Harry's GPS Suite Forum

Hello all,

I'm currently using Harry's LT Petrolhead addition on my iOS6 iPhone 5 and have been loving it. Such great bang for the buck. Great job, Harry!

Recently I added the PLX Kiwi Wifi OBD II link so I could add throttle position, gear, etc. I used it for the first time this weekend and realized that the data it transmits to the app is a little laggy and out of sync after it's been overlaid on top of the video (using the iPhone's camera for that, too.)

I suspect this is due to the fact that I'm using the 1 Hz on-board GPS service native to iOS and the sample rate is too low for the OBD II data to sync smoothly at such a low rate. Is this a correct assumption?

If so, I'm assuming moving up to one of the 5 Hz bluetooth devices would be the solution? The 20Hz Vbox Sport is tempting but begins to defy the low-cost/bang for the buck justification.

I've been thinking the Dual XGPS 150A hits the price/performance target.

Two questions:
1) Will all these components play nicely together? (ie. iOS 6, Dual, Kiwi Wifi, etc.)
2) Will it smooth out the data overlay lag issue I described above?

Many thanks in advance for any help anyone can provide!

Cog

1) Yes.
2) No. The lag is not from the 1 Hz GPS update rate. LapTimer interpolates both OBD data to any GPS update rate, and any GPS update rate to the individual video frames. So even with a 1 Hz GPS and 1 Hz OBD, you will get smooth videos. In case you do not get smooth videos currently, there is a problem with the OBD connection in general. I have seen many effects like this for disturbed wifi connections. There is no common pattern, but mostly - although not always - setting network parameters like suggested by PLX, and turning off all other radio frequency units in your car (there are probably more than you would think in the beginning - for example your copilot's mobile) helps. Please watch your OBD update rate: it should show a pretty constant value (e.g. 3 and 4 Hz, alternating). In case it falls to 0 Hz from time to time, the connection is lost in between - resulting in the named "lags". In this case, you need to work on the connection.

- Harry

Harry wrote: setting network parameters like suggested by PLX, and turning off all other radio frequency units in your car (there are probably more than you would think in the beginning - for example your copilot's mobile) helps.

Okay, I would think that the Wifi would select a clear channel to communicate over (?), but there could be some issues. I can confirm that I'm using PLX's recommended settings. I'll take note and try to eliminate other competing RF transmitters.

Harry wrote:Please watch your OBD update rate: it should show a pretty constant value (e.g. 3 and 4 Hz, alternating). In case it falls to 0 Hz from time to time, the connection is lost in between - resulting in the named "lags". In this case, you need to work on the connection.

Is this monitored under GPS when the OBD is connected?

Would I be better off returning the PLX and going for the bluetooth equivalent? The whole reason I went with the wifi version was because I heard the OBD BT connection "crowded out" the refresh rate of the accessory BT GPS receivers resulting in a slower effective refresh rate, ie. consistently sub 3-4Hz rate.

Thanks, Harry.

Easiest way to monitor the OBD update rate is in LapTimer's Sensor List. The Kiwi and the GoPoint BT1 have pros and cons. I have seen connection issues for both (wireless is always less stable than plugged / wired connections), but more frequently for wifi devices in general. BT is a little slower (around 1 Hz).

- Harry

Okay, noted. Appreciate the feedback.