Hi All,
I need some advice on a particular project to fit my needs, and I expect would be useful for others. I have been using Raspberry Pi computers with DACs via I2S. These work pretty good using Moode (Thanks, Tim). So far so good.
I really would like something more portable, that could run for a few hours on battery power.
I have a transportable version using the full size Pi boards (3b, etc.). I can run it on line voltage with an internal switcher, but I also put four AA LiFePO4 batteries and a DC-DC converter to drop it down to 5v. The AAs will run it for about an hour. When the batteries are out of it, I can plug 12v into it. A bigger LiFePO4 battery (12v 10AH) will run it for about two hours, which seems surprisingly little.
Here are my requirements:
– Minimal size, whatever that means—maybe old-school Walkman cassette player?
– Run for 4–8 hours on internal or external battery power
– Run on 12v from a car
– Be able to use USB SSDs in the terabyte range, since I have a large library
– RPi with Moode or other Pi player software
I have built a smaller version with a Pi Zero W and an Allo Mini-Boss. My first thought was to use an M.2 memory module with a USB adaptor. I also included a postage-stamp sized headphone amplifier in it for a little more signal. No batteries, but a DC-DC converter and a 12v input in addition to the 5v.
I got the Pi Zero running and set up, but for whatever reason, the M.2 memory wouldn’t mount. Plan B was a 1TB MicroSD card, less than I wanted, but it did mount and compile the library. I also picked up a 2 TB USB-C portable SS drive (Crucial X6). I have been unable to get that to mount.
This small Pi player does play, but it has a loud ticking sound at about 4–5 hz in the headphones, and some scratchy noise as well. These sounds are always at the same level, so when the volume is turned up, the music gets relatively louder making the ticking somewhat less obvious, but it’s nowhere close to usable. I have shorted across the inputs and outputs of the headphone amp board, thereby bypassing the amp, and the volume lowers but the ticking does not go away. The case is aluminum and titanium with a plastic insert on the lid where the Pi is to allow WiFi signals to pass. If I put my hand on top of this, the ticking gets quieter.
The ground is not connected to the case, but when I temporarily connect either the power or signal ground (should be the same here), the sound does not change.
I have heard this kind of ticking before on RPis, and have no idea what could be causing it or how to fix it. I have a Pi Zero 2 W on order, as well as a couple of different USB cables to fit this tight space. We’ll see if any of that makes any difference. Any thoughts or suggestions of things to try?
Ultimately the goal is to come up with a workable, low-power and compact design, than perhaps design a case that can be 3D printed to make it easy for anyone to implement.
I need some advice on a particular project to fit my needs, and I expect would be useful for others. I have been using Raspberry Pi computers with DACs via I2S. These work pretty good using Moode (Thanks, Tim). So far so good.
I really would like something more portable, that could run for a few hours on battery power.
I have a transportable version using the full size Pi boards (3b, etc.). I can run it on line voltage with an internal switcher, but I also put four AA LiFePO4 batteries and a DC-DC converter to drop it down to 5v. The AAs will run it for about an hour. When the batteries are out of it, I can plug 12v into it. A bigger LiFePO4 battery (12v 10AH) will run it for about two hours, which seems surprisingly little.
Here are my requirements:
– Minimal size, whatever that means—maybe old-school Walkman cassette player?
– Run for 4–8 hours on internal or external battery power
– Run on 12v from a car
– Be able to use USB SSDs in the terabyte range, since I have a large library
– RPi with Moode or other Pi player software
I have built a smaller version with a Pi Zero W and an Allo Mini-Boss. My first thought was to use an M.2 memory module with a USB adaptor. I also included a postage-stamp sized headphone amplifier in it for a little more signal. No batteries, but a DC-DC converter and a 12v input in addition to the 5v.
I got the Pi Zero running and set up, but for whatever reason, the M.2 memory wouldn’t mount. Plan B was a 1TB MicroSD card, less than I wanted, but it did mount and compile the library. I also picked up a 2 TB USB-C portable SS drive (Crucial X6). I have been unable to get that to mount.
This small Pi player does play, but it has a loud ticking sound at about 4–5 hz in the headphones, and some scratchy noise as well. These sounds are always at the same level, so when the volume is turned up, the music gets relatively louder making the ticking somewhat less obvious, but it’s nowhere close to usable. I have shorted across the inputs and outputs of the headphone amp board, thereby bypassing the amp, and the volume lowers but the ticking does not go away. The case is aluminum and titanium with a plastic insert on the lid where the Pi is to allow WiFi signals to pass. If I put my hand on top of this, the ticking gets quieter.
