Does anyone here have a circuit diagram of an RPM switch? I've been trying to find one by searching to no avail. The only thing I've found is a kit to build your own for the sum of 45 bucks, when you could just as easily buy one for 50 or so from Summit or MSD. What I'm trying to do isn't really for my tib, but I know there are better electrical gurus here than on the other forum I've asked on.

Essentially, the circuit will switch on a relay when the engine hits a certain rpm and above, and will turn it off below the same setpoint, which is adjustable.

What I came up with earlier (and totally fried) was an IC chip with 2 opamp comparators on it. The first opamp amplified the rpm signal to 12v, which fed its output to a very simple high pass filter (a resistor in series and a capacitor in parallel). This signal was fed to the non-inverting terminal of another opamp that had an adjustable voltage divider bias on the inverting terminal to adjust the trip point. The output went to a relay with a freewheeling diode to shunt inductive kick and prevent damage to the IC.

I had no idea what size components to use, so I just pretty much guessed, and I think I fried the IC anyways, despite my best efforts.

 

I think it is referred to as a window switch. It would onyl be activated in certain RPM range. I think you would be best off just getting one from MSD or whatever. Maybe DTN will know more about how to do your own.

 

only 23 views... half of them are probably me trying to see if I spelled anything wrong or if what I wrote was incoherent.

Nobody has any idea on this one?! Not even DTN?

 

I would add a power transistor on the output of A2 to prevent overloading it.

You'll also need a voltage leveling capacitor on the output of A2

What is the VCC? 12V? It might be too much unless you're using CMOS logic. You may need to tone it down a bit.

Make sure your input to A1 is regulated as well.

High pass filter... swap R1 and C1, i think you've got that configured as a low pass filter. Also, if you can get a varriable capacitor, it will make it able to adjust. Or you could swap the inputs so that a low frequency will cause it to be off and a high frequency will allow it to be on.

For A1, i'd make a voltage divider for the A1- input to make it adjustable, also it will eliminate random noise.

You did not include the grounding for A1 and A2's ground source. Are they grounded?

That's all i can really say about this circuit without knowing the numbers on top of the ICs and your relay.


As it's configured now, anything including random static noises will be processed and fired as an output from A1.
A2 will fire when RPM is lower then the resonant frequency of R1,C1 and the + input is satisfied

I can draft a schematic for you if you'd like. I need part numbers to work with though.

 

Whoa... looks like I was at least on the right track, but I still fuggered it all up! owned.gif

Ok, I think I get what you're saying... mostly. I added the power transistor, although I thought the opamp was capable of handling the output to the relay (which is just a regular automotive 4 pin 12v relay, rated for 30A max, no idea on the numbers for that one) so I'm not too sure why it needs to be there, but I'll believe, since I am asking for help after all. I added the voltage leveling capacitor to the output of A2, again not too sure why it's there, but ok.



The VCC is 12v, and I think the IC is TTL, so that's probably where I got really screwed. The number on the chip is BA728 623 H16, which is just a dual opamp IC.

<div class='quotetop'>QUOTE </div><div class='quotemain'>Make sure your input to A1 is regulated as well.</div>

Don't get that part. Why would I regulate the rpm signal?

<div class='quotetop'>QUOTE </div><div class='quotemain'>High pass filter... swap R1 and C1, i think you've got that configured as a low pass filter. Also, if you can get a varriable capacitor, it will make it able to adjust. Or you could swap the inputs so that a low frequency will cause it to be off and a high frequency will allow it to be on.</div>

lol.... i feel like a retard now laugh.gif

<div class='quotetop'>QUOTE </div><div class='quotemain'>For A1, i'd make a voltage divider for the A1- input to make it adjustable, also it will eliminate random noise.</div>

confused.gif

<div class='quotetop'>QUOTE </div><div class='quotemain'>You did not include the grounding for A1 and A2's ground source. Are they grounded?</div>

Fixed. I usually don't draw the ground. If it's not a reference voltage, it's ground.

<div class='quotetop'>QUOTE </div><div class='quotemain'>I can draft a schematic for you if you'd like. I need part numbers to work with though.</div>

hail.gif Much appreciated. Otherwise, I'm pretty lost!

Btw, you're probably going to laugh your ass off about this... I didn't have any circuit components lying around, so I grabbed my old radio shack electronic project lab and used it as a prototype. Funny how I didn't understand anything about it as a kid, but now it's fairly simple... and useful

 

I'll draft it when I get a chance.

The suggestions that you did not know why I suggested... I suggested them to bulletproof your schematic because you said you blew things up.

You need at least a 10 ohm resistor under the leveling cap.

 

It might sound like a noob question, but what would you use this for?

 

Specifically, it's for my other car, a 1988 Mazda Rx7. The 13b rotary engine found in 86+ Rx7's has 6 ports, as the old ones had 4. The 5th and 6th ports remain shut under 3800 rpm to increase torque in the low rpm ranges, and they open after 3800 to increase power in the higher rpms. The way they're activated is really archaic. It uses a backpressure tube from the catalytic converter and an engine driven air pump to work kind of the way an automatic transmission works (governor pressure vs line pressure) to tell the ports when to open. I removed all that crap... the 3 catalytic convertors, air pump, other misc. emissions parts, etc. I've since had to wire the ports open to get the high band power, but I'm working on this electronic circuit to open the ports at just the right time to get all that "rotary power" all throughout the powerband.

Other more general uses would be a shift light, nitrous controller, exhaust flamethrower kits, etc. Just anything that would require a certain rpm before it can be activated.

Reason I posted here is because Rx7 owners seem to be of the blue-blooded "my $h!T doesn't stink" kind of people. Purists, if you will. So by posting this same question on another forum, they all attempt to attack you on stuff like "why don't you put your air pump and catalytic converter tube back on?" and "I did that one time and I didn't like it" instead of.... "oh, I have one of those schematics right here, please take it and make it work". Or my personal favorite (that happens way too often) "why don't you just swap in a TII (TurboII) drivetrain?" As if everyone has the money nevertheless resources to find a TII Rx7, even harder to find one that's not blown to pieces.

This Hyundai forum is much friendlier, and the people are smarter as a whole. That's why I had to post here. I didn't get any retarded comments on what their opinions are on transistors. I actually got answers.

 

btw... remove R4 and R5. that's a common collector amplifier configuration you have there. If you were boosting a signal, that would be the proper choice, but this transistor will function as a switch. It needs to be a 1W or higher transistor, or a set of 12V+ MOSFETs in a row.

my electronics workbench copy is not working right now. I'll get it going soon.

 

HAH!!!! I FOUND IT!!!!!!

http://www.rx7club.com/showthread.php?t=745906