Learning electronics: Release the Magic Blue Smoke

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BattleMaster: Aug 14, 2000

Are there any downsides to using an op-amp IC that only requires a single positive supply such as the LM2904?

# ? Mar 19, 2009 19:08

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# ? May 22, 2024 00:53

Hubis: May 18, 2003; Boy, I wish we had one of those doomsday machines...

Hubis posted:

Of course, that makes perfect sense. The two-battery configuration worked fabulously (although now there's some hum in the sound, which I assume is coming from the preamplifier not expecting a DC-offset in its input signal).

Do you have any suggestions on how I'd go about applying a DC-offset to the input using only a single battery? Every pedal I've ever seen or worked with uses a single bipolar supply (usually either 9v or 12v, unless it has tubes), so I assume there's a fairly simple solution. Looking at some simple schematics online like this one (posted earlier), it seems like they produce a +4.5v source (Vb) using a resistor divider, then somehow use that to pull up the input voltage. I'm not quite clear on how that works, however.

So, what do I have to modify to make this work:

(Thanks for the assistance, btw. There's a huge amount of really great resources for learning this stuff all over the internet, but all that bootstrapping turns to crap when something goes minorly wrong and you have no idea what the right questions are to find a solution )

OK, thinking about it a bit more, I came up with this:

Which should mix the AC input with the +9V DC leads to give me (9v + 1vAC) / 2 = 4.5v + Signal/2

Is this a sane approach? Should I be using lower value resistors in the mixing stage? Is there a way to do this without cutting my signal in half, or should I just add some gain to my OpAmp stage?

# ? Mar 19, 2009 19:26

Delta-Wye: Sep 29, 2005

Hubis posted:

Do you have any suggestions on how I'd go about applying a DC-offset to the input using only a single battery? Every pedal I've ever seen or worked with uses a single bipolar supply (usually either 9v or 12v, unless it has tubes), so I assume there's a fairly simple solution. Looking at some simple schematics online like this one (posted earlier), it seems like they produce a +4.5v source (Vb) using a resistor divider, then somehow use that to pull up the input voltage. I'm not quite clear on how that works, however.

I'll give a shot at this: if you unplug the analog input (just use the DC input) the resistor divider will bias the opamp input to 1/2 of 9V, or 4.5 V. The output will also go to 4.5V DC, but because there is a capacitor that blocks the DC component, the final output of the circuit is 0V. When you add a AC signal (guitar, whatever) it is superimposed on the 4.5V, amplified, and assuming the capacitor is correctly valued, passes through just fine.

Lets say you have an AC signal that is -.5/+.5 V (I want to say guitars look like 100mV p-p, but I'm going from memory and its not truly important anyways). The V+ input on the opamp will look like it is +4/+5 V as a result, and the output of the circuit should be -.5/+.5 V again.

# ? Mar 19, 2009 19:36

Delta-Wye: Sep 29, 2005

Hubis posted:

OK, thinking about it a bit more, I came up with this:

Which should mix the AC input with the +9V DC leads to give me (9v + 1vAC) / 2 = 4.5v + Signal/2

Is this a sane approach? Should I be using lower value resistors in the mixing stage? Is there a way to do this without cutting my signal in half, or should I just add some gain to my OpAmp stage?

No, this shouldn't work. If I'm reading the schematic correctly, the V+ pin on the opamp is held to ground. The last schematic you posted is the best - you want a steady 4.5 V to the V+ pin, and then mix in your AC signal.

BattleMaster posted:

Are there any downsides to using an op-amp IC that only requires a single positive supply such as the LM2904?

That is effectively what he's doing - he needs to keep both the positive and the negative portions of the signal, or else it turns out extraordinarily distorted (and probably not a good way). What he's doing is running the opamp off of a single sided supply (0-9V) and biasing the AC input halfway between so that it will amplify both parts. He then is putting a capacitor on the output to filter the DC back out, so he gets a, relatively speaking (potentially speaking?), +/- signal.

# ? Mar 19, 2009 19:40

SnoPuppy: Jun 15, 2005

Hubis posted:

OK, thinking about it a bit more, I came up with this:

Which should mix the AC input with the +9V DC leads to give me (9v + 1vAC) / 2 = 4.5v + Signal/2

Is this a sane approach? Should I be using lower value resistors in the mixing stage? Is there a way to do this without cutting my signal in half, or should I just add some gain to my OpAmp stage?

Your first one was more correct. Just make sure to add a DC blocking cap to the input.

edit:
I'm also assuming that you're not grounding your + input. It looks like the ground wire is broken, but I just want to make sure.

