The sound sample (see link below) was taken from an SKRM module on power up. If I switch off and immediately back on again, there is NO noise but if I wait about 5 seconds and power up, the noise is there again.
The clip LED also flashes briefly when there is NO noise but remains on longer when there is a noise.
Any thoughts? I suspect the built-in output mute is not allowing the output coupling capacitors long enough to charge to VDD/2 as per the FV-1 datasheet, but why? Is the crystal taking too long to start oscillating?
Presumably when quickly turning power back on the caps have not fully discharged?
Thanks,
Phil.
http://www.4shared.com/mp3/8d3VYGfz/eTa ... noise.html
Start up Noise
Moderator: frank
Hmmm, I don't know why that is happening. I'll try to see if I can replicate it here. It could simply be a chip that went bad after test, it is called "infant mortality" when a chip (or other electronic item) fails shortly after passing test.
Frank Thomson
Experimental Noize
Experimental Noize
Hi Alex. The SKRM boards already have that but if something changed at the assembly house then the value of the capacitor may need to change.
We are working on this outside the forum since the SKRM boards are an OCT product and I shouldn't use the Spin forum for it.
We are working on this outside the forum since the SKRM boards are an OCT product and I shouldn't use the Spin forum for it.
Frank Thomson
Experimental Noize
Experimental Noize
This is not just a problem on the OCT SKRM boards, I have built a few of my own designs lately and have this same problem.frank wrote:Hi Alex. The SKRM boards already have that but if something changed at the assembly house then the value of the capacitor may need to change.
We are working on this outside the forum since the SKRM boards are an OCT product and I shouldn't use the Spin forum for it.
It has only occurred on builds that I have used the cylinder type of watch crystal with a 15p cap. Other builds with a ceramic SMD oscillator did not have this problem.
I have since been using a 100p cap to ground on the cylinder type oscillator and this has stopped the start up squeal. I hope this is of some use.
The noise is created because the crystal enters a high harmonic on start-up. Normally a cap will stop this and all is fine but the actual value may need to be adjusted as the crystals vary from one manufacturer to another.
Frank Thomson
Experimental Noize
Experimental Noize
I know this is an old post but, a 47p cap or thereabouts cures this problem, just in case anyone else still has this issue.frank wrote:The noise is created because the crystal enters a high harmonic on start-up. Normally a cap will stop this and all is fine but the actual value may need to be adjusted as the crystals vary from one manufacturer to another.