A pilot departed on BTM Runway 33 and once airborne took evasive action to avoid an aircraft departing Runway 29 which he did not hear because his G1000 had switched from the CTAF frequency.

Narrative

After broadcasting my intentions to taxi to Runway 33; I noticed Aircraft Y that looked like he'd be taxiing soon. While taxiing I saw the windsock and decided to use Runway 29 and broadcast my intentions. I completed the before takeoff checklist and as I was about to taxi; when realized I'd not heard Aircraft Y on the radio. I looked toward the terminal but only saw the very top of it; if Aircraft Y was still there I could not see it. I then looked toward Runway 33 and did not see Aircraft Y. I then announced taxiing into position and departing 29 straight out. A few hundred feet down the runway I glanced at the terminal; no airplane where it had been. I then looked toward to 33 and saw Aircraft Y on the takeoff roll. I was airborne by then; and instantly did a hard right turn to the east. I never did get to Runway 33 in the turn and kept climbing. Only after eastbound did I notice the active frequency was on the wrong frequency and toggled the correct frequency into the active spot. I do not know when the CTAF frequency was toggled away. The G1000 has several small buttons; squelch volume control; frequency transfer; and a button to switch to the other radio to change frequencies. More separation would be helpful.