SnoPuppy fucked around with this message at 20:10 on Mar 19, 2009

# ? Mar 19, 2009 19:44

Hubis: May 18, 2003; Boy, I wish we had one of those doomsday machines...

Delta-Wye posted:

I'll give a shot at this: if you unplug the analog input (just use the DC input) the resistor divider will bias the opamp input to 1/2 of 9V, or 4.5 V. The output will also go to 4.5V DC, but because there is a capacitor that blocks the DC component, the final output of the circuit is 0V. When you add a AC signal (guitar, whatever) it is superimposed on the 4.5V, amplified, and assuming the capacitor is correctly valued, passes through just fine.

Lets say you have an AC signal that is -.5/+.5 V (I want to say guitars look like 100mV p-p, but I'm going from memory and its not truly important anyways). The V+ input on the opamp will look like it is +4/+5 V as a result, and the output of the circuit should be -.5/+.5 V again.

(Just did a measurement; my guitar seems to put out around 10-30 mV if I clip the leads to the cable)

So I should have something that looks like this?

It seems to work in the simulator, at least. I've seen a lot of circuits use a capacitor in the input like this, which if I understand properly is to prevent overloading the inputs? Would I be better using a resistor there or something? I'm kind of at the stage right now where I can just think of capacitors as frequency-dependent resistors, but I'm not sure if that's always a valid assumption...

Also, how do I determine if my capacitor to remove the DC offset is the right size? I understand how high-pass filters work in terms of R-C circuits, but (based on your comments) in this case I am just running the output through a capacitor without a resistor shunt to ground. Is this ok, and/or does it simply require that I assume a high-impedance input on whatever this is plugged into?

e:

SnoPuppy posted:

Your first one was more correct. Just make sure to add a DC blocking cap to the input.

edit:
I'm also assuming that you're not grounding your + input. It looks like the ground wire is broken, but I just want to make sure.

Yeah, sorry for the confusion; that's a virtual scope lead that I left on the circuit when I took the screenshot.

# ? Mar 19, 2009 20:52

Delta-Wye: Sep 29, 2005

Hubis posted:

(Just did a measurement; my guitar seems to put out around 10-30 mV if I clip the leads to the cable)

So I should have something that looks like this?

It seems to work in the simulator, at least. I've seen a lot of circuits use a capacitor in the input like this, which if I understand properly is to prevent overloading the inputs? Would I be better using a resistor there or something? I'm kind of at the stage right now where I can just think of capacitors as frequency-dependent resistors, but I'm not sure if that's always a valid assumption...

Also, how do I determine if my capacitor to remove the DC offset is the right size? I understand how high-pass filters work in terms of R-C circuits, but (based on your comments) in this case I am just running the output through a capacitor without a resistor shunt to ground. Is this ok, and/or does it simply require that I assume a high-impedance input on whatever this is plugged into?

e:

Yeah, sorry for the confusion; that's a virtual scope lead that I left on the circuit when I took the screenshot.

The capacitor on the input is for the same reason as the cap on the output - while you want the signal to pass straight through unaffected, you don't want the previous stage's biasing to goober up your pedal, just as you don't want your biasing to goober up the next stage.

As far as the value of the cap, .1u should be fine - you are building an RC network even if it isn't directly following one of the example circuits. While you want to block DC, there is a whole shitload of frequencies you want to pass largely unaffected and .1u seems to be the standard value to do this.

In the complex plane, capacitors are seen as complex resistance. It is a bit of a jump, mathwise, but once you've made the jump, you can use Ohms law and such without having to worry if you're dealing with resistors, capacitors, or some combination therein.

# ? Mar 19, 2009 21:22

ANIME AKBAR: Jan 25, 2007; afu~

Hubis posted:

(Just did a measurement; my guitar seems to put out around 10-30 mV if I clip the leads to the cable)

So I should have something that looks like this?

It seems to work in the simulator, at least. I've seen a lot of circuits use a capacitor in the input like this, which if I understand properly is to prevent overloading the inputs? Would I be better using a resistor there or something? I'm kind of at the stage right now where I can just think of capacitors as frequency-dependent resistors, but I'm not sure if that's always a valid assumption...

Also, how do I determine if my capacitor to remove the DC offset is the right size? I understand how high-pass filters work in terms of R-C circuits, but (based on your comments) in this case I am just running the output through a capacitor without a resistor shunt to ground. Is this ok, and/or does it simply require that I assume a high-impedance input on whatever this is plugged into?

e:

Yeah, sorry for the confusion; that's a virtual scope lead that I left on the circuit when I took the screenshot.

