Neil, it's not about sampling and averaging, it's about decreasing the impedance on the supply point of your inductive loads by using electrolytic capacitors. You can keep the diode suppressors onboard, but very close to the power connector. Usually you don't use the same connector for power, communications and analog signals, this is against of any good practice rule. You can do it but it's your choice. You do not need other regulator for inductive loads, just as you split the ground, split the power. Arrange the paths of your currents radially, so the digital/analog current will not flow through the same path as power current. On Wed, Aug 26, 2015 at 6:12 PM, Neil wrote: > The connector is polarized, so that's not an issue. A lot has to happen > simultaneously -- analog sampling, solenoid driving, etc. But yes I am > averaging and filtering the analog signals -- up to 128 samples on some > of the signals that don't change rapidly. My concern is more with the > digital serial signals getting corrupted by the higher-voltage signals. > > I do have one signal] which has a pull-up and that's a shutoff-switch > input (ie: tells the system to shut off completely). I'll have to look > into keeping this further away. > > I had not thought about ferrites but I'll look into those. I did find > this neat doc on EMI which I'm still going through, and it too mentions > ferrites... > http://www.ti.com/lit/an/szza009/szza009.pdf > > None of the serial is differential -- one is RS232 (actual RS232 level > from a MAX232) with error checking. Another is also RS232, with no > error checking, but that comes from a different system so I don't have > much control over that. The third serial data-stream is a 5V level > custom protocol. It does have a checksum in both directions. > > I'm confused about using 2 grounds yet merging them where they enter the > board. Wouldn't that mix any noise generated by the motor side onto the > logic-side? > > Cheers, > -Neil. > > > On 8/26/2015 3:07 AM, Jesse Lackey wrote: > > Hummm.... neat question. > > > > One aside: if the connector isn't polarized, you could use strategicall= y > > place the spare pin such that if the connector is inserted backward and > > power applied, the +12V goes to this unused pin, and the user gets > > nothing happening vs. smoke. > > > > Can you arrange things such that you aren't sampling the analog sensors > > while motors are running (or starting/stopping), or solenoids switching= ? > > Or maybe at least take an average over time to minimize bad data. > > > > Digital I/O ... it would be best if all signals are driven, i.e. not > > have pullups, for better noise immunity. Not sure how much it matters. > > > > You could use that spare pin for a ground for digital and/or analog, an= d > > have the digital and/or analog ground therefore be separate from the > > rest, and connect the grounds together where the power comes in from > > whatever is plugged into this and making the +12V. That said, I have > > seen cases where the best performance was to use the same ground all > over. > > > > A ferrite on the +12V @ the connector would be a polite thing to do, > > maybe on the motor as well. They're cheap. > > > > I assume the serial is differential (rs485?). Doing it packetized with > > a CRC and having both ends of the communication keep count of how many > > packets are damaged is a good way to monitor signal integrity. i.e. do > > things all command/response style and be able to ask that count to > > determine % damaged. > > > > I look forward to this thread! > > J > > > > > > > > Neil wrote: > >> I'm trying to figure out how best to allocate connector pins for a > >> mixed-signal board. The system has high-current, high-voltage, > >> repeated-switching signals (motors and solenoids), serial data signal > >> pairs, and a number of analog sensor signals coming in. The catch is > >> that this board has only one 30-pin connector (3 rows of 10 pins each)= .. > >> > >> Currently, I have, in order starting from one end towards the other: > >> - Motor + and - (12V, 6A max) > >> - Solenoids (up to 4A, but with reverse spikes will see 30V+) > >> - Power & ground (12V) > >> - Serial signals (3 pairs) > >> - Digital I/O > >> - Analog sensor signals > >> > >> The PCB has the motor and solenoid drivers on one side of the board, > >> power supply in the middle (but off towards the back), and 2 PICs that > >> handle all the logic near the other side. The analog circuitry is kep= t > >> really short and off in one corner of the board nearest the end of the > >> connector with those signals. > >> > >> So what I'm wondering is: > >> - Is there a better way to organize the signals on the connector? > >> - I have one spare pin -- should I run a separate logic ground? > >> - If so, where would I connect these on the board (or wouldn't this > >> cause a ground loop)? > >> - If I do or don't, should I split the ground plane so the logic side = is > >> separate from the motor/solenoid side? > >> - Anything else I should do? > >> > >> Cheers, > >> -Neil. > >> > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .