device connected to client computer, while it needs to get data from database (server side ASP. NET)

Question

dear friends,

i have a case like these :
1. we have a card reader (usb port connection)...
2. we must connect this reader to client (there are some clients in different cities)....
3. reader's function is to read and write from a card, whereas the card's source data is from database (ASP .NET)
4. firstly, i tried to add reference in ASP .NET to the reader's DLL, but it can not make a live event trigger/connection to the clients since the DLL is installed in the web server...
5. then i think of other solution : client side programming..and i install the reader's DLL in client computer...so reader can interact lively...
6. but i don't know how to do DLL creation, event, trigger in client side programming...can anybody help ? i think of JavaScript (i don't know how to call the DLL event, methods, properties in JavaScript)....

 but perhaps other have better solution..

Thank you,
hendy