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I recently purchased a Female DC power adapter with screw block terminals (this is the exact product: http://adafruit.com/products/368).  I've been trying to use it with a breadboard and a 6 volt battery pack with four AA batteries to power a Standard Servo (https://www.adafruit.com/products/155).  I know the battery pack works; when I plug it into my arduino, it turns on, but when I plug it into the DC power adapter and wire that to my breadboard to power the servo, it doesn't work.  I know this sounds like a simple wiring problem, but I know for sure the wiring is correct, at least to my knowledge of electronics.  I tried rearranging wires on the breadboard several times and I hooked up my 5V and ground pins in the place of the DC Power Adapter wires and the circuit worked and my servo received power.  I've never used screw block terminals before, so I'm not sure if I'm using it right.  To my understanding you unscrew them slightly, push the end of the wire in until it reaches the back, and screw the screws back in tight enough to hold the wires, but not tight enough to cut them.  Does anyone know what the problem might be?  I'll attach some pictures of what I'm talking about...


Summary:
--------------------------
-6 volt battery IS WORKING
-I plug it into a Female DC power adapter
-I wire the adapter to a breadboard
-my servo does NOT recieve power

-I try the exact same thing, but with the 5V and GND pins on my arduino
-the servo DOES recieve power



What I've tried:
-------------------------
-different wire configurations
-checked to make sure the adapter's wires are plugged into the correct rails
-tried different wires with the adapter
-replaced all the batteries in the battery pack
-tried different servos
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Did you remove several millimetres of insulation from the wire ends before you fitted them into the screw connector block ??
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Did you remove several millimetres of insulation from the wire ends before you fitted them into the screw connector block ??

Yeah.  I tried using different lengths of exposed wire and tried using pre-cut jumper wires that came with my arduino starter kit.
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Are you sure of the polarity of the 2 wires???

Doc
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Have you checked with a meter to see if there's any voltage on the screws? (Edit... which in accord with what Doc just said, would allow you to verify the polarity)

(More edit... very handy gadget that, I need a couple of those!)
« Last Edit: July 08, 2012, 11:20:23 pm by JimboZA » Logged

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Are you sure you have the right socket type for the plug you are using?

The barrel jacks come in different sizes with different sized pins in the center.  If the pin is too small for the hole in the plug you are using then you won't get any power as the pin won't be making contact.
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Have you checked with a meter to see if there's any voltage on the screws? (Edit... which in accord with what Doc just said, would allow you to verify the polarity)

(More edit... very handy gadget that, I need a couple of those!)

The adapter has the polarity of the screws written on it, but I'll go ahead and check it.
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Are you sure you have the right socket type for the plug you are using?

The barrel jacks come in different sizes with different sized pins in the center.  If the pin is too small for the hole in the plug you are using then you won't get any power as the pin won't be making contact.

I'm new to electronics and I'm not exactly sure what you're talking about.  What's a barrel jack?  I think everything is the correct size; the battery pack plugs right into the adapter without any trouble and I'm using standard sized wires which fit into the screw block terminal just fine.  Can you explain what you mean?
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Oh, and I just thought of something.  This probably sounds like a stupid question, but does it matter if I push the wires all the way to the back of the screw block?  Is there plastic or something back there that grounds the wires if they go in to far.  I don't really see why that would happen, but I'm trying to think of everything.  Like I said, I'm a gigantic newbie.
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"Barrel Jack" is the proper name for the kind of connector you are using.  The socket (your adapter) has a pin in the center of it, which fits inside the hole in the end of the plug (on the end of your wall-wart).

That pin is one of the two power connections - usually the positive (known as "Positive Center") and must fit snugly.  There are usually 2 sizes of plug/socket that are the same width, but with a different width of pin in the center.

If the pin isn't fitting snugly then you won't get one of your two power connections.

