[QUOTE=chaz13;40676767]I want to mess about with an op-amp to make a super simple audio/signal amplifier..
If I want volume/gain control and I'm using a non-inverting op amp configuration, is it better to use a pot for the feedback resistor, or to make a voltage divider after the op-amp?
Using it as the feedback resistor may be too sensitive, and also non-linear, but uses less parts - so it's probably better to have a potential divider after the op-amp, right? But then you lose half the output voltage.
Basically, is A or B better:
(ignore the resistances, didn't bother changing them)[/QUOTE]
There is really not much difference in having the volume control in the feedback loop or outside, the only possible advantage I can think of using a pot in the feedback would be reduced loop gain at lower volume settings which would increase loop stability, but that's not really an issue unless your using a really really shit op-amp or driving a massive capacitive load.
R4 is not needed at all, just have the signal go in one side of the pot, the other side to ground and the tap to your output amplifier.
k = potentiometer position (0 to 1)
So Vout = k * Vin
Zout = |(k / 1-1)| * Rpot (assuming the pot is linear)
So Zout = 0 when Vout = Vin
Instead of 1 potentiometer, why not two?
one would be for coarse adjustment, the other for fine adjustment.
[img]http://www.beavisaudio.com/techpages/Pots/images/FinePot.png[/img]
[QUOTE=Van-man;40678893]Instead of 1 potentiometer, why not two?
one would be for coarse adjustment, the other for fine adjustment.
[img]http://www.beavisaudio.com/techpages/Pots/images/FinePot.png[/img][/QUOTE]
Or you could use a nicer 10 turn potentiometer and still get the fine adjustment, but not have to mess with 2..though it does cost more.
Fine adjustment in my experience is not really needed that much for audio use, you can get a pretty fine adjustment of a single turn quite easily by using a large knob.
[QUOTE=ben1066;40679007]Or you could use a nicer 10 turn potentiometer and still get the fine adjustment, but not have to mess with 2..though it does cost more.[/QUOTE]
they're either itty bitty one's you'd have to adjust with a screwdriver, or costly motherfuckers (as you stated).
[QUOTE=Chryseus;40679296]Fine adjustment in my experience is not really needed that much for audio use, you can get a pretty fine adjustment of a single turn quite easily by using a large knob.[/QUOTE]
Log Pot?
[QUOTE=LoneWolf_Recon;40679766]Log Pot?[/QUOTE]
Log pots give a much smoother change in volume level.
Cross-post between here and waywo because it's relevant to both..
[img]http://i.imgur.com/DNwEHrY.png[/img]
[QUOTE=thomasfn;40691945]Cross-post between here and waywo because it's relevant to both..
[img]http://i.imgur.com/DNwEHrY.png[/img][/QUOTE]
Just post it in either one, but not both
Need some help with battery charging here.
I've got a moped without a battery, and I want to put a 12V, 5Ah battery on it. I've got a 12-15V DC regulator/rectifier, that's got a max capacity of 6W. Would this be enough? According to a Wikipedia article, 6W will be just enough at 12V, and it'll have to be a fair bit more than that to charge the battery (as you probably know)
[QUOTE=Gulen;40692365]Need some help with battery charging here.
I've got a moped without a battery, and I want to put a 12V, 5Ah battery on it. I've got a 12-15V DC regulator/rectifier, that's got a max capacity of 6W. Would this be enough? According to a Wikipedia article, 6W will be just enough at 12V, and it'll have to be a fair bit more than that to charge the battery (as you probably know)[/QUOTE]
6W is about 0.5A so at that current it should at least get a 60-80% charge in about 10 hours, you won't get a full charge unless you use a combination of constant current and constant voltage charging.
Make sure you use a constant current regulator unless the supply is already current limited.
Let's see what the university trash has besides a boxed copy of AutoCAD 12
[IMG]http://i11.photobucket.com/albums/a166/ballsandy/CGS_001.jpg[/IMG]
Ohh.
[IMG]http://i11.photobucket.com/albums/a166/ballsandy/CGS_002.jpg[/IMG]
[i]Hey![/i] Tubes!
[IMG]http://i11.photobucket.com/albums/a166/ballsandy/CGS_003.jpg[/IMG]
Alright! It works.
The one adjustment knob that is broken also had a wrecked 10K pot. Otherwise it's in fully working shape.
[QUOTE=Chryseus;40692913]6W is about 0.5A so at that current it should at least get a 60-80% charge in about 10 hours, you won't get a full charge unless you use a combination of constant current and constant voltage charging.
Make sure you use a constant current regulator unless the supply is already current limited.[/QUOTE]
But will it only handle a 6W draw, though? After all, it is going to have several light bulbs, all of which are above 6W, so in my head, that would mean that I'm drawing more from the battery than I'd put in.
[QUOTE=Gulen;40696770]But will it only handle a 6W draw, though? After all, it is going to have several light bulbs, all of which are above 6W, so in my head, that would mean that I'm drawing more from the battery than I'd put in.[/QUOTE]
Use LEDs instead of lightbulbs, save the environment!
[QUOTE=DrLuckyLuke;40697846]Use LEDs instead of lightbulbs, save the environment![/QUOTE]
drop-in LED replacements for incandescent bulbs are often horribly shitty.
You'd need a light housing with reflector and lens that's designed with the specific LED modules in mind to replace incandescent properly.
[QUOTE=Gulen;40696770]But will it only handle a 6W draw, though? After all, it is going to have several light bulbs, all of which are above 6W, so in my head, that would mean that I'm drawing more from the battery than I'd put in.[/QUOTE]
What I'm confused?
