things at low prices. The phrase "you get what you pay for" is pretty much an eBay mantra but when you're very patient and diligent enough you can get lucky, like the time I got a £350+ multimeter for £65.

 

[manuka]

Was this the same model Dippy willingly paid a £1000 for ?

 

[BCJKiwi]

There are many reputable companies selling quality goods on EBay.

Have purchased a number myself (not just in the electronics field). Can be a real money saver with no sacrifice to quality when sourcing items for New Zealand.

Biggest issue I have found is the dramatic variations of shipping charges - must be watched carefully!

 

[Haku]

Was this the same model Dippy willingly paid a £1000 for ?

Don't think so, I got a Metrix MTX3282 and my friend got an identical one for a few quid cheaper from the same seller a week later he then splashed out on the opto isolated serial data cable & a couple of power supplies because it can power/charge the 3x AA's it runs off.

 

[moxhamj]

Re fernando G "The LP2950 mentioned below is a good choice and is available in 3.3 volt versions, and can be had very cheaply (US$ 0.50) from the following site:

http://www.westfloridacomponents.com...lator+LDO.html"

Yes, even though I'm in Australia, I buy those regulators also from westfloridacomponents. Just watch the part number - the LP2950 is the part but then you have to specify 3V3 or 5V.

And, FWIW, I bought some 3V3 regulators off ebay once and they were actually 8V regulators. Grr. So to be sure, I now go back to westfloridacomponents. Having said that, I originally found westfloridacomponents on ebay. Oh, the irony!

Actually regulated 3V3 is quite a good way to run a picaxe, as you need less batteries than running on 5V, but also you get the huge advantage of all the analog I/O working accurately if you use a regulated supply. Just have to change the math for ADC.

So I'm going to second fernando's suggestion.

Addit: I note our original poster is using this for servos/RC so in that case, if there is no ADC involved, how about just 4 NiMH, unregulated?

 

[fernando_g]

This subject on regulators comes up so often that I believe that it should warrant a "sticky". I can volunteer to write one (as my time allows), but what would be the best way to upload it?

 

[lbenson]

fernando_g: A discourse on regulators would be very helpful. There may be no better place to put it than in "Finished User PICAXE Projects" under "User Projects - Miscellaneous". Make sure the subject has "Tutorial" and "Regulators" in it. A search on "tutorial" in the subject line brings up 32 hits. Some of them are not tutorials, but I'm not sure there is a better way to enable people to find what you write.

 

[Dippy]

Good idea.
I use the LP2950 and LM2936 derivatives a lot - that's why I tend to advocate them on low power stuff on this and other threads.

A few nice schematics and a brief discussion on capacitor selection would be a handy addition.

Go for it!

 

[hippy]

Go for it ...

This subject on regulators comes up so often that I believe that it should warrant a "sticky". I can volunteer to write one (as my time allows), but what would be the best way to upload it?

The most expedient solution is to write it as text document then simply copy and paste as a new thread under "User Projects - Miscellaneous". Alternatively include it or a PDF as an attachment, or put it on your own web site and provide a link to it.

Having the content is the most important thing so almost any format is acceptable and it doesn't have to be perfect. The more common the format the more people will be able to access it. Other people will almost certainly be prepared to put it into another format if required.

 

[MartinM57]

On another forum I use, they have a lot of donated tutorials and they use a convention in the thread titles:

"[TUT][SOFT]PWM - getting the most out of" - a tutorial about software PWM
"[TUT][HARD]Regulators - choosing and using " - well, no need to explain - you've sussed it already

Seem to work very well...

 

[D n T]

I missed the ebay part of the thread, bugger

With reference to another thread,
Back when I was a boy, we didn't have Ebay

I think the tutorial section would be a great help to some of us because;
some ov us aint very brite butt we can lift eavy fings an we need all da elp we can git.

Thanks people

 

[westaust55]

With reference to another thread,
Back when I was a boy, we didn't have Ebay

I think the tutorial section would be a great help to some of us because;
some ov us aint very brite butt we can lift eavy fings an we need all da elp we can git.

Thanks people

A tutorial section separate from the Finished Projects but with a similar sub-breakdown for topics would be good.

As a poissible starting point
Audio,
Video,
Sensors (Temps, Humidity, Pressure, Compass, Magnetics, Accelerometers, Current, etc)
Drivers/Controlled items (Darlingtons, H-Bridges, BJTs, FETs, etc),
Power Supplies & Heatsinks,
Memory/Clocks/Co-processors,
etc, etc
and that catch all - "Miscellaneous"

No one section would necessarily have many tutorials but it would be easier to find tutorials. Searches do not find them all and do pull up a lot of posts that are not tutorials

 

[BeanieBots]

Whilst I like the idea of a tutorial section, how would it be managed?
In the projects section, there are an assortment of examples of both good and bad code, hardware and general practices.
These can be taken at face value.

In a tutorial, the reader needs to have confidence that everything is OK.
Who is going to check that what is posted is valid, working and (subjectively) good practice? What if there is a difference of opinion.

Great in theory, but a nightmare in practice.

 

[Dippy]

You could do it in your coffee-break BB - I've heard they last several hours each

 

[Minifig666]

I agree, I got 400 mixed colour LEDs (form everones favrourite Chinese island) for about £4. Then again places like poundland sell stuff that hasn't even bee completed byvthe factory, I got a SCART switchbox and none of the video leads where soldered on to the board.

 

[BeanieBots]

I agree,

What with? That my coffee breaks are longer than an hour
Everyone knows I don't have time for coffee breaks
what with lunch being an all day affair

 

[westaust55]

Whilst I like the idea of a tutorial section, how would it be managed?
In the projects section, there are an assortment of examples of both good and bad code, hardware and general practices.
These can be taken at face value.

In a tutorial, the reader needs to have confidence that everything is OK.
Who is going to check that what is posted is valid, working and (subjectively) good practice? What if there is a difference of opinion.

Great in theory, but a nightmare in practice.

As mentioned by hippy in the Idestructables thread, http://www.picaxeforum.co.uk/showthread.php?t=14796

Do you think it would be a good idea for potential Instructable PICAXE projects to be posted here first for a 'peer review'?

Ideally would then first need publishing in general area by the originator as &#8220;not-reviewed&#8221; and then after peer review period (couple of weeks?) then the Originator could update and finally a Moderator to move to the Tutorial section (a modified WORM as Moderator Write + All Read.)

That way only tutorials and no further discussion/heckling/etc in that forum area. Any questions, raise then do it in the active forum area.


All the final tutorials as well as peer reviewed high quality projects could then be put on Indestructables and/or maybe somewhere with a list of these tutorials/projects linking back to the Rev Ed sites to bring more people into the Rev Ed domain.

I don't disagree that it would require some effort but if Rev Ed wishes to have the PICAXE noticed more then they may need to provide some labour as input as well.

While I am not about to jump ship just because of some statistics, Rev Ed and members here can help bring the PICAXE to the awareness of more folks searching the Internet.

Getting a little further away from the original topic

As at 12:30pm Perth time today on the internet and
this PICAXE forum versus the Arduino forum,

item/topic . . PICAXE vs Arduino
Google hits 110,000 vs 9,860,000
Members 51108 vs 21211
Members on line 9 vs 27
Guests on line 57 vs 109
Active members 780 vs ?????
Threads 14,416 vs 28,739
Posts 126,128 vs 186,917

On the PICAXE forum, a check indicates that around 21,000+ of the members have never made a single post.