tach signal and F-V converter

[shortbus=]

Next is it a square wave or AC output?

 

[audioguru]

The IC that he is using requires an input that goes positive and negative. The tach signal might go only positive and 0V. Then the input of his IC will not work unless a coupling capacitor and resistor to ground are added.

 

[joe_rocket]

it is square wave, 14.2v - 0v .. the datasheet provides some sample circuits but it does not provide the capacitance of the "coupling capacitor", I used a 4.7uf 35v

I used a -8 instead of the -14 b/c i didn't know that they were different. after i burnt the first chip I looked around and found the -14's and ordered 3 of them (not cheap at all).
they looked basically the same in the PDF datasheet so I thought I could make a smaller circuit with the -8's so I tried it. It did work and I drove around with it but then it died. I am thinking maybe the zener diode I have is the wrong size also, is there any way to test it (I suspect it is the culprit b/c it worked until I killed the car which sounds like maybe an alternator spike from what I have read)?

I will buy a new diode when the chips come in.

 

[audioguru]

Did you read these notes in the datasheet?

If you use the 14 pins version then I was wrong, a coupling capacitor is not needed.
Connect the 0V to 14.2V signal to the filter and voltage divider. Connect the output of this filter and attenuator to input pin 1.
Make a nother voltage divider to reduce the supply voltage to half the signal's max voltage at pin 1 and connect it to pin 11.

 

[joe_rocket]

you must have a different datasheet, although mine does have something very similar.

If I'm understanding correctly, I still use my tach input to the 4.7uf cap run that though the 10k resistor to pin one and back off pin to ground using a 20k resistor and .02uf cap. Then measure the actual voltage at pin 1 (or what would be pin 1 after assemble?) after that circuit has been built take my primary supply voltage and run it through a resistor to pin 11 and from pin 11 back to ground, and that voltage should be approx 1/2 the measured voltage at pin #1.

I do have a couple questions here, how do I know what size resistors to use, b/c I'm sure several different combinations will result in 1/2 voltage. It does say something about 3mA...

#2 is on the datasheet it counts (in several places) 11 - 12- 10 -9 - 8 ... won't pin #11 always have a full ground, is it pin #12 you mean or is my datasheet wrong (having 11 & 12 swapped), or ... actually set pin #11 at 1/2 trigger voltage??

==================================
added:

Looking around I find another datasheet.... with better schematics. It assumes the capacitor is already on the engine and I do not need a capacitor one on the input. BUT it also says:
V = 6v @ 400 Hz or 6000 ERPM (8 cylinder engine)
6000 ERPM should be 3000 pulses per minute... which is 50 hz on an 8 cylinder engine, right?

further reading says I can "clamp" the output voltage (pin 5& 10) with a resistor back to V+

also, if I follow this diagram won't pin 11 always have zero volts or is a diode not "absolute" and acts as a resistor in one direction (I must assume)

**broken link removed**

 

[audioguru]

If I'm understanding correctly, I still use my tach input to the 4.7uf cap run that though the 10k resistor to pin one and back off pin to ground using a 20k resistor and .02uf cap.

The 4.7uF input capacitor in your first schematic has its polarity backwards. Your tach signal is a positive voltage and should connect to the positive wire of the 4.7uF capacitor.
The capacitor is needed only with the 8-pins ICs. The capacitor must not be used with the 14-pins ICs.

Then measure the actual voltage at pin 1 (or what would be pin 1 after assemble?) after that circuit has been built take my primary supply voltage and run it through a resistor to pin 11 and from pin 11 back to ground,

Your tach signal goes up to 14.2V. The 10k and 18k at the input resistors attenuate it to 9.1V.
Connect one 22k resistor to the positive supply voltage and pin 11. Connect a 10k resistor from ground to pin 11. Then the two resistors divide the supply voltage and provide about 4.4V at pin 11.

#2 is on the datasheet it counts (in several places) 11 - 12- 10 -9 - 8 ... won't pin #11 always have a full ground, is it pin #12 you mean or is my datasheet wrong (having 11 & 12 swapped), or ... actually set pin #11 at 1/2 trigger voltage??

The schematic shows what the pins do. They are not in sequence. Pin 12 is the ground pin of the IC. Pin 11 is a reference voltage for the opamp and can be any voltage that you make it (within the power supply voltage range).

6000 ERPM (8 cylinder engine)[/I]
6000 ERPM should be 3000 pulses per minute... which is 50 hz on an 8 cylinder engine, right?

Yes.

further reading says I can "clamp" the output voltage (pin 5& 10) with a resistor back to V+

It is not shown in my National Semiconductor datasheet and is wrong.

if I follow this diagram won't pin 11 always have zero volts or is a diode not "absolute" and acts as a resistor in one direction (I must assume)

The 10k resistor turns on the diode continuously and provides a voltage of +0.7V.

 

[mbarazeen]

if you use pin11 with diode connected as audioguru told the voltage would remain 0.7 and it will be triggered by a voltage more than 0.7,
if you stil fear of burning the ICs, why dont you try a input transformer than via capacitors. make a 10:1 turn ratio and primary for 15V, check it with osciloscope before connecting. (may need a diode to get only +ve half)

you can go for a optical isolation using photo couplers too

another idea you can use a 741/ 394 op-amp in between your tach wire and the IC, so that any damamge will not cost you much

 

[joe_rocket]

Ok, pin #11, with the diode it is .7v ... what do you fellars mean by this:
it will be triggered by a voltage more than 0.7

Pin 11 is a reference voltage for the opamp and can be any voltage that you make it (within the power supply voltage range).

what voltage should it be, 1/2 of my KOEO voltage of 14.2v



Your tach signal goes up to 14.2V. The 10k and 18k at the input resistors attenuate it to 9.1V.
Connect one 22k resistor to the positive supply voltage and pin 11. Connect a 10k resistor from ground to pin 11. Then the two resistors divide the supply voltage and provide about 4.4V at pin 11.

