XU4: External Power Button & External power indicator LED

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XU4: External Power Button & External power indicator LED

Unread postby Sashby » Thu Oct 05, 2017 10:23 am

xu4_external-power-button_external-led-power-on-status.png
xu4_external-power-button_external-led-power-on-status.png (76.37 KiB) Viewed 1638 times

My Odroid XU4 will be inside a PlayStation 1 case. What I hope to do is add an external push button to power up/shut down the system and an LED that will turn on/off. Exactly like a PC. I don't want the LED to be lit when the DC jack is connected (Like the ALIVE LED that is already soldered to the board), only once the system boots, is running and turns off when the system shuts down.

I'm not sure what LED and resistor I should use or if the wiring diagram is correct. If someone could suggest one I would be greatly appreciated. I'm terrified of frying the board due to the expansion connectors being limited to 1.8v.

I'm after a green LED (Size isn't an issue whether it be 3mm or 5mm).

I would have used the Shifter Shield but for this project, but it is too large.

Thank you :)
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Re: XU4: External Power Button & External power indicator LE

Unread postby odroid » Thu Oct 05, 2017 7:43 pm

Normally, we have to add a NPN-transistor/FET to drive a generic LED with 1.8Volt GPIO.
This is an example to send a signal to a 5volt input pin on Arduino with a LED monitor.
gpio_led.png
gpio_led.png (10.34 KiB) Viewed 1625 times


But I could find some 1.8Volt green LEDs from Digikey.
https://www.digikey.com/products/en/opt ... ageSize=25
I think you can add a 68ohms ~ 100ohms resistor to drive the LED even you need a trial-error to find a best value.
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Re: XU4: External Power Button & External power indicator LE

Unread postby phaseshifter » Fri Oct 06, 2017 5:05 pm

if your circuit is correct just use a a red or equivalent..so it uses 1.8 volts..for a pure green led you would have to up the voltage not lower it..it may run and work but maybe very dull..

i am going to try your method when i get a chance..i have all the components available..


Standard red, orange, yellow and yellow-green LEDs have a Vf of about 1.8 V,
while pure-green, blue, white, and UV LEDs have a Vf of about 3.3 V
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Re: XU4: External Power Button & External power indicator LE

Unread postby Sashby » Wed Oct 11, 2017 3:18 pm

odroid wrote:Normally, we have to add a NPN-transistor/FET to drive a generic LED with 1.8Volt GPIO.
This is an example to send a signal to a 5volt input pin on Arduino with a LED monitor.
gpio_led.png


But I could find some 1.8Volt green LEDs from Digikey.
https://www.digikey.com/products/en/opt ... ageSize=25
I think you can add a 68ohms ~ 100ohms resistor to drive the LED even you need a trial-error to find a best value.


Thank you Odroid for the suggestion. Unfortunately I live outside the US and the best LED I can find from Digi-Key is LTL2R3KGD-E (1.8V 2mA 30° 38mcd) made by Lite-On. I can't find any other suppliers. The shipping is far too much and would be a last resort.

Another solution could be to desolder the ACTIVE LED (Blue) on the board and rewire an external green led. Do you have a Datasheet for the ALIVE LED and it's resistor so I can determine a suitable LED?
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Re: XU4: External Power Button & External power indicator LE

Unread postby Sashby » Wed Oct 11, 2017 3:28 pm

phaseshifter wrote:if your circuit is correct just use a a red or equivalent..so it uses 1.8 volts..for a pure green led you would have to up the voltage not lower it..it may run and work but maybe very dull..

i am going to try your method when i get a chance..i have all the components available..


Standard red, orange, yellow and yellow-green LEDs have a Vf of about 1.8 V,
while pure-green, blue, white, and UV LEDs have a Vf of about 3.3 V


That's incredibly kind of you to try this. Thank you.
I've heard of logic level convertors. I'm guessing the shifter shield uses these. Can you power 3.3v led's with the shifter shield?

Can I do the same with a Sparkfun Bi-Directional Logic Level Converter
https://www.sparkfun.com/products/12009
Can I supply this with 5v using the CON11 or CON10 5V pin?
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Re: XU4: External Power Button & External power indicator LE

Unread postby odroid » Wed Oct 11, 2017 3:39 pm

This is the blue LED datasheet.
http://www.seoulsemicon.com/upload2/NB104.pdf
The actual Vf is 2.9Volt and we added a FET 2N7002 to drive the blue LED.
Refer the XU4 schematics page 33.
http://www.hardkernel.com/main/products ... &tab_idx=2
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Re: XU4: External Power Button & External power indicator LE

Unread postby Sashby » Fri Nov 10, 2017 2:31 pm

odroid wrote:Normally, we have to add a NPN-transistor/FET to drive a generic LED with 1.8Volt GPIO.
This is an example to send a signal to a 5volt input pin on Arduino with a LED monitor.
gpio_led.png


But I could find some 1.8Volt green LEDs from Digikey.
https://www.digikey.com/products/en/opt ... ageSize=25
I think you can add a 68ohms ~ 100ohms resistor to drive the LED even you need a trial-error to find a best value.


Thank Odroid for suggesting this! It worked out great :D
I do have some questions though.
How many mA can PIN1 5V provide? I used a LED that was rated below 15mA and used a resistor to limit it to below 7mA. Can I use an LED with a higher current, say 20mA?
Which expansion pin goes high as soon as the board powers on? I used PIN 11 (CON10) because I believe it goes high and stays high, only going low for a short period of told to, from what I've read on the forums. PIN 11 (CON10) doesn't go high from boot for at least 20seconds, tested this with a 1.8V LED to begin with. I'm after one of the pins that will go high the moment I push the momentary power button on the board itself.
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Re: XU4: External Power Button & External power indicator LE

Unread postby odroid » Fri Nov 10, 2017 2:53 pm

5V pin can supply over 200mA. So you can use 20mA LED without any issue.
But 20mA is a quite big number for small LED driving.

It is not easy to know the initial state of the GPIO pin level in the boot-loader stage.
You might need to find a pin with a LED connection or DMM.
If you find any proper pin, please share it with other people.
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