Veketti
Full Member level 3
Dear All,
Here's my circuit
When input voltage gets to 47mV LM358P OP AMP U1:A strengthens that voltage by 48 times and OP AMP U1:B compares it against reference voltage 2.18V and turns on output to PIC digital input. I get around 3.75V to the pic input pin. According to PIC12F683 datasheet min 2.0V needed to recognize it as HIGH state. So that is ok and it actually works just fine on breadboard.
However I decided to change the OP AMP to LM2902N and end up in troubles. Around 47mV +-~3mV if connected to pic input it starts to oscillate. If it is not connected anywhere it will not oscillate. Around 43mV it is low and around 50mV it is high stable. I have tried positive feedback resistor in U1:B but that didn't help. Please help me to understand why this type of OP AMP is not working and how could this be fixed?
Thank you in advance
Here's my circuit
When input voltage gets to 47mV LM358P OP AMP U1:A strengthens that voltage by 48 times and OP AMP U1:B compares it against reference voltage 2.18V and turns on output to PIC digital input. I get around 3.75V to the pic input pin. According to PIC12F683 datasheet min 2.0V needed to recognize it as HIGH state. So that is ok and it actually works just fine on breadboard.
However I decided to change the OP AMP to LM2902N and end up in troubles. Around 47mV +-~3mV if connected to pic input it starts to oscillate. If it is not connected anywhere it will not oscillate. Around 43mV it is low and around 50mV it is high stable. I have tried positive feedback resistor in U1:B but that didn't help. Please help me to understand why this type of OP AMP is not working and how could this be fixed?
Thank you in advance