I'd like to create a scan where a hammer appears at the bottom of a stocks bollinger bands. 

Thanks very much.

If you just want say the entire body to be at the top third of the candle as your definition of a hammer.

3 * O > 2 * H + L AND 3 * C > 2 * H + L

And you want the low of the candle to be at or below the bottom of a simple Bollinger Band 20, 2.00.

3 * O > 2 * H + L AND 3 * C > 2 * H + L AND L <= AVGC20 - 2 * SQR(ABS(C ^ 2 + C1 ^ 2 + C2 ^ 2 + C3 ^ 2 + C4 ^ 2 + C5 ^ 2 + C6 ^ 2 + C7 ^ 2 + C8 ^ 2 + C9 ^ 2 + C10 ^ 2 + C11 ^ 2 + C12 ^ 2 + C13 ^ 2 + C14 ^ 2 + C15 ^ 2 + C16 ^ 2 + C17 ^ 2 + C18 ^ 2 + C19 ^ 2 - 20 * AVGC20 ^ 2) / 20)

If you need the entire candle at or below the simple lower Bollinger Band 20, 2.00.

3 * O > 2 * H + L AND 3 * C > 2 * H + L AND H <= AVGC20 - 2 * SQR(ABS(C ^ 2 + C1 ^ 2 + C2 ^ 2 + C3 ^ 2 + C4 ^ 2 + C5 ^ 2 + C6 ^ 2 + C7 ^ 2 + C8 ^ 2 + C9 ^ 2 + C10 ^ 2 + C11 ^ 2 + C12 ^ 2 + C13 ^ 2 + C14 ^ 2 + C15 ^ 2 + C16 ^ 2 + C17 ^ 2 + C18 ^ 2 + C19 ^ 2 - 20 * AVGC20 ^ 2) / 20)

If you have different requirements, please let us know.