Hey all! Me again :D. So I was messing around with my electronics and decided to make a pulse sensor, but I ran into a couple of problems along the way! My project is based off of this, http://makezine.com/projects/ir-pulse-sensor/, but I didn't have a LM324, so I was trying a workaround. So grabbing my infrared light detector, and new multimeter, hooked my IR sensor up between 5V and and A0 and a 10k resistor from A0 to GND, just like with a light sensor, but obviously, it wasn't sensitive enough, so I kicked it up notch. Since I didn't have the specific amplifier that MAKE used I decided to use what I had, which was a LM358. After visiting the datasheet and finding a schematic, I came up with this circuit (image below). Now it's not sensitive enough yet to measure pulses. The circuit from MAKE makes use of the the 2 of 4 internal op amps in the LM324, and I thought I could make the same circuit on my LM358, since it had two op amps inside of it. So basically, replacing the LM324 int the circuit with a LM358. The image below is a circuit I made up using just one of the LM358's op amps. Tonight I will try to use both just like in the MAKE circuit. If you guys could just give me a few pointers and set me on the right track that would be great, or if I even need two amplifiers! Why can't I just make the first one more powerful? And the capacitor between the - and the output varies. I'm still trying out different caps. The 0.1uf is too much, so I'm experimenting. Thanks!