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5v on Fez Panda II


#1

Hi,
Sorry, new to all this…

Note: using 3-pin E-Block Component Shield with Panda II

Is it possible to turn on/off the 5 volt pin (digital E-Block) on a Fez Panda II? Or do you only have control over the 3.3 volt pin (to blink an LED)?

I’m wanting to blink a 5v raw LED (not using the “Plug and Play” LED eblock unit)

thanks,
Ron


#2

the e-blocks are “fixed”. You get one power pin, one GND pin, and one “signal” pin that you can change. So the simple answer is NO you can’t control the 5v output with the e-blocks; but there are always ways, as long as you’re handy with a soldering iron and have some resistors?

edit: whoops, submitted before brain dump ended

You may also find that running at 3v3 is sufficient for your LED, but you would want to test that.

You also need to know is that the 5v port on the edge of the component shield is the only point you can get 5v; the VCC pin on each e-block is 3v3.


#3

You could also use a transistor (or FET) in combination with the LED and use the 3V3 to enable/disable the transistor and still get the higher voltage to the LED.


#4

Thanks Brett and Ian,

The 3.3 volts does light the LED, but about 1/3 the brightness. It would be best if I can use the 5 volts to get a very bright LED. The transistor solution sounds interesting (kind of like a relay?). Any recommendations for a source?


#5

@ Ron5, BTW welcome to the community and Merry Christmas!

Read over the below discussion - specifically the schematic. You can replace “fan PWM” with 3V3 light pin and you’ll get 5V to your LED. Recommendations for source? Do you mean source for transistors or 5V? You can get 5V off the Panda. If you just need one or two transistors, go to Radio Shack and pick up one of the NPN assortment packs for about $3. The 2N2222 should do you just fine.

http://www.tinyclr.com/forum/1/5179/#/1/


#6

Thanks Ian, and Merry Christmas to you too!

Yes, a source for the transistor. We (in Canada) don’t have Radio Shacks any more, “The Source” replaced them but I’ll have a look there (same kind shop).


#7

If you’re in no hurry or if you are going to need more, then go to eBay and you can buy 200 for about the same price as 10 at one of those stores :slight_smile:


#8

Yes, I think I’ll order through eBay. At The Source, they had NPN and PNP transistors. I just wrote down 2N2222 so I didn’t know which to get (and customer service did not know either).

Do you always require a resister for the transistor signal (3.3v)? Are the amps coming off Panda too high for the transistor? Does the Panda control the amps that are piped through each pin or does it depend on the power source connected to the Panda (USB or AC/DC power supply)?

Thanks!


#9

Ron, transistors require only a very small amount of current for their base signal. So, a resistor is required since there is nothing inside the Panda that is going to limit that current for you. Use resistors not only with transistors but in switches/buttons, LEDs, etc. - anything that can be harmed by too much current or could draw too much (short) current and harm the Panda.

Merry Christmas!


#10

Thanks Ken,

I was able to get transistors and resistors locally.

I found this calculator online that helped me calculate what I needed.
http://wolfstone.halloweenhost.com/Lighting/litlec_LEDCalc.html#CalculatorForLEDsInSeries

Not sure if it matters if the resistor is before LED or after. It appears that it’s best to have the LED first (positive side) then the transistor.

Thanks!


#11

Ron - We (or at least I) need to see a bigger picture of that fish in your avatar photo. Good to see you balance your geek time with some quality outdoor recreation. Now if I could just get a FEZ board to tie some flies…


#12

If your intent is still to amplify the voltage to 5V then you will need a resistor and LED on the collector side (‘before’) of the transistor. Please review errol’s comments in the previous thread I referenced. If you put the LED on the other (emitter) side then you will only amplify the current and not the voltage. You could do that w/o the transistor simply by reducing the size of the resistor.


#13

Right on, thanks Ian!

Hi ransomhall,
The lakes are frozen over now, but here is a rainbow caught in Fountain Lake (near Lillooet, BC).


#14

That’s a beauty! I’m as envious of your lakes and rivers as I am your mountains.