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basics | Electronic-Optical Counter


There are 17 messages in this thread.

You are currently looking at messages 1 to 10.

Electronic-Optical Counter - Mohib - 2010-12-03 12:50:00

Hi,

My students are in need of an Optical-Electronic counter to count the
revolutions/minute (rpm) of a propeller driven by an electric motor.
The maximum expected rpm is around 20,000 rpm with most of the results
being in the 5,000 rpm range.

My initial thoughts are to be able to have a light source and a photo-
detector, with the light being interrupted by the rotating propeller.
The pulses from the photo-detector can be counted and compared to a
timer to give revolutions per minute.

Please let me know the most economical way of combining (the students
can solder etc.) parts to produce a DIY product.

Thanks,
Dr. Mohib. N. Durrani
Montgomery College, MD

Re: Electronic-Optical Counter - tuinkabouter - 2010-12-03 13:09:00

Op 3-12-2010 18:50, Mohib schreef:
> Hi,
>
> My students are in need of an Optical-Electronic counter to count the
> revolutions/minute (rpm) of a propeller driven by an electric motor.
> The maximum expected rpm is around 20,000 rpm with most of the results
> being in the 5,000 rpm range.
>
> My initial thoughts are to be able to have a light source and a photo-
> detector, with the light being interrupted by the rotating propeller.
> The pulses from the photo-detector can be counted and compared to a
> timer to give revolutions per minute.
>
> Please let me know the most economical way of combining (the students
> can solder etc.) parts to produce a DIY product.

Feed te output of a foto transistor to a frequency counter.

-- 
pim.

Re: Electronic-Optical Counter - George Herold - 2010-12-03 15:50:00

On Dec 3, 12:50 pm, Mohib <dr.mo...@gmail.com> wrote:
> Hi,
>
> My students are in need of an Optical-Electronic counter to count the
> revolutions/minute (rpm) of a propeller driven by an electric motor.
> The maximum expected rpm is around 20,000 rpm with most of the results
> being in the 5,000 rpm range.
>
> My initial thoughts are to be able to have a light source and a photo-
> detector, with the light being interrupted by the rotating propeller.
> The pulses from the photo-detector can be counted and compared to a
> timer to give revolutions per minute.
>
> Please let me know the most economical way of combining (the students
> can solder etc.) parts to produce a DIY product.
>
> Thanks,
> Dr. Mohib. N. Durrani
> Montgomery College, MD

Do you have access to an oscilloscope?  Your idea is fine.  Get a
photo diode, or even a solar cell may be fast enough.  Connect a
resistor across the photo diode or cell and look at the voltage signal
on the 'scope.  (The detector produces a current proportional to the
light, the resistor turns the current into a voltage.)  You'll have to
play around a bit with the resistor value.  Perhaps start with 10 k
ohms or 100k ohms.  You won't get more than ~0.5 Volts out of the
detector.  You'll want a nice bright source for the light.  A red
diode laser pointer might be nice... easy to align it.  Once you can
see pulses on the 'scope you can try sticking it into a counter.

At some point the capacitance of the photo diode or solar cell is
going to limit the response time.  (tau = RC)  But this is all good
fun and your students might learn something.  Ask them how to make it
faster?

George H.

Re: Electronic-Optical Counter - John Fields - 2010-12-03 16:55:00

On Fri, 3 Dec 2010 09:50:54 -0800 (PST), Mohib <d...@gmail.com>
wrote:

>Hi,
>
>My students are in need of an Optical-Electronic counter to count the
>revolutions/minute (rpm) of a propeller driven by an electric motor.
>The maximum expected rpm is around 20,000 rpm with most of the results
>being in the 5,000 rpm range.
>
>My initial thoughts are to be able to have a light source and a photo-
>detector, with the light being interrupted by the rotating propeller.
>The pulses from the photo-detector can be counted and compared to a
>timer to give revolutions per minute.
>
>Please let me know the most economical way of combining (the students
>can solder etc.) parts to produce a DIY product.

---
The most economical way would be to build a counter using CMOS digital
logic; either the CD4000 or 74HC families, or both.

