This will decrease the amount of time to wait for the signal to stabilize, increasing the possible bit rate. If the can't, try reducing the bit rate. The higher the data rate and the longer the cable, the more likely it will be that you have to add termination resistors. This converter can handle up to 36 VDC in and provides up 5 V up to 500 mA downstream- more than enough for Starfish. Starfish is open source, so you can check out the original source files on GitHub. This is an inexpensive way to keep high-frequency AC ripple in check while the board deals with dynamic loads from the motors, pumps, and solenoids. If you'd like to learn more about reverse polarity circuitry and their tradeoffs, check out AN-013 by Rod Elliot. The drawback to using literally every I/O pin is that the bypass capacitors are a little further away from the RP2040 than they could be, but, the RP2040 seems more than happy with this layout in practice.
Last, but not least, is a large bulk capacitor (C203) to give the board a little more breathing room when dealing with sudden current draws. RS-422 has one or more pair of wires. One of the main problems with RS232 is the lack of immunity for noise on the signal lines. RS232 has numerous handshaking lines (primarily used with modems), and also specifies a communications protocol. The RS485 and RS232 serial communication protocols have been in use for over 50 years and are still widely used throughout business and industry. These motor controllers use a single-wire serial bus for communication and that resistor is required to tie the separate TX and RX lines together. This article will explore the hardware design of Starfish, a control board for a pick and place machine built around the Raspberry Pi RP2040 microcontroller and Trinamic TMC2209 motor drivers. Also note R305 which connects TX and RX for the TMC2209 motor controllers together.
Special care must be made with the 1.1 V rail as it provides power to the CPU core. Ensure that the TVS diode is close to the power connectors to reduce the overall current loop for an outside transient voltage spike. The exact voltage of high and low are not usually specified, rather a voltage difference between the two outputs is specified. Onboard unibody digital isolation, allows signal isolation, high reliability, strong anti-interference, and low power consumption. Onboard unibody power supply isolation, provides stable isolated voltage and needs no extra power supply for the isolated terminal. The resistor (R201) and diode (D202) protect the MOSFET's gate against transients that may exceed the maximum gate-to-source voltage (VGSS). A higher value termination resistor will reduce the DC losses associated with extreme line lengths, allowing for much longer line lengths at the cost of ringing on the wires. The transmitter and receiver compare the voltages of the data- and handshake lines with one common zero line. The RS485 standard defines a balanced two-wire transmission line, which may be shared as a bus line by up to 32 driver/receiver pairs. It's also well suited for this project: there's a lot of digital peripherals to talk to but no analog stuff to deal with which pairs well with the RP2040's abundance of digital I/O and near lack of analog I/O.
It needs to accurately move the gantry around, control vacuum-powered picking nozzles, and communicate with various digital peripherals such as RGB LEDs and automated feeders. This eventually lead to me wanting to create my own control board for the machine. Fist, some background: Back in May, I assembled my very own pick and place machine - a LumenPnP from Opulo. These valves are used to control the vacuum on the pick up head's nozzle - when the valve is open the nozzle can pick up parts using the vacuum, and when closed the nozzle is vented to atmospheric pressure so that it can let go of the parts. If the circuit common is truly isolated from earth ground, then scuffing your feet on carpet (to pick up an ESD charge) and touching the wires can cause the wires to shift potential several thousand volts. The exact voltages will depend on the driver, the loading, biasing, termination, and any shift in ground potential between the driver and receiver. It shows a diagram of the driver and receiver with two wires connecting them, and a third point "C" that is called a common.