You've got the right idea. Your main concern will be your source impedance (in the case, the impedance of you pickups or whatever feeds into the input). You want the AC impedance of the biasing network to be low and the DC impedance to be high. The capacitor effectively kills all DC and passes all the AC. However the biasing resistors can still load down the AC signal, which is bad. So you should make those resistors bigger; like maybe bump them to 100K. Don't go to high or they'll lose their effect, though.

Also on the output you'll want another bias resistor coupling the output signal to 0V (the same thing the output ground connects to). This will result in a pure AC output (with respect to ground).

Here's what you'll end up with. Import this into the falstad simulator:

code:

$ 1 5.0E-6 37.11724081536377 50 5.0 50
a 560 400 656 400 1 15.0 -15.0
r 528 384 528 304 0 100000.0
r 528 384 528 464 0 100000.0
c 512 384 448 384 0 1.0E-6 3.3091063244183205
r 752 400 752 464 0 100000.0
c 688 400 736 400 0 1.0E-6 3.3085477228158027
g 752 464 752 480 0
g 528 464 528 480 0
R 528 304 528 272 0 0 40.0 9.0 0.0 0.0 0.5
w 656 400 688 400 0
w 736 400 752 400 0
w 512 384 528 384 0
w 528 384 560 384 0
w 560 416 560 464 0
w 560 464 640 464 0
w 640 464 656 464 0
w 656 464 656 400 0
r 384 384 304 384 0 100000.0
w 384 384 448 384 0
v 256 384 256 464 0 1 300.0 2.0 0.0 0.0 0.5
w 256 384 304 384 0
g 256 464 256 480 0
x 639 161 691 167 0 24 hello
o 19 64 0 35 20.0 3.90625E-4 0 -1
o 2 64 0 35 40.0 3.90625E-4 1 -1
o 16 64 0 35 20.0 9.765625E-5 2 -1
o 4 64 0 35 10.0 9.765625E-5 3 -1

The resistor directly from the AC source isn't an actual component. It's meant to symbolize the source's inherent impedance. Go ahead and play with its value and see what happens.

# ? Mar 19, 2009 22:06

Hubis: May 18, 2003; Boy, I wish we had one of those doomsday machines...

ANIME AKBAR posted:

You've got the right idea. Your main concern will be your source impedance (in the case, the impedance of you pickups or whatever feeds into the input). You want the AC impedance of the biasing network to be low and the DC impedance to be high. The capacitor effectively kills all DC and passes all the AC. However the biasing resistors can still load down the AC signal, which is bad. So you should make those resistors bigger; like maybe bump them to 100K. Don't go to high or they'll lose their effect, though.

Also on the output you'll want another bias resistor coupling the output signal to 0V (the same thing the output ground connects to). This will result in a pure AC output (with respect to ground).

Here's what you'll end up with. Import this into the falstad simulator:
code:
$ 1 5.0E-6 37.11724081536377 50 5.0 50
a 560 400 656 400 1 15.0 -15.0
r 528 384 528 304 0 100000.0
r 528 384 528 464 0 100000.0
c 512 384 448 384 0 1.0E-6 3.3091063244183205
r 752 400 752 464 0 100000.0
c 688 400 736 400 0 1.0E-6 3.3085477228158027
g 752 464 752 480 0
g 528 464 528 480 0
R 528 304 528 272 0 0 40.0 9.0 0.0 0.0 0.5
w 656 400 688 400 0
w 736 400 752 400 0
w 512 384 528 384 0
w 528 384 560 384 0
w 560 416 560 464 0
w 560 464 640 464 0
w 640 464 656 464 0
w 656 464 656 400 0
r 384 384 304 384 0 100000.0
w 384 384 448 384 0
v 256 384 256 464 0 1 300.0 2.0 0.0 0.0 0.5
w 256 384 304 384 0
g 256 464 256 480 0
x 639 161 691 167 0 24 hello
o 19 64 0 35 20.0 3.90625E-4 0 -1
o 2 64 0 35 40.0 3.90625E-4 1 -1
o 16 64 0 35 20.0 9.765625E-5 2 -1
o 4 64 0 35 10.0 9.765625E-5 3 -1
The resistor directly from the AC source isn't an actual component. It's meant to symbolize the source's inherent impedance. Go ahead and play with its value and see what happens.

