I want to amplify the small DC signal that produced by O2 sensor. So, it can be read by Arduino. I change AD8572 to OP07CP Op Amp because AD8572 is a SMD type component. But the problem is, I unable to amplify the signal that received from O2 sensor. There is any idea how to amplify the signal?
The output voltage at SIG OUT is around 0.5V.
After I connect -5VDC to the amplifier circuit, the voltage drop to -2.8VDC.
All +5VDC are using Arduino Mega +5VDC supply.
Attached is the OP07CP, AD8572 datasheet and circuit.
"I would put them on pin 1 and 8 also."
What did you mean?
On your amplifier, put .1uF capacitor on each pin to ground.
I cannot confirm the colors on your actual resistors in the photo.
What are the colors?
Test:
To check the -5V drive capability, disconnect the Amp from the -5V supply.
Try different resistor (10K, 4.7K, 2.2K, 1K, 560R) values on the -5 output to ground (0V).
At what value does the -5V level start to drop below -4.5V.
After I connect -5VDC to the amplifier circuit, the voltage drop to -2.8VDC.
Seems normal for the NE555. Look at the datasheet.
"Low" volt drop is ~0.2v@10mA, but "high" volt drop is ~1.5volt@10mA.
That gives a square wave of 3.3volt t/t@10mA.
Plus the rectifier diode drop.... (schottky diodes are better here).
You could use a PWM Mega pin (or two pins in push-pull) to generate -5volt.
Leo..
After I connect -5VDC to the amplifier circuit, the voltage drop to -2.8VDC.
The OP07CP is not rail to rail type, the output can only get to within a few volts of the supply rail at best.
Furthermore, I think your oxygen sensor (type?) would have a unipolar output but your amplifier circuit is bipolar type.
There are a few through hole op amps available that have comparable features to the AD8572 (single supply, rail-rail, low drift, etc). Perhaps this one is close enough: ALD1702
The OP07C needs at least 3V clear of each rail, get a low voltage R2R opamp and forget
about using 1980's opamp chips! They are usually intended for +/-15V.
MarkT:
The OP07C needs at least 3V clear of each rail, get a low voltage R2R opamp and forget
about using 1980's opamp chips! They are usually intended for +/-15V.
dlloyd:
The OP07CP is not rail to rail type, the output can only get to within a few volts of the supply rail at best.
Furthermore, I think your oxygen sensor (type?) would have a unipolar output but your amplifier circuit is bipolar type.
There are a few through hole op amps available that have comparable features to the AD8572 (single supply, rail-rail, low drift, etc). Perhaps this one is close enough: ALD1702
Well, you have the point. But, it's hard for me to find that type of IC in my place.
This circuit has gain of 83, probably the best you can do without being limited by the upper rail. Reading Arduino's analog input should give range of 0-374. Could add a series resistor of around 4.7K to protect Arduino's input in case the signal ever goes negative (i.e. powerup).
dlloyd:
This circuit has gain of 83, probably the best you can do without being limited by the upper rail. Reading Arduino's analog input should give range of 0-374. Could add a series resistor of around 4.7K to protect Arduino's input in case the signal ever goes negative (i.e. powerup).
Yes, I got the idea. I try to reassemble the circuit and the result is positive I think. There is some changes in value but it's small. BTW, the output voltage is 0.84V. I dont't know either it caused by normal oxygen level or there is something wrong with my circuit. Need to test it in vacuum chamber.
*P/S: For feedback resistor I change it to 20k because I don't have 82k resistor right now and for negative voltage, I just connect it to GND.
nazreen:
......and for negative voltage, I just connect it to GND.
Can't do that.
For the output to go to zero volt, the negative supply has to be at least -2volt.
A supply of +5volt and -2.8volt is fine.
The output can then swing between -0.8volt and +3volt. Maybe a bit more.
You have to read that with a lower Vref enabled if you want the full range of the 10-bit A/D.
As said, use a resistor between opamp and Arduino pin (4k7-10k), to protect the Arduino input.
Leo..
Wawa:
Can't do that.
For the output to go to zero volt, the negative supply has to be at least -2volt.
A supply of +5volt and -2.8volt is fine.
The output can then swing between -0.8volt and +3volt.
You have to read that with a lower Vref enabled if you want the full range of the 10-bit A/D.
Leo..
After I change it, the output voltage increase to 3.94V and sensor become less responsive.
TomGeorge:
Hi,
Have you got pin2 connected to pin6 on the LM555, it is hard to see.
nazreen:
After I change it, the output voltage increase to 3.94V and sensor become less responsive.
Maybe the opamp just started to work.
Did you "load" the sensor with a 100ohm resistor, as on the datasheet.
Without load resistor, the sensor might produce a higher output voltage.
That could explain the maximum output voltage (clipping) of the opamp.
Leo..