You want to put this battery on a moped, is it entirely electric powered or does it have an engine with an alternator ?
Using lamps to limit current is not really a good idea except for really crude applications, use a simple transistor / op-amp current source.
It's a normal engine with an Alternator. Currently, the alternator supplies the moped with its electricity on its own. I want to put a battery in here, so that the voltage doesn't vary as much (revving it makes the bulbs go brighter) The bulbs aren't there for current limiting, they're there to make the moped legal, and I just used them as an example because I know how many watts they need. I'm just worried that everything connected to the battery will drain it faster than the rectifier can recharge it.
[QUOTE=Gulen;40700301]It's a normal engine with an Alternator. Currently, the alternator supplies the moped with its electricity on its own. I want to put a battery in here, so that the voltage doesn't vary as much (revving it makes the bulbs go brighter) The bulbs aren't there for current limiting, they're there to make the moped legal, and I just used them as an example because I know how many watts they need. I'm just worried that everything connected to the battery will drain it faster than the rectifier can recharge it.[/QUOTE]
Using a lead acid battery may not solve your problem since it will float at the average alternator voltage and as a result not really compensate for any increases in voltage above that, it will however help if there are any drops in voltage from high current draw but that does not sound like your problem.
The best solution I can think of would be to install a linear LDO voltage regulator on the output of the rectifier which will ensure the voltage remains stable at all times.
Using a large capacitor or automotive super capacitor may also help reduce or eliminate your problem.
Incandecent lightbulbs also help heat your house.
I've been playing around with measuring inductance with the less common but more accurate (for a DIY solution) phase measurement.
[t]http://u.cubeupload.com/Chryseus/JQz6Rv.jpg[/t]
[t]http://u.cubeupload.com/Chryseus/qn7Nqq.jpg[/t]
The results do not have absolute measurement accuracy of course due to inductance of my probes but once calibrated that's not an issue.
Usually a fixed frequency oscillator of 10kHz, 100kHz or 1MHz (sometime 10MHz for measuring very low inductance) is used but to make things easier I just adjust the frequency until
I get a -45 degree phase shift so I then know the inductive reactance Xl is equal to my resistance R, so then the inductance is L = Xl / 2 * Pi * f
Here is a bonus picture as I don't think I've posted it yet.
[t]http://u.cubeupload.com/Chryseus/y1VTkW.jpg[/t]
[QUOTE=Nikita;40702267]Incandecent lightbulbs also help heat your house.[/QUOTE]
But that's the argument I use for my servers :(
So I'm an EE noob and after spending several months ocasionally taking things apart and salvaging components, I've started my first permenent project.
[img_thumb]http://www.controlcircuitdiagram.com/wp-content/uploads/2011/01/circuit-motor-control-1-300x246.jpg[/img_thumb]
I'm using this diagram for a motor controller.
[img_thumb]http://filesmelt.com/dl/20130520_201323.jpg[/img_thumb]
[img_thumb]http://filesmelt.com/dl/20130520_204116.jpg[/img_thumb]
This is what I have for the driver.
Now please excuse how basic my question is; How do I create and use a proper ground for this project?
Using negative voltages is rather tricky, I suggest you use a split level driver:
[img_thumb]http://www.robotroom.com/BigTrak/MotorDriverSchematic.gif[/img_thumb]
The easiest and by far most effective way is to get a center tapped transformer and build a power supply like so:
[t]http://i.imgur.com/aPvwL.png[/t]
(R2 & R3 is not needed)
It is also possible to convert a single rail supply into a dual rail supply, depending on what your driving this can be done with either a simple resistive divider or a slightly more complex driver using transistor(s), there are also many switchmode ICs that can generate a split supply.
Here are some example circuits you can try, I recommend the lower one if your trying to drive a motor.
[img]http://u.cubeupload.com/Chryseus/jL6STv.png[/img]
Do what Chryseus said, or if you're using a series of batteries then tap the centre of the series for ground, then take +-V from the ends.
Be careful though, as this will discharge the batteries asymmetrically.
Thanks
[QUOTE=Fuxed;40643391]Ah, but then we have glorious concurrent end-results if you do it right. Plus there's nothing to stop you throwing in a soft-core and doing large parts with C with HDL backend and custom peripherals. FPGAs are a great thing in their own right and totally worth the effort to learn the intricacies of.[/QUOTE]
What would you recommend I start with then? Verilog or VHDL? I see lots of people recommending both, and lots are things are written in both, but as pretty much a total newcomer what would be a better start?
[QUOTE=ben1066;40756944]What would you recommend I start with then? Verilog or VHDL? I see lots of people recommending both, and lots are things are written in both, but as pretty much a total newcomer what would be a better start?[/QUOTE]
I'd really recommend a look into both, just to see what what rings well with you; personally though, VHDL is the way I'd go, once you get past the odd syntax and formatting (Or learn some Ada!) , it's easy to start working with. There's a wealth of resources too ranging from The Designers Guide, the VHDL bible of sorts, to nice little things like [URL="http://hamsterworks.co.nz/mediawiki/index.php/FPGA_course"]the Hamsterworks course[/URL].
You might need a little more solder on that.
[QUOTE=pentium;40774380]You might need a little more solder on that.[/QUOTE]
I once soldered an SMA connector, and kept adding solder, not realizing it was droping out the other end. At some point I noticed that, and saw that I've basically completely engulfed an QFN44 device + a shitton of passives in solder. Luckily it was rather easy to clean up.
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