can I hire somebody here?

[joe_rocket]

I've been reading and building stuff using yenka for a day now and all I have is a headache.

I am willing to pay somebody to help me build a circuit... if it's not against forum rules.

The circuit needs to use the tach wire from a GM HEI module
measure the rate change of the frequency, if the rate change is too great it needs to output a ground signal so I can trip a light or buzzer.....

If this is the wrong place to ask this can somebody point me to a place where i can hire somebody to help me ....

 

[bryan1]

Hi Joe,
I'm a bit far away to help but I recommend you go look at the siliconchip website

Silicon Chip Electronics Magazine for Hobby Electronics, Computing, Kits and Projects.

Then go look for some of their vehicle projects, you will be able to view snippets of the articles and find which one would suit you and more than likely you can buy a kit and put it together yourself.

Go have a look and if you have any more question just sing out I'd be glad to assist.

Regards Bryan

 

[joe_rocket]

Went to the link you left, a lot of projects but nothing exactly what I'm needing here. I followed the link to the voltelectronics.com where they had some pretty neat stuff... and i got distracted with the fancy stuff i want, even found something I'm probably going to buy, but for now I need to focus on this current project instead of getting distracted. They did have something close, a "frequency switch" but it only worked by tripping with a set frequency range, where as i need something that trips with a change in frequency rate.... make sense?

I think I could assemble it if I had a diagram.. maybe. I'd pay for a working diagram

 

[Dragon Tamer]

i want $5000 for my idea!!! jk, butt it sounds like what you need is PWM controller (maybe, i'll probably get corrected on that)

 

[mbarazeen]

i got your point, you need to alarm when df/dt is above a limit, for what you need alarm? for +ve or -ve gradiant?
you have to have a frequency to voltage convertor, trhen pass it through a capacitor and have to use one/ two comparators(slope detector) . for +ve rate of change and -ve rate of change. then combine both to get final alarm

 

[Dragon Tamer]

told you i'd be corrected

 

[3v0]

The hardware is easy enough.
WHy give up on the code you have been writing in Yanka ?
Post the flow chart and tell us what you can not do with it etc.

I live in the Oklahoma panhandle.

 

[joe_rocket]

you need to alarm when df/dt is above a limit, for what you need alarm? for +ve or -ve gradiant?

i don't know what df/dt is? digital frequency divided by digital time? and also +ve or -ve?

Yenka ... i have found some circuits i thought I might be able to make work but yenka does not have the chips these circuits call for and many of the online diagrams i find do not do in yenka what they say on the site.



here is what I know:
OK, I need to take a tach wire input signal, which is a square wave that grounds an ignition coil (lots of feedback from what I read)

as the engine revs the frequency increases proportional to RPM, 4 pulses per revolution, up to 5000 revolution per minute, both with the engine accelerating and decelerating.

on each acceleration i need a circuit that checks and makes sure the engine is not accelerating too fast, I would like this to be simple without using PIC programming (whatever that is>?). and I don't mind paying, but would really prefer a simple circuit that I can learn from.

 

[tcmtech]

What application do you need such a function for?
I am fairly familiar with the GM HEI systems but I cant come up with a logical reason to need to know how fast an engine changes speed?
Over rev protection is logical and commonly used but I have not seen a need for rate of change protection or indication?

There are frequency to voltage converter IC's like the LM2907 that can put out a simple voltage reference in relation to the input frequency and with some basic comparators an simple circuits an all analog device can be fashioned that would give a output for an excessive increase or decrease of RPM's.

 

[Sceadwian]

In case an output shaft broke wouldn't the engine over rev so fast it would blow before the rpm limit kicked in? Being able to measure the rise in RPM would all you to stop the engine before it even reached it's high RPM limit if the RPM rise was too fast, kind of like short circuit protection on power supplies which measure dI/dT

 

[joe_rocket]

What application do you need such a function for?
I am fairly familiar with the GM HEI systems but I cant come up with a logical reason to need to know how fast an engine changes speed?
Over rev protection is logical and commonly used but I have not seen a need for rate of change protection or indication?

