Re: Progress
Adam - I just double checked and mine is a rev-A board and that the wire goes between pin 4 (VCC) and pin 32 (AVCC). I don't know what other changes happened between rev A and Rev B but based on the note on the schematic title page, there shouldn't be any functional differences if the board has been modded.
Re: Progress
I was just curious as mine seems to be missing the wire must be a later mod strike.
Hope the vacation was good ;)
Re: Progress
Adam - I do feel like I'm making progress and I agree. It is a neat little device. The chip with the mod wires is, I beleive, an Atmel MCU that acts as the USB interface for the board. The schematic diagrame notes "Floating Avcc pin 32 was connected to +3V3_USB_A for Rev B." So, I think the red wire fixes an oopsie.
Re: nice job
Jacek - Then I'd need green, blue and red LEDs instead of just yellow. :-)
Progress
Sounds like you are making excellent progress with the LX9, it is a neat little device.
What are the other wires on the board arounf the IC ?
nice job
Hi Duane,
Maybe you could add few more leds and we're ready for Xmas? ;)
But to be honest, nice job! Every blog brings more cool stuff.
Re: Why 680-ohm resistors?
Hi Brian - Thanks for the kind words. I'm glad this is helping.
As for the 680 ohms, it's somewhat of a personal choice. In reality I could likely have gotten away with no resister at all for this board. If I read their schematic right, they don't have any current limiting resistors on those 1.8 volt outputs. If the LED drops about that much and draws, say, 20 mA, then it should be okay without the resistor.
That being said, I'm never comfortable without some sort of a current limiting resistor. 680 ohms is large, but it will light up at 1.8 volts (at least with the LEDs I had on hand) and will also work fine in 5v, 9v and 12v applications. With the higher resistor, I have the flexibility of using them for test in other projects and I can use lots of them without ever worrying about jumping over the total current limit of an MCU or FPGA I'm fiddling with.
Brian
6/25/2012 3:20:15 PM
User Rank Guru
Why 680-ohm resistors?
Hi Duane,
Minor question, but why did you choose 680-ohm resistor values for your current-limiting resistors?
We learned from your More About the UCF blog that the "LVCMOS18" identifier means 1.8V. So, using 680-ohms limits the current to ~2.65mA (nominal). That seems a little low (reads: a dim LED).
Just curious...
Brian
6/25/2012 3:09:51 PM
User Rank Guru
Thanks for the Baby Steps...
Hi Duane,
Thank you a lot for this. I really like following your blogs one step at a time. They are easy to follow and very helpful!
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