The simplest approach would be to use the output pulses from the
propeller interruptor to clock an up-counting counter chain, while
using a pulse of a fixed width to gate the counter.

Doing that, and using decimal counters, would allow the counter
outputs to drive seven-segment displays and have the displays read out
directly in RPM.

Would you like a schematic?

  
---
JF

Re: Electronic-Optical Counter - Jasen Betts - 2010-12-03 19:34:00

On 2010-12-03, Mohib <d...@gmail.com> wrote:
> Hi,
>
> My students are in need of an Optical-Electronic counter to count the
> revolutions/minute (rpm) of a propeller driven by an electric motor.
> The maximum expected rpm is around 20,000 rpm with most of the results
> being in the 5,000 rpm range.
>
> My initial thoughts are to be able to have a light source and a photo-
> detector, with the light being interrupted by the rotating propeller.
> The pulses from the photo-detector can be counted and compared to a
> timer to give revolutions per minute.
>
> Please let me know the most economical way of combining (the students
> can solder etc.) parts to produce a DIY product.

hook a photodiode to the microphone inpput of a PC and use free
frequency counter software.

if ypur propellor has 6 blades multiplying the frequency (in Hz) by 10 will
yield RPM.

-- 
⚂⚃ 100% natural

Re: Electronic-Optical Counter - Mohib - 2010-12-03 21:52:00

Hello again,

Thanks to all for the replies and valuable info.
I should probably give a few additional details.

We want to only use economical electronic parts that can be easily
obtained from an electronics store (online, RadioShack etc.). We will
appreciate references to reliable sources.

We do have a continuously varying voltage/current power supply (one of
the Mastech models).
We do not want to have additional accessories (no oscilloscope, PC
etc.)

We also want a continuous (and varying) display of the rpm of the
rotating shaft (accuracy of ~ 0.1%). The students will note down the
changing rpm (as displayed) with changes in supplied voltage in their
lab report.

Please also note that some of the propellers have 2 blades and some
have 3, 4 or even 5 blades :)

Mohib.

On Dec 3, 1:50 pm, Mohib <dr.mo...@gmail.com> wrote:
> Hi,
>
> My students are in need of an Optical-Electronic counter to count the
> revolutions/minute (rpm) of a propeller driven by an electric motor.
> The maximum expected rpm is around 20,000 rpm with most of the results
> being in the 5,000 rpm range.
>
> My initial thoughts are to be able to have a light source and a photo-
> detector, with the light being interrupted by the rotating propeller.
> The pulses from the photo-detector can be counted and compared to a
> timer to give revolutions per minute.
>
> Please let me know the most economical way of combining (the students
> can solder etc.) parts to produce a DIY product.
>
> Thanks,
> Dr. Mohib. N. Durrani
> Montgomery College, MD


Re: Electronic-Optical Counter - Mohib - 2010-12-03 22:01:00

Hi John,

Thanks for the info.
Yes, a schematic will definetely be very useful :)

Mohib.
PS: I posted some additional details of the project, relplying to my
initial post.

On Dec 3, 4:55 pm, John Fields <jfie...@austininstruments.com> wrote:
> ---
> The most economical way would be to build a counter using CMOS digital
> logic; either the CD4000 or 74HC families, or both.
>
> The simplest approach would be to use the output pulses from the
> propeller interruptor to clock an up-counting counter chain, while
> using a pulse of a fixed width to gate the counter.
>
> Doing that, and using decimal counters, would allow the counter
> outputs to drive seven-segment displays and have the displays read out
> directly in RPM.
>
> Would you like a schematic?
>
> ---
> JF

> On Fri, 3 Dec 2010 09:50:54 -0800 (PST), Mohib <dr.mo...@gmail.com>
> wrote:
>
> >Hi,
>
> >My students are in need of an Optical-Electronic counter to count the
> >revolutions/minute (rpm) of a propeller driven by an electric motor.
> >The maximum expected rpm is around 20,000 rpm with most of the results
> >being in the 5,000 rpm range.
>
> >My initial thoughts are to be able to have a light source and a photo-
> >detector, with the light being interrupted by the rotating propeller.
> >The pulses from the photo-detector can be counted and compared to a
> >timer to give revolutions per minute.
>
> >Please let me know the most economical way of combining (the students
> >can solder etc.) parts to produce a DIY product.
>

