In my line of work, I wind up having to fight with debugging various serial protocols, and find I spend half of my time trying to either get an adapter or line card to work, or trying to snake a cable where it needs to go. So I decided to take a cue from the Bus Pirate (one of the most useful tools in my bag) and make a version just for serial protocols.
So I'm working on a board that can perform TTL to RS232, RS485 and RS422 conversion. I'm designing it such that signal and power is provided through a pin header, so I can clip it to the device I want to work with (most have their own PSU). Power is regulated, so it can take 5 to 16V. The TTL output can also be switched between 3V and 5V and is designed to work with a BT adapter, making the device wireless.
To make things simple on the user end, I have ganged all of the transceiver TTL receivers into a common TX bus (with added load resistor) and ganged the drivers to a single RX bus through AND gates to prevent bus contention. If multiple drivers are attempting to transmit at once, it will corrupt the data, but I'm considering that acceptable.
The RS422 transceiver has permanent termination and fail-safe resistors (the fail-safe resistors are built into the transceiver), but they are connected through jumpers on the RS485 lines so that I can disconnect them and insert the device as a slave node to monitor traffic.
So far I have everything drawn up in eagle and have the board layout done. I still need to look up resistor values and double check the nets.
I've attached my current schematic. Any comments or criticism would be appreciated.
So I'm working on a board that can perform TTL to RS232, RS485 and RS422 conversion. I'm designing it such that signal and power is provided through a pin header, so I can clip it to the device I want to work with (most have their own PSU). Power is regulated, so it can take 5 to 16V. The TTL output can also be switched between 3V and 5V and is designed to work with a BT adapter, making the device wireless.
To make things simple on the user end, I have ganged all of the transceiver TTL receivers into a common TX bus (with added load resistor) and ganged the drivers to a single RX bus through AND gates to prevent bus contention. If multiple drivers are attempting to transmit at once, it will corrupt the data, but I'm considering that acceptable.
The RS422 transceiver has permanent termination and fail-safe resistors (the fail-safe resistors are built into the transceiver), but they are connected through jumpers on the RS485 lines so that I can disconnect them and insert the device as a slave node to monitor traffic.
So far I have everything drawn up in eagle and have the board layout done. I still need to look up resistor values and double check the nets.
I've attached my current schematic. Any comments or criticism would be appreciated.
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