There are sophisticated gate driver chips that get around this, but I`m actually already using a part that can act as a reasonable driver in this situation: the 74HC2G34 buffer. However, I wasn`t going to get away that easily- Starfish needs two sensors and the XGZP6857D unfortunately has a fixed I2C address so they can`t share the same I2C bus. To keep things simple, I went with the same transciever IC used in the Lumen motherboard, the MAX3078E. I went with the PCA9545A four channel I2C bus switch. PURPOSE AND SCOPE OF COVERAGE - This standard is intended to provide a method of interconnecting data terminal equipment and a data communication channel when each is furnished by different companies. PURPOSE AND SCOPE OF COVERAGE - This standard is applicable to the interconnection of data terminal equipment (DTE) and data circuit-terminating equipment (DCE) employing serial binary data interchange. Again many thought that the UART protocol used in the serial port were part of the RS-485 standard, but the RS-485 standard contains even less of the OSI model layer one than RS-232 does. The Lumen`s upcoming powered feeders will communicate using RS-485, a multidrop serial bus common in industrial applications.



































Multiple receivers may be connected to such a network in a linear, multidrop bus. The RS-485 standard title is "Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems". For this task, I chose to use three TMC2209 stepper motor drivers. There`s one motor for the X axis and two for the Y axis6. The driver`s ENABLE signal is driven by one of the RP2040`s GPIO pins. Since all the TMC2209s share the same UART bus, this is used to give each one a unique address so they can be individually addressed. The vacuum sensors I`m using for Starfish are the CFSensor XGZP6857D I2C gage pressure sensors, the same ones used on the latest revision of the Lumen motherboard. These examples are for a single 120 Ω termination. And since a 120 Ω termination resistor can cause enough signal loss with an extremely long 120 Ω cable to stop the network from functioning, a 500 Ω or even a 1kΩ termination resistor may improve the signal quality enough without causing too much signal loss for the network to function. C801 is the obligatory bypass capacitor and R801 is the 120 Ω termination resistor required by the RS-485 bus.



































C1202 is a bypass capacitor. The charge pump capacitor has to be located as close as possible to to the CPO and CPI pins. The bypass caps are close to their respective power pins and the ESD diodes are snuggled up next to the connectors. Keep the flyback diode (D1002) close to the connector to reduce the loop area for the flyback current. C1201 sets how long the peak current (Ipeak) is held before dropping down to the hold current (Ihold). 4.7 µF sets it to 350 ms. Again, the solenoids I have are more than happy with this. R1201 sets the PWM frequency used to drive the solenoid. All with adjustable transmission interval, and being able to use WiFi, Radio frequency and / or GSM. They draw less than 500 mA so I chose to use MOSFETs. It works in the basic version with 4 affordable AA batteries (1.5V, alkaline or Lithium; in the V5 version it can be powered at 5V instead of batteries, for example via the USB cable included) and has been expressly designed to have low or very low consumption and to use the cheapest batteries available.



































This third example would be a good place to use an isolating RS-485 transceiver. It has a special capacitive sensor designed by us, efficient and of good precision, waterproof, resistant to oxidation and not subject to variations due to salinity and soil composition: better than this there are only the "extraction pressure" sensors (which we do not propose because they are not durable and also the sensor alone costs hundreds of euros). 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, RS485 standard and when closed the nozzle is vented to atmospheric pressure so that it can let go of the parts. The next part of the vacuum system is the two pneumatic solenoid valves. The other two signals, RE and DE, enable the transceivers input and output respectively. The TX output of a first device connected to the RX input of a second device, and the TX output of the second device connected to the RX input of the first device. RS-485 simply defines the interface connection points as "A" and "B" and shows the voltage relationship between "A" and "B" for the binary states of the two wires, not the binary state of the input to the driver.