spencer2004
- May 1, 2013
- 17
- Joined
- May 1, 2013
- Messages
- 17
Hi, first of all I'd like to say that I am pretty new to electronics and as I have learned everything I know from the internet there are massive gaps in my knowledge so forgive me for using the incorrect terminology, etc.
I am building an LED tester which logs the current draw of an LED across a pre-set voltage range, to measure the current draw I am measuring the voltage drop across a 0.1 ohm shunt resistor, the voltage drop is amplified by a LM358 op amp with a gain of 30 then read by an Arduino. The problem I have is the op amp does not work correctly for voltage drops below 0.03v which means that I can't measure current draws below 300mA. I measured the output of the op amp with different voltage differences in 0.01v steps and from a voltage difference of 0.03v onwards it works as it should.
I have checked that I have built the amplifying circuit properly about 10 times, and I have made sure that the LM358 is not defective. The LM358 is powered by a 12V rail.
I have Googled this a bit and I'm not sure if there is a way to modify the circuit to allow smaller currents to be measured without increasing the resistance of the shunt resistor.
If someone could give me some guidance on the matter I would be very grateful.
I am building an LED tester which logs the current draw of an LED across a pre-set voltage range, to measure the current draw I am measuring the voltage drop across a 0.1 ohm shunt resistor, the voltage drop is amplified by a LM358 op amp with a gain of 30 then read by an Arduino. The problem I have is the op amp does not work correctly for voltage drops below 0.03v which means that I can't measure current draws below 300mA. I measured the output of the op amp with different voltage differences in 0.01v steps and from a voltage difference of 0.03v onwards it works as it should.
I have checked that I have built the amplifying circuit properly about 10 times, and I have made sure that the LM358 is not defective. The LM358 is powered by a 12V rail.
I have Googled this a bit and I'm not sure if there is a way to modify the circuit to allow smaller currents to be measured without increasing the resistance of the shunt resistor.
If someone could give me some guidance on the matter I would be very grateful.