L-Jetronic Altitude Switch

[The Mighty Gryphon]

Is the high altitude jumper really necessary for older bikes?  I'm looking at taking a trip out to Colorado, and will be doing a bit of mountain riding.  Wondering about my missing high altitude jumper.  I am becoming very memory disabled, and figure I would lose it or worse just leave it in for  year or two of low altitude motobricking when I come home. 

Solution seems to be an altitude switch A.K.A. barometric pressure switch set to close at air pressures below 12.7psi or 87.5kPa that would make the changeover automatic.

So I do a search and all I find are Arduino boards that look pretty cheap and able to do the job if I can figure out how to program the damn things which will take a lot more time than I want to spend.  There are lots of tutorials on making cute little readouts and recorders, but nothing on making them actually close a contact to make something useful happen. 

Is there anyone here who could do the job if I buy the parts?  I am guessing that there would be others with older K bikes who may also want this device for their bikes. 

[rbm]

Interesting idea.  Getting the Arduino to operate a normal switch is easy.  Use a digital output to enable a miniature reed relay.  There isn't a lot of current being switched in this application and a reed relay can easily handle 500mA.  This would be an ideal circuit for a Digispark arduino.

Your problem will be calibrating the barometer to current conditions based on temperature.  Calculating altitude with reasonable accuracy requires knowledge of  sea level pressure for your position at the moment the data is converted, as well as the ambient temperature in degrees celsius.  If you don't have these values, a 'generic' value of 101.325 kPa can be used, but this isn't ideal and will give variable results from one day to the next.  You'd have to figure out a way to program the unit while in use so that the reference sea pressure level is correct at all times. Every 10 kPa difference you're out represents 8.5 meters of height error.

You'd also have to build in some sort of hysteresis so that the turn-on pressure is different than the turn-off pressure.  If you didn't, then at the switchover pressure, your circuit would oscillate.

[billday]

You could also just wire a manual switch into the circuit:

http://www.motobrick.com/index.php/topic,3044.msg18123.html#msg18123

[WayneDW]

I think have two altitude plugs.  If so, do you want one of them? 

When will you be in Colorado?  I and the gang will be zooming the canyons there the week of July12.

[The Mighty Gryphon]

Bill, a switch would have the same drawbacks as the jumper with respect to my failing short term memory.  Crap, I have ridden 200 miles with the "choke" on.

Robert, thanks for the reply.  You sound like you have a lot more knowledge of these things than I do.  Right now I am totally confused by the plethora of devices available and the techno gibberish that describes them and their functioning.  Trouble is, I have been away from this stuff for way too long, and don't have enough years left to get back up to speed.

About the pressure.  The sensors on the BMP-180 module are incredibly sensitive.  I read where people can read the air pressure difference between the floor and a table top.  However, in this application the switch is only to be used to let the Engine Control Unit know that it needs to lean out the mixture.  The 4000ft altitude for installation of the jumper is merely a nominal point easily determined by the rider where the air density leads to a mixture that is becoming overly rich and needs compensation.

Since the mixture is dependent on air density it will be more accurate to trigger on a specific pressure setpoint which is consistent rather than altitude which as you pointed out can represent a wide range of actual pressures.  With a constant pressure setpoint, one day it will trigger at 3900ft while the next it might trigger at 4200.  However, although the altitude is changing, the density and the fuel/air mixture at changeover will be constant.  In this application, the simplest solution is actually the best.

[The Mighty Gryphon]

Wayne, thanks for the offer.  With the way I misplace things these days, a switch, be it automatic or old school click-click is the way to go.  Also, I am afraid of leaving it in at low altitude and the lean mixture that will cause.

About the trip, I start working for the summer around mid May, so I am hoping to do the trip from May 1 to May 14.  Main thing is to visit my daughter who lives in Fort Collins, and make a few 1-2 day trips into the mountains from there.

Am still a few years from being free to do any summer trips.