Rotary switches for calibration changes, type question

[secure]

3. I have calibrated my 25036751-GM IAT Sensor according to 3KΩ pull-up resistor value. I believe the value is right but Solaris should have already been confirmed that.

http://www.syvecs.co.uk/forum/viewtopic ... 424d8#p609

[Benkku]

For me, that's the nail in the coffin for diodes...
...The only argument for using diodes is if the voltage at the top of the chain is unknown.

Nail in the coffin - indeed. One note yet, needs to say... I think that the voltage at the top of the chain is always known, be it Syvecs or any other ecu, so there absolutely is no technically sound reason to use diodes.

'Sir William Thomson, i mean Lord Kelvin said it times ago.... Measure and you know.

My favorite is this - somewhat lengthy one.

"When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."

http://zapatopi.net/kelvin/quotes/

[pat]

It is possible to miss the bigger picture when you only look at one small part of it. Whilst I am not going to pretend that a diode chain in a panacea, it is by a long way, the most flexible option available. Furthermore, whilst I do not dispute the temperature dependancy of the forward drop vs juntion temperature per se, I should point out that most people would opt to turn on the heater in the car rather than endure a journey at -20C; most people I know would open the window or activate the aircon if the inside temp goes up to 50. If one follows this logic further then one comes to the conclusion that the ambient temperature that the switch will see at any point of importance will be within a much narrower "comfort band" that someone would actually want to drive the car within. Whilst there may be a problem at extremely cold temperatures, the warm up limiter would be in operation anyway; ergo one wouldn't be able to cause damage by being in the wrong cal whilst warming up; and by the time it is warm, with well thought out thresholds, the problem wouldn't exist.

When coming up with ways of doing things, we place an emphasis on flexibility, sometimes this comes at the expense of absolute correctness. A diode chain with pull up is universal, it can be used on any available input. For 12 of the 16 inputs it does NOT require that the installer find a spare supply pin, it is just plug and go. It is short circuit safe; if you want a cal override, just put a switch between the wiper and ground, instant selection of CAL1 at any time without fried wiring. It is possible to do CAL banding; that is to say one can reduce the number of positions to 4 and insert another 4 diodes in series with the input and a switch parallel to them - close and open the switch to jump up or down 4 positions (great for when you don't NEED all 8 and you have no spare inputs for ALS left). Indeed you can extend that concept to just 2 cal switch positions and banding by 4 and by 2 giving ALS, Launch and Lo/Hi boost on a single input with one rotary and two toggles that make sense rather than having to remember which position you're in and what it does!

Since we still have hundreds, if not thousands, of resistors for cal switches, we can supply them as resistor chains if people are prepared to have a more laborious install and lower flexibility for the sake of absolute correctness under unrealistic conditions

Cheers,

Pat.

[Benkku]

Yeah right... One must need to realize, that 'cabin temperature' is not same, than temperature inside instrument cluster or panel. Agree, that the whole picture must be seen always, but the typical temperature differences in places where switch is usually installed is 'easily' over 30 degrees. Cars have different type of heater for example, some types circulates water constantly thru the heater matrix and mix air, exhaust system underneath the car heats cabinet insides etc. etc.

I like that expansion vision, but in reality people have one or two switches - that can be handled with resistors also.