http://forums.leaflabs.com/topic.php?id=253 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:22:22 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=253#post-2062 Wed, 27 Oct 2010 13:38:13 +0000 poslathian 2062@http://forums.leaflabs.com/ <p>yea, make sure to subtract off the offset in digital to get everything 0 centered again! (or just adjust all your DSP to account for it....which you probably dont want to do) </p> http://forums.leaflabs.com/topic.php?id=253#post-2032 Mon, 25 Oct 2010 23:00:56 +0000 structuresound 2032@http://forums.leaflabs.com/ <p>@post</p> <p>looks like what you've drawn basic inverting summing amplifier configuration, I never thought to use that to add dc bias since in normal audio applications you usually want to AVOID that. Good idea, I'll try it out. </p> http://forums.leaflabs.com/topic.php?id=253#post-1922 Fri, 22 Oct 2010 12:05:16 +0000 poslathian 1922@http://forums.leaflabs.com/ <p>I certainly thought so, I think you can do this:<br /> <a href="http://imgur.com/fE2hz.jpg" rel="nofollow">http://imgur.com/fE2hz.jpg</a></p> <p>which also works for non-inverting if you want to go this route. I use this circuit when I want to rebias -1.5V,1.5V audio signals to 0-3.3V ADC signals centered around 1.15V </p> http://forums.leaflabs.com/topic.php?id=253#post-1917 Thu, 21 Oct 2010 20:38:22 +0000 structuresound 1917@http://forums.leaflabs.com/ <p>@ poslathian is that possible without AC coupling or a clamp circuit? I'd be curious if one can do that with a single opamp stage! </p> http://forums.leaflabs.com/topic.php?id=253#post-1913 Thu, 21 Oct 2010 19:20:11 +0000 poslathian 1913@http://forums.leaflabs.com/ <p>@okie - oops, I left out the feedback trace from output to negative input. I was actually going for a unity gain amp re-centered at 4.5V, which I still think I got wrong. I need to just stop it... </p> http://forums.leaflabs.com/topic.php?id=253#post-1908 Thu, 21 Oct 2010 18:59:27 +0000 structuresound 1908@http://forums.leaflabs.com/ <p>Schematic, works well on breadboard so far.</p> <p><a href="http://www.structuresound.com/eric/pwmLPF.png" rel="nofollow">http://www.structuresound.com/eric/pwmLPF.png</a> </p> http://forums.leaflabs.com/topic.php?id=253#post-1907 Thu, 21 Oct 2010 18:54:37 +0000 structuresound 1907@http://forums.leaflabs.com/ <p>@Okie, yes it's an audio application. Eventually controlling SSM2164, works really well I think. I've thought about looking into those "rail to rail" versions, I'll also order a TLV274.</p> <p>@ poslathian, I'm running it as fast as possible (or at least without a scalar on my clock). Open drain would be when the pin swings low, correct? Although the output seems perfectly square on my scope, I also don't care that much because I want to end up with DC anyway.</p> <p>@gbulmer I'll look at how much current is going into out of the pin, I think it's &lt;1mA, at least HOPE so! </p> http://forums.leaflabs.com/topic.php?id=253#post-1897 Thu, 21 Oct 2010 16:10:42 +0000 okie 1897@http://forums.leaflabs.com/ <p>poslathian, that circuit's (<a href="http://imgur.com/zBi11.jpg" rel="nofollow">http://imgur.com/zBi11.jpg</a>) output will never change. It's a comparator that compares Maple's output to 9V/2, and Maple's output is always at or below 3.3V. Make the resistor divider give 3.3V/2 and it should work nicely. </p> http://forums.leaflabs.com/topic.php?id=253#post-1896 Thu, 21 Oct 2010 16:06:50 +0000 okie 1896@http://forums.leaflabs.com/ <p>gbulmer, for sure--a comparator would work. I am also doing filtering, and I used one of the opamps in the quad-opamp chip for buffering PWM. </p> http://forums.leaflabs.com/topic.php?id=253#post-1887 Thu, 21 Oct 2010 15:16:25 +0000 poslathian 