How to use the external trigger to take pictures?

It is recommended to choose square wave or sine wave as the trigger signal; the external trigger circuit of FL-20BW and Dhyana 401D cameras is an optocoupler isolated circuit. The current common optocoupler isolation circuit, the internal collector open circuit, is no output and drive capability, to achieve the level and signal drive through a pull-up resistor, so these two cameras need to be pulled up externally to trigger properly.