However, if the power supply works OK in a normal Arduino power socket, then it should work fine in the adapter as I would expect it to be using the same type of socket.
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Oh, and I just thought of something.  This probably sounds like a stupid question, but does it matter if I push the wires all the way to the back of the screw block?  Is there plastic or something back there that grounds the wires if they go in to far.  I don't really see why that would happen, but I'm trying to think of everything.  Like I said, I'm a gigantic newbie.

As long as the metal of the wires is being trapped by the screws of the terminal blocks then it should be fine.
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Okay, well the barrel-jack pin is definitely the right size.  It's exactly the same size as the Arduino's and the connection is snug. 

Is there a specific way of connecting batteries to breadboards?  I can't remember successfully wiring up a battery, I've always just used the Arduino 5 volt pin.  Whenever I've tried - including this time with the adapter - I've connected the positive battery wire to the positive rail and the negative battery wire to the negative rail and wired everything else up accordingly.  I'm not using resistors or anything else other than that one servo and normal wires.  I'm pretty sure the battery pack I'm using supplies 6 volts (it has four AA batteries).  The documentation for the servo says it can handle up to 6 volts, but works best at 5 volts.  Do I need some sort of electronic part in my circuit to run the servo off the battery and am wiring everything up right? 

Also, since I can't seem to get this stupid battery to work, is there another part that I can use to power 5 or 6 servos via my Arduino's 5V pin?  I think I read somewhere about something like that.
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Do you have a DMM? if not a 1K resistor and an LED and some hookup wire? connect the resistor to the + end of a 9V battery (its the female or the bigger of the two connectors. The LED has one wire longer than the other, that lead is usually always the + Led connection. Connect it to the open end of the 1K resistor. Now take 2 20 cm lengthe of wire and strip 10 mm off of each end (4 ends/2 wires) connect one wire to the open (- or the side of the LED with the little "Flat") end and the other wire to the - end of the battery (the male or bigger of the two terminals) when you touch the two open ends of the 2 wires together the LED should light... If it is good and the resistor is... at any rate put one wire in the hole in the end of the "Barrel {Co-axial}" connector and the other wire to the screw marked +, the light should light. Repeat with the "shell" or outer connector and the other wire to the - screw of the "Barrel {Co-axial}" connector, the light should light. Next and last connect the 2 wires to the screws + and - and see that the light doesn't light. If the connector failed any of the test's it is bad...

Doc
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Do you have a DMM? if not a 1K resistor and an LED and some hookup wire? connect the resistor to the + end of a 9V battery (its the female or the bigger of the two connectors. The LED has one wire longer than the other, that lead is usually always the + Led connection. Connect it to the open end of the 1K resistor. Now take 2 20 cm lengthe of wire and strip 10 mm off of each end (4 ends/2 wires) connect one wire to the open (- or the side of the LED with the little "Flat") end and the other wire to the - end of the battery (the male or bigger of the two terminals) when you touch the two open ends of the 2 wires together the LED should light... If it is good and the resistor is... at any rate put one wire in the hole in the end of the "Barrel {Co-axial}" connector and the other wire to the screw marked +, the light should light. Repeat with the "shell" or outer connector and the other wire to the - screw of the "Barrel {Co-axial}" connector, the light should light. Next and last connect the 2 wires to the screws + and - and see that the light doesn't light. If the connector failed any of the test's it is bad...

Doc

That was really helpful!  I did your tests and it turns out the positive screw block works, but the negative one does not for some reason (when the positive wire is connected to the adapter and the negative wire is connected directly to the battery, it works.  When the positive wire is connected directly to the battery and the negative is connected to the adapter, it does not).  My adapter must be defective.  I'll have to use a different battery than I was planning to use, but I can work without an adapter.  I might buy another one, they are pretty cheap.  Thanks agian.
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For future reference, here's how to make a permanent one of those testers, with instructions for testing a range of components.

I'm sure adafruit will be interested to know that the gizmo they sold you was doa and will have a word with their supplier...
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