Awesome, I'll give this try and see if I have any more stupid questions

# ? Mar 20, 2009 00:49

Delta-Wye: Sep 29, 2005

So I'm building a multichannel light dimmer, and I need 5V for the PIC from AC, but I don't have space in the box for any of the transformers I have handy. Is there a neat trick to get regulated 5v from AC other than your typical transformer->rectifier->filter->regulator circuits?

EDIT: Hmm.. I don't think I've emphazied how little space I have to work. Alternatively, has anyone seen any small transformers? I have lots of horizontal room, but ~1/2" of vertical space, if not a little less.

EDIT2: Like this: http://www.discovercircuits.com/DJ-Circuits/acdc1.htm

I know these oddball circuits are out there, I'm just not so sure personally what I'm looking for and I was hoping one of the electron jockies who frequent this thread have heard of something suitable.

Delta-Wye fucked around with this message at 06:11 on Mar 20, 2009

# ? Mar 20, 2009 04:33

Mill Town: Apr 17, 2006

Delta-Wye posted:

So I'm building a multichannel light dimmer, and I need 5V for the PIC from AC, but I don't have space in the box for any of the transformers I have handy. Is there a neat trick to get regulated 5v from AC other than your typical transformer->rectifier->filter->regulator circuits?

Cut the jack off a 5V cellphone adapter that you don't need any more.

# ? Mar 20, 2009 05:42

Bush Ant: Jan 4, 2009; by Fistgrrl

voltage divider > single diode to act as a half bridge rectifier > capacitor >linear voltage regulator.

If its just one IC drawing a few milliamps then this will work, sure its crude as hell but will take up next to no space

edit: here you go, it has the added benefit of not being isolated, now you can create circuits just like KBR!!

Bush Ant fucked around with this message at 07:28 on Mar 20, 2009

# ? Mar 20, 2009 07:12

Delta-Wye: Sep 29, 2005

Bush Ant posted:

voltage divider > single diode to act as a half bridge rectifier > capacitor >linear voltage regulator.

If its just one IC drawing a few milliamps then this will work, sure its crude as hell but will take up next to no space

That's so stupid it might just work (perfectly). I had completely overlooked the obvious - I'll give it a try.

# ? Mar 20, 2009 07:20

ANIME AKBAR: Jan 25, 2007; afu~

Delta-Wye posted:

So I'm building a multichannel light dimmer, and I need 5V for the PIC from AC, but I don't have space in the box for any of the transformers I have handy. Is there a neat trick to get regulated 5v from AC other than your typical transformer->rectifier->filter->regulator circuits?

EDIT: Hmm.. I don't think I've emphazied how little space I have to work. Alternatively, has anyone seen any small transformers? I have lots of horizontal room, but ~1/2" of vertical space, if not a little less.

EDIT2: Like this: http://www.discovercircuits.com/DJ-Circuits/acdc1.htm

I know these oddball circuits are out there, I'm just not so sure personally what I'm looking for and I was hoping one of the electron jockies who frequent this thread have heard of something suitable.

There are simple ways to do it, but they're essentially tricks that defy a lot of conventional design rules. They are also inherently quite unsafe without great precaution.

When I TA'd the practical circuit design class, there was a project where students had to do exactly this kind of thing. They were given 1:1 isolation transformers to use, but even so we had them use protective enclosures for safety. You wouldn't even have the isolation. Given the hazards you'd have to deal with, I'd advise you to take the safe rout and get a wall wart supply and use that.

edit: hell, with that little space the heat dissipation might be a factor in any case.

ANIME AKBAR fucked around with this message at 08:50 on Mar 20, 2009

# ? Mar 20, 2009 07:38

Delta-Wye: Sep 29, 2005

ANIME AKBAR posted:

There are simple ways to do it, but they're essentially tricks that defy a lot of conventional design rules. They are also inherently quite unsafe without great precaution.

When I TA'd the practical circuit design class, there was a project where students had to do exactly this kind of thing. They were given 1:1 isolation transformers to use, but even so we had them use protective enclosures for safety. You wouldn't even have the isolation. Given the hazards you'd have to deal with, I'd advise you to take the safe rout and get a wall wart supply and use that.

I suspect it would be safe enough - if the knobs on the pots are plastic, the entire enclosure is plastic except for the AC jacks, which are going to be hot anyways. That said, getting shocked is really not that much fun, so I should probably look into alternatives.

So now is my opportunity to show my digital-only colors: can someone detail a bit why it is so unsafe? Is it the direct ground->neutral connection? Is the fear a ground(neutral) to earth path?

Bush Ant posted:

edit: here you go, it has the added benefit of not being isolated, now you can create circuits just like KBR!!

