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Hi friends,
first of all, excuse-me for my Biiig delay in posting this message.
I was on vacation and far away from computers ! It was hot and sunny and very peacfull and there were girls and drink and all the other things.
Well, IÂ'm doing my speedometer using a processor.
The Timer 0 counts a 250 MS period and Timer 1 works as a pulse counter.
I know that my Opel Corsa has a Speed Sensor (VSS) which could be used to give me the right number of pulses for each carÂ's wheel revolutin (i guess it is 8 pulses / revolution in a 14 inch wheel)
IÂ'm trying to do a Schmitt Trigger with a Ne555 to capture de pulses from a sensor
The problem is that in this bad country no one wants to give the right information about the sensor. Everybody wants to sell the information in book for about US$ 80,00 ! ! ! ! ! !
have you ever did something with carÂ's Speed sensor ? Is the output of this kind of sensor in low voltage enough to work with the 555 ?
If you have any information about the speedometerÂ's implementation... Anything.... Iwould be happy !
thank you !
Sérgio
Erik Mallard,
i do not know if you joke or being faseshious????
no you misunderstanding what i sayed. i was connect schmitt to ne555 input not as to use it as one!
look at tthe scematic and you see it clear.
i do not know if you joke or being faseshious???? Neither, I know of no way to scope with a cars wheels moving other than jacking it up.
look at tthe scematic and you see it clear. I can't find my crystal ball and thus can not look at any schematic you have not posted a link to.
Erik
"you misunderstanding what i sayed."
Your actual words were, "I'm trying to do a Schmitt Trigger with a Ne555"
"look at tthe scematic and you see it clear."
What schematic? Where?
You haven't even mentioned any schematic before - let alone given any indication of where your schematic can be viewed!
"i was connect schmitt to ne555 input"
Does any of this have anything at all to do with microcontrollers - let alone Keil software tools??
I'm still claiming that as long as you make sure that the signal is strong enough to be picked up by the microcontroller but not strong enough to be dangerous for the input, the simplest thing is normally to connect the signal directly to a digital or analog input (depending on what form of signal the oscilloscope shows).
It is quite simple to let the software filter out a lot of noise, since you know that your car has a very limited accelleration and top speed. There is a known minimum/maximum distance between pulses. The bigger question is how to handle locked or spinning wheels - but that is a problem that external signal conditioning can't help you with anyway.
the simplest thing is normally to connect the signal directly to an ... input simplest?, maybe but can be quite 'dangerous'. If the rise/falltime of the input is slow enough you can have some really 'funny' effects without a schmitt trigger. Per. I basically agree with you re noise, but for 'shaping' the input I'd always use a schmitt.
i gave link on the other one but you want to see what i say so here swms
www.mcselec.com/index.php
maybe circut is too difficult for Erik Mallard to understand so she can read all about the workin here also.
i must link to microcontroller and have 8051 for code so I thiNK i wiLL use keil FOR taht.
maybe circut is too difficult for Erik Mallard to understand That may be, but Erik Malund understands it quite well and consider it gross overkill. the datasheet for the sensor www.nxp.com/.../KMI15_4_4.pdf (how does the OP know that this is the sensor Opel used for the Corsa) show a digital (current) output and a reasonably fast rise/fall time and as such can be intefaced directly to the uC.
this is a two wire device and as such a comparator should be employed.
The 555 is overkill and the fact that the comparator in the referenced schematic does not have positive feedback (schmitt) is even more stupid. Having the comparator drive a capacitive load (C2) defies the rule every article/book re op-amps states.
"i gave link on the other one"
What "other one"?
What are you tealking about?
Yes, if the processor has a lot of things to handle, I would make sure that the signal is normalized with a schmitt trigger (or if the frequency is very low I might decide to use the ADC instead).
But if the processor isn't required to run at very low power levels, or it is important to reserve the processor capacity for other actions, it really doesn't matter if it gets a hundred quick interrupts on each flank. As long as the "spurious" interrupts comes very quickly in relation to the normal period time of the pulse, they are easy to handle in software.
It's all a question of what parameters should be optimized for. For a unit running on small batteries, I would not dream of skipping the schmitt trigger.
Anyway - I don't like the linked schematics. Much too much external hardware that consumes board space and increases production costs. I'm a lot more interested in protective components around the processor.
i ask profesional and he say that the one i saw was very good and reliable and not stupid.
If you think you do better circit you must give it for me to try.
Why do you single-out Erik?
Note that Per has aslo said, "I don't like the linked schematics"
There is really no point in discussing schematics until you've confirmed that this is the sensor that is actually fitted in your car!
Or, at least, that it's the same type of sensor.
Have you done that yet?
Of course, this is not the right forum for discuccing schematics at all - it has nothing whatsoever to do with Keil software tools, does it?!
"There is really no point in discussing schematics until you've confirmed that this is the sensor that is actually fitted in your car!"
For instance, see takes its reading from the position of the speedo needle" (my emphasis)
If your car is the same, then it will require an entirely different approach from the link you posted!
This is most probably a person who cross-posts to a number of forums, resulting in a lot of wasted time when the same question is answered multiple times
If you think you do better circit you must give it for me to try. Again if we ASS U ME that the Corsa has a sensor like the one the bascom link refer to the first thing is do nothing that interfer with the ECU (Engine Control Unit). If you attach the bascom circuit your car will probably malfunction because the ECU does not pick up the speed info (probably the Bascom circuit will not work either). so much for "i ask profesional and he say that the one i saw was very good" That, of course, could be because you witheld vital information from him.
Thus you have to pick up the signal from whatever the ECU employs and NOT the 100 ohm resistor the Bascom thingy uses. So, jack up the Corsa attch a scope and rotate whatever wheel drives the speedometer. You should see some pulses, till risietime falltime and voltage of those is known there is no way I can "give it to you to try".
PS I get the impression that the "bascom" circuit the OP keep referring to is not of Bascom origin, but posted at the Bascom site by someone.