wh7qq
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Re: Pi Portable Recorder - Project Progress

Wed Jul 11, 2018 1:13 am

I rec'd the Fe-Pi in the mail today...might have arrived sooner but we had not gone to the box after last Friday. These guys are serious. Now to trying it out. The total for the Audio Z V2 was $15.39 ($3.50 shipping). The order was placed on the 4th of this month (July) and today is the 10th...not bad to Hawaii PO box address. More on this as I get the RPi loaded up and going but the zero and the Fe-Pi together are really tiny even with the roughly 1/2" space between them. As per the pictures on their web page, there are line-in (pink) and line-out (green) jacks and a black apparently combined mic/headphone jack...not sure how the combo works. More to come as we get acquainted.

Edit: Installed it and powered up and all seems to be happy. At least, the config.txt change in the instructions seems to work and aplay -l recognizes the device. I have not gotten any files loaded on this uSD yet so can't speak to its playback. I missed a link on the instructions page that pointed to a schematic of the jack wiring. Mic is strictly mono. I asked about how the codec knows about sample rate or bit density but that may be determined by the aplay command. The uSD has an older version of Raspbian on it and in the early am, I will upgrade the distribution and add audacity...satellite ISP with data cap here and free time at "oh-dark-hundred" :roll:

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Wed Jul 11, 2018 6:53 am

Thanks for the update. So far it sounds decent apart from the mono mic bit. Now I just have to wait until the pop up on Amazon.

wh7qq
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Re: Pi Portable Recorder - Project Progress

Thu Jul 12, 2018 5:13 am

I don't think I'd wait. I spent some time with the Z V2 and an RPi zero this morning and was never able to get any sound from the headphone (or line out) jack. Also, the zero cannot find Audacity in the repositories to load and in a desktop, it is glacially slow even to post an email from the browser. I installed the Z V2 on an RPi 3B and was able to install Audacity 2.2.1 and could play a .wav file directly with just a click on the file and the playback quality was excellent. The zero just does not have the horsepower for the Z V2 and Audacity. I would think the zero is also over its head with the AI Stereo. I have run the AI with an RPi 2B and it is liveable but any desktop usage at all, even a browser, etc. on the zero is really painful. With the relatively slow 700 MHz, single core processor and only 512K of memory...

If you need stereo mic recording, with either board, I think you need to go to an outboard preamp/mixer with line outputs. This could be homebrewed pretty easily with a low noise/power op amp and would not eat much power or space. http://www.zen22142.zen.co.uk/Circuits/ ... 1_mic.htm

I have yet to attempt to record with the Z V2 so more to come after this post.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Thu Jul 12, 2018 6:08 am

Thanks again for your help. Surely with the pre amp I am just record with arecord and play with aplay, even if it doesn’t mean I can use audacity :( . At least the sound quality is good so far! Also, thanks for the link to the pre amp I was looking for a good one last night but had no luck. One question, is IN+ the same an non inverting input?

Thanks,
LouisP

Edit - My understanding is the pre-amp needs 12V :( . However, if I used the NE5534 chip could I use 5V as the actual chip accepts 5V could I use 5V from the Pis GPIO pins?

wh7qq
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Re: Pi Portable Recorder - Project Progress

Fri Jul 13, 2018 3:30 am

From the web page quoted:
The design is a standard non-inverting design, the input is applied to the non-inverting input of the op-amp which is pin 3 in most cases. The input impedance is 23.5k, the overall voltage gain is determined by R2 and R1according to the following formula:
The data sheet from On-Semi calls out a minimum of +/- 3V so you would need a larger supply voltage and buck it down to the RPi. You might have to play with the gain (R1 and R2) depending on the mic you choose. Further, the frequency response is excellent for normal audio work but may fall well short of your needs for the bats. I don't see that as a realistic goal for such an inexpensive system as you are putting together.

As far as bats are concerned, the upper end of bats frequency range is well in excess of even the 192 KHz sampling rate. The most you would be able to reconstruct would be 95 KHz according to Nyquist and even that would be a stretch and assumes a sinusoidal wave form. I am not sure about the range of the mics...you might have to get pretty costly transducers to "hear" that high. I have not investigated that at all.

As far as the zero is concerned, for me it is a non-starter for its slowness. I was able to load a full-up copy of Audacity with the 3B and 2B before that but the Zero could not access it in the Raspbian repository. When I tried to play a .wav file recorded at 48000 samples, it never seemed to play but with the 3B, the same file loaded to Audacity from the file manager and played very nicely...certainly as good as the inexpensive ear buds I use could hear. Waiting around for the zero is much like watching grass grow. A 3B+ would be a nice choice with its higher speed, on-board wifi, on-board ethernet and USB ports. Still, the power consumption is high for a remote device.