If it's good enough for our soldiers... :clint:

Delta-Wye fucked around with this message at 09:25 on Mar 20, 2009

# ? Mar 20, 2009 08:57

ANIME AKBAR: Jan 25, 2007; afu~

Delta-Wye posted:

So now is my opportunity to show my digital-only colors: can someone detail a bit why it is so unsafe? Is it the direct ground->neutral connection? Is the fear a ground(neutral) to earth path?

Pretty much. In nonisolated circuits, touching hot while your body is a low impedance to earth ground is dangerous. Isolation eliminates the earth ground path, so the only dangerous connection is from hot to neutral, which is much easier to avoid.

One key piece of safety is use heatshrink on any wire connections on the hot line.

quote:

If it's good enough for our soldiers...

http://www.msnbc.msn.com/id/22425001/vp/29605697#29605697

this kind of poo poo is so absurd it's just mind boggling.

ANIME AKBAR fucked around with this message at 09:41 on Mar 20, 2009

# ? Mar 20, 2009 09:39

All About Trout: Jul 17, 2007

Does anybody have any interest in a Ramsey FM30B kit? It's a complete kit for a 25mw digital FM transmitter. I actually won one from their site but I don't really have enough interest in it to do ~500 solder points. If there's interest I'll put it up in samart.

This: http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=FM30B

All About Trout fucked around with this message at 11:22 on Mar 20, 2009

# ? Mar 20, 2009 11:17

ANIME AKBAR: Jan 25, 2007; afu~

I might be interested. I'll read more on it when I get the time.

# ? Mar 20, 2009 14:18

Hillridge: Aug 3, 2004; WWheeeeeee!

Delta-Wye posted:

So I'm building a multichannel light dimmer, and I need 5V for the PIC from AC, but I don't have space in the box for any of the transformers I have handy. Is there a neat trick to get regulated 5v from AC other than your typical transformer->rectifier->filter->regulator circuits?

EDIT: Hmm.. I don't think I've emphazied how little space I have to work. Alternatively, has anyone seen any small transformers? I have lots of horizontal room, but ~1/2" of vertical space, if not a little less.

EDIT2: Like this: http://www.discovercircuits.com/DJ-Circuits/acdc1.htm

I know these oddball circuits are out there, I'm just not so sure personally what I'm looking for and I was hoping one of the electron jockies who frequent this thread have heard of something suitable.

The wall to USB plug for the iPhone 3G is stupid small. Like amazingly tiny. Of course, knowing Apple it's probably also stupid expensive.

# ? Mar 20, 2009 16:14

Delta-Wye: Sep 29, 2005

ANIME AKBAR posted:

Pretty much. In nonisolated circuits, touching hot while your body is a low impedance to earth ground is dangerous. Isolation eliminates the earth ground path, so the only dangerous connection is from hot to neutral, which is much easier to avoid.

One key piece of safety is use heatshrink on any wire connections on the hot line.

http://www.msnbc.msn.com/id/22425001/vp/29605697#29605697

this kind of poo poo is so absurd it's just mind boggling.

I think I might do it without a transformer - the circuit is a pic plus 3 optoisolated triacs triggering 3 power triacs, so most of the circuit is going to be hot no matter what I do. I'll just be super careful (iso transformer, etc) until I get it all buttoned up.

# ? Mar 20, 2009 17:29

Poopernickel: Oct 28, 2005; electricity bad; Fun Shoe

Delta-Wye posted:

That's so stupid it might just work (perfectly). I had completely overlooked the obvious - I'll give it a try.

Ummmm. Just for the record, the posted circuit will have to dissipate approximately 1.2 watts across the two input resistors. Don't even try to use "standard" resistors unless you like heat and melted ceramics.

I would suggest that the easiest way to get a good ground-referenced -5V is to use an off-the-shelf 5V wall wart. They make switching wall-warts these days which are pretty compact (and even moreso when you take off the plastic housing!).

Depending on how adventurous you're feeling, you could also try making your own switcher! With a pair of 400V MOSFETs, a microcontroller with a couple of A/D channels, and a capacitor and inductors you could make a pretty bitching little switcher!

# ? Mar 20, 2009 18:24

ANIME AKBAR: Jan 25, 2007; afu~

Okay, I'll spill one trick them.

Using a resistor to divide the AC voltage down will work but of course the power dissipation is a problem most of the time. However, you're not actually worried about wasting the energy, you're worried about the heat it produces. So the trick is to us a capacitor to drop most of the voltage. The circuit will still be very power inefficient, but since much of the power is in the capacitor instead of resistors, it's not dissipated as heat.

