DIY Cruise Control FAQ (2006-2010 Yaris)

[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

[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.

[bobor]

Originally Posted by CTScott

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.

Hi CTScott,
thanks for your response. I admit its time consuming process and there are many risks to consider, but it's my hobby At the moment I would say I have 90% of the source code ready, so there are only minor modifications to be done and a lot of testing and bug fixing But except my free time I invest into it, the parts will cost me not more than 20 EUR ( ~30USD).
Regarding the aftermarket models, the situation is slightly better than you expect, at least here in Slovakia. I can get one for ~450 USD, but still Rostra model even including shipping costs would be cheaper. And I don't see any reason why it should not work on European models.

But as I said, it's a hobby.

[CTScott]

Originally Posted by bobor

Hi CTScott,
thanks for your response. I admit its time consuming process and there are many risks to consider, but it's my hobby At the moment I would say I have 90% of the source code ready, so there are only minor modifications to be done and a lot of testing and bug fixing But except my free time I invest into it, the parts will cost me not more than 20 EUR ( ~30USD).
Regarding the aftermarket models, the situation is slightly better than you expect, at least here in Slovakia. I can get one for ~450 USD, but still Rostra model even including shipping costs would be cheaper. And I don't see any reason why it should not work on European models.

But as I said, it's a hobby.

OK. In that case, back to your original question - I would not use mechanical relays. I would stick with solid state switching, by transistor or FET, to avoid the switching delays.

[bobor]

Originally Posted by CTScott

OK. In that case, back to your original question - I would not use mechanical relays. I would stick with solid state switching, by transistor or FET, to avoid the switching delays.

Unfortunatelly I do not have any experience with solid state switching. If you could point me to some good tutorial, I would appreciate it But AFAIK in this case, the input signal (voltage level) from either accelerator pedal (hall probes) or DAC would be somehow degradated (lowered) due to voltage drop PN junction.
Solid state switching is definitely faster than mechanical relay. But advantage of a relay is that it does not require power supply to interconnect one of the input lines to the ouput. I though of using this a safety mechanism, so in case anything goes wrong I would just switch off the power supply to cruise control module and the relay would (almost immediatelly) switch back to default state (direct connection of accelerator pedal). But if I find some good solution using solid state, I am about to change my mind.

[CTScott]

Originally Posted by bobor

Unfortunatelly I do not have any experience with solid state switching. If you could point me to some good tutorial, I would appreciate it But AFAIK in this case, the input signal (voltage level) from either accelerator pedal (hall probes) or DAC would be somehow degradated (lowered) due to voltage drop PN junction.
Solid state switching is definitely faster than mechanical relay. But advantage of a relay is that it does not require power supply to interconnect one of the input lines to the ouput. I though of using this a safety mechanism, so in case anything goes wrong I would just switch off the power supply to cruise control module and the relay would (almost immediatelly) switch back to default state (direct connection of accelerator pedal). But if I find some good solution using solid state, I am about to change my mind.

Here's a pretty good intro to transistor switching.

http://www.kpsec.freeuk.com/trancirc.htm


Rather than switching back and forth, it may actually make more sense to put the microcontroller in between the pedal and the ECM. That way, the ECM samples the pedal outputs and then in normal mode, just emulates what it sees. Then, in CC mode it ignores the input and sends its own output.

The other advantage of this method is that you can improve the throttle response in normal mode (like the Blitz throttle controller does).

[bobor]

Originally Posted by CTScott

Here's a pretty good intro to transistor switching.

http://www.kpsec.freeuk.com/trancirc.htm


Rather than switching back and forth, it may actually make more sense to put the microcontroller in between the pedal and the ECM. That way, the ECM samples the pedal outputs and then in normal mode, just emulates what it sees. Then, in CC mode it ignores the input and sends its own output.

The other advantage of this method is that you can improve the throttle response in normal mode (like the Blitz throttle controller does).

Thanks for the link, I will have a look on it. Your idea seems quite interesting, maybe I will change my plans a little bit and implement it that way. But I still have a feeling, that switching between DAC and pedal accelerator outputs is a little bit more safer.

Another idea came to my mind how to avoid switching delays with a relay. If I connect the DAC output directly to output line of the relay (to ECM) and accelerator pedal to one input of the relay (the second input remains unused), I can first set the output voltage on DAC and then switch the relay (cut the accelerator pedal line). On a switch back, the accelerator pedal is switched on first and then DAC disabled. This way, there is no voltage drop on signal line to ECM.

The only drawback is, that all time, when DAC is not in use (even just before switching off the accelerator pedal line, when DAC output is set) there is voltage from accelerator pedal to DAC output. I have no idea, if it can harm it in any way and what the impedance between DAC output and ground. If the impedance is too low, it can make a short connection and damage the ECM, that I obviously would like to avoid

And finally, do you have any idea, what size the input impedance of ECM could be?