[RossTech]

Instead of all the pop ups, or ads etc, how about just a simple message to users asking for a contribution. It's a much more direct, and far less abrasive approach, plus it's personal and seems reasonable. I'm betting it will convert at 5 - 10% of users aged 16+.

E.g. Hi, I hope you are enjoying this app and finding it useful. Could you support this app by paying a one-time fee of just $1? It will allow me to keep the app updated and best of all running ad-free! Thanks in advance.

[speedyapoc]

Based off of OP's user demographics, I'm really doubtful that a donate option would convert 5-10% or make him any considerable money at all.

I own a similarly popular free app and I offer an option to pay a very small fee to remove ads and get other features within the app. The income from this purchase (which actually benefits the user as opposed to a donation) takes about 5 months to equal what I do in a day off of ads.

[comeonnow]

I agree I think this approach would appeal more to me as a user. I'd also set the options as:

1) Happy to donate 2) No, and don't ask again