Kenny Spade

Can you supply the N+ with 5V through the header at the same time as having the USB connected?

If yes, then will the USB power be disconnected and still allow debugging?

Regards,
Mark

From what I'm seeing, the only thing that plugging in the USB and powering the 5V through the header would do is make the current flow between everything connected. I isolated the flow from the Netduino using a diode connected to the 5V header so that it could flow in, but not out, which I think will keep me safe from drawing an excessive load from the Netduino in the case that something big were plugged into it. When I did have my LEDs connected and not isolated, they worked, they were just really dim. I didn't want to chance it, though, so I isolated it. The way my project works now is that it can be powered by either the USB or the external power supply, or both, and in the case of only the USB, the LEDs receive no power. With the combination of a cable that lets me supply current through an ethernet cable, I now have a single cable connecting to the project with a USB port exposed that I can use for updates. I'm going to be running with this configuration for a few days and see how it goes in the wild. If it blows up, I'll post back here.

Did some more measuring. With nothing plugged into the N+, just USB power, I'm getting 4.97 volts. I add in the RFID reader, and it drops down slightly to 4.77 volts. With the lights plugged in to the Netduino but isolated from the +5V line with a schottky diode, the measurement is still 4.77 volts. With just the power supply, no USB, I'm seeing 4.95 volts at the source, with 4.65 volts after the diode. Measuring through the N+, I'm seeing 4.63 volts. With both the power supply and the USB, I'm getting 4.80 volts. I think that based on the requirements of my project, these should all be well within tolerance. I would probably look at getting a separate power source if I needed a clean 5V signal for something, but with the components that I have it seems to be doing fine. One interesting thing, I tried upping the draw from the lights by turning them all white with just the power supply connected, no USB, and I ended up reading 4.55 volts through the N+. Still within the tolerance for my project, and I don't plan to do that in any of the scenarios I have in mind, but interesting nonetheless. Pretty sure it's caused by the forward voltage drop of the LEDs as the current going through them rises. Thanks for the help figuring this out. Once a few more components come in I'll finish it all up and write up the project. Should be neat.

I second this! I was wondering the same thing... when it says limit to 12 Volts, but cars routinely show 14+ volts when charging.

IF I understand you Chris... The issue is not the voltage (up to 20 V), but a matter of what I'm driving off the Netduino pins and thus trying to pull through the voltage regulator(s) on the Netduino board. As long as I'm using small, low current stuff, I should be ok on a car's voltage system?????? Or am I overly simplifying things too much?

If so, I'm guessing there should be some upper limit of current... would that be the 200 mA on the specs... or something less? And No! I wouldn't hold you to it... if I fry a Netduino by putting it on a car, its totally my fault.

I've powered it through a car USB adapter that was rated at 5V 2.1A for iPad charging. The Netduino worked great, but it would be interesting to know if I was courting disaster. I know that I have experienced some instability in power coming from my car outlets before, though the car I am driving now seems to have better isolation than others I have tried. I can think of a few neat ideas for using a Netduino in my car, so it would be good to know that it would be safe to do so.

So far, this thing has been incredibly tough. I stayed away from hardware because I always ended up frying electronics when I touched them in the past, but the Netduino has performed admirably considering how many times I thought I must have killed it.

I am sorry, but how is that you read 4.76V instead of +5V?
I tried right now, and the voltage on the +5V pin is exactly +5V, when USB only powered.
NOTE: I also own a N+.
Are you measuring the power with all the leds connected? If so, try to detach them, and make the readings again.
Cheers

The LEDs are connected, but should be mostly isolated because of the diode. There may be a difference in voltage caused by where I read the USB versus the output past the N+. The voltage I was reading on the USB was taken with nothing plugged in but a USB to barrel jack adapter, whereas I read the N+ by plugging it in with a different cable from the same USB jack and then measuring from the +5V pin to the GND pin, which was routed through a breadboard. There is probably some resistance in there that accounts for the voltage drop. I'll measure it again with nothing connected going straight pin to pin and let you know what I get. I also picked up a new Schottky diode last night that is rated for a much lower voltage forward drop. I'll see how that affects things.

When I was looking for diodes, I found a few places that had them, but most required a fairly large order or had a large S&H cost. Any suggestions on where to pick these up? I ended up killing a couple hours in Fry's and picked up a few components, but they didn't have exactly what I wanted, just closer than what I had.

Hi Mario,

Thank you for sharing all your electrical wisdom with the community!

The built-in LEDS are 5V LEDs and only draw a few mA of power. If one has a bunch of external LEDs (several 100s of mA) connected to the Netduino then, yes, external power should be supplied.

USB is rated to supply 500mA, and there is a resettable fuse on the Netduino to help protect against overcurrent draws.

Chris

Thanks for the response, Chris. I am pretty sure I read somewhere that the N+ can provide up to 800mA output. If I am powering the N+ through USB with a port that gives more than 500mA, could that damage the N+? I have powered it through a 1A wall jack and a 2.1A car adapter and it seemed like it ran great.

Nope!
As long the schematic of the Netduino (std and Plus) is correct, the USB power is controlled by a MOSFET, which is controlled by an OPAMP. If you check its inputs, the OPAMP's output will switch when the voltage is above +3.3V. Since the voltage divider is actually a halver, and there is a protection diode, the overall voltage should be (approx) above +7V. +7.5V is a good choice, for a decent margin.
Cheers

This looks correct to me. The schematic shows that the +VIN header is essentially equivilant to the barrel jack, so it would require 7.5 to 12 volts before it kicks off the USB power.

I dropped in a diode between the power supply and measured the voltages. The power supply itself measures at 4.97 volts. After the diode, it falls to 4.20 volts. My USB port is measuring at 5.13 volts. If I plug in the USB port to the N+, the power supply jumps slightly to 5.01 volts. If I measure the +5v on the N+ with both the power supply and USB, it reads 4.76 volts. When I unplug the power supply, leaving only the USB plugged in, it still reads at 4.76 volts and the power supply shows no voltage. I read up on diodes, and I'm going to pick one with less of a voltage forward drop. This one works, but I might as well get as close to ideal as I can. I'll let you know if that works.