[Ovmsdev] Feedback request: HUD sleep behavior work-around

Mark Webb-Johnson mark at webb-johnson.net
Tue Oct 24 11:08:30 HKT 2017

I’ve got two.

The first doesn’t sleep (supposedly). It has a manual on/off switch on the OBDII power line.
The second supposedly goes to standby mode after a configurable time after “engine flame out” (love those Chinese google translations).

I’ll have a look at the second one (which is the one I like the most anyway) to see what it says about configurability (“flame out” rpm threshold, and time setting).

Regards, Mark

> On 24 Oct 2017, at 6:29 AM, Greg D. <gregd2350 at gmail.com> wrote:
> Hi folks,
> To those who care about such things, I have a dilemma to solve and can use some guidance:   How to keep the various OBDII peripherals (HUDs, Dongles, etc) awake when the car is on but is not moving.
> I have a small sample of devices (three to be exact) to use for developing the OBDII ECU Simulator (translator).  The devices that are intended for installation in a car use various methods to determine when to shut down to conserve power, since the OBDII 12v power from the battery does not turn off with the car.  They are clearly not designed to work with EVs.
>  - HUD:  If not moving (speed = 0) for more than a second or two, turn off if below some minimum engine RPM.
>  - SyncUp Drive dongle:  Turn off if no variation in Engine RPM, regardless of value, for more than 10 minutes
> Since an EV's motor has a direct gearing to the wheels, a straight feed-through of RPM to the device causes them to shut down when the car stops.  Since they stop polling the ECU when off, the devices do not start back up when the car starts moving.  They require a power cycle to resume.  The current OVMS ECU code is sufficient to keep the SyncUp dongle from shutting down, as I simulate a very small (0-15 RPM) motor "jitter" to make the dongle think that there is something mechanical connected.  But it's not sufficient to keep my HUD alive; it takes about 500 RPM to keep it from shutting down if the car isn't moving.
> My questions:
> 1.  For those who want to attach a HUD-type display to the OVMSv3 product, is a "500 RPM when at zero speed" algorithm acceptable?  I'm guessing that motor RPM isn't important if not moving.  If you want to map Engine RPM to some other source, be aware that might be affected by this behavior.  (Note: the mapping of these 4 PIDs is static right now.)  My own use of the SyncUp Drive dongle is for the Wi-Fi hotspot it provides, so I don't care about what it reports.
> 2.  The Diagnostic dongles (OBDwiz in my case) seem to stay connected as long as there are responses to its polling, regardless of value.  Mine is USB powered, however; I don't know how the Bluetooth-based devices behave.  If anyone has one, I'd like to know what it does.
> 3.  Are there any HUD / Dongle PIDs that you are especially interested in seeing displayed / tracked?
> As for the real power cycling of the external device, the current plan is to match the enabling of the external 12v feed-through with the state of Vehicle On.  That will drop the external device power when the car turns off, and turn it on when the car is "started".  You can also control it manually from the command line.
> If you want to try the OBDII ECU simulator, it currently supports vehicle speed, engine RPM (derived from speed, assuming a Roadster's gearing), coolant temperature (reported from motor temp), and fuel flow (reported from Battery SoC, but the math is currently wrong).  There are ten other PIDs respond with simulated values (e.g. engine load, air intake temp, etc.).
> OVMS > obdii ecu start can3
> OBDII ECU has been started
> OVMS > power ext12v on
> Power mode of ext12v is now on
> I (14194) ext12v: Powering on external 12V devices
> Attach your HUD/Dongle to CAN3 on the Accessory port.  
>  DB26    OBDII Female     Signal name
> -------   -------     --------------------------
>    6        14        CAN3-L
>   16         6        CAN3-H
>                       (also 120 ohm resistor between 14 & 6 for termination)
>    8        4 & 5     Chassis & Signal Grounds
>   18        16        +12v switched output
> Also, there is a command "obdii ecu privacy [on|off]" to disable / enable the reporting of your vehicle VIN, should you want to keep the dongle from seeing it.  Default is privacy on (not reported).  The SyncUp folks appear to have a relationship with the car insurance industry, and the implications of that could be "significant."
> Enjoy,
> Greg
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