Some kind of RPM counter

[Untitled_user]

Hi everybody...

I'm need a help about a designing one, I hope, simple electronic circuit.
So... I will try to explain what should it be... I posted an image (i know it's poor, my english isn't far away from that too...  ) to understand what I mean.

So, the disk has four stripes on it, and the disk is spinning on AC motor with variable rotation speed. I need to count this stripes and show their number in one second.
I explained it this way (with stripes) because I belive it can be done with LED and phototransistor. So this looks like some kind of tachometer, just it shows number of 'stripes'/second. I was been looking on net for some tacho circuits, but i didn't find anything usefull. Yeah ... i forgot to tell: the result needed to be shown on LED display (LCD acceptable too... ;D).

I hope you know what I meaned... If someone has a idea or some circuit that can be used, please help... 

View attachment 38209

 

[Tony_Stoynov]

Hi,
yes LED and phototransistor is ideal for this application, but if this disk is not very wide, you can use optocoupler with air gap, like a this in some PC mouse. If this disk is made from metal, steel or other magnetich material, also you can use the hall sensor.
For counting have different ways, use the onchip counter, or use uControler, Pic, AVR etc.
But .....i don't know what is the accuracy that you want. For example if you have 4 impulse per turn, and the speed is 3600 rpm this is a 60 turn per second, or 240 impulse per second. The resolution will be 3600/240 or 15 rpm. This is the +/ 0.41 %. But if your speed is low, 360 rpm for exampel this is a 6 turn per second or 24 impulse per seconds, then the resolution is 360/24,again 15 rpm, but this is +/- 4.1 %.
p.s. my english too is no very good, i hope that you will understand me

 

[Untitled_user]

Hi, thanks for jumping in... 

Well... The disk would be made from plastic, and it would be something around 15 cm wide, and more maybe.

Counting: I would like that circuit be as simple as possible - without uControlers and need for programing them. Just a sensor, counter and LED display driver. But OK, I will understand if that will not be possible.

Speed of motor is high. But, its a variable, and I actually belive that minimum will be somewhere on 1800 rpm. (120 impulses/sec)
Of course, I would like accuracy to be as high as possible, but +/- 5% won't bother me to much...

 

[Tony_Stoynov]

Hi,
OK, in this case +/- 5% you can use counter mode, because if you want high precision you must measure impulse time, and for this some suitable is uControler, but in your case this is unnecessary.
You can use something like a ICM7226.
For sensor, in this case using of reflective sensors is a most suitable, because 15 sm is the long distance, and have a big possibility to wrong detection.

 

[Untitled_user]

Hi again...  ;D

Well.. don't know where to begin... You surprised me a bit... 
I have to say that ICM7226 looks very powerfull and suitable for this operation.
But, there are 2 problems:
1. I can't get one in my area... (samples maybe  ;D)
2. I belive it's way to complicated for me...  :-[

So, i would ask you if you can tell me some alternatives to ICM7226?
And a basic hookup?  ??? Maybe?

Btw. i was trying to re-made some tacho circuit that uses 555 timer. On the exit you get a square wave, and I belive that it drives some comercial tacho display...
So, I was thinking... maybe output wave could be converted with some freq - to -voltage converter to drive a analog scale... But, now I see that it can be done digital way, and even easier maybe... So, i will just forget 555 and wait for answer...
Thank you on cooperation...   

 

[Tony_Stoynov]

Hi,
the ICM7226 is the most simple decisiaon, this or somethin like this chip. The next possibility is to use the uControler, in the web yu can find many diagram with PIC 16F84. But for this you must have programer etc.
Another way is to use frquency to voltage converter, and use the standad module wit ICL7106 or some equalent, but this is i thin is not a more simple. You can bay the frefuqncy meter modul and use it.
But i can't understand were is the problem ith 7226, the circuit is a very easy to use, you wil need only several external component. No need to use all 8 LED, you can use only 4.
To realize this with the standart logic will be more expensive, and will need to use no less that 6 IC if use counter with a LED output, or 13 IC if use standart counter and binary to 7 segment decoder.