Here's an example for the falstad simulator:

code:

$ 1 5.0E-6 3.7524723159601 50 5.0 50
z 288 288 288 240 1 0.805904783 12.0
d 304 240 368 240 1 0.805904783
c 384 240 384 288 0 9.999999999999999E-5 10.94645241728797
c 288 160 288 224 0 1.0E-6 50.097296248873114
g 288 288 288 304 0
g 384 288 384 304 0
g 432 288 432 304 0
r 432 288 432 240 0 1000.0
w 432 240 384 240 0
w 384 240 368 240 0
w 304 240 288 240 0
w 288 240 288 224 0
r 288 160 224 160 0 10.0
R 224 160 176 160 0 1 60.0 170.0 0.0 0.0 0.5
o 13 64 0 35 320.0 0.1 0 -1
o 3 64 0 35 320.0 0.1 1 -1
o 10 64 0 35 20.0 0.1 2 -1
o 8 64 0 35 20.0 0.1 3 -1

Instead of a resistor divider, you have a capacitor and a zener giving a sort of square wave from -0.6 to +12V (with a 12V zener). I also put in a small amount of resistance on the input to protect things from big transients that are bound to show up on the AC line. Enough to roll off high frequency spikes but not enough to dissipate much power at 60Hz. Then you just rectify that 12V square wave off the zener to get a decent DC voltage. It will probably be ripply, so put another good regulation step after that. This circuit here can deliver about 100mW to the load while "only" dissipating less than a watt as heat.

One :siren:

IMPORTANT

things to consider. The input capacitor must be carefully selected. It MUST be nonpolarized (no electrolytics) and it MUST tolerate voltages of over 200V. And of course for it to be able to deliver decent power, you want its capacitance to be as high as possible. High voltage, nonpolarized caps with decent capacitance are tough to find. Your best bet is some polyester-type dielectric like Mylar. You may have to try a series/parallel combination of multiple caps to get the voltage and capacitance you need. You might have to squeeze stuff pretty tight in there.

Obviously a short circuit capacitor failure will likely destroy whatever is on the load.

Also, get a zener that can handle at least a watt. More is better.

# ? Mar 21, 2009 00:58

Bush Ant: Jan 4, 2009; by Fistgrrl

Just to be clear, the values of the resistors/caps in my circuit were pulled out of my rear end just to show the layout, wire up the microcontroller and everything, see how much power it draws, then simulate and mess around with component values until you get something that can reliably deliver 2x the max power requirement.

Of couse the linear regulator in my circuit would best be replaced by a pre packaged one, it will be smaller and is only one or two dollars, the best option would be to replace the voltage divider by a small transformer for isolation and a full wave rectifier, still inefficient but its the way it should be done if you want to be safe.
Also dont forget to put in some protection

# ? Mar 21, 2009 01:59

Delta-Wye: Sep 29, 2005

Bush Ant posted:

Just to be clear, the values of the resistors/caps in my circuit were pulled out of my rear end just to show the layout, wire up the microcontroller and everything, see how much power it draws, then simulate and mess around with component values until you get something that can reliably deliver 2x the max power requirement.

Of couse the linear regulator in my circuit would best be replaced by a pre packaged one, it will be smaller and is only one or two dollars, the best option would be to replace the voltage divider by a small transformer for isolation and a full wave rectifier, still inefficient but its the way it should be done if you want to be safe.
Also dont forget to put in some protection

code:

$ 1 5.0E-6 1.8479586061009856 50 5.0 50
v 384 496 384 384 0 1 60.0 170.0 0.0 0.0 0.5
r 384 384 480 384 0 10000.0
d 480 384 576 384 1 0.805904783
r 576 384 576 496 0 330.0
c 624 384 624 496 0 3.3E-4 14.14697969925521
w 576 384 624 384 0
w 624 496 576 496 0
w 576 496 384 496 0
r 384 352 480 352 0 10000.0
r 384 320 480 320 0 10000.0
r 384 288 480 288 0 10000.0
r 384 256 480 256 0 10000.0
w 384 384 384 352 0
w 384 352 384 320 0
w 384 320 384 288 0
w 384 288 384 256 0
w 480 256 480 288 0
w 480 288 480 320 0
w 480 320 480 352 0
w 480 352 480 384 0
o 3 64 0 35 20.0 0.1 0 -1
o 1 64 1 35 5.0 9.765625E-5 1 -1

...And this is why 2W resistors were invented. I think it averages out well below 1W, but I have a supply of 2Ws so whateva. This seems embarrassingly ghetto, but it appears to work.

