Signal Amplification

Adjuster

Joined Dec 26, 2010
2,148
If you use an amplifier with some full power bandwidth in hand, and an adequate output swing to start with, this should not be a problem. Struggling with an LM324 with only a 5V supply, I fear you are on a hiding to nothing. The fact that you may have scraped 3.7Vp-p in one configuration does not prove much. By the time the amplifier was delivering a few mA for the LED and a few more for that zener the level would probably be lower still.

I can't tell you what amplifier to use, as I'm far from up to date with these things. If you wait a while, with a bit of luck someone else better informed may help you out. Perhaps you would also do well to be guided by someone at your school - they may even have something a bit more suitable going for free.
 

Thread Starter

Pooperman

Joined Feb 23, 2011
30
I've asked the lab tech and the lab overseer. The things they suggested and that I've tried should be working (the lm324 should work if it wasn't inverting the output). Would an inverter after make it positive again?
 

Ron H

Joined Apr 14, 2005
7,063
Apparently your oscillator does not have a 50%duty cycle at its output. If it did, why would inversion matter?
And I'm not picking on your design, I'm just trying to help you with your original questions.
 

Thread Starter

Pooperman

Joined Feb 23, 2011
30
Not quite. It is, by nature, 50% duty cycle. It just that it has a dc voltage bias of +0.75V so that the bottom is at 0, not -0.75V. In that case, then it shouldn't matter when I amplify it to ±1.5V.
 

Ron H

Joined Apr 14, 2005
7,063
Will your final design always have +5V available? If so, all you need is an LM311 comparator and a couple of resistors and a capacitor or two.
 

Thread Starter

Pooperman

Joined Feb 23, 2011
30
My final design will run off of +9V so anything less can be obtained. If I can run things at 9, that simplifies my circuit a bit.
 

davebee

Joined Oct 22, 2008
540
Have you considered using a transformer to raise the voltage? I've seen circuits that use a transformer for just that reason; to move the signal into the range that a clamping diode will work.
 

SgtWookie

Joined Jul 17, 2007
22,230
Just FYI - Ron's circuit will work as-is with the shown LM311 comparator, with about 10mA current through the IR LED emitter. However, LM393/2902 and LM339 comparators have less current sink capability; about 6mA tops.
 

SgtWookie

Joined Jul 17, 2007
22,230
Note that Ron_H grounded both pins 4 and 1 of the LM311. Pin 4 is the Vee/-V pin. Pin 1 is the emitter of the open-collector output. If you omit either ground, you won't get any output.
 

Thread Starter

Pooperman

Joined Feb 23, 2011
30
Yes. I used it, that's how I know. It should be working. Ron, your design actually does the two things I needed at the same time: limit output voltage and amplify the signal as well. If only I can get it to work on Sunday or Monday. As I posted earlier, good results in PSpice, but having difficulty getting the simulation to be reality.
 

Ron H

Joined Apr 14, 2005
7,063
Keep working. If you build it correctly, it will work.
BTW, where are you probing to see the output that you are expecting?
 

Thread Starter

Pooperman

Joined Feb 23, 2011
30
Before the opto to ground and before the opto to after the opto. About 2/3 of the DC supply and 1/2 of the DC supply respectively. I set the supply separately so as to tune to max input to the opto later. I checked in PSpice and that made no difference to overall function. So instead of 9V, I tried 5V and other voltages. Either way, I should have gotten some sort of AC signal with the DC.
 
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