Hi. A rookie question. I bought an MB102
breadboard to power my Arduino. But what is the polarity of the DC in plug? Looking at the card I deduced that the positive is on the outside and the negative is the central contact, is that so?
Thanks
breadboard to power my Arduino. But what is the polarity of the DC in plug? Looking at the card I deduced that the positive is on the outside and the negative is the central contact, is that so?
Thanks
If you don't have a multimeter then now would be a good time to buy one. Something cheap and cheerful would be plenty good enough for working the the Arduino
It would be fairly unusual, but not impossible, for barrel jack to be centre negative but you need to be sure even though the circuit is likely to be protected against reverse polarity input.
What electronic components do you have to hand ? An LED and a 3V coin cell would be handy to carry out a polarity check
Standard easy way is to "ohm" between ground and each plug contact. You can assume that ground is negative in this circuit.
Hi. Thanks to you. I followed your advice. I bought a multimeter. The polarity is positive internal and negative external. Thank you
You won't regret your purchase
The reason that I asked about any components that you had was that with a 3V coin cell and an LED it is easy to construct a continuity tester
Perhaps you did.
This is a MB102 breadboard:
What you have is a power interface module for this sort of "MB102" breadboard (including the shorter version).
Frankly, it is not very useful at all as it suffers the same limitation as the regulator on the UNO (or Mega 2560, Nano ...) board that the 5 V regulator has no heatsink. If powered at 9 V, you may be able to draw a couple of hundred milliamps from the 5 V terminals (and you must include whatever you draw from the 3.3 V terminals) but if you power it from 12 V, then just drawing 100 mA will dissipate 0.7 W in the regulator and it will shut down.
The only really practical way to use it if you require any more current is to use a USB male-to-male adapter lead to plug it into a USB "phone charger" rated at 1 A or so.
That is the almost universal standard, except for some "rogue" devices. For example you will find these adapters presume that convention:
And that is what virtually all available power adapters use.
Within 7 hours? That was fast. 
But it is a simply essential piece of equipment for working with electronics.
Hi.
I live in a big city, there are many Chinese shops that sell cheap things. I got one and spent about 10 euros. I think that's enough for a start. I was able to do some tests. I have a 12V 1A power supply. I plugged it in and I verified that the board provides accurate 3.3V, but instead of 5V it gives about 7V. In your experience, could it be damaged?
Thank you
See here MB102
That certainly sounds wrong. I cannot give any simple explanation for it.
That is the component visible in the picture immediately below the push-push switch. 
What happens when you connect a USB power supply to the USB jack that is provided?
Sure, such damage is possible. But it's extremely unlikely. Have you made a close visual inspection of the board?
Need a particular cable for that - Male to Male USB "A" as I mentioned in #6.
But that really is the proper way to use that rather annoying module.
I am just going to check it out with my buzz box so that I am totally confident of the wiring.
I think the push-push switch (DPDT) actually switches both the incoming supply from the "Barrel Jack" (via the diode) and the 5 V coming out of the regulator. But the black solder mask and a smattering of dust are making it difficult to trace! 
OK, the PCB pattern is a trifle strange as it has two separate traces on the underneath running closely parallel and actually connected together on the top side!
One side of the push-push switch switches the incoming supply from the "Barrel Jack" to the diode which then goes to the input of the regulator. Note that input is bypassed only by the tiny SMD "chip" capacitor. The large electrolytic is on the 5 V regulator output which also supplies the green LED.
The other side of the push-push switch switches the 5 V pin of the USB "A" female to the same 5 V line. This clearly implies that socket actually is intended as a 5 V input, not an output in case you might think it was.
Why use a socket/ female for that? Clearly because PCB angle mount USB "A" male connectors are not so practical as the way this module is designed makes it quite impractical to plug it directly into a power supply, you always need to use a cable.
There are so many better choices of USB connector they could have used there - the same ones that are on almost every kind of Arduino. It is a mystery.
I suspect it is not a mystery; the module has been around for a very long time. It's just some shoddy design, (one of three or four similar in fact) that presumably one of the "hobby" suppliers made and now in the Chinese Clone process. Remember, the Duemilanove had the USB-B connector which is obviously more appropriate, but clearly too bulky.
"Shoddy"? The PCB lands for the regulators are only about as big as the tab itself - essentially no heatsink at all. 
Agree 100%. Especially considering the problem that it purports to solve - convenient, reliable power for a protoboard. I was tempted, now extremely happy I didn't spring for one.
Perhaps it reflects my naivety that shoddiness is a mystery to me. 
So I always assume there must be a good reason when it's actually just ignorance.
I am afraid it is not ignorance but fraud/deceit.
They know they cannot make a proper thing for that money. And they still do. Hoping starting hobbyist think it will be very handy.
The songle relays are even worse. They are simply dangerous to the hobbyist, everyone in his house and the neighbours too. Criminal would be a good description...
I have seven of them in a (emptied, washed) Hommus tub (1 kg) on the desk in front of me behind the monitors.
Actually there are a lot of other things in that tub as well, and in the other three or four tubs plus bottles, pill containers, envelopes (you know the ones - from China) and ziploc bags.
Why did I get seven?
Well, they were cheap, and (more to the point) people keep talking about them, so if nothing else I like to be able to provide details. 
It is not deceit when the purchaser looks only for the rock bottom lowest price and nothing else. In that case, they are giving the buyer what they ask for.
They are advertised as 'handy' which according to some here is a lie.
Looking at the price, they are actually pretty good value for the money. Cheaper than the so disguised 9V block battery...
IANAL, but "handy" is a pretty broad claim.
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