 

[Untitled_user]

Hi,
OK, I see that ICM7226 is probably the best and simplier solution.
You said that it's very easy to use... but I have never before doing something similar... I have some knowledge about digital electronic but I can't say that im master... I'm far away from that... That's the reason why I'm asking you...
So, i have downloaded a ICM7226 datasheet from Itersil web...
It contains some basic circuits with this IC. (universal counter, frequency, period counter... you know for shure...) I picked up a universal counter and tried to re - made circuit for my use... I made a schematic and I'm posting it (1024x768, would be nice wallpaper...  ;D) Please, take a look and tell me what is wrong (maybe it would be easier to tell what's right...  :-[) (And don't laugh to much...)
Thank you very much...

View attachment 38214

 

[Tony_Stoynov]

Hi,
you need a frequency meter mode, with 1 Hz time for measuring.
See the attached file, only i'm not suare how must set the channel, if may be you can connect to input together, to be sure that every time will measure the signal.
And .... im not suare if the chip have a current limit for the LED, if not have internal limitation you must put external resistor on a,b,c.....g wire, around 200 Om.
The good idea is to use comparator for the input signal, with hysteresis.

counter.pdf

 

[Untitled_user]

Hi,
Thank you very, very much for helping me.
And a question about comparator - simple LM will do the job?

 

[Tony_Stoynov]

Hi,
Yes, the LM393 for example, but you must have a hysteresis.

 

[Untitled_user]

Hi,
look, I'm terribly sorry about this, but I messed up... and i will completely understand
if you don't want to help me anymore...  :-[
Situation is next: i was looking for ICM7226 circuit, and I found it's price in my country is almost $50... plus everything else... I must say it's way to much for me... because this counter is just a part of bigger project and I can't spend so much just on this...
I know, i'm stupid... I should look that first...
I'm realy, realy sorry about your effort, your work, your replays...
So, if you want, you can help me, if not, I understand you.

So, anybody, now I'm switching to analog meter...
Can simple 555 and an analog scale driven by freq-to-voltage converter get the +/-5% accuracy?
Or anybody has an other idea (analog/digital, doesn't mater, just to be cheaper)?
Please, help me, I realy need this circuit...

 

[Tony_Stoynov]

Hi,
yes you can use 555 or something other chip, actually 55 may be not a very suitable for this application. I know that exist, but never not use a on chip converter, this is small chip that convert frequency to voltag.
Ok i will see for some good analog decision that is not a very expensive. Why you dont want to use a microcontroller ? Will be very easy and simple
I will try to make this schem for you in the next several days, if have some free time today or tomorrow.

Edit You can find the LM2917 chip in your country?

 

[Untitled_user]

Hi,
don't know how to say thank you...

Well, I have never used uControlers - I know something about them, but I don't have a programer, and I don't have any idea about programing language... I'm planing to learn that because I belive they're future, but... not yet...

LM2917 is availabile.

100 x Thank you!

 

[Untitled_user]

Hi,
c'mon, please help me...
I realy need help...

 

[audioguru2]

So why not download the datasheet for the LM2917 and use one of the tachometer circuits it shows?

 

[MP1]

Perhaps this will help:
http://www.shumatech.com/dro-350/add-ons.htm


or this:
http://electronickits.com/kit/complete/meas/vek2625.pdf

or here:
http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml

or a combination of them.
Hope this helps.

MP

 

[Untitled_user]

Hi,
writing just to say thank you on your posts...

I have some ideas, but curently I dont have time... Will write back tomorow...

Thanks!

 

[Untitled_user]

Hello again...

Well, MP && Audioguru, i realy appreciate your efforts... Thank you...

So, simpliest possibile solutions seems like this one posted bellow (from datasheet ... thx audioguru), and this one at

(thx MP...)

Which one do you reccomend to use and what modifications should I make to use them for my application?

Regards, Marc

View attachment 38353

 

[MP1]

They are different types and either will work. In looking at your application, perhaps you will know if one setup is better than the other for your particular application. One uses a light beam with a chopper wheel to count pulses and the other uses magnetism and a reluctor to count pulses.
I think the light chopper with 555 would be the least expensive.

MP