KanoMaster22
Posts: 185
Joined: Wed Oct 05, 2016 6:06 pm

Re: Pi Portable Recorder - Project Progress

Fri Jul 13, 2018 6:09 am

Thanks for the help. The bats was just really a thing I was just curious about and not the main aim of the project. The Pi 3 would definitely be nice but I would have to solder of the USB ports and Ethernet ports to make it practical in my project and cut down the power consumption by disabling a few things.

Would it be possible to make the gain adjustable with a potentiometer?

Thanks again,
LouisP

Edit - first progress has been made, my 128 x 64 OLED is fully working as expected and I have got it to display custom images.

wh7qq
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Re: Pi Portable Recorder - Project Progress

Fri Jul 13, 2018 8:12 pm

KanoMaster22 wrote:
Fri Jul 13, 2018 6:09 am
Would it be possible to make the gain adjustable with a potentiometer?
If you are speaking of the mic preamp circuit, of course, but you would probably want to have the pot in series with a fixed resistor, at least the same as the other one (R1=R2) for a minimum 1x gain. There was a homebrew amp using the same basic circuit on a you-tube clip that did that.

As for the USB port soldering, you are in the same boat but worse with the Zero...just the single OTG connector for USB; and the Ethernet would require a USB port on the Zero as well, so some kind of a USB hub is needed. Both Zero and 3B+ feature on-board wifi, so the ethernet is not absolutely necessary if you are in range of your router or AP. The main disadvantage I see for the 3B+ is size and power consumption but a hefty (3 Amp or more) power supply for the 3B+ would also handle a small boost regulator for your op-amp supply (Gnd becomes the negative rail and the input resistor would go to a divider pair acting as a ground point. Just be sure the output never goes over 3.3 volts or below ground).

You might get better response out of a different/leaner OS like Diet-Pi on the Zero. Aplay and arecord are probably in their repositories but I cannot swear to that. Use of the Zero with a GUI will age you even if Audacity could be loaded.

KanoMaster22
Posts: 185
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Re: Pi Portable Recorder - Project Progress

Fri Jul 13, 2018 9:01 pm

Thanks for the help. Any idea in the name or channel of the YouTube vid, is it the one by HackaweekTV? My project does not require an internet connection but it would be an good extra feature to have (code to directly upload the audio to a seperate phone is possible). I also only need 1 USB port for use when prototyping as I have an adapter hub to add more USB ports and will probably not need USB in the actual build.

DietPi is definelty a good idea and one I had not considered. No harm in trying a Pi Zero to start with and switching over to a full size Pi if it doesn't work out.

Thanks yet again,
LouisP

KanoMaster22
Posts: 185
Joined: Wed Oct 05, 2016 6:06 pm

Re: Pi Portable Recorder - Project Progress

Sun Jul 15, 2018 9:57 am

Going back to the Audio Injector Zero, I have looked closer and it seems it has input LGR pins broken out on the right of board. From my quite limited knowledge LGR is used in a TRS jack which would mean I can just wire it directly up to a TRS jack. Am I right saying this?

Thanks,
LouisP

wh7qq
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Joined: Thu Oct 09, 2014 2:50 am

Re: Pi Portable Recorder - Project Progress

Tue Jul 17, 2018 3:07 am

Nice try, but I think not...silk screen on the board calls it out as "video". Been up to my *** in ISP problems this weekend so no chance to try recording features yet. Finally got it all worked out this am but still sorting out the aftermath.

KanoMaster22
Posts: 185
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Re: Pi Portable Recorder - Project Progress

Tue Jul 17, 2018 9:46 am

Okay thanks for the help. Glad to hear you got your internet problems sorted as they are very annoying - I recently had a guy high on drugs crash into my wifi box recently (not my ISPs fault though).

wh7qq
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Re: Pi Portable Recorder - Project Progress

Tue Jul 17, 2018 8:48 pm

Adapters from mini-phone jack to 1/4" are out there...not hard to find on-line.

KanoMaster22
Posts: 185
Joined: Wed Oct 05, 2016 6:06 pm

Re: Pi Portable Recorder - Project Progress

Tue Jul 17, 2018 10:30 pm

Thanks for the help again! :D I presume you are talking about the Audio Injector Ultras 1/4" jacks. The adapters would be the best option but trying to make the product portable will probably mean I can't fit the 1/4" jacks and adapters inside the recorder. I have 10 days to decide whether to back the Kickstarter (I probably will).

Currently, I am improving my PCB designing skills (or lack of) so I can hopefully use a few custom PCBs to attempt to keep size to the minimum. Big issue right now is getting the CPU usage of the screen down. The I2C OLED is too needy it terms of CPU usage but I've heard a SPI OLED is a better option from multiple websites (apart from the fact it uses to more GPIO pins than the I2C one).

KanoMaster22
Posts: 185
Joined: Wed Oct 05, 2016 6:06 pm

Re: Pi Portable Recorder - Project Progress

Sun Aug 12, 2018 8:50 pm

Looks like I am not the first to try this :( . Just found this (https://hackaday.io/project/28716-ultim ... o-recorder) project.

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