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
"I'm trying to do a Schmitt Trigger with a Ne555"
Why on earth would you use a 555 for that?!
Why on earth would you use a 555 for that?! seems a vey illogical choice when '14s and '17s exist.
Erik
I seem to remember that there was an example in the 555 datasheet of using it as a tachometer - maybe that's what he's thinking of?
Nothing to do with making a Schmitt Trigger, though...
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.
"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.
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.
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