Breadboard Real Estate and Power Supplies

I am building a smallish project on a mini Breadboard (14 rows, 140 tie points...). I want to be able to power it from a Wall wart, and I will be using some micros (Attiny85) in it, so I need a steady 5V. I'll be using this switch-mode 9V wall wart. Since it is switch-mode regulated, do I need all the fuses and filtering caps on my regulator?

Or, in an effort to conserve space on the breadboard, can I get away with [u]just[/u] the regulator?

Thanks!

You can dispense with the fuse but all the filtering is needed for the regulator chip to work correctly.

Hmm... Any ideas on how to conserve space?

My project:

adapted from http://tronixstuff.wordpress.com/2010/08/02/blinky-the-one-eyed%C2%A0clock/

DS1307 sends time to ATtiny85, which blinks RGB LED accordingly.

Here's everything I'll need to fit on the breadboard:

2 8-pin DIP ICs (RTC + ATtiny) 1 RGB LED, common cathode 1 resistor DC barrel jack LM7805 Regulator + components 6 pin female header CR2032 holder (RTC backup) Jumper wires Power switch

And I don't think I can get rid of anything...

My advice is simply not to use solder less bread board. Use perf board or strip board instead. Use sockets for all the ICs and solder things in place. It will compress greatly.

If you want small, go surfacemount. with the right layout, you should be able to design a board for this that's less than 2" x 2". If you can use a vertical battery mount, you might be able to squeeze it into 1" x 2". and that would be with all components except the ATTiny85

Nah... I'm not to good at SMD. I have enough room to use PTH. Thanks, though.

I suspect you don't need such a large 100uF on the regulator input side, just a 1uF ought to be enough - what do the datasheets say for your particular regulator?

Voltage regulators as standard have over current and over temperature detection and shutdown...

Yep. see attachment. But I don’t have .33u caps. I only have mults. of 10 (1 u, .1 u, 10n, 1n, etc.) What should I use?

Thanks!

Screen shot 2011-02-25 at 4.25.43 PM.jpg

But I don't have .33u caps.

Then use at least the next biggest. You can always add extra large ones as well as small ones. The small ones take care of the high frequency stuff and the large ones cover the low frequency stuff.

Hmm... Any ideas on how to conserve space?

The easiest way would be to substitute a regulated 5v wall wart (http://www.sparkfun.com/products/8269) for your 9v one.

Don

Yes... but most people don't have 5V wall warts. 9V is much more standard and would therefore make the device more versatile.

Now you are changing the parameters. I got the impression that you were going to purchase a specific wall wart for your project so I suggested a different specific wall wart that would suit your situation more closely.

Don

No. I already have the 9V wall wart for this project. I just learned how to use a voltage regulator, so I want to use that as a learning experience.

perfboard. You may even have space to stack two layers in your small box.

Yep. I'm going to buy two 1" perf boards and stack them. One for power regulation, the other for the actual circuit. Then I can screw them into the enclosure.

Thanks everyone!

baum

How did this project work out? Did you finish it? I am trying to make a watch too that uses an ATTiny85 and an RTC, but I am having a hrd time.

baum: Or, in an effort to conserve space on the breadboard, can I get away with [u]just[/u] the regulator?

Strictly speaking, the 9V adapter probably has an output capacitor of at least 100 uF. If you assume that that's good enough (which is "okay" but not "super robust") then all you REALLY need is the regulator and C2. You really do need C2. However, because C2 goes between Vout and GND, it doesn't use any more rails on your breadboard -- you can plug it in the same rails as the regulator already is mounted in.