Originally Posted by Tom Frank
I could hear two distinct different buzzing sounds... one short buzz at exactly one second intervals, and one more sporadic buzz of slightly higher frequency and longer duration, starting every one to 2 seconds. Some of that could be caused by the write period to the memory card as you theorized. Some might be an artifact of the real time clock.
Right. I also hear two different buzzing sounds like you. I determined the duration of the buzz that appears at the one second intervals.
I also noticed that the sound frequency (tone pitch in english?) is different for each card.
I think it's really a problem with component tolerances. Maybe a problem with capacitors, that cannot properly buffer some peak power consuptions? As I cannot stop the full battery buzzing by connecting to a power supply, it should be somewhere "within" the circuit.
I'm not an expert in SD details. But I take from your ref. 2 that the card can take different max currents depending on bus speed (Table 3-4)? My two Sandisk cards both are standard SD (SDSC), while the others are SDHC. According to the table, SDSC is limited to 200 mA, while SDHC can take up to 800 mA. Can you shed light on this?
What bus speeds are usually used with the different cards? Does #11 use variable speeds for different cards? I think it's difficult to find out...