Habib Syahputra Banurea, Beni Satria, and Solly Aryza. “A Design Of Prepaid Electricity Credit Recharge System Based On Dual Tone Multiple Frequency”. Jurnal Scientia, Vol. 13, no. 03, Aug. 2024, pp. 548-63, http://seaninstitute.org/infor/index.php/pendidikan/article/view/2529.