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Preset cruise control?

I will be buying shortly a 2004 to 2006 Scion xB. Those years because of the body size. I wanted one with a cruise control and it turns out that they did not come with a cruise control option. Instead, if you ordered one with cruise control the dealer installed it and only one company made the device specifically for the xB. These are still available so I will be installing one if the car doesn't already have one. So now that the background info is out of the way here is my question. The cruise control gets some sort of pulsed signal from the car, probably the same pulse stream the speedo gets. If I can measure this pulse stream at various speeds then maybe I can copy it and have the cruise control sense my pulse stream. Then I can get on the highway, turn the dial on my pulse generator to the desired speed, and press set on the cruise control. I would need to have a switch that disconnects the cruise control from the pulse stream from the car to my manufactured pulse stream while the speed was being set, and then back to the car once the speed is set. I know, why not use it the way it's made and just drive at the proper speed to set the control. The answer is just because I think it would be a fun project. Does this sound like it would be a hard thing for someone with only pretty basic electronics knowledge to do? I'm thinking that something as simple as a 555 based pulse generator would work and I have made 555 timers from scratch. Eric

Reply to
etpm
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I worked on the original speed control at Philco-Ford, Santa Clara, in

1968. There's a LOT more to speed controls than just pulses. Like all kinds of (forward and side) acceleration sensing, automatic disengage and braking under adverse conditions.

Somewhere around here I still have a paper on all the dynamics of a car's movement.

I used to scare my boss by test driving my circuits, driving up and down 101 at 80+ MPH, while sitting cross-legged in the driver's seat, using only the buttons on the steering wheel to control gas and braking, whilst watching a Tek scope in the front passenger foot space

If you're not careful, "you'll shoot your eyes out kid", wreck your car, kill yourself... and your family will NOT collect on your insurance. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Greetings Jim, I appreciate your comments. Especially tghe ones about insurance after I get in a wreck. But I'm not considering tampering with the control itself. I just want to connect the wires that sense the vehicle speed temporarily to a pulse generator thatI make. Then after the cruise control has a set speed it will monitor the vehicle speed and do everything it is supposed to do. So no modifications will be made to the cruyise control. Eric

Reply to
etpm

Actually, that's one of my basic diagnostic (and design) schemes.

When I did the Bosch EC Motor Controller Chip Design I had their discrete implementation in my lab (this pre-dates CAD).

I, in my usual modus operandi, had NO CLUE about motor controls, so I would breadboard a section that behaved exactly as the Bosch discrete system behaved.

When satisfied, I would jumper it in to the Bosch system. Pretty soon, the breadboard was all mine. NOW I knew how it was supposed to behave... this is called spec extraction the hard way >:-}

Then I went back, smoothed out all the edges, and reduced it to device-level for a chip... now manufactured by NatSemi Scotland.

So, in retrospect, have fun! It will be a very educational, and enjoyable, experience. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

suppose you have it set at a radically different speed to the one you're currently doing, what's going to happen?

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Reply to
Jasen Betts

I'd say your thinking is flawed. You want to preset the speed? The speedo pulses reflect the car speed, they have to be compared to some other (relatively fixed) signal like a digital word/analog voltage level. (2004 probably means digital)

If your introduced pulse train is lower than the setting of the control the car would just keep increasing speed - and the converse; higher and the car would probably slow to a stop.

Doesn't sound like something you want to mess with IMO.

Reply to
default

It occurs to me that you "have the cart before the horse".

The pulse train is feedback from the wheel sensor that is compared to a setting in the speed control, so you don't want to emulate the feedback, you want to emulate the "command". For that vintage a car I have no idea how it's done, probably a DAC. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

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