This page is a general guide for hardware items and suggestions on how to design and work with things like a PCB layout.
General suggested environment
- Allows an ambient temperature from -30C to +50C (-22F to 122F)
- Voltage regulators that are compatible with ISO 7637-2 (spikes up to 100V for short periods of time).
- Voltage regulators that follow Maxim's suggestions here (cold cranking down to 4V for up to 40mS)
- Reverse polarity protection as noted in this video (P-MOSFET style)
- Humidity allowed up to 100% (water resistant enclosure, perhaps fully potted)
- Sensor inputs are capable of human body model ESD (100 pF 1.5 kohm 500V to 1kV class 1B or better)
- All sensor inputs can survive a sustained short to 12V or GND. (fused as required)
- All sensor GND references are fuse protected such a dead short to 12V can be repaired, with out replacing the entire PCB.
- Connectors should be keyed such that it is difficult to accidentally swap connectors
- Connectors should be able to carry the max possible load with one pin, no doubling up pins to get increased current ratings. It is OK to double up pins to decrease connector resistance for a lower voltage drop.
- Connectors should survive the currents passed when inputs are shorted to GND or 12V as noted above in the suggested environment.
- GND(s) should be properly sized such that 99% duty on the fuel injectors will not raise the GND voltage and prevent the MOSFET's from operating correctly.
- Suggested to use twisted pair PVC wire as a minimum for signal wires, silicon jackets are more costly, but also much better.
- Suggested to use the "Tin Commandments" found here
PCB design rules
- 1oz copper suggested
- Trace/via temperature rise should be 10C or less
- Suggested to use 12/12 traces and setback's such that low cost MFG houses can produce quality product. This can not always be followed, especially when you have a chip with 7 mil spacing, but if you try to follow this 12/12 rule, you'll get a higher yield from your PCB's. Even an 8/8 house can have issues as 8/8 is X/Y, a 45 degree angled traces would have a tolerance of √(8² + 8²)= 11.3, which rounds up to 12 mil. Most PCB layout programs will keep your angled setbacks at 8 mill instead of 12 mil. So you should set your setbacks to 12 to prevent MFG issues.
- Silk screen should include header information when possible, things like PA1, or PE4. Resistors and caps should be ref designators and a revision level. Of course a URL for more information and using the free bill boards is suggested.
- Test points are suggest as a way to diagnose various potential issues.
- Any signal of about 1kHz or higher, will have GND currents that try to follow the adjacent trace. Us this practice to follow current loops and to prevent signals from coupling.
- GND plane should not have physical barriers, signals and chips should be routed accordingly such that they do not cross naturally. GND plane barriers are almost never needed unless you get into RF circuits with strip line requirements. Which is not very likely with an automotive PCB.
Links to specific hardware projects
The brain board can be the off the shelf STMDiscoveryF4. However the Discovery has several circuits like the analog microphone circuits which change how a particular pin is loaded. We have noticed that this pin loading cause the injector circuits to vary pulse widths. Because of this we have developed a stripped down version of the discovery board with out the extra circuits. Both boards have the same general specifications, same clock rates, same IO headers with the same pin out's, ect.
Frankenstein is a combination of individual modules, such that you can make sub modules, then combine them with a script. The end result allows you to prototype a small board, then once you have verified the small board, you can combine it with the larger module. If you don't want all the features of Frankenstein, you can mix and match as you so choose. Frankenstein is a combination of the below.
- Forum thread about this PCB found here
- 12 low side 1A injector driver module found
- 6 high / low side drive .125A capable ignition pre-drivers, for use with external ignitors.
- 12 channels op-amp analog input module (TPS, MAP, IAT, ect)
- Variable reluctor / Hall input module
- SD card module
- USB FTDI communications module
Links to misc schematics
J701 NEON engine schematics
Found in this thread http://rusefi.com/forum/viewtopic.php?f=3&t=360&start=52