Tachymeter design

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
K

Karen Gallagher

Guest
Can any electronics whizzes help me out with a simple design for a
tachymeter to display the RPM of a propshaft?

I'm looking to monitor the output of my rear PTO so it does not over-rev
while negotiating rough terrain - mostly a creek bed I have to drive through
frequently while weed-spraying. Max RPM needs to be kept below 1000, but
sometimes seems to sneak up well beyond, judging by the odd sounds coming
from the rear.

I'm pretty handy with a soldering iron, but gave up on modern electronics
when they replaced valves with these new fangled transistors :)

Karen

--
"I'd far rather be happy than right any day."
- Slartibartfast


 
On 2006-04-25, Karen Gallagher <[email protected]> wrote:

> Can any electronics whizzes help me out with a simple design for a
> tachymeter to display the RPM of a propshaft?

Do a quick google for "shaft tachometer", there's a fair few on the
first page that look promising, all intended for fit-it-yourself to a
nondescript shaft, i.e. not tailor made for a car so should be
possible to sort it out.

I'd imagine you can even get them with alarms etc. if you try such
sites.

--
Blast off and strike the evil Bydo empire!
 
On Tue, 25 Apr 2006 11:56:56 +0100, Ian Rawlings
<[email protected]> wrote:

>Do a quick google for "shaft tachometer", there's a fair few on the
>first page that look promising, all intended for fit-it-yourself to a
>nondescript shaft, i.e. not tailor made for a car so should be
>possible to sort it out.

Shouldn't think it'd be too difficult to glue a very small rare earth
magnet to the prop and use a reed relay to signal a cheap engine
tacho.


--
"We have gone from a world of concentrated knowledge and wisdom to one
of distributed ignorance. And we know and understand less while being
increasingly capable." Prof. Peter Cochrane, formerly of BT Labs
In memory of Brian {Hamilton Kelly} who logged off 15th September 2005
 
On 2006-04-25, Karen Gallagher <[email protected]> wrote:

> Can any electronics whizzes help me out with a simple design for a
> tachymeter to display the RPM of a propshaft?

Further to my earlier hint re tachs with alarms, they certainly seem
to be available, for example;

http://www.controlability.com/sensor/sfm130-speedometer-tachometer-with-alarm.html

Set the max RPM at it operates relays when it hits it, and can be used
with a variety of sensors, optical, electrical, magnetic etc. Handles
12 or 24 volt.

Gawd knows what the prices on these things are like though ;-)

--
Blast off and strike the evil Bydo empire!
 
Karen Gallagher wrote:
> Can any electronics whizzes help me out with a simple design for a
> tachymeter to display the RPM of a propshaft?
>
> I'm looking to monitor the output of my rear PTO so it does not over-rev
> while negotiating rough terrain - mostly a creek bed I have to drive through
> frequently while weed-spraying. Max RPM needs to be kept below 1000, but
> sometimes seems to sneak up well beyond, judging by the odd sounds coming
> from the rear.
>
> I'm pretty handy with a soldering iron, but gave up on modern electronics
> when they replaced valves with these new fangled transistors :)

Go and have a chat to your local Jaycar store. They do an inductive
pickup tachometer that will probably work happily (maybe with a very
slight modification) off the signal from a magnet mounted on the PTO
shaft and a pickup coil. If the store has the usual resident
electronics freak they will probably even help you get it all working.


--
EMB
 
Karen Gallagher wrote:
> Can any electronics whizzes help me out with a simple design for a
> tachymeter to display the RPM of a propshaft?
>
> I'm looking to monitor the output of my rear PTO so it does not over-rev
> while negotiating rough terrain - mostly a creek bed I have to drive through
> frequently while weed-spraying. Max RPM needs to be kept below 1000, but
> sometimes seems to sneak up well beyond, judging by the odd sounds coming
> from the rear.
>
> I'm pretty handy with a soldering iron, but gave up on modern electronics
> when they replaced valves with these new fangled transistors :)
>
> Karen
>


Martyn suggests a reed switch as a sensor, but at 6000 RPM =10msec/rev -
its pushing it for a reed to have had time to stop bouncing around
before it has to move again, and a glass tube next to V8 is not going to
be too happy.

It would be better to pick it off with a hall switch instead.

A crude RPM to volts detector needs only a single transistor, a couple
of diodes and a capacitor, with sundry resistors. Would you like to see
the circuit ?

Steve


 
On 2006-04-25, Ian Rawlings <[email protected]> wrote:

> Gawd knows what the prices on these things are like though ;-)

Rats, the moment I hit "post" my eyes fall on the price tag displayed
prominently at the bottom of the page, £120. Not too bad if you don't
have the time or inclination to put together your own job. You could
probably get something much cheaper if you don't want it to ring an
alarm when the revs get too high.