How does 10k & 18k = 9.1v? ie, how do you calculate that?? i tried 10k/18k * 14.2 = 7.8 ...

 

[audioguru]

If you use a diode that continuously has 0.7V across it as the reference voltage for the opamp then the circuit is triggered whenever the input voltage goes higher and lower than 0.7V (plus a small voltage for the hysteresis). But since 0.7V is so close to 0V then noise that is more than only 0.7V will also trigger the circuit so I selected a reference voltage of half the input voltage.

Ohm's Law is the most basic rule in electronics.
Use ohm's Law to calculate the current in the two resistors in series then again to calulate the voltage across the lower one.

 

[tcmtech]

3) b/c you posted a link and didn't elaborate... car guys sure a lot nicer and more helpful than electro-geeks.

Actually the electro-geeks here are just as nice as the car guys. The problem your having is that you seem to feel some need to go and piss off the car electronics geeks here and now most of them are just sitting back watching you burn expensive little IC's out and having a good laugh at your expense!

If you want to learn we will teach. If you want to give insults and attitudes to those who have what you want because they wont just hand over what you need you need to learn to follow their rules or you will continue to get near nothing. Thats how it works.

If someone posts a link or some type of reference material I suggest you read it and study it and ask questions about it until you understand what it is that made that material worth posting. Its not our time or money you are waisting.

 

[joe_rocket]

I'm all ears...

 

[audioguru]

Why are nOObs who know nothing about electronics and don't want to learn about electronics so RUDE!
Maybe the car guys are nice to each other because they all know the same about their hobby: Nothing. They are all nOObs.
There should be special forums for nOObs.

 

[joe_rocket]

the thing I've seen about car forums are there are guys who work on fuel cars will help explain how to change a spark plug on a minivan, in detail, if somebody asks.
Guys that design indy car and nascar cams will help a guy find the best choice for his hobby stock dirt car. and seem happy and eager to do it.
I'm a newbie and don't deny it one bit. i'm going to study and learn ohms law, no problem there....and yea, I may be slightly rude but it's only b/c i came asking for help and caught a lot of slack.. and IMO not much help from the get-go.
Maybe the forum needs laid out differently, a basics section and an advanced section. Don't hate on me b/c i grew up in the country with no computer and a school that had two grades combined into one class room. I'm intelligent and can learn if given the chance. If it's obvious I need to know something (like ohms law for example and how to calculate a voltage divider) let me know.. but don't roll your eyes and laugh at me for goodness sake...
and it would be nice if I knew WHY i needed to have X.XX voltage at pin #XX....

I wouldn't be here for help if I didn't need it.

 

[tcmtech]

I'm a newbie and don't deny it one bit. I'm going to study and learn ohms law, no problem there....and yea, I may be slightly rude but it's only b/c i came asking for help and caught a lot of slack.. and IMO not much help from the get-go.

From many of our prospectives you came here with a "secret intention" which is seen as suspicious and is treated as so by anyone who is familiar with how people approach topics here.
Then you expected that what you wanted could be done for an unreliably low price without full disclosure of the actual intention plus gave us many highly questionable explanations for what you where doing which didn't stand up to any solid scrutiny from those who also know automotive electronics and custom device design work. That just gave people here more reasons to not want to work with you or trust you.
First you pulled an attitude with me because I said no to doing your project over what is the realistic cost of custom work which anyone who does such work would see was as a reasonable and fair price. Then you insulted me about my skills and knowledge about what I know and have done in regards to custom vehicle electronics.
Now you have another thread here where information was given to you and you flat out admitted to not reading it or made any attempts to try and understand it and have now given others an attitude about it, again.
The pleases and sorries or where you grew up sob story doesn't help from my prospective. I went to school in a town for four years where I too had combined classes because my personal class had three people in it. I don't see how you could go to a small school like that and not have ever learned about social respect or manors.

Thats what all of this comes down to. Perhaps you should spend a few months learning the basics of social etiquette, manors, respect, honesty, and maturity then a come back here and try asking all of your questions again. I promise you that you will receive much more help, answers and a far nicer treatment from everyone here if you do!

 

[audioguru]

I think there should be a special forum for little school kids who know nothing about electronics but they think they know everything.

EDIT:
Little school dropouts?

 

[joe_rocket]

I think you guys are a bunch of dicks, I'm sure i can find another forum somewhere that has people willing to help, not berate. I don't need this ****.

MODS DELETE THIS ACCOUNT

 

[tcmtech]

Good luck with that. Many who help out here also help out on other sites as well and your pretty easy to pick out.
Change the know it all attitude and show some up front honesty and you will get what you need.
However first pick up some basic electronics books and learn the basics before you start asking questions.

You don't build a high performance engine the first day of shop class and you don't build what you're trying to build without a reasonable foundation in basic electronics application principals as well.

 

[audioguru]

Another rude schoolkid is gone.

 

[joe_rocket]

Hey uncle $crooge and TheCockMuncherTECH can keep stroking each others ego's off and being general dicks... have a nice life

 

[mbarazeen]

Hi all,

what i feel is he has explain enough about what he wanted to do mathematically. no matter where he wants to use this for, our guys could help. he just needed some electronics that would receive frequency and give a flag when df/dt ecceeds a set limit.