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
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.
Erik
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.