--
Blast off and strike the evil Bydo empire!
 
Steve wrote:
> Karen Gallagher wrote:
>
>> Can any electronics whizzes help me out with a simple design for a
>> tachymeter to display the RPM of a propshaft?
>>
>> I'm looking to monitor the output of my rear PTO so it does not
>> over-rev while negotiating rough terrain - mostly a creek bed I have
>> to drive through frequently while weed-spraying. Max RPM needs to be
>> kept below 1000, but sometimes seems to sneak up well beyond, judging
>> by the odd sounds coming from the rear.
>>
>> I'm pretty handy with a soldering iron, but gave up on modern
>> electronics when they replaced valves with these new fangled
>> transistors :)

>
>
> Martyn suggests a reed switch as a sensor, but at 6000 RPM =10msec/rev -
> its pushing it for a reed to have had time to stop bouncing around
> before it has to move again, and a glass tube next to V8 is not going to
> be too happy.
>
> It would be better to pick it off with a hall switch instead.
>
> A crude RPM to volts detector needs only a single transistor, a couple
> of diodes and a capacitor, with sundry resistors. Would you like to see
> the circuit ?

1000RPM max of the PTO - reed sw should be fine.

--
EMB
 
On 2006-04-25, Mother <"@ {mother} @"@101fc.net> wrote:

> Shouldn't think it'd be too difficult to glue a very small rare earth
> magnet to the prop and use a reed relay to signal a cheap engine
> tacho.

At engine speeds, a reed switch would meet its maximum contact
lifetime very quickly, so you'd need to go solid state.

--
Blast off and strike the evil Bydo empire!
 
EMB wrote:

> 1000RPM max of the PTO - reed sw should be fine.

Nah, it'll bounce like the clappers.

Steve

 
On Tue, 25 Apr 2006 12:49:43 +0100, Steve
<[email protected]> wrote:

>A crude RPM to volts detector needs only a single transistor, a couple
>of diodes and a capacitor, with sundry resistors. Would you like to see
>the circuit ?

Yes I would, I have a small anemometer with three wires coming off it
so would like to know how to connect it to a readout. I'm guessing it
contains a hall effect transistor that counts the metal blades as they
go past.

AJH
 
On Tue, 25 Apr 2006 13:04:35 +0100, Ian Rawlings
<[email protected]> wrote:

>Rats, the moment I hit "post" my eyes fall on the price tag displayed
>prominently at the bottom of the page, £120. Not too bad if you don't
>have the time or inclination to put together your own job. You could
>probably get something much cheaper if you don't want it to ring an
>alarm when the revs get too high.

It looks reasonable to me.

When Karen posted her query I thought I'd like something similar to
disconnect a tractor pto, to prevent stalling. I was thinking it
should be simple, a magnet on the shaft, a Hall effect transistor to
sense it and a standard rev counter to pick up the pulses, designing
the electronics would cause me a problem so this device is just the
job.

AJH

 
On or around Tue, 25 Apr 2006 12:49:43 +0100, Steve
<[email protected]> enlightened us thusly:

>Martyn suggests a reed switch as a sensor, but at 6000 RPM =10msec/rev -
>its pushing it for a reed to have had time to stop bouncing around
>before it has to move again, and a glass tube next to V8 is not going to
>be too happy.

if the propshaft's doing 6000 rpm, then you'll be going so fast you'd not
notice the counter anyway...

--
Austin Shackles. www.ddol-las.net my opinions are just that
Travel The Galaxy! Meet Fascinating Life Forms...
------------------------------------------------\
>> http://www.schlockmercenary.com/ << \ ...and Kill them.
a webcartoon by Howard Tayler; I like it, maybe you will too!
 
On 2006-04-25, AJH <[email protected]> wrote:

> When Karen posted her query I thought I'd like something similar to
> disconnect a tractor pto, to prevent stalling.

A device like the one I posted should do it as you suggest, although
if Karen didn't want the relay operation I reckon she'd be best off
with an analogue display, personally I find monitoring a rapidly
altering measurement on a digital display to be much harder than on a
good analogue display, especially where vibration comes into it.

--
Blast off and strike the evil Bydo empire!
 
On 2006-04-25, Steve Taylor <[email protected]> wrote:

> Nah, it'll bounce like the clappers.

Would the switch even have time to switch in the first place, let
alone bounce? Perhaps with a large-ish curved magnet?