There are frequency to voltage converter IC's like the LM2907 that can put out a simple voltage reference in relation to the input frequency and with some basic comparators an simple circuits an all analog device can be fashioned that would give a output for an excessive increase or decrease of RPM's.

I don't have the lm2907 in yenka .. but if you can make an all analog device or circuit i'd really appreciate it, as noted, if something breaks it can be used to save the engine.

 

[tcmtech]

In case an output shaft broke wouldn't the engine over rev so fast it would blow before the rpm limit kicked in? Being able to measure the rise in RPM would all you to stop the engine before it even reached it's high RPM limit if the RPM rise was too fast, kind of like short circuit protection on power supplies which measure dI/dT

In every application I have ever seen the over rev function is what keeps things from flying apart. You dont set the rev limit above the engines designed maximum RPM.

I have a MSD ignition system on my old Ford 460 engine that has a built in rev limiter I have set at 5000 RPM although the engine itself is capable of holding together to well over 5500.

When you kill the ignition that generally tends to stop all RPM increases instantly anyway.

 

[Sceadwian]

tcmtech something bothers me about that, if the rotor shaft is accelerating fast enough inertia should keep it going up briefly you can't instantly stop acceleration instantly there has to be some kind of overshoot possibility.

 

[joe_rocket]

well this sounds easy according to some, I'm sure it depends on your knowledge. Building a 400hp motor is very easy for some, not so much for others.
I know how to build motors, I don't know how to build electronic circuits...

So what say you guys? can anybody write me up a schematic for this with less than $20 in parts?

 

[Sceadwian]

Ahh, tcm, it suddenly dawned on me cause I'm slow to remember these things sometimes.
It's called inertial moment, it's how flywheels allow a buffering of energy. Ever seen what happens when a heavy fly wheel is stopped instantly? Generally things tend to explode =) Granted you obviously haven't had problems with it and it may not even be applicible to the original poster, depends entirly on the mass and how fast things are spinning to see if it'd be a problem. But if the load to a motor is suddenly cut and the engine starts accelerating even once the energy supply to that engine is cut it will still have inertial mass that will keep it accelerating. Engine compression will slow it down and it really depends on how fast the engine is accelerating when it his the RPM cutoff as to what'll happen.

It's kind of like what happens when there's enough joule energy in the wire when a breaker trips, the device will fry anyways.

 

[3v0]

I have used Yenka to teach simple PIC programming. So when I seen Yenka my mind jumped to that version of their product offering.

There are many designs for PIC based tachs. It is simple to add the limiting based on RPM or change in RPM over time. But I expect this does not interest you.

 

[joe_rocket]

It is simple to add the limiting based on RPM or change in RPM over time. But I expect this does not interest you.

actually it does, the part in bold. do you have a yenka file i could watch?

 

[MrDEB]

MSD sells a rev limiter already. They are used extensively in drag racing aps.

 

[3v0]

It is simple to add the limiting based on RPM or change in RPM over time. But I expect this does not interest you.

actually it does, the part in bold. do you have a yenka file i could watch?

If I had that I would give it to you. But it goes like this.

The RPM is proportional to the time between pulses. The microcontroller has built in hardware to do determine the time from the pulses. The shorter the time between pulses the faster the engine is turning.

Save the time for each pulse in a block of memory, replace the oldest sample with the current sample. When you reach the end of this memory block you go back to the start.

Subtract the newest value from the oldest. If the number is positive RMP is increasing. The function (oldest-newest)/(sum of all time samples) will give you the change per unit time.

The choice of memory block size together with RPM will determine how far back in time you go to find the old sample. The response time will go down as RPM increases.

--------------------------------------------

It is possible code it to use a fixed time between old and new. The memory block needs to be large enough to hold the samples generated in that fixed time at you max allowed RPM. Instead of using the oldest pulse time to do the caclculation you add backward from the current pulse up to the point where the sum of the pulse time is equal to the desired time period.



If

 

[joe_rocket]

what you are saying is making sense, but I don't have a clue as to what items to use or how to wire it all up.
I have like $53 in my paypal, could you make me one for that much that would not take any programming, just assembly?