I bought a used elliptical trainer that has an input for a wrist strap in which to input heart rate to the machines control council. The machine I bought is missing this wrist strap and they aren't available anymore for this model. Is it possible to make your own? I haven't seen one and don't know whats inside or where to begin. Anybody have any ideas? I don't want to spend $100 for a check strap transmitter and receiver.