I built my MiniPOV3 kit, and have it working, but the messages are very hard to read in anything other than a very dark room. The kit I got had 100 ohm limiting resistors, and that's a large value even if they were being driven by 5V, rather than 3 (or 2.4 if I use NiMH.) In fact, based on the source pin characteristics outlined here: http://www.atmel.com/dyn/resources/prod ... oc2543.pdf (Figure 106 on page 196)
it looks like when Vcc is 2.7 volts (a good approx) it might not be necessary to have a limiting resistor at all, since it would seem to hit 17 mA at 2V, which is pretty close to what standard LED should be driven at.
As a first step I was thinking about replacing them with 50 or 33 Ohm resistors, but then I had a wacky idea. To avoid de-soldering all of them, I could piggy-back an additional 100 ohm resistor on top of the existing one to give the equivalent of 50 ohms (or piggy back a 50 ohm for 33 ohms.) I don't know if this would end up being a mess or not. Does anybody have experience trying to solder on piggy-backed resistors?
-- Mitch
Changing/removing limiting resistors on a MiniPOV3
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- pneumatic
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Re: Changing/removing limiting resistors on a MiniPOV3
one leg at a time
- pneumatic
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Re: Changing/removing limiting resistors on a MiniPOV3
With that (very small) encouragement, I decided to give it a try using a 75 ohm resistor in parallel.) I did R1 as a test, and that seemed to work fine, making the bottom-most led significantly brighter. I decided to do the rest in order of increasing accessibility, so I started next with R5. To avoid damaging the uC, I pulled it out, and when I put it back in afterward, I got no lights, and the ATtiny chip just got really hot. I checked for solder bridges and other obvious faults, but I suspect I just got bitten by static discharge taking out the chip. I suppose I could put it in a breadboard and just give it Vcc/gnd and see if it still heats up.adafruit wrote:one leg at a time
Is there anything else I could have damaged that would cause this? If I order a replacement ATTiny2313 from mouser, do I have to just start with a "make burn-fuse" after powering it up for the first time?
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Re: Changing/removing limiting resistors on a MiniPOV3
don't supposeyou put the chip in backwards?
yes.If I order a replacement ATTiny2313 from mouser, do I have to just start with a "make burn-fuse" after powering it up for the first time?
- pneumatic
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Re: Changing/removing limiting resistors on a MiniPOV3
Wow... that was embarrassing. I missed the notch and mistook the circle on the package for the registration mark.mtbf0 wrote:don't supposeyou put the chip in backwards?
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Re: Changing/removing limiting resistors on a MiniPOV3
don't let it go to your head. you're hardly the first.Pneumatic wrote:Wow... that was embarrassing. I missed the notch and mistook the circle on the package for the registration mark.
and look at the bright side. it wasn't your mods that did it. and there's a good chance the tiny2313 survived the ordeal. did it?
- pneumatic
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Re: Changing/removing limiting resistors on a MiniPOV3
It did, and now I have a spare, which I also put in backwards, and also survived.mtbf0 wrote:....
and look at the bright side. it wasn't your mods that did it. and there's a good chance the tiny2313 survived the ordeal. did it?
On the downside, I cut out the resistors I had added as part of the diagnostic, and now no longer have enough 75 ohm resistors to complete the project unless I can reuse the ones with extremely short leads. It may be easier just to desolder and put in new resistors after all. I have a strip of 33 ohm resistors that should do the trick.
-- Mitch
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Re: Changing/removing limiting resistors on a MiniPOV3
I am a fan of driving LEDs directly from AVR pins, but only if you are sourcing current at the AVR. If you are sinking current, I have heard it's a Bad Idea(TM) to send unrestricted current into the chip.
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