Still reckon solid state is the best. Even with a 100,000,000 cycle
lifetime (which is high for a reed switch), at 1,000 RPM that's a
lifetime of 1,666 hours if I've done my maths right. Depending on how
much the engine is run, that's a lifetime of between 70 days to
one or two years.

--
Blast off and strike the evil Bydo empire!
 
On Tue, 25 Apr 2006 13:59:38 +0100, Ian Rawlings
<[email protected]> wrote:

>A device like the one I posted should do it as you suggest, although
>if Karen didn't want the relay operation I reckon she'd be best off
>with an analogue display, personally I find monitoring a rapidly
>altering measurement on a digital display to be much harder than on a
>good analogue display, especially where vibration comes into it.

I shall be talking with them, one of their sensors does exactly what I
want.

I agree the analogue versus digital display and this thing does
vibrate!

AJH

 
On Tue, 25 Apr 2006 13:57:12 +0100, Ian Rawlings
<[email protected]> wrote:

>Still reckon solid state is the best. Even with a 100,000,000 cycle
>lifetime (which is high for a reed switch), at 1,000 RPM that's a
>lifetime of 1,666 hours if I've done my maths right. Depending on how
>much the engine is run, that's a lifetime of between 70 days to
>one or two years.

Depends really. A simple reed and magnet is fine for taking
measurements - probably not best for a permanent fix, but once you
have the measurements you wouldn't need full time monitoring.

Solid state, although sexier, takes slightly more than three small
wires :)

I built a similar measure (using a s/h revcounter) for a go-cart which
worked, after a fashion, for years and cost less than a fiver.


--
"We have gone from a world of concentrated knowledge and wisdom to one
of distributed ignorance. And we know and understand less while being
increasingly capable." Prof. Peter Cochrane, formerly of BT Labs
In memory of Brian {Hamilton Kelly} who logged off 15th September 2005
 
AJH wrote:
> On Tue, 25 Apr 2006 12:49:43 +0100, Steve
> <[email protected]> wrote:
>
>> A crude RPM to volts detector needs only a single transistor, a
couple of diodes and a capacitor, with sundry resistors. Would you like
to see the circuit ?
>
> Yes I would, I have a small anemometer with three wires coming off it
> so would like to know how to connect it to a readout. I'm guessing it
> contains a hall effect transistor that counts the metal blades as they
> go past.

Here is a circuit we use with a water flow sensor. Its a pretty useful
universal frequency to voltage converter and is very linear. It drives a
moving coil panel meter from SKT 2. Pin 7 on Q2 drives an alarm o/p,
whose trigger point is set by R10. The output will need to be buffered
to do anything but light an LED.

If you ignore everything after Q2 pin 3, volts on R2 is directly
proportional to Frequency, and you can do what you like with it. Keep
the load on the pin very low, or you WILL need the opamp.

The time constant of R2/C2 affects the scale and range. As shown here,
it will work with the 1000 RPM signal nicely I think, but otherwise make
R2 a bit bigger.

Here is the picture of the circuit.

http://www.thetaylorfamily.org.uk/cmine/displayimage.php?album=8&pos=0

The input is shown as +12, signal and ground. In fact the input pin SKT
1 pin 2 can be driven with anything from about 1V to 12V, or you can add
another little transistor amplifier.

Steve
 
Mother wrote:

> Solid state, although sexier, takes slightly more than three small
> wires :)

A hall sensor has exactly three wires, supply, ground and output. And
they aren't (too) brittle.

Steve
 
On Tue, 25 Apr 2006 18:09:37 +0100, Steve
<[email protected]> wrote:

>Here is a circuit we use with a water flow sensor. Its a pretty useful
>universal frequency to voltage converter and is very linear. It drives a
>moving coil panel meter from SKT 2. Pin 7 on Q2 drives an alarm o/p,
>whose trigger point is set by R10. The output will need to be buffered
>to do anything but light an LED.


Thanks Steve but 'scuse my ignorance, what are the op amps?

AJH
 
You must log in or register to reply here.

Similar threads

Nodge68
Freelander 2 (LR2) LR trouble codes.
Replies
6
Views
38K
Keith Kernow Kernewick
Keith Kernow Kernewick
300bhp/ton
Driven: New Defender - On & Off Road. Is it a Pretender?
2 3
Replies
50
Views
8K
Squonker
S
P
Freelander 1 Fuel rail Connector.
Replies
12
Views
2K
blodge
blodge
Dr_evil
Series King Cab
61 62 63
Replies
1K
Views
144K
discomark10
discomark10
The Mad Hat Man
Rust Removal Using Electrolysis
Replies
15
Views
39K
Paul D
Paul D
Back
Top