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How important is a power connector?!


I had a hot debate today on the importance of the power connector on an electronics board, like Panda for example. Someone said, USB is very common now and even becoming a standard for phone chargers so why use power connector, just use USB for power (from PC or from phone charger). There is also a VIN pin if someone wanted to use external power.

So, on your FEZ Panda (or domino, arduino…etc.), do you use the power connector? Do you see it as an “unneeded option”, a “nice option” or a “mandatory option”?


It’s nice to have options when prototyping or just messing around. Over the years I’ve collected dozens of wall warts that work long after whatever they were originally for died. Many of these are not 5V, but are usable on FEZ (and other) boards. It is a “nice option” to be able to use these as an alternative to a USB power source. I agree that the mini USB connectors are almost as ubiquitous these days, but they just don’t stand up to abuse like a barrel jack. I’ve known several folks who had to get a new cell phone just because they were not careful and busted the USB charging jack. My personal painful example of this problem: my 6 year old attempted to plug in a wired xbox 360 controller “cause he saw dad do it”, bent the contacts, and shorted out the console! The red ring of death had me freaked, but I was luckily able to correct the short and revive my Xbox. Try shorting a barrel jack! It is much harder.

The connector does occasionally bump up against a shield so it doesn’t sit quite parallel with the FEZ. This may or may not be a problem depending on what the shield has for parts in that corner. I could see getting rid of it if you needed very narrow clearance in some enclosure. This would also assumes removing the pin headers for the same reason.

[edit] As others have mentioned, having enough current is important. 5V/500mA just ain’t enough sometimes. I’ve used some sturdy 2pin JST connectors on other boards that were rated for plenty of juice. My vote - design the board to have a couple of options, and leave the soldering up to the customer.


It is a “nice option”. When I use a bus powered hub with the Cobra (LCD) mounted, I do need the power connector.

So when the USB power is not enough or the application draws more current than the USB spec. a standard power connector is needed.


I use the power connector/Vin on the header extensively on my boards. I have a 7V SMPS that has a JST male output connector which connects to an M size barrel to the target board.

I also have a 5V SMPS that I connect directly to the 5V header on my boards.

USB is usually not always an option because I don’t really like having to swap connectors.


Usb power is not done in my case. I included a switching power supply IC (LT1176-5) in a lower PCB so the input can range from 8v to 35v without smoke. Much better when the electronics goes in a electrical cabinet.

But, to answer Gus question: I do not use the power connector. But I would for other projects where you want the board sdcard and display powered. Which seemed often a problem when only powered from usb. So I would not remove the connector but it could be replaced with screw terminals and better input range (switching supply)


If cost is that much of an issue…

I would recommend supplying the footprint for a barrel connector, as well as having a Vin and GND pad for soldering a custom cable/connector to.

As another note, I’d love to see SMPS being used on dev boards like the FEZ.


I second Chris’ SMPS thoughts…

Personally I think you want an easy connection for when you need more current than the USB can (reliably) source. If you have anything that is in any way power hungry attached, you should use that connection. The barrel jack is a reliable and safe way to provide that.

I also think that for this kind of large-run device you should move from mini USB to the micro USB format. There’s a couple of reasons. I think mechanically the mini USB connection is not as robust as USB or micro USB; it certainly doesn’t have the retention capability that the micro does. I also think that the phone industry has moved on and I don’t see new devices with anything other than micro USB, so now this becomes the defacto connector that people have around the home.


I use the power connector a lot.


With SDCard and/or Graphics and/or Ethernet, the USB connection is often too weak.
And with USB Host, you need external power as well.
I use the barrel connector with external power often.
A two-pin 90° header (front or back) would take less space and be easy for most people to use. Vin is sometimes hard to get to when cards are stacked. And losing the adjacent ground pin is not easy.


BIG +1 to Lurch…

…As well as Brett…


It is absolutely needed.
When using shields or building larger electronics project the usb power is not sufficient.


Hello all,
Long time not seen.

I’m also in favor for the power connector. As described by above people.
Also i found out my self that the USB power can be unstable and gives disturbance in reading some of the data from my IR reader.

But when you want to change it … i love to see a battery powered version.


Maybe the question is, “is the barrel connector the best option?” I like the plugable screw terminal blocks myself. They make for an easy connection from about any power source.


Not bad also. ;D


screw terminal blocks are ok if you want to permanently connect something up, it’s certainly the most reliable connection since it can’t be pulled out.

I suspect (no scientific evidence, just personal thoughts) that most “hackers” tend to have only a few boards that are re-used across projects; therefore less likely to want to be “tied” to a power source. I know I do, so I use USB when its appropriate and barrel jack when it’s not.

An option of polarised .1" headers somewhere for BOTH +5v regulated and 6.5v or more input to the regulator would also be great. Again, with options to increase board size and potential complexity, so those things go somewhat against the true Fez concept and I can understand why GHI would discount them.