How is it possible to get "-"sing with BCD seven segment LED display. With combination of four bits we get digits from 0 to 9. What should we do to get - and . ?
Here's a link to a typical circuit: http://www.doctronics.co.uk/4511.htm
By definition, a BCD to 7 segment display only provides for displaying 0-9 on the display, so to show a minus sign requires additional circuitry (not shown on any site I've seen so far) to drive segment 'g'. The good news is that the decimal point does have its own pin so that can be controlled separately (again, by additional circuitry).