What's the best wall wart to use with a Picaxe?

Jeff Haas

Senior Member
I have a project that I want to set up in a situation where it will run all day, for at least two days in a row. It's got a Picaxe 08M and one of the Tenda MP3 boards, powered from the Picaxe. I don't think that AA batteries will make it all the way through, and I don't want to get a frantic phone call telling me that the project is down and that I need to get back and change the batteries!

So I'm looking at regulated power supplies. Jameco (near me) has several that look good, such as this one:
https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&pa=1940660&productId=1940660

But a quick look at Manual 1 tells me that I should use a 9V supply and build a small circuit to regulate it down (see page 26). Why is this? Shouldn't I just get the 5V supply and be done with it?
 

JimPerry

Senior Member
5V would be the way to go if it is well regulated - the manual recommends regulating a cheap 9V down to 5V as a lot of low-cost supplies can give 6V or even 7V out with low loads. :confused:
 

geoff07

Senior Member
You might try a spare SMPS phone charger of the right voltage. Make sure there is decent decoupling across the supply near the Picaxe (0.1uF in parallel with an electrolytic of say 100uF).
 

westaust55

Moderator
Ensure that the scull wart/plug pack power supply that you buy clearly states "regulated" if you want a 5 V supply without further regulators on board the project.
My experience has been that switch mode power supplies (SMPS) are well regulated.
Several different makes and models of both 5 volt and 9 volt (9V for some motors) have outputs that are within 0.05 volts from no/very light load through to high load levels.

Many/most unregulated supplies can be several volts high (being polite here) when lightly loaded and due to droop/regulation through internal impedance reduced to the stated output voltage at near full load.
 

neiltechspec

Senior Member
Try & buy a better quality one.

Ex-mobile phone chargers are usually 5v - Nokia, Sony Ericsson, Apple etc... (originals, not clones) and are ideal for PIC projects up to 1amp.

Avoid the really cheap imports from 'you know where' that are quite likely to catch fire !!.

Neil.
 

Goeytex

Senior Member
Head down to your local Goodwill or Salvation Army Store and sort through the bins of cell phone chargers and wall warts. Look for the small ones that are marked "DC Out : 5.0V". In my area these cost from 50c to $1.00 each, so I usually get 5 or so. Then take them back to the lab where I test them for voltage and ripple.
 

geoff07

Senior Member
It is probably worth mentioning that if a phone charger is heavy, then it isn't a switch-mode supply, as the weight comes from the 50/60Hz transformer. An SMPS will be very light weight as the transformer is small and operates at high frequency. SMPSs are intrinsically regulated (up to a point at least), because they have a feedback loop via an optocoupler. They are isolated by the transformer winding and the opto-coupler from the line voltage.
 

Jeff Haas

Senior Member
Thanks for all the replies. I have some spare cell phone chargers lying around but the reason I'm considering the one I linked to is that the data sheet is available. I don't have the equipment to test them like Goeytex does to verify that they're OK.
 

geoff07

Senior Member
You must have a voltmeter, if not then you should get one as without one Picaxing will be terribly frustrating. The meter will tell you if it is 5v or not, and how regulated it is (draw say 200mA and see how much the volts change). Then give it a go. A couple in my box were rated at 550mA and 700mA at 5v, they are all well marked. That is about all the data you need!
 

Goeytex

Senior Member
A "full kit" is nice, but not really necessary. Just use a DVM. Measure the DC volts with no load and then again with a 50-100 Ohm load. The readings should be close. Then switch the DVM to AC Volts to measure the ripple (with and without the load. )

Even a cheapo DVM will show if a supply is a POC or not.
 

John West

Senior Member
I'd just use "C" cells instead of the "AA" cells. They should have much more capacity than the "AA" cells. Then you don't need to worry about all of these other things.
 
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