Electronic – How to simulate the CNY70 IR reflectometer with TINA or LTSpice

Edit: Actually, I found out the answer I posted is already given in the question you rejected as "too complicated". I ask you to reconsider that judgement, as anything involving operational amplifiers (suggestions also found in that question) will be even more complicated.

While the commentors are right that your circuit is a really bad idea in practice, your thoughts that lead you to the that circuit are actually quite good. You notice correctly that the voltage you obtain at typical volumes is too low to turn on the transistor (you need around 0.6V to get a significant effect). Using a darlington transistor doesn't help, as you experienced, because you need even more voltage to turn on a darlington transistor, but you can get away with a lot lower current. You problem is that your voltage is too low, not that your supply can't deliver enough current, so forget about darlingtons.

Increasing the "baseline voltage" as you call it, is exactly the way to go. Electronics people often call this process "adjusting the DC bias" of a transistor amplifier. It can be done quite easily on your circuit without adding a dangerous low-impedance power source like a battery. Let's work on your circuit. First, add a current limiting resistor into the LED circuit and put the LED on the other side of the transistor. It makes no difference in your circuit as it is now, but it will make soon:

^{simulate this circuit – Schematic created using CircuitLab}

You can fix your problem, as you correctly identified, by providing DC bias (a baseline voltage) to the transistor base. But you should not force a DC voltage into the headphone jack, so you need a capacitor for DC decoupling. This capacitor should pass the AC music signal, but block the DC required to bias the transistor. With the circuit as drawn, you can get the required DC bias (around 0.45V) from the battery using a voltage divider like this:

^{simulate this circuit}

Just add a protection diode between emitter and base. It'll limit the negative base voltage to about 0.7V and might even improve the circuit's performance by discharging the base capacitor at the end of each cycle.

^{simulate this circuit – Schematic created using CircuitLab}

Edit: You might have to play a little with the other components' values when you add the diode, however. I've added some example values in the diagram above. Note that the base capacitor is way smaller than in your circuit. This makes the capacitor only deliver a short current spike when the transistor switches on or off in order to get it into and out of saturation quickly. For most of the on-time of the transistor, R1 delivers its base current, which makes the transistor not saturate as hard as with the 100nF capacitor, resulting in improved switching performance.

You should simulate it and check the performance however, I just estimated the values. They might be off a bit.