electronicsfreak
Member
Well, here's my situation. Small hobby project that has found varying frequencies of noise winding it's way into the Micro's ADC. Sweet, looks like I've done a "fantastic" job at keeping everything clean
Overall, I have a sensitive circuit feeding the ADC to a microcontroller. The micro also uses an LED matrix display through a driver....a very noisy LED display driver as I've now found, the Holtek HT16K33. Power is supplied to everything in a "star" route from 3 AAAs, but it looks like I'll need to go further that just that.
Checking my "4.5v" (note the quotes ) I get this stuff the whole way across, regardless of where I probe on my rail.
Low and behold, the frequency of that stuff seems to line up to a T to the settings I have put the display driver in, matching the refresh and duty rate described in the datasheet. I am fairly positive I've done a wonderful job of overlooking the ESR of those AAAs, but I could be wrong.
Taking a 100uF electrolytic cap and tagging it...anywhere on that rail (to gnd), I get a reduction of that peak by ~15mV. Cool to see an effect, but far lower than I was hoping for.
Further investigation, ditching the batteries and powering the thing from an LM7805 across ~1ft of 20AWG wire, the result looks about the same as above. However, bread-boarding one, and tagging the circuit's power rail less than 2 inches from the LM7805 regulator (with same wire gauge), I get this fantastic result below.
(apologies for the quality, only soo many hands when snapping the pic)
Again, I get the same looking scope result, regardless of where I probe on that rail.
Sweet, progress! Or, I think it is................that ~6uS edge looks a looot easier to clean.
Anyways, I am looking for opinion, or bits of advice of what I could try to keep that noise away from sensitive stuff on my circuit. I have a 100uF electrolytic at the center of the star, and 10uf, 1uF, and 0.1uF of ceramic bypass right next to the Holtek IC. Looking at adding a decoupling circuit (inductor/cap) to the feed of the Holtek IC, or....would it be better to put one on the power input of my sensitive stuff...or both? If I can't get away with just passives, I'm looking at adding a switching regulator, feeding a linear regulator. I would prefer to avoid it if possible, but I know that could mean adding an absurd amount of bypass?
As stated, just looking for any opinions, suggestions, tips, etc.
Thanks in advance for the input!
-EF
Overall, I have a sensitive circuit feeding the ADC to a microcontroller. The micro also uses an LED matrix display through a driver....a very noisy LED display driver as I've now found, the Holtek HT16K33. Power is supplied to everything in a "star" route from 3 AAAs, but it looks like I'll need to go further that just that.
Checking my "4.5v" (note the quotes
Low and behold, the frequency of that stuff seems to line up to a T to the settings I have put the display driver in, matching the refresh and duty rate described in the datasheet. I am fairly positive I've done a wonderful job of overlooking the ESR of those AAAs, but I could be wrong.
Taking a 100uF electrolytic cap and tagging it...anywhere on that rail (to gnd), I get a reduction of that peak by ~15mV. Cool to see an effect, but far lower than I was hoping for.
Further investigation, ditching the batteries and powering the thing from an LM7805 across ~1ft of 20AWG wire, the result looks about the same as above. However, bread-boarding one, and tagging the circuit's power rail less than 2 inches from the LM7805 regulator (with same wire gauge), I get this fantastic result below.
(apologies for the quality, only soo many hands when snapping the pic)
Again, I get the same looking scope result, regardless of where I probe on that rail.
Sweet, progress! Or, I think it is................that ~6uS edge looks a looot easier to clean.
Anyways, I am looking for opinion, or bits of advice of what I could try to keep that noise away from sensitive stuff on my circuit. I have a 100uF electrolytic at the center of the star, and 10uf, 1uF, and 0.1uF of ceramic bypass right next to the Holtek IC. Looking at adding a decoupling circuit (inductor/cap) to the feed of the Holtek IC, or....would it be better to put one on the power input of my sensitive stuff...or both? If I can't get away with just passives, I'm looking at adding a switching regulator, feeding a linear regulator. I would prefer to avoid it if possible, but I know that could mean adding an absurd amount of bypass?
As stated, just looking for any opinions, suggestions, tips, etc.
Thanks in advance for the input!
-EF