mrfunkyjay
New Member
Hi guys,
anyone has been playing with TL084, the quad op-amps chip for a while?
I have my schematics attached in this post. Please take a look. The idea is to create:
Instrumentation Amplifier with variable gain of 3, 5, 10, 15, 20, 30, 40, and 50. The RGain is then controlled by a switching arrays of eight SPDT Relays. The Relays are driven with ULN2803 darlington and connected to microcontroller for a shift bit simulation via software. Thus, the RGain will decrease in value, in such a way to give the increasing gain from this instr.amp.
The fourth op-amp is used as a voltage comparator, before connected to ADC, the voltage comparator only accepts voltage above 1V. What below will not be fed up to the ADC in my microcontroller.
This is what I get:
-The chip is warm, temperature might be around 30 degrees Celcius.
-The output to ADC reads 11.75V at all times!
-The output from 8th pin of TL084 which is the output of my instrumentation amplifier reads 5V >> this is weird since my input voltage is around 20mV, gained voltage should be 60mV (gain = 3x).
Does anyone know what is wrong with my schematics?
The relay board is perfectly tuned to remove contact debouncing effect. The pin headers are connected to the relay board via cables and the resistors are properly installed (values). Please kindly give me some advice. Thank you!
PS: The resistance of my resistors are all tested by protoboard before etching the layout onto the PCB. I thought it should be working but I dont get it why it is not working!!!
Best regards,
Kelvin
anyone has been playing with TL084, the quad op-amps chip for a while?
I have my schematics attached in this post. Please take a look. The idea is to create:
Instrumentation Amplifier with variable gain of 3, 5, 10, 15, 20, 30, 40, and 50. The RGain is then controlled by a switching arrays of eight SPDT Relays. The Relays are driven with ULN2803 darlington and connected to microcontroller for a shift bit simulation via software. Thus, the RGain will decrease in value, in such a way to give the increasing gain from this instr.amp.
The fourth op-amp is used as a voltage comparator, before connected to ADC, the voltage comparator only accepts voltage above 1V. What below will not be fed up to the ADC in my microcontroller.
This is what I get:
-The chip is warm, temperature might be around 30 degrees Celcius.
-The output to ADC reads 11.75V at all times!
-The output from 8th pin of TL084 which is the output of my instrumentation amplifier reads 5V >> this is weird since my input voltage is around 20mV, gained voltage should be 60mV (gain = 3x).
Does anyone know what is wrong with my schematics?
The relay board is perfectly tuned to remove contact debouncing effect. The pin headers are connected to the relay board via cables and the resistors are properly installed (values). Please kindly give me some advice. Thank you!
PS: The resistance of my resistors are all tested by protoboard before etching the layout onto the PCB. I thought it should be working but I dont get it why it is not working!!!
Best regards,
Kelvin