I have started the FW on the ECU that will take a while, but I can outline the main design principles I use:
ECU Hardware consist of a a motherboard with a M12-4 Power connector. I use the same format as NMEA2000, but allow for 8V to 30ichV PSU rather than only 12V. I do however add the CAN port so that we can re-use NMEA2000 infrastructure as well as claim NMEA2000 compability. So that gives us CAN as primary interface.
I also add an USB as a serial port because it is convenient to just plug the main board to a PC for direct, first time configuration this way. Through this we can do CLI scripting to configure the node and detect what’s on it.
My current motherboards have PCB layout for one Ethernet, but I am not sure I want to keep that. I have two Ethernet modules that are better as they have separate MCU’s offloading some of the work. So – I think the Ethernet port can be dropped in favor of other features on the motherboard.
Disk is SPI-Flash, SPI-FRAM or SPI-PSRAM. Each motherboard will as a minimum have a SPI-Flash.
The Motherboard is a powerfully MCU acting as a switch between all interfaces. I want to keep this as simple as possible, but it also have capabilities to run automation based on data from multiple modules.
What makes this design special is the add-on modules, because you take a small box and add up to 8 modules to get the IO you want. Each modul vary in IO, but they have the same interface to the motherboard. This is a star design so one module will need to send messages to another module through the motherboard – or more correctly the motherboard is configured to forward seleced messages to the modules – something you can configure.
My modules that are in progress are as follows:
- CAN Module. Fitted with a small MCU and fully galvanic CAN interface using NMEA2000 standard we can make a CAN Hub with 8 ports easely. In fact we can link Nodes and create a CAN Hub that is as large as we want as long as we remember to do bandwidth calculations.
- RS485 my newest board is mostly for Modbus. This old protocol is hard to avoid and is a very handy interface as many 3rd party components will support this.
- Single Ethernet connection so we can hook up standard Ethernet and work.
- Tripple Ethernet connection with a switch in the connection so that we have two external ports and one internal. This is needed for low level Profibus or Ethercat support, but it also allows us to daisy chain Ethernet and avoid a centralized switch.
As for the rest we need some actual IO:
- Analogue IO. I designed a fast, high precision AI board capable of recording 3 channels at 65Kbps with 24 bit resolition. This is primarely designed for vibration sensors, but it is a generic 3 – single lines, or 2 delta lines fully galvanic isolated.
- Digital Out – An 8 port digital out capable of multiple ampers and PWM with load detection and current sensors. This can be used as a Power source or as a 3-phase motor driver, solenoid driver, stepper motor driver or DC motor driver.
I have plans for multiple boards, but the only one I actually need fast is a Power Servo Controller. I have some 150Kg Servo drivers I want to put into usage and they need multiple voltages and proper servo signals – which brings me to one more module:
I will need a PSU capable of delivering some Ampere on multiple voltages from 48V, 24V, 12V, 8V and 5V. I use 24V as base, but IO modules sometimes need a secondary source with different voltage, so the 24V is basically for control systems and remember that we talk 8-30V and not just 24V.
I have one more module coming up – this is work in progress, but it is a motor controller targeting 12KW motors. It’s actual capacity is 48V-1200V and some 50A, but it will be designed to sustain 12KW and hence be in the smaller and lower side of motor controllers. The interesting part on this is that total size is very small and that it comes with 10 possible Add-On modules.
It has current sensors, but Resolver, Encoder, Hall Sensors and end points + extra sensors you add through an add-on module. On the left side I have space to add a break-resistor or a sinus filter – the later is needed for induction motors as this can drive all type of 3-phase motore. The design parameters are 600V/20A, but the board is capable of 2 x that.
This is designed for a standard aluminium box and MOSFET’s are underneath directly connected to heatsinks, but we talk about something like 15W in loss on 12KW. I can mount extra heat sinks if needed, but I am not sure I need to on this one.
In short – this is a motor controller where you add the PLC as modules inside the controller to reduce need of extra space and components. My calculations indicate a cost base on ca 300.- USD even for low volumes, and these controllers are usually priced between 1000 to 4000.- USD depending on content.
As this also is an ECU motherboard it will use the same FW as the ECU’s but add current sensors and motor control – I hope to mount the first prototype during x-mas. I need to finish the design and order PCB’s, because I will probably need 3 rounds on this before I am happy.
The content of this HW summary will change as we move forward, but it serve as a reminder of what we need to solve in SW – that will be described in part 2.