fetch data from database using dropdownlist

Hello im trying to fetch data from database and display it in textbox. I don't know what's wrong with my code. nothing is being displayed in the dropdown so as i can select an item
my html code is as folllows:
<form id="form1" runat="server">
<asp:Label ID="Label1" runat="server" Text="Weight"></asp:Label> <asp:DropDownList ID="ddl_weight" runat="server">
</asp:DropDownList> <br /> <asp:Label ID="Label2" runat="server" Text="voltage"></asp:Label> : <asp:TextBox ID="txt_voltage" runat="server"></asp:TextBox> <br /> <asp:Label ID="Label3" runat="server" Text="amp hours"></asp:Label> &nbsp;<asp:TextBox ID="txt_amp" runat="server ...