[0:01] Hey everyone!
[0:02] In the last video, I was looking at some noise that I was seeing in my walkie-talkie project
[0:12] “testing testing one two three”
[0:20] It’s a weird one as normally I’d associate this kind of noise with

[0:24] noise on the power supply when sending WiFi data.
[0:27] We’ve seen this before with analogue microphones and their very sensitive pre-amps

[0:32] but I’ve never seen it with I2S MEMS microphones which have always seemed to be much more robust.
[0:38] I’d also checked the 3.3-volt line with my oscilloscope during wifi transmission

[0:43] and I couldn’t see any noise.
[0:46] One of the viewers suggested that it could be physical noise from vibrating components

[0:51] and for a while, I did believe this could be the case as I could actually hear some

[0:55] noise that seemed to coincide with the WiFi transmission.
[0:58] I even managed to capture some of this noise with my desktop microphone.
[1:03] However, the majority of people were pretty convinced that it must be power line noise.
[1:08] So I thought I’d better double-check.
[1:11] Previously to fix this kind of issue I’ve taken a feed off the 5 volt supply.
[1:15] Passed it through an LC filter
[1:17] and followed that by an LDO regulator.
[1:20] This gives you a really nice clean signal for the microphone.
[1:24] So I wired this up on some breadboard and here’s the result:
[1:34] “testing testing one two three”
[1:42] The noise has gone!
[1:43] Problem solved you may think?
[1:45] But I thought I would double-check and wired up the microphone directly to the 3.3-volt line
[1:57] “testing testing one two three”
[2:04] There’s a bit of noise but nowhere near the amount we see on the walkie-talkie.
[2:09] After a bit of head-scratching, the only real difference between my test circuit

[2:14] and the walkie-talkie circuit is that I’m using a different ground pin on my walkie-talkie circuit.
[2:20] This is what happened when I changed the ground pin
[2:28] “testing testing one two three”
[2:35] The noise is still there but it’s considerably reduced.
[2:39] What’s really interesting is if I use the same ground pin in my test circuit

[2:43] I still don’t see any noise.
[2:44] So this is really board specific and quite strange.
[2:49] But the quality is probably good enough for my use case.
[2:52] I am going to make up some PCBs though with the power filter so that we get the best quality.
[2:57] I’ll do a new video once the PCBs arrive and we can test them together.
[3:01] So, thanks for watching and I’ll see you soon!