Hi. I am thinking about building an RPM window & wot switch. It's to control the clutch of an automotive A/C compressor. The compressor must only be active if engine RPM is between, e.g. 1,200rpm and 4,800rpm, and if the gas pedal is not floored (wide open throttle..WOT).
So, I guess I need the LM2907 frequency to voltage converter ("tacho chip"). I suppose I need two of these do I ?
The WOT will come from the electronic throttle pedal or throttle butterfly, which in this application is a lowering voltage, so the further the pedal is pressed, the lower the voltage is (5v down to 0v), so WOT would probably be detected as ~0.2v and below.
I think I'd like to have three little trim pots.. low rpm, high rpm, wot point.
Am I correct that I should be looking at 2x LM2907 and 1x LM211 ?
I suppose thinking in terms of logic, I would need the first LM2907 to signal "above 1,200rpm", the second one to signal "above 4,800rpm", but have the second one (the "above 4,800rpm") output inverted, and then the two going into an AND gate along with an "above 0.2v" from the voltage comparator (i.e. not WOT), and .. uh.. no, I'm losing myself already.
Any hints for getting a total novice started on the right track? I've recently taken up milling machines, so I probably shouldn't be trying to learn something else new as well, so if I could have some hints, but perhaps something that might lead me to achieving some sense of success in short time would be good if possible
I have gEDA and gschem here, but I have no idea what I'm doing with them, and even whether there's any point/benefit on something such as this.
thanks very much
cheers,
Carl
So, I guess I need the LM2907 frequency to voltage converter ("tacho chip"). I suppose I need two of these do I ?
The WOT will come from the electronic throttle pedal or throttle butterfly, which in this application is a lowering voltage, so the further the pedal is pressed, the lower the voltage is (5v down to 0v), so WOT would probably be detected as ~0.2v and below.
I think I'd like to have three little trim pots.. low rpm, high rpm, wot point.
Am I correct that I should be looking at 2x LM2907 and 1x LM211 ?
I suppose thinking in terms of logic, I would need the first LM2907 to signal "above 1,200rpm", the second one to signal "above 4,800rpm", but have the second one (the "above 4,800rpm") output inverted, and then the two going into an AND gate along with an "above 0.2v" from the voltage comparator (i.e. not WOT), and .. uh.. no, I'm losing myself already.
Any hints for getting a total novice started on the right track? I've recently taken up milling machines, so I probably shouldn't be trying to learn something else new as well, so if I could have some hints, but perhaps something that might lead me to achieving some sense of success in short time would be good if possible
I have gEDA and gschem here, but I have no idea what I'm doing with them, and even whether there's any point/benefit on something such as this.
thanks very much
cheers,
Carl
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