Explanation of V BAT IN, Vin, 5 Volts in


Can someone please explain the following pins please:

  1. VBAT IN
  2. Vin for external power 6 -12V
  3. 5 Volts In/Out

Questions about the above:
1.1) What range of battery voltage is allowed?
1.2) Will this alone power the Fez?
2.1) is this pin the same as the ‘External power connector’?
2.2) Will this alone power the Fez?

The wirimg is described in the FEZ Domino schematics. You can download the schematic from the website

It is only used for the RTC and internal 2kb RAM. Normally you can use a 3V coin battery like a CR2032 battery

This input is used for an external power supply. You should use a 7V power supply(I have some problems with more voltage). This input powers the FEZ and external component through 5 Volts In/Out

This input is used for a regulated 5V power supply. You can power the FEZ and external components

Answer 1.1 : I described the voltages in my comments
Answer 1.2 : No , also for external components (see comments)
Answer 2.1 : ?? I seems this pin goes directly to the 3.3V regulator
Answer 2.2 : No , also for external components (see comments)

I hope it is clear and I’m correct :smiley:

Thanks for your explanation Cyper.


I want to know if I can control the 5 volts in/out. I mean as an output voltage pin like the output pins of FEZ Domino. Because I need an output pin with 5V and I want to control this pin as an output pin (And FEZ Domino Output pins power is not enough).

If you have some ideas that will be great

This voltage is coming directly from the regulator so not you can’t control it.

Take a look at schematics please.

That’s what I saw before but I was waiting for some idea or something that may be I didn’t see.

ok so one thing I can think of here is to use a separate circuit and a transistor on the IO pin to switch it on and off.

Alternatively, if it’s signal level constraints that you can’t meet, you could use a level shifting IC like a 74LS245 connected to 5v, with the 3v3 input pin being reflected on the 5v output pin.

It all depends on what your scenario is, what you want to control and why…

That could be an interesting solution. In fact, I want to control the power of a wifi module. But it needs 100 mW. So I try to use a relay reed to control it, but the voltage coil is 5V (50 mW) that the Embeded Master gave me before with the Outport pins. But now I need to adapt my project to FEZ Domino thinking in the cheapest solution.

Hi all,
My question related to this topic: when I have a 16V power source, is the best way to power the board by adding a (5V) voltage regulator and connecting to the 5V in? or do I have to use the Vin for external power and thus regulating to something between 6-12V?

You could regulate it down to 9V and connect it to VIN, or you could regulate it down to 5V and connect it to 5V. It’s pretty much your choice.

can someone give me the link to the FEZ Domino schematics?


For future reference it on the hardware page where the hardware is described.

Go to the top of this page, click on Hardware, then Domino. Look right at the very top section of the page where it shows the Domino. The link to the schematic is there. It is in the same place for each product that has schematics.

Maybe it’s just me, but from experience I have found that having just the usb cable or 5V plugged in is not the best when you start having a few things hanging off the Fez (Motor, Servos).

I personally preferred using a 11.6V battery hanging off the DC in, then your Vin has a healthy 11.6V for some serious power (Motor shield) if you need it and when your 5V is being used by a few components, the Fez won’t cut out due to the voltage dropping.
::slight_smile: :smiley:

USB is notorious for not being able to provide an excess of current. So when you are running solely from the USB 5v power, you can guarantee you can’t draw more than 500ma (which is the current output from all USB 5v chargers). If you are using motors, servos etc then you need more current and you’re pretty much sure you’ll have issues.

Just keep an eye on input voltages when you’re drawing high current, since the regulators might heat up a lot more than they should - if you keep the voltage back down about the 7v mark then the heat dissipated is less and you will be better off in the long term

6 volts is fine for motors and servos. Unless you want to have some HEAVY power, I would suggest 9v or 12v.