Re: Electronic-Optical Counter - George Herold - 2010-12-03 23:43:00

On Dec 3, 9:52 pm, Mohib <dr.mo...@gmail.com> wrote:
> Hello again,
>
> Thanks to all for the replies and valuable info.
> I should probably give a few additional details.
>
> We want to only use economical electronic parts that can be easily
> obtained from an electronics store (online, RadioShack etc.). We will
> appreciate references to reliable sources.
>
> We do have a continuously varying voltage/current power supply (one of
> the Mastech models).
> We do not want to have additional accessories (no oscilloscope, PC
> etc.)

Oh, not even a counter?  That's a lot harder.  How much electronics
have you done?
Do you have digital multimeters?
They're dirt cheap.  Hey some even have counters!

George H.


>
> We also want a continuous (and varying) display of the rpm of the
> rotating shaft (accuracy of ~ 0.1%). The students will note down the
> changing rpm (as displayed) with changes in supplied voltage in their
> lab report.
>
> Please also note that some of the propellers have 2 blades and some
> have 3, 4 or even 5 blades :)
>
> Mohib.
>
> On Dec 3, 1:50 pm, Mohib <dr.mo...@gmail.com> wrote:
>
>
>
> > Hi,
>
> > My students are in need of an Optical-Electronic counter to count the
> > revolutions/minute (rpm) of a propeller driven by an electric motor.
> > The maximum expected rpm is around 20,000 rpm with most of the results
> > being in the 5,000 rpm range.
>
> > My initial thoughts are to be able to have a light source and a photo-
> > detector, with the light being interrupted by the rotating propeller.
> > The pulses from the photo-detector can be counted and compared to a
> > timer to give revolutions per minute.
>
> > Please let me know the most economical way of combining (the students
> > can solder etc.) parts to produce a DIY product.
>
> > Thanks,
> > Dr. Mohib. N. Durrani
> > Montgomery College, MD- Hide quoted text -
>
> - Show quoted text -


Re: Electronic-Optical Counter - bw - 2010-12-04 03:38:00

"Jasen Betts" <j...@xnet.co.nz> wrote in message 
news:idc2au$4j4$1...@reversiblemaps.ath.cx...
> On 2010-12-03, Mohib <d...@gmail.com> wrote:
>> Hi,
>>
>> Please let me know the most economical way of combining (the students
>> can solder etc.) parts to produce a DIY product.
>
> hook a photodiode to the microphone inpput of a PC and use free
> frequency counter software.
>
> if ypur propellor has 6 blades multiplying the frequency (in Hz) by 10 
> will
> yield RPM.
>
> -- 
> ?? 100% natural

Nice idea. So many people have hand held electro-impulse or optical counters 
and RPM meters that I'd forgotten that PC sound cards have pretty good 
linearity.
Here are some more ideas
1. If the OP has a PC with a spare 3-pin fan connector on the MB he might 
try the fan sensor pin, I don't know how it counts or if it has a simple 
interface.
2. I made hand-held two transistor rpm meter with analog output from a 1960s 
Popular Electronics. It's a charge pump circuit and uses an old radio 
antenna to pick up the EM pulsed by the ignition wires. Still works today.
3. The OP can look up VU meter or audio frequency meter. I hope the OP knows 
Hertz times 60 equals RPM 



Re: Electronic-Optical Counter - John Fields - 2010-12-04 08:00:00

On Fri, 3 Dec 2010 19:01:18 -0800 (PST), Mohib <d...@gmail.com>
wrote:

>Hi John,
>
>Thanks for the info.
>Yes, a schematic will definetely be very useful :)

---
OK, I'll have something for you the early part of next week.

>Mohib.
>PS: I posted some additional details of the project, relplying to my
>initial post.

---
OK.

BTW, the convention here is to bottom post and to in-line post when
required for clarity.

Thanks,

---
JF

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