Low Tech Smart Board

I use an old TV, a laptop, and my iPad all the time as a low tech Smart Board.  I use an HDMI adapter for the iPad.  There is a port on both the TV and laptop.  Anything I type is broadcast  on the TV.  I have a graphing calculator app, GraphNCalc 83, on the iPad.  Desmos is a free graphing calculator I can use on my laptop.  If you have a math Co-op class, this low-tech solution can be a game changer.