I’m using an Uno, an MP3 card, a LOSC LQ-10w amp, and a 4ohm/3w speaker. I know not to power the amp from the Uno, but what kind of connection do I make to my power supply? I haven’t seen rails which look like what I need. I have a bag of connectors (see photo), is this what I should connect the supply to, and split it between the amp and the Uno? Power supply is 9v, 1A.
Or, alternatively, I have some LM386 boards. Can the Uno power those, using the same 4ohm/3w speaker? Thanks for your help!
Nope. Uno, or any kind of Arduino, is not a power supply.
You can power a small number of LEDs or sensor chips for example because they only require a few milli-Amps. Anything more significant needs an external power supply.
First, your amp, alone, will need more than 1 A. 10 watts at 9 volts is how many amps?
Do you have the matching wire and the matching crimper for the terminal you pictured? If you do not power the amp to the full 10W, then you can power it all from the supply. But it may get warm.
Thanks, forgot to mention (ahem) that I have a 24 LED ring plugged into the Uno as well. I’m guessing it should be powered off-board as well?
Undoubtedly. using a step-down to 5V.
Thank you for your quick reply, I do not have a crimper, was planning to just use pliers. Is there a different type of connector/splitter that would be more appropriate?
This LOSC amp is 5 volts , so I’d need to step down the voltage from the power supply for that device and the LED ring, correct?
The use of automotive type crimp terminals is up to you. It's all temporary, anyway.
If your 10 watt amp is 5 volts, tell me how many amps that will require at full volume! How many amps will your step-down device need to produce? How many amps will it need to produce those amps? Homework is necessary!
Thanks Paul, I’m working on a permanent, interactive sculpture, so I’m open to other, better connectors if you have recommendations.
Not sure about the homework, but I’ll take a look at some formulas and see if I can get those answers figured out. I’ve used external, powered speakers on other projects, but I want this one to have a single power supply and internal speakers. This is what it looks like.
My recommendation is to use terminals that fit your wire size. That is why crimp terminals have different colored plastic insulators on them.
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Pliers usually don't work very well. If your power supply has screw terminals you can directly connect the wires. Household light switches are normally wired by wrapping the wire around the screw (but it's solid ware which works a little better in this situation).
Or you can get un-insulated spade connectors (or cut-off the insulation) and solder. Then optionally use heat-shrink to replace the insulation. (Don't forget to slide the heat-shrink over the wire before soldering. 
) I have some "Molex" crimp contacts and since I don't have the right crimper and I have better luck soldering.
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Hi Doug, your advice given in this post looks like what I need for stepping down and powering each element (LEDs, amplifier, Uno):
Split 12 volts between Uno and buck. One buck since all downstream elements are at 5 volts, parallel, does that sound right?
The Uno is also 5V, so power that from the buck converter too. Connect the 5V output from the buck converter in parallel to the Uno (5V pin), the LEDs and the amp.
The amp will need 2A, the LEDs another 1.2A, the Uno will not need much by comparison. Allowing a sensible safety factor, you should be looking for a buck converter with around 4A output.
The 9V 1A PSU you mention will only provide enough current for the buck converter to output around 1.5A at 5V, and even then will be maxed out with no safety margin. So forget that PSU and get a 5V PSU with at least 4A output, then you won't need the buck converter.
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Beautiful! Thanks for the advice. It didn’t occur to me that the Vin Pin was 5v. That makes everything simple!
It isn't. The Vin pin connects to the input of the Uno's onboard regulator, which needs at least 6.5~7V input to give 5V output. So you can't run the Uno with only 5V connected to Vin.
The 5V pin bypasses the onboard regulator and powers the rest of the Uno directly, which is more efficient. But care must be taken not to connect anything over 5.5V to the 5V pin, or the Uno can be easily damaged, because it doesn't have the protection of its regulator.
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Thank you for clarifying that for me.
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