ANIME AKBAR posted:

Okay, I'll spill one trick them.

This circuit is badass.

This is the first time I've really delved into the falstad simulator, and it is pretty cool for a free java applet. I'll have to show it off to some of my classmates, I think they'll get a kick out of it.

Delta-Wye fucked around with this message at 11:29 on Mar 21, 2009

# ? Mar 21, 2009 11:26

ANIME AKBAR: Jan 25, 2007; afu~

Delta-Wye posted:

This circuit is badass.

This is the first time I've really delved into the falstad simulator, and it is pretty cool for a free java applet. I'll have to show it off to some of my classmates, I think they'll get a kick out of it.

Just don't show them a schematic and say "do this." Pass on my warnings on capacitor selection. I've seen what people do when they go to build this circuit: they immediately reach for electrolytics. One person actually wanted to try a tantalum at first and I literally yelled at him that he would blow his face off. The course's teacher actually told the entire class that they weren't allowed to start assembling the supply until he or I had approved a schematic, and we had to be there when they did it.

ANIME AKBAR fucked around with this message at 18:29 on Mar 21, 2009

# ? Mar 21, 2009 17:18

Delta-Wye: Sep 29, 2005

ANIME AKBAR posted:

Just don't show them a schematic and say "do this." Pass on my warnings on capacitor selection. I've seen what people do when they go to build this circuit: they immediately reach for electrolytics. One person actually wanted to try a tantalum at first and I literally yelled at him that he would blow his face off. The course's teacher actually told the entire class that they weren't allowed to start assembling the supply until he or I had approved a schematic, and we had to be there when they did it.

Sorry, I was referring to the simulator.

I uh... will probably not be showing many people these circuits :downs:

# ? Mar 21, 2009 19:38

SnoPuppy: Jun 15, 2005

ANIME AKBAR posted:

Just don't show them a schematic and say "do this." Pass on my warnings on capacitor selection. I've seen what people do when they go to build this circuit: they immediately reach for electrolytics. One person actually wanted to try a tantalum at first and I literally yelled at him that he would blow his face off. The course's teacher actually told the entire class that they weren't allowed to start assembling the supply until he or I had approved a schematic, and we had to be there when they did it.

psh - where's the fun in that?

A few years ago, a friend was working on a design that had a decent number of tantalum caps. The first prototype run through the manufacturing line was built with all the tantalum caps placed backwards.
Apparently when the board was plugged into the chassis, and powered on for the first time, flames shot out the front!

# ? Mar 21, 2009 20:42

ANIME AKBAR: Jan 25, 2007; afu~

SnoPuppy posted:

psh - where's the fun in that?

A few years ago, a friend was working on a design that had a decent number of tantalum caps. The first prototype run through the manufacturing line was built with all the tantalum caps placed backwards.
Apparently when the board was plugged into the chassis, and powered on for the first time, flames shot out the front!

yes, that's the point. In my circuit if a tantalum cap was used, it would have blown (very violently) regardless of polarity (since it's AC). I've also run into a batch of axial electrolytics that explode by splitting in half and flying apart incredibly fast. The first time it happened one of the pieces dented a metal PC case. Luckily the thing was oriented so that it didn't hit anyone. Ever since then we avoid using those things...

Overall I avoid using tantalum completely.

ANIME AKBAR fucked around with this message at 22:15 on Mar 21, 2009

# ? Mar 21, 2009 22:11

Aluminum Record: Feb 2, 2008; When you rip off the breakaway pants, thrust your pelvis toward the bachelorette.

I remember seeing on here or somewhere else a schematic for a cell-phone signal jammer, basically just transmitted noise on the same RF bands that cell phones use so any phones close enough to the device would get no signal. Anyone got a link to it? Seems like it would be a good project for learning a little about RF transmission (and a good lesson in ethics too I'd imagine ha)

# ? Mar 21, 2009 22:52

ANIME AKBAR: Jan 25, 2007; afu~

Aluminum Record posted:

I remember seeing on here or somewhere else a schematic for a cell-phone signal jammer

well if it was posted here then it was probably removed because discussing that kind of stuff is against forum rules.

# ? Mar 21, 2009 23:15

Bush Ant: Jan 4, 2009; by Fistgrrl

there is some MIT chick who has a website that has lots of nifty circuits and makes a few kits and has circuits for other stuff *cough*, like those tv-be gone things and 5v usb power supplies from 2 aa's I think its called a mintyboost

# ? Mar 22, 2009 07:19

Nerobro: Nov 4, 2005; Rider now with 100% more titanium!

http://www.adafruit.com/ that's her website.

