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DIY Portable Recorder

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Old Tuesday 22nd January 2019, 21:55   #1
Louis_P
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DIY Portable Recorder

Hey everyone,

My hobbies are electronics and birdwatching and quite a few months ago I had the idea to combine the hobbies to make a high quality portable recorder for birdwatchers. As well as allowing the user to record audio, their will be features such as listing (to log sightings on the go without having to carry a notebook and pen), conditions logging (temperature, altitude etc. to provide extra information when logging sighting, GPS logging (to log the location lf sightings) and more! This will all be run on a Pi Zero - a British designed and made mini computer which is half the skze of a credit card! Of course the features provided in the device are subject to change as I work on prototypes. At the moment I am busy designing schematics and PCBs (the electronic circuits) as well as the first app - the listing app. Soon I hope to develop and app for making and playing back recordings. To follow the progress of this project and find more details check here - https://hackaday.io/project/159744-pi-portable-recorder. On the webskte you can register to recieve updates.

If you have any questions please do ask.

Regards,
Louis

Last edited by Louis_P : Tuesday 22nd January 2019 at 22:18.
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Old Friday 25th January 2019, 10:41   #2
ermine
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Just because it can be done with a Pi doesn't mean it has to be Something like a LS-10 runs for half a day from two AA batteries, it's small, light and works well. You could add your functions by using one of the stereo channels as a slate channel and on the other side of the slate SPDT switch put the GPS signal or AFSK encoded version. Simpler, smaller and more field-friendly.

But if this is an itch you want to scratch, good luck, perhaps there's a market for a large, power-hungry but slightly more full-featured field recorder. Audioinjector zero is a half-decent recording capable sound card for the Pi.
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Old Sunday 27th January 2019, 22:05   #3
Louis_P
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Haha =D. I do like to have the power and ease of use of the Pi Zero but a SAMD51 chip or the Sony Spresense (which comes with GPS on board) are both viable options although the latter is not yet fully documented whereas the former has a 1732 page datasheet to work from. Thank you for the advice but could you elaborate what a slate channel is?

As for the Audio Injector Zero, I actually have one I just bought to try whilst I put together an order for these two audio boards (https://github.com/skiselev/i2s_audio_phat and https://gitlab.com/kakar0t/audiosense-pi). The first one uses the WM8731 board as does the Audio Injector Zero and the second uses the TLV320 chip. I plan on testing both of these board and deciding on which to use, although redesigning the PCBs would be a must to keep wasted space to a minimum.

Regarding
Quote:
perhaps there's a market for a large, power-hungry but slightly more full-featured field recorder
this project is just really for my own benefit at the moment but if I create a good finished result it would be great if other people used it but if not at least I've learnt a lot along the way. I certainly think it can be done but keeping the size to a minimum will be tough (especially maintaining a balance between battery life and device size). I will be adding MOSFETs to the main board to turn off parts of the device not being used and I have some tips from https://hackaday.io/project/19035-ze...-pi-smartphone. It is actually possible the entire device (yes, even a Pi Zero) from a 3.7V battery with no voltage step ups as long as a good battery management system is in place. This has been tested a lot by the project I linked.

Thanks,
Louis
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Old Monday 28th January 2019, 20:39   #4
ermine
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How are you planning to overcome the lack of audio sensitivity on these boards? I used a Pi with PiJuice battery module (which gives me a RTC and a sort of sleep/autostart and I plan to use some of these to scout places without having to get up early and be in several places at once. But the Audioinjector only has stereo line level inputs, which seems to be a limitation of the WM8731. I bought some MAX9812 fixed 20dB gain mic preamp boards from ebay to fix that. They have a pretty disgusting 40nV/√Hz EIN but that probably matches the quality of sort of throwaway electret capsules I'd use.

Wolfson/Cirrus studiously avoid the subject of EIN on your WM8731, citing -85dBA ref 1V on the mic input. Sure, I could do better noise-wise with a LM833 but then I get into a world of hurt getting the power rails off the Pi without al the digital and switchmode hash. I took a look at your TLV320 but it has the same problem of only a mono mic input, or a weedy +12dB PGA on the line inputs which are referenced to 1VRMS for 0dBFS @ 0dB gain. A Sennheiser ME66 is a high output mic but still only 50mV/Pa, and you ain't getting 1Pa out of any bird while you're holding the mic. 5mV RMS is probably more what you'll get. So you may want space for an audio preamp upstream of the chip when you lay out the board.

Real bird recording is all about getting system noise down because birds aren't loud and they don't usually want to get anywhere near you. A run and gun audio record shot can still be useful with a noisy rig though it won't win awards. OTOH if that's level of performance in mono is good enough for you then there's much to be said for a smartphone, perhaps with a slightly amplified microphone.
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Old Monday 28th January 2019, 22:55   #5
Louis_P
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Thanks for your further advice. I plan on testing several pre amp circuits from the cheap one mentioned to some supposedly higher quality ones I have bookmarked the schematics for.
Quote:
So you may want space for an audio preamp upstream of the chip when you lay out the board
I will keep that in mind when designing the PCBs.

As for the actual microphone, I plan on using a mono EM172 electret microphone although I am yet to test this as different voltages and information about it is scarce.

Let's be honest there will not be much in this device that is better than a smartphone other than it being open source and easily configurable (to add whatever microphone you like or extra sensors etc.) and possibly cheaper. Of course I am aiming for the highest quality audio possible in the device as well, hopefully better than that of a smartphone.

Last edited by Louis_P : Tuesday 29th January 2019 at 18:38.
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Old Wednesday 20th February 2019, 15:09   #6
Suffeaked
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My brother decided to make a portable, wearable, audio player. For a start, he decided on the body. Made USB connector and installed in a regular place in the case, connecting the wire. He installed the microUSB connector in a regular place of the case, soldering to the plus and minus enameled wire from the transformer. He cut the hole with a drill for the headphone jack and brazed with enameling.
It is a lightweight, compact, long-playing MP3 player. Now I can easily download birds singing -https://notmp3.com - It has a calming effect on me.
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Old Thursday 28th February 2019, 16:55   #7
Louis_P
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That sounds like a nice little device. How is it worn? Also, do you have any more information on the body as it is an aspect of the project I am currently uncertain on, with my 3D design skills (to design my own from scratch) currently very limited.

Thanks,
Louis P
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