The system consists of a commercial USB to Serial RS232 adapter and a simple voltage limiting circuit consisting of one or two diodes and a resistor for each TTL signal.
Our Adapter output swings from +6.5 to -6.5 volts and only requires one diode.
Only one BNC output was used for our dual Medoc TSAII application, but both jumpers (DTR to CD and RTS to DSR) were connected to allow the software to auto detect the hardware.
FYI: other serial port TTL in out diagram.
Auto Detection :The software normally can auto detect the hardware, but it is conceivable that in some cases this auto detection may not work properly. In such a case the user should find out to which COM port the hardware is connected and enter its value manually. To find out to which COM port the hardware is connected, the user can go to WINDOWS "Control Panel" >> System >> Hardware >> Device Manager >>Ports (COM & LPT).
Once the device Manager is displayed, as shown on the right, plugging and unplugging the USB Serial Adapter will make the port connection appear and disappear from the tree display, indicating the COM port assignment.
Should the COM port number be higher than 16, you may need to modify the MSCOMM32.OCX file
Pulse Duration :The TTL pulse duration can be changed by simply typing the desired duration in seconds into the "Pulse Duration in Sec." text box. The duration is automatically saved to a disk file when the software is properly exited.
2008 May 1
Last reviewed 2008 May 7