The ground is not connected to the case, but when I temporarily connect either the power or signal ground (should be the same here), the sound does not change.
I have heard this kind of ticking before on RPis, and have no idea what could be causing it or how to fix it. I have a Pi Zero 2 W on order, as well as a couple of different USB cables to fit this tight space. We’ll see if any of that makes any difference. Any thoughts or suggestions of things to try?
Ultimately the goal is to come up with a workable, low-power and compact design, than perhaps design a case that can be 3D printed to make it easy for anyone to implement.
Attachments
We would need schematics and more info in order to be of much help. Also, you need to figure out how power is being used. You can take some measurements of what is using power. Displays are often power hungry. Using a cpu with lots of unnecessary services running, using higher clocks speeds than really needed, and similar sorts of things can affect battery life. When you want long battery life, then you have to take a hard look at everything that consumes power and consider the tradeoffs.
I have two devices. I understand that running a full-sized Pi on battery power is not practical, which is why I've been attempting to get a Pi Zero device working. They're both pretty similar in their organization; there's only so many ways to put one of these together. I'm not using a screen on either. A block diagram of the Pi Zero device in the photo is attached. It's the one for which I'm having the noise problem. The full-sized Pi one is pretty much the same, except batteries or an external 12vdc power source are connected to the DC-DC converter.
As I mentioned, the noise problem remains the same even when I temporarily ground the negative rail to the case. I'm still looking for suggestions for what to try to fix that. I have a Pi Zero 2 waiting to be installed to see if there's something wrong with the zero w that's in there now.
Any thoughts appreciated, including where is the appropriate point in a device like this to make the ground to negative rail connection.
As I mentioned, the noise problem remains the same even when I temporarily ground the negative rail to the case. I'm still looking for suggestions for what to try to fix that. I have a Pi Zero 2 waiting to be installed to see if there's something wrong with the zero w that's in there now.
Any thoughts appreciated, including where is the appropriate point in a device like this to make the ground to negative rail connection.
Can you isolate the area where you think the noise comes from. An example disconnect the amp and listen if the tick, tick is in the audio. Power each module individually to see if it is the power supply, you must have a lot of phone chargers available. If you have maybe a few batteries around try powering each box individually with its own power source. I had a similar problem once that my modem was running off the USB power of my PC, so was everything else. Took a while to figure that out. The culprit is usually what you expect least.
Sorry for the delay in responding. I've been traveling.
I have tried several different 5v power supplies, and all give the same (noisy) results.The ticking and other noise comes out of the DAC, but I don't know whether it originates in the Pi or the DAC. When I bypass the little amp board, the same noise remains, but obviously at a lower level. As I mentioned, the noise is constant; when I turn the potentiometer up, the music gets louder, but the noise stays at a constant level. At higher volume levels it's not that noticeable.
I'm using Moode 8.5 (released in February of this year). I have the DAC/driver set for Mini-Boss.
I have tried several different 5v power supplies, and all give the same (noisy) results.The ticking and other noise comes out of the DAC, but I don't know whether it originates in the Pi or the DAC. When I bypass the little amp board, the same noise remains, but obviously at a lower level. As I mentioned, the noise is constant; when I turn the potentiometer up, the music gets louder, but the noise stays at a constant level. At higher volume levels it's not that noticeable.
I'm using Moode 8.5 (released in February of this year). I have the DAC/driver set for Mini-Boss.
Don't use a pot on the output of the DAC. Use digital volume control (hardware volume) in Moode with chip set settings.
I certainly don't want to dissuade your DIY efforts, but it seems like one of the offerings from FiiO could do most of what you're looking for. Many (all?) of their portable players have dual SD card slots. Worth a look IMO, even if just for a benchmark of size, layout, battery life, etc for your diy development.
Phones now have 1 TB of storage. That can store a lot of audio, especially if you're willing to accept 256 or 320 kbit/s MP3 while travelling.
But getting back to the DIY solution: I'd strip the system down to its bare minimum. Can you get it running with a USB DAC and a single power supply? Build out from here.
How's the switching between power supplies handled? That's not clear from the block diagram.
Tom