Adjustable breadboard power supply

posted Nov 8th 2008 9:18pm by Eliot
filed under: classic hacks, misc hacks, tool hacks

psboard

This looks like a great addition to your breadboard. [Nerdz] wanted a power supply that was easily portable and adjustable. He built a custom board that plugs directly into the breadboard’s power rails. It has a pot attached to the ground of a 7805 voltage regulator so the output can be adjusted from 5V to just under the supply voltage. Anything that makes a breadboard less of a rats nest is definitely a good thing.

Comments [14]

tagged: 7805, adjustable voltage regulator, breadboard, power supply, ps, voltage regulator

14 Responses to Adjustable breadboard power supply

Sam says:

November 8, 2008 at 9:46 pm

Very nice. The LM7805 will ensure the 5V no matter what DC supply is used (granted it is 5v or above since this is not a switching voltage regulator) but I would use a switching regulator to have something better and more efficient at hand.

And what is the purpose of the capacitors in this case there? Are they needed really?

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dirk says:

November 8, 2008 at 10:43 pm

@sam

It’s never a bad idea to include capacitors in your power supply, as insurance against any sudden increase in power consumption. Don’t want your whole circuit resetting every time those LEDs light up (or something like that)

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Mike Collins says:

November 8, 2008 at 11:32 pm

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hex4def6 says:

November 9, 2008 at 12:54 am

Not completely convinced as to this circuit’s usefulness. 5v / 12v are really common voltages from wall warts. the problem is that if you want either of these voltages, you’re going to use a 9v / ?v wall wart (not even sure what a common wall wart voltage is above 12 — 15v? 24v?)

Me, I’d strip the leads off a 5v cell phone / USB charger, and if you want to get fancy, make some of current limiting circuit instead of this to help avoid letting out the magic smoke. much more useful.

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ledtester says:

November 9, 2008 at 1:01 am

I’ve found that modules like this which plug directly in the breadboard are less than ideal. The power cable puts a lot of stress on the board which requires you to secure it to another platform. Moreover, any movement of the cord helps the module to work itself out of the breadboard. In short, there is no strain relief.

I’ve found a better solution is to connect the module to the breadboard with flexible wires. I’m fond of the gauge wire that you find in old Centronics printer cables (26 ga.?) For a little extra strain relief just tape the wires down to your table or whatever support platform you are using for your project.

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tony says:

November 9, 2008 at 2:39 am

lm317?

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tony says:

November 9, 2008 at 6:19 am

lm317 is a much better choice. 1.2 – 37 gives you a lot more flexibility.

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Hazard says:

November 9, 2008 at 7:05 am

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bearsinthesea says:

November 9, 2008 at 8:12 am

sparkfun has one too, but it can switch from 5v to 3.3v

http://www.sparkfun.com/commerce/product_info.php?products_id=114

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Nerdz says:

November 9, 2008 at 9:40 am

Wow, thanks for the replies!

Theres a reason for me Not choosing the LM317T. Most likely, I will need 5V for Logic Circuits (such as PICs ) and didnt want to use a volt meter Just to set the voltage. When the pot is turned all the way down, I get 5V out, and when its turned all the way Up I get Almost Full Voltage Out.

The thing about wall warts is that They dont put out their rated voltage Unless Under the specified Load. For example, I have a 12V 500mA Wall wart that Puts out 18V DC Under No Load.

Granted, I could have Used a SMPS controller, but I used what I had on hand. Granted, At best I’ll get 50% of the power delivered to the load, But What application using 5V uses that much current?

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cde says:

November 10, 2008 at 11:33 am

This is similar to the Breadboard power supply ( http://www.uchobby.com/index.php/2008/04/29/sbbpwr2-revised-design-for-breadboard-power-supply-module/ ) that Dave at uCHobby ( http://www.uchobby.com ) created (Actually, he created two revisions of it).

He actually uses the LM317 but with two/three fixed resistors, which can be jumped, to choose between 3.3v and 5v operation, instead of using a pot you need to calibrate and check.

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carlton says:

November 14, 2008 at 9:12 am

nice use of floating ground.

as to questions about caps, you need them for two reasons: 1) dc stability and 2) transient performance. Without an output cap (typically in a certain range), a regulator will not be stable (as a rule of thumb) and will oscillate like crazy, or even not regulate at all, following input or being messed up another way.

as for transient response, the input and output caps hold the output voltage in case of a input voltage change and output load change, respectively.

as to “what application at 5v requires a lot of current”, well, probably nothing you’ll do on a breadboard! pre-regulators for lower voltage supplies powering dsp’s and such could require many amps, depending on application. another possibility is in higher temp applications, where you can’t deal with watts of dissipation in a linear, of course.

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Steve says:

April 14, 2009 at 4:20 pm

hi guys,
hope this isn’t hijacking a thread or anything!

total newbie question if i may:

are 5v and 3.3v the standard voltages for most breadboard projects? i am looking at getting one of those 500-in-one kits and don’t want to use batteries.

i intend to build mostly analog music stuff (oscillators, filters, etc)

just wondering if i need one that is switchable / linear / 5v / 3v / what milliamps, etc to get started…

Thanks so much for any help!

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MichaellaS says:

July 20, 2009 at 8:05 am

tks for the effort you put in here I appreciate it!

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