Need help with a bi-phasic signal amplifier

Thread Starter

JBee

Joined Jul 13, 2016
24
The COM pin of the signal generator is tied to GND, which is the negative power connection for the opamp. This means that the opamp output is trying to swing below GND because that's where part of the input signal is. There are several ways to fix this. First, to test what is happening, change the LM358 pin 8 connection to +15V, and change the pin 4 connection to -15V.
Well that appears to work wonderfully in terms of waveform creation etc. Though it appears as though my peak to peak output has dropped significantly even when maxing out the inputs(30v).

Another question I have for this, is how will this could be replicated on the board? ie, is the -V any different from ground in RW application?

PS. I do apologize if my questions come across as ridiculous, as my understanding of circuits is limited at best. :/
 
Last edited:

AnalogKid

Joined Aug 1, 2013
10,986
The issue is the relationship between the input signal's middle or average or DC value (all of these are the same for a symmetrical waveform) and the midpoint between the opamps two power pins. The opamp doesn't care if it is powered by +/-15 V, or +30 V and GND, but the power system and the signal system have to agree. If the input signal is centered about GND but you want to power the opamps with +30 V only, then a coupling capacitor and a couple of bias or "virtual ground" resistors are a standard solution. In the post #35 schematic, this is the function of R1 and R2.

So - What is the preferred power system for the circuit?

ak
 

Thread Starter

JBee

Joined Jul 13, 2016
24
What is the preferred power system for the circuit?
The system will run off a battery source. The amp section could receive up-to 30v DC. No clue as to what voltages the signal generator and other sections will need however(if that matters)

That said, would it be possible to use a virtual ground configuration as is shown in the lm358 oscillator circuit, or would I be better off using another approach?

PS. I'm not hellbent on using the lm358 packages either. Though it would be convenient as I already have those parts on hand. Otherwise, I could simply order a different op-amp if this proved to make the task easier.
 
Last edited:

AnalogKid

Joined Aug 1, 2013
10,986
1. Is the signal source centered about GND?
2. Is it important that both of the outputs be centered about GND, or only that they have the same DC value and perfect out-of-phase matching?

ak
 

Thread Starter

JBee

Joined Jul 13, 2016
24
1. Is the signal source centered about GND?
2. Is it important that both of the outputs be centered about GND, or only that they have the same DC value and perfect out-of-phase matching?
To be frank, I have no idea... I was planning on using a simple Arduino frequency generator, if that's of any help.
I was under the impression that it would simply output a discrete signal, though never really considered if this implied a ground connection.

That said, here's a simple sketch of the code I was thinking of using: https://www.arduino.cc/en/Tutorial/DueSimpleWaveformGenerator
 

Thread Starter

JBee

Joined Jul 13, 2016
24
"simple Arduino frequency generator" part number / data sheet / schematic / link / anything?
Sorry about that. The link may not have posted properly due to my forum permission. That said here's the info. that came with circuit design section of the project;

Circuit
Connect power and ground on your breadboard to the Arduino. In the image below, the red (power) and black (ground) wires connect to the two long vertical rows on the breadboard, providing access to 3.3V and ground.

Connect a wire from digital pin 2 to one leg of a pushbutton. That same leg of the button connects through a pull-down resistor (10-kilohm) to ground. The other leg of the button connects to the 3.3V power.

Wire up another button in the same fashion, but to digital pin 3.

Hook up the potentiometer by connecting one side to power and the other side to ground. The pin in the middle of the potentiometer goes to analog input 0.

Pins DAC0 and DAC1 wil generate the waveform.​


Hope this helps
 

Thread Starter

JBee

Joined Jul 13, 2016
24
Anyone know of a reputable place that I could go to hire someone to design this particular circuit?
 
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