So I'm building a project with a cmoy inside it. I'm using tangent's resistive voltage divider to power everything. In addition to the cmoy I have a CD4052 Mux and a DS1802 digital pot for volume control. All of these work perfectly fine and sounds amazing,
However there is one last problem, powering a microcontroller. Right now I have an arduino uno while I prototype and when I plug in the +9V into its regulator the rail voltages are lowered to like 3-4V. I'm guessing its because the uC is a much larger load than anything I have right now but I dont know what to do about it.
So any ideas on fixes, hopefully as cheap as possible.
Also, I feel like a noob for asking this but how do I measure the amount of current drawn by this design. I was looking at some of the other virtual ground setup's over at tangents and the biggest factor is current draw. I tried disconnecting on side of the transfromer and putting the meter in sereis. However none of the power LEDs light and the meter reads like 2A while the transformer is rated for 24V, 500mA.
However there is one last problem, powering a microcontroller. Right now I have an arduino uno while I prototype and when I plug in the +9V into its regulator the rail voltages are lowered to like 3-4V. I'm guessing its because the uC is a much larger load than anything I have right now but I dont know what to do about it.
So any ideas on fixes, hopefully as cheap as possible.
Also, I feel like a noob for asking this but how do I measure the amount of current drawn by this design. I was looking at some of the other virtual ground setup's over at tangents and the biggest factor is current draw. I tried disconnecting on side of the transfromer and putting the meter in sereis. However none of the power LEDs light and the meter reads like 2A while the transformer is rated for 24V, 500mA.
It sounds like you're making your measurements mostly correctly, but consider which side of the transformer you're metering. 2A on the mains side of a 24V transformer is a different measurement than 2A on the 24V side of your transformer. Nevertheless, something is obviously wrong if you're drawing 2 amps from a transformer specced for only half an amp!
In the absence of a schematic it's tough to say exactly why the circuit behaves as it does when you connect the arduino, but my guess is that it's related to the way your virtual ground is designed. As tangent describes, the problem with "simple" virtual ground circuits implemented with two resistors is that they have a tendency to become unbalanced if the load on the two rails isn't perfectly symmetrical. If you were to, say, throw a complex device with significant current draw across the rails (
), who knows what would happen? If you plugged the Arduino's ground into the virtual ground instead of the negative rail, then you would certainly cause things to behave strangely.
Remember, a virtual ground is more of a signal reference than a return path for current.
Tangent describes all sorts of ways to buffer your virtual ground to cajole it into behaving better, but those methods are basically compromises you must make when designing battery operated equipment. In your case, since your project is mains powered, you have access to the magic solution that makes all this go away: a center-tapped transformer.
One caveat: grounding in mains powered audio systems is a complex topic that begs careful attention.
Good luck!
In the absence of a schematic it's tough to say exactly why the circuit behaves as it does when you connect the arduino, but my guess is that it's related to the way your virtual ground is designed. As tangent describes, the problem with "simple" virtual ground circuits implemented with two resistors is that they have a tendency to become unbalanced if the load on the two rails isn't perfectly symmetrical. If you were to, say, throw a complex device with significant current draw across the rails (
), who knows what would happen? If you plugged the Arduino's ground into the virtual ground instead of the negative rail, then you would certainly cause things to behave strangely.Remember, a virtual ground is more of a signal reference than a return path for current.
Tangent describes all sorts of ways to buffer your virtual ground to cajole it into behaving better, but those methods are basically compromises you must make when designing battery operated equipment. In your case, since your project is mains powered, you have access to the magic solution that makes all this go away: a center-tapped transformer.
One caveat: grounding in mains powered audio systems is a complex topic that begs careful attention.
Good luck!
Well I'm using a AC-AC wallwart instead of a separate transformer. The wallwart is terminated into a barrel connector. I have a barrel jack with some wires soldered to it that I use for breadboarding. I put the meter in series with one of these wires that go in to the AC side of a rectifier bridge.
I guess I could buy a center tapped transformer but that would be very costly because I'd have to buy another enclosure for it.
I thought I could power the arduino using the -9V rail as ground but then I'd have a problem with logic levels right? The uC references to -9V and the mux and digipot reference to 0.
I've read over tangent's article a couple times but I can't find a solution thats both cheap and doesnt take up board space (really dont have much room on the board I have and the enclosure to match).
I guess I could buy a center tapped transformer but that would be very costly because I'd have to buy another enclosure for it.
I thought I could power the arduino using the -9V rail as ground but then I'd have a problem with logic levels right? The uC references to -9V and the mux and digipot reference to 0.
I've read over tangent's article a couple times but I can't find a solution thats both cheap and doesnt take up board space (really dont have much room on the board I have and the enclosure to match).
Use a double half-wave rectifier, like in this circuit:
Power Supply for Preamps
Ideal for your situation. No center tap transformer needed.
Use 7809 and 7909 regulators for your application.
Same idea is used for the O2 headphone amplifier in this thread:
http://www.diyaudio.com/forums/headphone-systems/193977-objective2-o2-headphone-amp-diy-project.html
Power Supply for Preamps
Ideal for your situation. No center tap transformer needed.
Use 7809 and 7909 regulators for your application.
Same idea is used for the O2 headphone amplifier in this thread:
http://www.diyaudio.com/forums/headphone-systems/193977-objective2-o2-headphone-amp-diy-project.html
hang on, you tried to measure the current by doing nothing except placing one lead on one side of the winding and the other lead on the other with it in ammeter mode? i'll tell you why you got such high readings and the les went out, because of the design of an ammeter you created a direct short circuit, that 2a was real!! never do that again. measure the voltage drop across a resistor and then use ohms law to figure what the current was based on that, much safer.
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