1887@http://forums.leaflabs.com/ <p>I am not sure of the pwm performance over open drain (although it does work). I imagine with a big enough resistor and pulling up to a high voltage you would start to get a distorted square (depending on the speed, obviously). But this might be the easiest way to get started. </p> <p>An opamp circuit sounds like the way to go here, as okie mentioned, if you are going to run the pwm fairly fast (10's of KHz) youll need a rail to rail opamp otherwise you wont get a nice square output. </p> <p>[ EDIT - NOT this<br /> <a href="http://imgur.com/zBi11.jpg" rel="nofollow">http://imgur.com/zBi11.jpg</a> </p> http://forums.leaflabs.com/topic.php?id=253#post-1885 Thu, 21 Oct 2010 14:25:37 +0000 gbulmer 1885@http://forums.leaflabs.com/ <p>Okie - If it's only level translating PWM, a comparator would do, wouldn't it? </p> http://forums.leaflabs.com/topic.php?id=253#post-1883 Thu, 21 Oct 2010 14:06:24 +0000 okie 1883@http://forums.leaflabs.com/ <p>structuresound, is this an audio application?</p> <p>You could use a rail-to-rail opamp to avoid having to AC couple the PWM. I've been using the TLV274 for audio stuff using the Maple. I think it won't misbehave too much with rail-to-rail input and output. </p> http://forums.leaflabs.com/topic.php?id=253#post-1848 Tue, 19 Oct 2010 17:53:42 +0000 gbulmer 1848@http://forums.leaflabs.com/ <p>Can you explain a bit more about what your trying to achieve?</p> <p>I'd recommend getting hold of a copy of the "Art of Electronics" by Horowitz and Hill<br /> (<a href="http://www.amazon.com/Art-Electronics-Paul-Horowitz/dp/0521370957" rel="nofollow">http://www.amazon.com/Art-Electronics-Paul-Horowitz/dp/0521370957</a>)<br /> Maybe from a local library. They cover interfacing in depth.</p> <p>It sounds like you might get the effect you want by switching the pin between OUTPUT (Push-Pull) HIGH, and OPEN_DRAIN, HIGH, and use suitable pull-up resistor+maybe a zener diode. How much current is being sourced (or sunk) by the Maples pin? </p> http://forums.leaflabs.com/topic.php?id=253#post-1836 Tue, 19 Oct 2010 04:39:38 +0000 structuresound 1836@http://forums.leaflabs.com/ <p>I suppose this is a more general question about microcontrollers, but I thought I'd see if anyone here has ideas about it. </p> <p>I'm looking at ways of scaling the voltage coming out of a pin to interface with analog circuits running at higher voltage, in this case 9v supplies running at virtual GND at 4.5v in some cases I need the PWM to swing from 4.5 to 9v.</p> <p>one solution I've come up with is to run a voltage divider being 9v -&gt; 100k -&gt; output -&gt; 100k -&gt; PIN. So when the pin is low, the output is 4.5 and goes up from there. Because of potential current draws I'm connecting the output to the non-inverting input of an opamp. I think this should make the current a reasonable amount for the GPIO to handle, at least in output mode (maybe there's a problem when set to input or at boot) and it seems to be working. My question is, is there a better way to do this (interface a microcontroller pin with a circuit at a different ground potential)</p> <p>one of the advantages of doing it my way as I see is that if I make the voltage divider this way with V+, then I don't have to AC couple the circuit and thus get very stable DC voltages when I run the PWM through a lo-pass etc. Maybe I should just buffer the PWM first, however if I do that then I need to AC couple it so that the LOW state doesn't hit the low rail of the opamp (causing the output to swing up to V+).</p> <p>Ideas? Possibly a good start to a general discussion about simple ways of dealing with GPIO as control source for low current (i.e. not motor control) situations. </p>