While troubleshooting an old but extremely robust threadmill, I came across an RS-232 data link between the device and its master computer. Since I do not have any instruments to sniff the messages flowing through a RS-232 link, I decided to build an extension board to add this capability to my Analog Discovery II instrument (AD). To give myself more flexibility, I am adding plenty of headers to monitor extra signal lines in addition to the main RxD and TxD. A total of five lines can be monitored at any time.

Use it at your own risk. I take no responsibility for any damage caused to any device attached to this board. Since this is an experimental circuit, I assume that whoever is reading this is a tinker and has basic skills dealing with extra-low-voltage circuits.

• Uses the Texas Instrument TRSF3243EIPWR Multichannel RS-232 compatible line driver/receiver
• Five channel RS-232 sniffer
• Passthrough DB9 Male to DB9 female
• RxD and TxD lines always connected to AD instrument DIO[0:1]
• Selectable signals can be connected to the AD DIO[2:4] via header shunt pins
• RxD and TxD signals connected to AD instrument oscilloscope channels
• Optionally, RxD and TxD can be driven by an AD instrument using DIO[8:9]
• It is also possible to select one more signal line to be driven by an AD instrument DIO[10]
• The driver power can be enable(disable) driving the DIO[15] high(low)

• A data link with RS-232 communication to sniff on
• Personal Computer
• Digilent Analog Discovery (R) Instrument
• Software Digilent Waveforms(R)
• Some extra db9 terminated cables to make the connections

Analog Discovery (R) and Waveforms(R) are Digilent trademarks. The license is described in the file 'LICENSE'.