DIY Cruise Control FAQ (2006-2010 Yaris)

[CTScott]

Originally Posted by bobor

Hi everybody,

I own my small Yaris and like the car very much. The only minor thing I miss is the CC feature. Since the european models do not have support for CC built in ECU and I do not want to invest too much money in some aftermarket model, so I decided to build my own one.
The idea is very simple. I would like to use a microcontroller to periodically check all necessary input data (current speed, brake & clutch pedal positions, etc.) and then set the digital2analog converter to emulate the accelerator pedal movement by increasing / decreasing the output voltages on both lines to ECU as the speed of the vehicle is under / over set value.
I currently have an open question related to accelerator pedal connection. There are 6 wires for 2 separate Hall probes to detect the pedal position. Of each set, one wire is +5V, second one is GND and the third one is the output, where voltage changes according to accelerator pedal depression level. I would like to cut these two signal lines and put them as input to CC module and connect another two wires (output from CC) as input to ECU. So far so fine.
But my idea is, that during the time CC is switched off, the signal input and output are directly interconnected and when CC is enabled, the output is fed from DAC. I would like to use a relay controlled by microcontroller for this purpose (see fig.). but I am not sure, if it is a good idea. What is your opinion. Is there any better solution for this?
If I use the relay, will there be any problem with temporary loss of signal to ECU during relay switching (the actual switching time is approx. 5 ms)? Or shall I add some small capacitor between output & ground to smooth the glitches. But I have no idea what capacity to use in order not to influence the response time of accelerator pedal too much.
And finally, do you know about any place where can I get at least accelerator pedal connectors (male & female) or the whole accelerator interface harness from ?
I appreciate any ideas. Thanks

With the amount of development required to safely implement cruise control, I would think that in the end run it will be less expensive to use an aftermarket cruise control system. I realize that the primary aftermarket system available in Europe is very expensive (~$700 US), but I believe that the Rostra aftermarket cruise control system, which is sold in the US and Canada for ~$200 US, will work on the European Yaris.