tearful LTC1298 woes SOLVED
Solar Furnace Guy
Posts: 1
I've spent around a month trying to figure out why my ltc1298's weren't working. Poor Joshua Donelson, he's so helpful. I have my BS2P40 hooked up to a quadrant photodiode laser beam positioning sensor. I hope this prevents other people from having the same problems I do.
Here are some unforeseen problems I'm sure no one has written about that caused my readings to be very erratic and haphazard:
PROBLEM:
My Dual 12V power supply had only 20mV of noise measured with an oscilloscope probe. Power going into ltc was CLEAN with 10mF tantalums on the reference end. It was quite a surprise to find that the power supply had a lot of dirty RF coming from a transformer that produced noise on the order of 1 whole volt!!!!! THIS CAN'T BE MEASURED WITH A VOLTMETER OR AN OSCILLOSCOPE CONNECTED DIRECTLY TO THE DIP PINS!!! I used a Smile probe and just waving it over the transformer revealed a mess of bizarre noise.
SOLUTION: I surrounded the entire 12V power supply with those static shielding bags to block the ADC chips
PROBLEM:
Expensive signal line is shielded for a reason. Even though my 12V power(GARBAGE)supply was shielded my signal lines were not. Did you know that fluorescent lighting in old buildings is sufficient enough to cause signigicant noise in unshielded signal wires just by being near them? Well it's very annoying, they do.
Solution:
I operated my ADCs elsewhere where there was no fluorescent lighting.
PROBLEM:
IT WAS STILL NOISY. After some inspection I realized that there was no longer any disturbance in my board. The quadrant photodiode (much like a solar panel 7mm across) had artificial light shining on it. America runs on a 60Hz power supply. If we could slow down time you would realize that the lights are actually flashing 60 times a second due to the alternating current. It's just too fast for us to see. So my diodes were measuring light at such a large sampling rate (5kHz) it would sometimes measure at the dark part of the flash, in between a flash, or at the bright part. This is the cause of the erratic readings without disturbance. These photodiodes have an enormously quick slew rate. They can be used to run a tachometer. Other photodiodes may not have a fast enough slew rate to be concerned about this.
Solution:
I operated with light sources that weren't using alternating current.
Josh D. thanks for all your help. You need a raise.
Here are some unforeseen problems I'm sure no one has written about that caused my readings to be very erratic and haphazard:
PROBLEM:
My Dual 12V power supply had only 20mV of noise measured with an oscilloscope probe. Power going into ltc was CLEAN with 10mF tantalums on the reference end. It was quite a surprise to find that the power supply had a lot of dirty RF coming from a transformer that produced noise on the order of 1 whole volt!!!!! THIS CAN'T BE MEASURED WITH A VOLTMETER OR AN OSCILLOSCOPE CONNECTED DIRECTLY TO THE DIP PINS!!! I used a Smile probe and just waving it over the transformer revealed a mess of bizarre noise.
SOLUTION: I surrounded the entire 12V power supply with those static shielding bags to block the ADC chips
PROBLEM:
Expensive signal line is shielded for a reason. Even though my 12V power(GARBAGE)supply was shielded my signal lines were not. Did you know that fluorescent lighting in old buildings is sufficient enough to cause signigicant noise in unshielded signal wires just by being near them? Well it's very annoying, they do.
Solution:
I operated my ADCs elsewhere where there was no fluorescent lighting.
PROBLEM:
IT WAS STILL NOISY. After some inspection I realized that there was no longer any disturbance in my board. The quadrant photodiode (much like a solar panel 7mm across) had artificial light shining on it. America runs on a 60Hz power supply. If we could slow down time you would realize that the lights are actually flashing 60 times a second due to the alternating current. It's just too fast for us to see. So my diodes were measuring light at such a large sampling rate (5kHz) it would sometimes measure at the dark part of the flash, in between a flash, or at the bright part. This is the cause of the erratic readings without disturbance. These photodiodes have an enormously quick slew rate. They can be used to run a tachometer. Other photodiodes may not have a fast enough slew rate to be concerned about this.
Solution:
I operated with light sources that weren't using alternating current.
Josh D. thanks for all your help. You need a raise.
Comments
P.S. Thanks, Josh
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- Stephen