Ok, so I'm building a synthesizer. I have some filter ICs that I want to control with an arduino (they are analog filters but have onboard digital controls). The filter ICs require bipolar power (+/-5V). I'm trying to figure out how to power both the chips and the arduino in the least convoluted way possible (not to mention the host of other components in this project that require different voltages, but that's a whole different can of worms).
My original plan was to have a 15V supply. I would regulate it down to 9V before running it into the Arduino. For the filter chips, I had planned on using a TLE2426 rail splitter to turn +15V into +/-7.5V, which would then be regulated down to +/-5V. But the more I think about it, the less I'm sure it will work. Since I'm using a virtual ground for the filter chips, I think this means that the arduino LOW will be at -5V, and the HIGH will be at 0V from the perspective of the filter chips, and that the arduino will never be able to generate a +5V signal that the chips will see as 5V. Does that make sense?
Can anyone suggest a better solution to powering this project? happy to answer any clarifying questions.
Edit: and before anyone asks, there is no datasheet available for the filter chips in question. There's a service manual available for the synth that the chips came out of that explains the pin assignments, but that's it.
Double edit: the arduino also needs to read analog signal from another part of the synthesizer, some between 0-2.5V and some between 0-5V (although the latter could be flexible).
I briefly considered connecting the arduino Vin directly to the 15V supply and the GND to the virtual ground of the rail splitter, but I don't think this will work either. For one, if the Arduino uses the virtual ground, I think that will draw current from the TLE2426 (I may be wrong), which has a relatively low maximum current (~20mA). I think that I would likely exceed 20mA if the arduino is drawing current... Additionally, that means that my analog voltages that the arduino needs to read will be in the negative range relative to the virtual ground, which I also don't think is good.
A dual-rail power supply would be great, but I have two issues there. One, I can't seem to find one at a reasonable cost, and two, other parts of the project require voltages higher than 5V.
The main section of the synth runs on 7.5-9V, and an effects section I'm adding runs on 9-15V. The effects section in particular needs a very clean power supply, so the plan was the start with 15V and use a linear regulator to bring that down to 12V. The main synth unit is not as particular about its power needs.
The Arduino is going to be reading analog control voltages from the main synth unit as well as a potentiometer, then converting those analog readings to digital signals that the filter chips can read.
Regarding dual rail power supplies, does a reasonably priced one exist that outputs +/-12V or +/-15V? And would I run into trouble bringing both rails down to 5V?
Why are you making it so complicated. Just order two 2-prong power supplies and connect one of the backwards ("+" output to arduino GND). That will give you a negative output and the other one will give you the positive output. What is so difficult about that ?
raschemmel:
Why are you making it so complicated. Just order two 2-prong power supplies and connect one of the backwards ("+" output to arduino GND). That will give you a negative output and the other one will give you the positive output. What is so difficult about that ?
It's not difficult at all, and trust me, I've considered this option. The main issue is that I'd like the keep the power supply external if possible and having two external power supplies strikes me as an inelegant way to design an instrument. Were I to switch to an internal power supply design, that's a lot of space and heat that I have not been accounting for.
Still, I'm keeping it in the back of my mind as a last-ditch solution.
jremington:
Yes, shop around and no (can use 7805 and 7905 regulators or buck converters).
So I am coming up completely dry on dual power supplies... I'm guessing it's because I'm looking for external power supplies. I'd like to avoid internal supplies due to the additional space it will take up and the extra heat it will produce, not to mention the peace of mind from not having mains voltage inside the box at any point. But if I want a power supply that gives bipolar power, it looks like I'm SOL for that.
This seems like it could be a decent solution, no? I could use a 12 or 15V wall wart, linear regulators for the parts that want 9V, and this board to supply +/-5V to my filter chips. They also make a 12V version if the switching regulators on the 5V version prove to be too noisy. Any reason this wouldn't work? Or am I maybe misreading the page and this simply provides another virtual ground situation, leaving me back where I started?
jremington:
What you are doing does not strike me as designing, but rather, simply hacking something together.
Seems like tomayto/tomato to me. Yes, I'm absolutely hacking stuff together. But at the end, I hope the end up with relatively polished and complete musical instrument that would be at home in a studio, and having two power supplies is at odds with that end goal.
I know it's not as glamorous as designing circuits from the ground up for eventual commercial release, but it's what I find interesting.
jremington:
Good luck doing so without the data sheets for the filter chips.
I'm not really too worried about that. Other folks have used these chips in new designs just fine without the datasheet, and they're really pretty simple chips to begin with. Is there anything specific you think I should be careful about?
I was hoping to have an external power supply, but it's increasingly looking like that's not an option. Still, the prices on those are well past what I was hoping to spend. I'll keep looking for other options, surely there's something out there.
Did you happen to see the link I posted to the Futurlec board? Does it seem like that might be a simple solution?
Jayteefos:
So I am coming up completely dry on dual power supplies... I'm guessing it's because I'm looking for external power supplies. I'd like to avoid internal supplies due to the additional space it will take up and the extra heat it will produce,
Not easy especially if you need low noise rails for sensitive circuits.
I have a regulated 18 0 -18 wall wart which i had to build myself.
Then i use an on board 15 0 -15 linear reg with additional filtering .
Keeps the mains off the board and the heat down.
Generally i find it far easier to use batteries.
What current do you need and what noise can you tolerate on the rails ?
Switchmode give of little heat but can need careful shielding and filtering.
Boardburner2:
Not easy especially if you need low noise rails for sensitive circuits.
I have a regulated 18 0 -18 wall wart which i had to build myself.
Then i use an on board 15 0 -15 linear reg with additional filtering .
Keeps the mains off the board and the heat down.
Generally i find it far easier to use batteries.
What current do you need and what noise can you tolerate on the rails ?
Switchmode give of little heat but can need careful shielding and filtering.
Yeah, I am a little worried about noise issues with a switching supply. There are parts of this project where clean power isn't necessary, but since this is directly powering an analog filter, it's probably best to stabilize it as much as possible.
I am unsure of current draw right now, but I expect it to be modest. Tens of mA, somewhere in that range.
Since it's only the one bit that needs the bipolar power supply, right now I'm looking into DC-to-DC 7805/7905-based supply circuits. Should give me better noise specs than the Futurlec supply I linked to above, and should be simple enough to work up on stripboard, which will be nice. That way I can stick with a regular +12-15V wall wart.
Thanks for your help. Seems like every time I clear a roadblock on this project (this has been a pipe dream/pet project of mine for almost 10 years, and I'm only just now getting knowledgeable enough to pull it off right) a new one pops up! Still, getting much closer! Onward!
Have a look at the Murata NMA series of DC-DC converters. I've used the NMA0505SC in audio circuits (Volume control circuit) with very good results. It does depend on how much current you require though, but they do similar modules with higher wattage.
ian332isport:
Have a look at the Murata NMA series of DC-DC converters. I've used the NMA0505SC in audio circuits (Volume control circuit) with very good results. It does depend on how much current you require though, but they do similar modules with higher wattage.
Ian.
Hey! Nice find, I think that'll be the one. Put 12V in, get +/-5V out. Perfect. I really can't imagine needing more than 100mA.
