The AcuDC 243 comes with standard Modbus-RTU via built-in RS-485 which allows the meter to communicate with any master devices such as computers or PLCs. From a software point of view, full-duplex RS-485 looks very similar to RS-232. Software features include input type, end-scale, start-scale, decimal point, visualization end-scale, visualization start-scale, filter time, alarm threshold, hysteresis (alarm), activation/deactivation alarms delay, type and scale output retransmitted, contrast and display brightness, etc. to mention a few. Typically RS-485 runs over twisted pair, so screw terminals or some type of modular jack would be expected. ↑ "How Far and How Fast Can You Go with RS-485?". The control board and feeders aren`t very far apart so noise might not be a big enough issue on untwisted cables in practice. 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. You can accomplish that current control scheme by driving a MOSFET using the PWM output of a microcontroller, but I wanted to try out the DRV120 - a single-channel relay, solenoid, and valve driver with current regulation.



















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. 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 ensure the appropriate device responds to a command, the signal includes an identification or address for the device to follow the command while others ignore it.Each device must have a unique address to avoid accidental command reactions. 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. According to the EIA-485 standard, RS485 can accommodate up to 32 drivers and 32 receivers on a single 2-wire bus, which allows for reliable communication over long distances. For this task, I chose to use three TMC2209 stepper motor drivers. It would require an isolated power supply and optically isolated drivers. This lowers the overall power demands of the system and extends the life of the solenoids by running them much cooler.



















The bypass caps are close to their respective power pins and the ESD diodes are snuggled up next to the connectors. In this case, they`re PESD3V3L1BA diodes rated for 3.3 V signal lines. The only thing of note here is the ESD diodes on each data line (D401, D403)- a good practice for external connectors. I absoutely could`ve used the same MOSFET circuit here. To keep things simple, I went with the same transciever IC used in the Lumen motherboard, the MAX3078E. RS-485 functions by defining the transmission of ‘0’s and ‘1’s via the positive or negative states of the transceiver terminals, A and B. To perceive the same logical state, all devices on the communication link must generate and detect signals of the same polarity.A reversed device will read and generate incorrect signals, leading to a communication breakdown. 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. When the driver increases the voltage on one of the wires, it simultaneously decreases the voltage on the other wire resulting in a differential voltage between the two wires.



















In RS-485, the receiver`s internal biasing will be such that the "receiver will remain in the intended binary state when a differential voltage (VR3) of ±0.40 V is applied through matched resistors equal to 1500/nUL 1/2 to each input terminal, as shown in figure 13, with the input voltages VR1 and VR2 (and resulting VR3) to achieve any allowed input condition.". Master Receives: The master device, like the slaves, is constantly monitoring the voltage difference between lines A and B, so it will receive the response from the slave. Server / SMS gateway, server, like the 1-Wire provides access to other network devices. Since the PCA9545A provides four channels and I only needed two for the vacuum sensors, I had two leftover. 2.2.28 provides the stability, and allows for new GPRS router libraries and access drives. Common SDK allows an extension of the programmable logic controller, and the whole is based on open standards (Linux, Modbus). RS-485 allows for multiple devices on the two wires. If an RS-232 to RS-485 converter is used, things start to get even more murky. The first bit a UART transmits is the start bit (0) and the receiving UART should see this transition. The first is that if the line is long enough, an AC "ohmmeter" connected to the input of the model will see the "resistance" of the wires as 120 Ω.



































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