If I'm going to learn anything, I have to start tinkering..... so I've decided to set up a low voltage DC breadboard on my work bench so I can build and test my future projects safely.

I have to 'crawl before I can walk' with electronics so I am not looking to build a power supply, but put one together out of cheap and readily available components (because of the good possibilty I'll melt something ). I was thinking of one of those cheap breadboard power supplies that I could plug into the USB of an old computer, which would give me 5/3.3VDC power supplies at my breadboard.

If I use a rotary resistor on the 3.3V supply with jumper leads to another breadboard, I would also have an adjustable <3.3V power supply available on the 2nd breadboard. Correct ?

If I am right in my assumptions, which rotary resistor would I use ? (I'm guessing linear, but what size ? ) I would not want a voltage of less than 0.25V

Also, is a multimeter okay for measuring the adjustable voltage supply on my 2nd breadboard (0.25 - 3.3VDC) ?

Thanks for any input

 

For breadboarding, get a wall adapter that puts out about 9VDC, 600mA
Then get a 7805 linear voltage regulator to give you 5VDC.
Add also a 3.3V linear voltage regulator to give 3.3VDC.

Good enough for starters. You can build a more power handling supply later.

 

Unfortunately MrChips, my first project requires the 0.25 - 3.3Vdc adjustable supply, so that is a must for my first breadboard setup.

I already have the old computer laying around, and the breadboard power supplies are dirt cheap (even cheaper if I buy the BB/wires/power supply as a package)

 

...is a multimeter okay for measuring the adjustable voltage supply on my 2nd breadboard (0.25 - 3.3VDC) ?

Yup, it'll be fine. Many have a 0-2V scale with two decimals and a 0-20V scale with one (as well as millivolt scales). So unfortunately you'll have to use the 20V scale for measuring at 3.3V, not 3.30V.

 

My non digital multimeter has a 2.5 & 10VDC scale, and my digital has a 20VDC scale with 2 decimal points.... so I'm hoping to get an accurate reading between the two

 

A bench power supply can be built with a simple LM317. With one IC (3 pin TO220) you can put in a breadboard with 2 capacitors, 1 resistor and variable resistor (potentiometer) to for min 1.25V to Vin max -1.25v (check datasheet for maximum i think 30-40V). Optionally you could then add a second LM317 configured as a current limiter and have the power facilities from a proper bench unit (less gauges).
Also you can cheaply get a DC needle volt meter off ebay for a few bucks which could be easily integrated.
Al

 

If you don't really need to go down to 0.25 volt, you could just buy an adjustable supply based on the LM2596 off eBay, for about $2-3.

 

I found something on ebay that I might be able to use as my adjustable breadboard supply

http://www.ebay.com/itm/15V-5V-2A-1...ltDomain_2&hash=item1c47f970bb#ht_2162wt_1105

It has a 5V switch, so I assume I would be able to adjust down to the 0.25V I want.

What do people think ?

 

My preference is to have a supply with a current limiter as when first testing circuits I like to dial down the current limiter so any short circuits do not fry the board. Also with an adjustable current limiter you can charge single cell lithium ion batteries.
The knob say 0 - 15V but there is no fine adjustment knob so it is possible that actually hitting 0.25 maybe tricky.
Al