1V to 5V transistor amplifier for arduino digital inputs

Question

I'm trying to use a soundcard to send a trigger signal to an Arduino. However, the software I'm using limits the output of the soundcard to between -1 and 1V, which is insufficient to trigger the digital pin on the Arduino.

Basically, I want to try and amplify this 1V signal to a 3.3-5V signal in the simplest way possible, maybe by using a transistor to route the Arduinos 5V supply to the digital pin.

This is somewhat time sensitive, and the only components I have available at the moment are some NPN transistors (2N2222) and a broad selection of resistors. Can I build a transistor amplifier to get the 5V I need? I'm new to this, so I am also not sure how/where to put resistors in this circuit. Any help would be greatly appreciated!

edit: Just to clarify, I'm using the soundcard to present a sound on one channel, and this trigger signal, in the form of a short pulse, to accurately estimate the onset of the sound from the arduino/for other experimental synchronization purposes

Answer 1

It would seem that you require a non-linear amplifier, because the digital input will only recognize a logic high (near Arduino + supply) or a logic low (near Arduino's ground).
This is complicated by a general CMOS requirement to drive an input very close to logic low, or very close to logic high - lingering near half-way stresses the logic gate with excess shoot-through current, or may cause oscillations. So a fairly high-gain amplifier is required, or a comparator.
Another complication involves AC coupling that a sound-card invariably employs: its average output will always be zero volts, even if you program full amplitude +1V or full -1V. So your threshold circuit will only be able to detect changes of amplitude.

^{simulate this circuit – Schematic created using CircuitLab} This inverting amplifier will boost small changes at its input to logic-level changes at its output (Logic out) for a microcontroller. With no input, or too-small input, base biasing is arranged that "Logic out" will be high, pulled up via R3. Positive-going pulses at the input will turn on the transistor, and produce a logic low at the output, for a short time only (probably milliseconds).
Audio output must have its ground connected in common with the microcontroller's ground. Since this is a non-linear amplifier, output is very distorted, and would sound unintelligible. A continuous, full-amplitude tone at the input would produce logic-level pulses of the same frequency at the logic output.

Answer 2

This will turn on the transistor when the audio voltage exceeds approx. 0.7V, this will pull the IO pin low. It will only trigger on the +ve going part of the audio signal.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 3

I assume your sound card output is capacitively coupled ...if not then you could put a capacitor (1 uF or more) in series with the input.
The Arduino input pin should toggle for signals above about 0.7-0.8 V positive peak. If you use low frequency sine/square waves you may be able to get both presence and a frequency indicator.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 4

You can use the below circuit. As you haven't any diodes to hand, Q1's base-emitter diode is used to protect Q2's base from large negative voltages, such as static or transients.

^{simulate this circuit – Schematic created using CircuitLab}