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Accelerometer interface (WiTilt)

ChronoGPS can monitor acceleration using a bluetooth accelerometer WiTilt Sparkfun. It seams it is the only one on the market. This accelerometer can be used with a PDA (unlike the Wiimote which works only with PC, see after).

You can buy this accelerometer here.

Unfortunately this electronic component is not sold with box and battery. You will have to do a little work (but no need to be a professional in electronics) buying a battery support, a connector and a box to put everything in it. You will find this support, the connector and box in an (online) electronic shop (like this one www.e44.fr)

Weld the connector to the battery support (be careful with polarity), put the support in the box (stick it in it). Place the batteries in the support, connect the WiTilt (fix it in the box, you can put rubber between the WiTilt and the box to insulate it from vibrations which can disrupt measures).

Put DEBUG/RF switch on RF (Bluetooth) and switch on the WiTilt (switch ON/OFF). Accelerometer is ready to be paired like a bluetooth GPS or OBD interface. See explanations here.

Once a serial port associated with the SparkFun peripheral, click on Conf. button, then Accel. button :

WiTilt settings

Check Use WiTilt. select communication port (see bluetooth paired phase) and baud speed (57400) of WiTilt interface, set the refresh rate (100 ms for example, 10 Hz). WiTilt can support up to 320 Hz refresh rate so you can set refresh rate to 3 ms in theory. Don’t forget the rate of your GPS : 1 Hz to 5 Hz, so no need to set a very different rate for the WiTilt. If you set 100 ms (10 Hz) for the WiTilt and you use a 1 Hz GPS, WiTilt will deliver 10 acceleration measures every second once GPS will return only 1 position and 1 speed. ChronoGPS will save (in the .log file) the max G measured during the elapsed second. The display of WiTilt data are identical to the OBD data.

You can test WiTilt by pressing Test button. The following screen appears :

WiTilt test

Move your WiTilt upside down, right to left to see if the WiTilt returns measures. Progress bar must follow movements.

Accelerometer calibration, installation advices

The box containing the WiTilt must be fixed on the car otherwise it won't work. Fixing must be perfect and must match the arrows on the WiTilt : X must be oriented to the back of the vehicle. Once fixed, you will have to calibrate the WiTilt to cancel out the incline of the WiTilt in the car (the car must be on an horizontal road when you proceed calibration). Click on the Conf., Accel. then Calibrate button. The following screen appears :

WiTilt reset

Press the WiTilt button (this screen appears when you run ChronoGPS just after switching on the WiTilt), ChronoGPS calibrate the accelerometer in order to have 0 g in all X, Y, Z directions for the current position of the accelerometer (X = longitudinal acceleration - acceleration & brake, Y = lateral acceleration - curve, Z = vertical acceleration  - compression/spring) :

WiTilt calibration

Once WiTilt interface settings done, you can proceed timing classically. All additional data monitored from WiTilt (X,Y,Z acceleration) can be displayed on the different graphs.

Acceleration measures

Wiimote support (PC version only)

ChronoGPS can handle acceleration data returned by a Wiimote (remote of the Nitendo console – no need to buy one : you can buy only the wiimote)

Hardware requirements :

·        A Wii remote (called Wiimote, $50 in any dealer shop which sell Wii console). This device is physically rated to measure accelerations over a range of at least +/- 3g with 10% sensitivity. More information here : http://www.wiili.org/index.php/Wiimote

·        A PC Computer running Windows with bluetooth interface to connect Wiimote (PocketPC under Windows Mobile doesn’t support Wiimote yet).

Be careful : communication with Wiimote is not possible with all bluetooth stack (see : http://www.wiili.org/index.php/Compatible_Bluetooth_Devices). I use this hardware / software :

·        Bluetooth Key Conceptronic CBT100U

·        BlueSoleil driver (you can download : http://www.bluesoleil.com/download/index.asp?topic=main_download ) because the standard driver doesn’t work with Wiimote.

Wiimote installation :

Install BlueSoleil driver, and launch BlueSoleil program, then call my Bluetooth / Search bluetooth devices and put the Wiimote into discoverable mode, by either pressing buttons 1 and 2 on the Wiimote or using the switch hidden near the batteries (to proceed Bluetooth pairing) :

Wiimote pairing

The Wiimote appears in the following screen :

Wiimote is detected

Right click on the Nitendo RVL CNT 01 icon, the following menu appears :

Services detection provided by Wiimote

Select Update services option menu, then  right click an other time on the Nitendo RVL CNT 01 icon, and call Connect / HDI service option menu :

HID service connexion

Wiimote is ready to work with ChronoGPS.

Wiimote ready to work

Call settings windows in ChronoGPS by pressing Conf button. Press Wii button, the following screen appears :

Wiimote settings in ChronoGPS

Check Use Wiimote and set the refresh rate (200 ms for example, 5 Hz). Wiimote can support 100 Hz refresh rate so you can set refresh rate to 10 ms in theory. Don’t forget the rate of your GPS : 1 Hz to 5 Hz, so no need to set a very different rate for the Wiimote. If you set 200 ms (5 Hz) for the Wiimote and you use a 1 Hz GPS, Wiimote will deliver 5 acceleration measures every second once GPS will return only 1 position and 1 speed. ChronoGPS will save (in the .log file) the max G measured during the elapsed second. The display of Wiimote data are identical to the OBD data.

Wiimote test, click here.

Wiimote calibration, click here.

 
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Send email to chronogps@free.fr for any question or suggestion about ChronoGPS, GPSTripMeter or GPSDetective.
Copyright © 2007-2013 Sébastien GUCHET - Dernière/last modification : 11/05/13