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
first of all, excuse-me for my Biiig delay in posting this message. HUH??? who cares about when the first post in a thread appear.
have you ever did something with car'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 speedometer's implementation... Anything.... Iwould be happy ! Jack the car up and scope the sensor output.
Erik
If the sensor detects wheel revolutions, then it doesn't care about the wheel diameter. It is only you who have to care about the diameter, to correctly convert from rpm to speed.
By the way - are you sure that you meant 250 megasiemens (MS)? It seems more logical to talk about milliseconds (ms).
Thanks for you're reply Per Westermark. I thougt the only one I was getting was from a comedy man Erik [Jack the car] Mallard!
Yes you are right.
I need to convert the rpm to a speed using some simple sums. Probably with some multiply by PI and other things.
I did meen milliseconds.
The answer from Erik was very relevant. Most people would connect an oscilloscope to the signal and verify what the signal looks like.
And since most oscilloscopes require mains power, it helps if you don't have to drive around with it. To be able to spin the wheel without moving the car, you would then have to lift up the wheel.
As long as the signal level is reasonable, most people would probably connect it directly to a processor pin, without bothering with external 555 chips. It is quite easy in the software to handle spurious noise on the signal.
"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.
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.
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.