Our engineering department is working hard on the next generation of the SpikerBox. The chief user request we’ve received is to make the SpikerBox louder; in fact, loud enough for large classrooms. Below is the audio component of our circuit, using the infamous LM386. Making this audio component both loud AND stable has been a major challenge, but we like challenges at Backyard Brains.
We know we can put a 10 uF capacity across pins 1 and 8 to increase to 200 gain, but stability goes out the window. If any analog electronics engineers in the world know an alternative low-cost, low-power audio driver, or a stable LM386 arrangement, please let us know; the solution is near.
Another common user request is to have the ability to both use the iPhone/iPad and hear the spikes at the same time. At the moment, the iPhone OS doesn’t allow playthrough (please Apple, do this for us?), but below is a cheap hardware solution that also solves the loudness issue. Go to your friendly neighborhood RadioShack, and purchase:
1) A mini Audio Amplifier for $14.99: This portable audio speaker amp will allow your spikes to be loud enough for a large classroom or lecture hall. It needs a 9V battery.
2) A Y-adapter for $3.59 to split the output of the SpikerBox to two outputs, so that you can plug in both the iPhone/iPad and the loud audio speaker
3) a 1/8 audio cablefor $3.99 to go from the SpikerBox (or Y-splitter plugged into the SpikerBox) to the audio speaker.
Note: the Y-adapter and audio cables listed are the monaural versions. The Stereo Versions (cable and Y-splitter links here) will also work fine but are $1-3 more. We usually buy the stereo versions anyway, as they are useful for other audio projects. Here is the standard lab class set-up. The iPad works even better for lecture halls.
Note: our kind friends at RadioShack customer service actually sent us the circuit diagram for the audio amplifier! This scan is how we actually received it. Notice they have put a transistor in front of the LM386. We are experimenting with a similar arrangement. Stay tuned!