Members | Sign In
Legacy MOVI User Community Forum (readonly) > MOVI Question & Answers

external Microphone

posted Jan 06, 2016 11:55:53 by Pilif
what is the line in voltage for the ext. microphone?
I guess that with the following circuit[1] Microphones that are pre-amplified could be connected ?
Can you give me an example of an Microphone without "pre-amplified" and more specific how can I search for such one?
page   first prev 1 2 3
39 replies
Dylan said May 25, 2016 04:56:28
I tried the Voice Bandwidth Filter circuit and the results are astounding but not without some effort and one open question. I imagine you won't be able to comment too much without trying the circuit and seeing its impact on the input to MOVI, but I'll wrap up with it in any case for your consideration.

The longer story - I tried the Voice Bandwidth Filter without any changes to my code and MOVI became less responsive initially with anything other than a quiet room (car). I put the microphone debug on and found that it was not hearing any engine rumbling, but it would tend to cut off my callsign about half way through. So I started dropping the tolerance. Once I got all the way down to 3, MOVI started to hear my complete callsigns and commands, but continued to "ignore" the engine rumbling at idle. I was encouraged so I moved on to the next trial using 3 as a fixed tolerance.

I was amazed to find that with the Voice Bandwidth Filter circuit in play and a tolerance of 3, MOVI would hear my callsign and commands quickly and accurately while driving up to about 50MPH. I even rolled the windows down at one point and still, MOVI was disinterested in the background noise, hearing and responding only to my voice (I wore only one earbud to listen to the microphone debug which in my understanding is legal!) After 50MPH, things got less reliable and I'll need an assistant to really listen to the microphone debug to see if it generates any ideas, but I wouldn't be surprised if it's just too much convoluted noise to do anything about. Regardless, I'm very impressed with the results I have achieved and would consider it a success!

The open question I have is - would it make any sense to allow us to drop the tolerance below 2 (ie. 1,0) for those of us who wish to filter the signal externally with a filter such as this Voice Bandwidth Filter?

I should probably reiterate the pieces I have in my microphone circuit here because it's quite a chain at this point:

ADAFruit 9814 Mic -> Voice Bandwidth Filter -> Line-to-Mic level attenuator -> Ground Loop Isolator -> MOVI

[Last edited May 25, 2016 17:48:52]
GeraldFriedland said May 26, 2016 15:06:23
I am assuming with 'tolerance' you mean the value to the THRESHOLD command? Dropping that value to 1 puts the internal noise threshold at 1%. This means that some MOVI boards will become completely unresponsive as the noise induced by the AGC will be interpreted as speech most of the time. 2% is really the lowest we can safely go. In fact, there is a reason I made the default 5%.

Having said that, let's look at your concrete problem. I haven't tried your circuit yet (thank you so much btw., I will!) but I wonder if you should put a small amplifier after your circuit, or for that matter, adjust the Line-to-Mic level attenuator to not be as strong. What is the peak and average voltage you get after the bandwidth filter?


Dylan said May 26, 2016 18:37:06
Apologies, old terminology from my previous VR board, yes I meant THRESHOLD.

I don't really want to change anything hardware wise just yet because I have it working so well. The question about the THRESHOLD limit was more out of curiosity than a need given that I was getting close to the minimum allowed. I actually tried 2 as a threshold and I didn't like it at all, MOVI went back to being slow and unresponsive at times. It looks like 3 is my sweet spot right now.

I don't have the equipment necessary to measure the average/peak voltages with any accuracy. That said, I did get to thinking that the attenuation may be a little strong with the Voice Bandwidth Filter and the Line-to-Mic attenuator together. I'll wait for your findings once you try out my Voice Bandwidth circuit and if you have any strong recommendations at that time in terms of optimizing the input level then I'll consider it again.

I'd like to make a new video sporting MOVI in action in my car, but I'd kind of like to have the new firmware first so I can combine MOVI's beeps (to prove it's MOVI doing the work!) with my custom audio callsign responses.

Thanks as always for your insights!
LeRoy said Dec 12, 2016 23:27:41
Dylan, Gerald -
I am very happy Dylan shared this thread with me, I think it will solve many of the problems I see. And the bandpass filter is probably what I will need as well. As the motors on the robot are a lot noisier than I would have first thought.
Speaking of the bandpass filter thou, the link Dylan gave is dead now, luck would have it thou that it was archived with "internet archive"
Dylan said Dec 12, 2016 23:40:33
Looks like "Paul" moved from having his own .com to blogspot. No need for the "Way Back Machine" after all.


GeraldFriedland said Dec 14, 2016 02:25:58
Dylan: Thanks!
Dylan said Dec 14, 2016 06:32:13
No problem Gerald, just trying to help a fellow hobbyist find some success.

BTW. I ended up taking a new position in Las Vegas, NV. If you're going to be out here for CES or some other show, let me know and I'll drive my MOVI enabled 1987 Chevy "computer controlled" (early car computer!) car over to show you!

GeraldFriedland said Dec 14, 2016 20:44:46
Sure thing!

LeRoy said Dec 15, 2016 01:19:19
Dylan -
I can see the promo now - "Before there was the Knight Thousand, Before there was K.A.R.R. - There was The E.C.C.C. or Early Computer Controlled Car. Powered by Arduino and MOVI."

:-) Just need the sensor lights, and a few sound effects....

(I'm going to change these to the black strips (to help blend into the grill), probably add more neopixels to see if I can't get them to brighten up, and go with a 12v strip (the ones here were only 5v), probably go to a larger amplified speaker too) But it's a concept at this point.
Login below to reply: