On Mon, 6 Jun 2016 10:12:43 -0700 (PDT), you wrote: >Hi, > >Yesterday I was trying to use some of the analog inputs on the BBB to read >my photodiode, and instead, I think I blew up the power supply on my board. >With power applied, I get no PWR led, so I'm pretty certain it's dead. >Short of replacing the power management chip, is there anything I can >do/replace to get the board working again? > > >Brief Background > >I hooked up the photodiode to an Arduino and was able to read 0 - 5V >easily, so I wanted to do the same on the BBB. >I read some of the materials re: AIN on the BBB, but apparently I missed >all the references to the max voltage of 1.8V! >I started by enabling the analog inputs on the BBB, and started with AIN0. > >With nothing attached, I was reading about 0 - so far, so good. >Then I figured I'd try to see what a full 5.0V read out, so I plugged in >the VDD 5V to AIN0, and all the LEDs went out instantly. >Now all LEDs stay off, even the PWR LED, when power is applied. > >No doubt, it was stupid, but I have a few additional takeaways - >1. Very minor references in most BBB documentation/webpages discussing >Analog Inputs and max voltages. >Coming from working with Pi's and Arduino's, it was common to have analog >inputs range from 0 to 5V, so the 1.8V was unexpected.
Actually, it's 0 to VCC on the MEGA and XMEGA chips. The Mega chips can run at 3.3 volts, and the XMEGA chips *must* run at no more than 3.3 volts. > >2. Isn't there any protection at all from this kind of damage? Or was the >main problem that I used the VDD 5V and fed it into the AIN0 port? These are generally direct chip inputs, and there's generally no buffering. >Would I have killed it if I used the VDD ADC instead of the VDD 5v or would >using the VCC ADC possibly have protected it? 1.8 volts maximum. > >3. What is the "normal" way of using the BBB analog inputs with 5V levels? > Is it possible - or is there where I would use a level-shifter or zener >diode? Level shifters are generally digital, and zener diodes don't help all that much (and are not really a good idea here). My standard advice would be to run the analog voltage through a non-inverting op amp configured as a gain stage. You run the op-amp (and have to pick one that does rail to rail and also runs from 1.8 volts) from the 1.8 volt supply. Harvey > >Thanks for the any comments or additional info provided! -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/hbeblb1809orgk011t8crt9ucj3m942qlm%404ax.com. For more options, visit https://groups.google.com/d/optout.