# ? Mar 22, 2009 07:31

ANIME AKBAR: Jan 25, 2007; afu~

Nerobro posted:

http://www.adafruit.com/ that's her website.

"awesome, I just got an engineering degree from MIT!"

*founds a company selling cute novelties and ripping off other people's work*

# ? Mar 22, 2009 07:53

Corla Plankun: May 8, 2007; improve the lives of everyone

The idea isn't really the product in these kinds of things.

# ? Mar 22, 2009 08:23

hobbesmaster: Jan 28, 2008

ANIME AKBAR posted:

"awesome, I just got an engineering degree from MIT!"

*founds a company selling cute novelties and ripping off other people's work*

The point of that website is more that the kits are available for sale.

My get rich quick plan was always to found a audiophile company selling cables for $10k/foot and little bags of rocks that you put under your stereo or something for $300. See, I was run out of electrical engineering for listening to the sound instead of looking at an oscilloscope. Or something, still working on it.

# ? Mar 22, 2009 16:59

Nerobro: Nov 4, 2005; Rider now with 100% more titanium!

An audiophile company could fund ALL of our stuff. ;-) Who wants to make the website. I'm handy with cable ends...

On a "I'm a teacher" note. Yeah.... me teaching. Laugh. I had my roomie build his first vreg circuit. And then use that to feed a 555 timer to flash a LED. He then did some experimenting. He found out that LED's have different voltage drops when he put a red LED with his white LED's and only the red LED lit.

Now here's the fun part. While I was out yesterday, he figured out that putting a resistor on the red led would bring it's voltage drop up to match the white leds.

I'm kinda proud of him.

# ? Mar 22, 2009 21:32

Mill Town: Apr 17, 2006

Nerobro posted:

An audiophile company could fund ALL of our stuff. ;-) Who wants to make the website. I'm handy with cable ends...

On a "I'm a teacher" note. Yeah.... me teaching. Laugh. I had my roomie build his first vreg circuit. And then use that to feed a 555 timer to flash a LED. He then did some experimenting. He found out that LED's have different voltage drops when he put a red LED with his white LED's and only the red LED lit.

Now here's the fun part. While I was out yesterday, he figured out that putting a resistor on the red led would bring it's voltage drop up to match the white leds.

I'm kinda proud of him.

It's funny, I was just thinking last night, "Man, I'm tired of being the guy who always tries to tell people about scams and flimflam and gets argued with. Maybe I should just throw my morals out the window and start selling ~~magnets with velcro on them~~ ELECTRON FLOW ENHANCERS to audiophiles for $100 each."

I've got hundreds of bits of velcro left over from some old telco gear. Who's got the magnets?

# ? Mar 22, 2009 23:04

Aluminum Record: Feb 2, 2008; When you rip off the breakaway pants, thrust your pelvis toward the bachelorette.

Someone also once posted a little project of turning a computer power supply into a bench top hobby supply with a bunch of different outputs. Anyone remember it? I think it may have been posted separate of this thread, probably in the archives by now. Maybe a good reason for me to finally buy access.

# ? Mar 23, 2009 00:07

ante: Apr 9, 2005; SUNSHINE AND RAINBOWS

Aluminum Record posted:

Someone also once posted a little project of turning a computer power supply into a bench top hobby supply with a bunch of different outputs. Anyone remember it? I think it may have been posted separate of this thread, probably in the archives by now. Maybe a good reason for me to finally buy access.

Can you remember a thread title, author, or even a thread icon?

Shouldn't be particularly hard, though. They already have a couple different outputs.

# ? Mar 23, 2009 01:34

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# ? May 22, 2024 00:53

ANIME AKBAR: Jan 25, 2007; afu~

Mill Town posted:

It's funny, I was just thinking last night, "Man, I'm tired of being the guy who always tries to tell people about scams and flimflam and gets argued with. Maybe I should just throw my morals out the window and start selling ~~magnets with velcro on them~~ ELECTRON FLOW ENHANCERS to audiophiles for $100 each."

I've got hundreds of bits of velcro left over from some old telco gear. Who's got the magnets?

One of my favorite audiophile scams is the Grado Labs headphone amp (under headphones > headphone amp). It's a two dollar op amp cased in a solid block of mahogany sold for $400.

# ? Mar 23, 2009 02:45

The Something Awful Forums > Discussion > Hobbies, Crafts, & Houses > Learning electronics: Release the Magic Blue Smoke

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