Nubie question

Question

Hi, I'm just starting out on electronics, spurred on by getting a Raspberry Pi. I'm accumulating some equipment and a crazy assortment of components.

So...

I've gotten a off-brand Multi-Meter. One thing I've noticed is that when measuring Amps, the value continually drops as I hold the probes against the power supply. Is this normal or is there something wrong with the meter? If it's normal, do I take the measurement from the moment I touch the probes?

Second, the collection of resisters, caps, trnasisters, ICs etc. will soon overwhelm my ability to identify these minescule pieces. How do you seasoned vets manage this stuff??

Thanks

michaelkellett · Accepted Answer

Are you connecting the meter directly across the power supply terminals and reading the current ?

If so this will be measuring the short cicruit current out of the supply which will likely be changing as the internals cook.

Connect the meter in series with a resistor to the power supply and the current should be equal to V/R. (It won't be exact because the meter has a finite shunt resistance when measuring current whic drops some voltage.)

MK

johnbeetem · Answer

Lou Gallo wrote:

Hi, I'm just starting out on electronics, spurred on by getting a Raspberry Pi. I'm accumulating some equipment and a crazy assortment of components.

Second, the collection of resisters, caps, trnasisters, ICs etc. will soon overwhelm my ability to identify these minescule pieces. How do you seasoned vets manage this stuff??

On a circuit board like RasPi, you try to get a schematic diagram. RasPi's diagrams are at RasPi Hardware Wiki along with high-quality photos of the bare boards so you can easily find the names of components. With purchased components such as SMT (surface mount technology) capacitors, resistors, etc. keep them in their bags until used. If you have an unknown board with a unknown components, you basically have to use your experience to guess at what things are. Sometimes small transistors and ICs have cryptic codes on them which you look up at the manufacturer's web site to see which component it is. However, figuring out which manufacturer can be problematic, particularly if they're cheap Chinese equivalents instead of well-known manufacturers like OnSemi and Fairchild.

We sometimes get questions here at element14 from someone who posts a high-quality photo of a component and asks for help identifying it. They usually get lots of replies because most engineers love to solve puzzles.