Part 2 ASL Success

Back again with another update, this time, with good news! Still fighting a few things but it IS useable!

The Cure

When you have noise on a circuit, it usually boils down to a few things. In my case, it was the use of separate grounds. Star grounding helped in this circumstance. Anything that had a ground or negative side of things I ran a line to a main grounding point. Now, the Pi, LM386, and even the buck converter are all grounded to a single point. Little to no annoying hum anymore. Everything is at the same ground potential.

Speaking of the LM386...turns out the gain was set to 200x. That'll do it actually. By default (without pins 1 and 8 connected), the LM386 has a max gain of 20x. Add a bridging 10uF capacitor and you can get signals from space. Well, not really...

So, off I went star grounding and removing the additional gain and boom - node sounds clean with a slight fizzle still. Now I think the only solution is filtering.

Mic and Speaker Issues

I still haven't found a solution yet to the microphone hum. Again, my best bet would be via filtering. I've jacked the input all the way up to 900 and will let a 10k potentiometer take care of manual adjustments. 

On the audio side, while I've solved the buzzing, and digital noise, I've found that I actually get popping and crackling now if the volume is up all the way. The LM386 input gain pot is about 1/3 of the way up - any lower and the audio just really doesn't peak at maximum volume. Probably makes sense, but keep in mind the speaker I have is rated around 20 watts at 8 ohms. Really crazy.

On the mic, there is still a bit of background hum. It's around 300Hz but it's quite evident that it's there. I connected to a node over in Britain with M7TMO and 2E0KXC. I had a wonderful chat with them, I just hope I didn't interrupt anything! :)

I asked how my audio sounded to the both of them and sure enough, there was a mention of a faint but noticeable humming sound. I figured as much, but between the two of them it didn't seem to bother them. We talked for about 15 minutes and ended when I had to come upstairs for a break. Britain has a 6 hour time gain so while it was 2pm where I was, it was 8pm over there!

So it looks like the mic may need some work, but that's okay! I currently have a 10uF electrolytic and a 430 ohm high pass which is only cutting off ~37Hz and below. This could be the issue. I may try a 47 ohm and 10uF filter as this will cut off ~338 Hz and below - perfect for what we need. AllStar/Asterisk audio has a bandwidth of 300Hz - 3KHz. In addition, I'll most likely throw these filters on both the mic lines and the audio lines.

I'll also add on a Class A common emitter amp to the microphone, as seen here:

Running off of 5V, a 1mV input signal gives around 40mV output and a 10mV input gives about 400mV out. Perfect for the CM108 soundcard! To put it in perspective, consumer-grade line level is about 300mV.

As a bonus...for an electret mic, here's the same circuit:

Instability

I have noticed lately that my node has been having connectivity issues. I believe this has to do with it being in a completely-metal box, so an external WiFi antenna is another to do. Ethernet would be better but I don't really want to run 80 feet of Ethernet line from my room to the router - seems like a PITA.

How do I know it's WiFi? I have very latent and choppy audio sometimes and in running several ping tests, at least a handful of times I got dropped packets. One time even showed a 100% drop rate!

I've also noticed that my node will up and quit randomly if it sits idle for a period of time, usually overnight or days when I'm at work. I've fixed this by "poking" the node every hour by announcing the time and temp. Thank you Freddie Mac KD5FMU once again for the cool and easy-to-use script! Usually I'll kerchunk the node when I wake up just to make sure it's online and sure enough, when I get up and before I go to bed, the node is still online. I do believe this is a connectivity issue but again, I won't know until I get an external antenna.

This instability also breaks the OLED code as well. I've noticed that if the WiFi pipe breaks, it usually takes the data that's stored in the OLED code with it, making it stuck on the screensavers. It's a simple restart of the OLED's service but you can tell this kind of gets annoying after a while.

iaxrpt

I also got iaxrpt set up for things like business trips that my job may take me on. This now gives me 2 options to access the AllStarLink network - my phone and my laptop. I do have EchoLink capabilities on my phone but I have yet to actually talk on EchoLink.

It wasn't too difficult to set up but once I did, it was straight forward. Audio quality sounds great and I can now use both my phone and/or my computer to connect to my node.

Check out the 2462 node in Seattle!

What's next for the node?

I still need to add the VU meter. This shouldn't be an issue as it's a direct connection to the CM108 plug and power. 

I also need to print off the custom-made bezels as well. Adding on an external WiFi antenna is a must too, which I will have on the way in the next week.

Stay tuned as I'll be working on this on Super Bowl Sunday!!!