Tachometer Input

[Richard]

I have a device which requires a signal for a tachometer. We have this
device in the training room for showing / teaching operation to mechanics.

The device gets it's normal input from a Magnetic Pickup (Inductive pickup)
used on the flywheel. It goes thru a series diode then then passes by a 5
volt Zener, then goes into a microcontroller and displays RPM as well as
other functions.

I need to make a simulator which I can adjust from 0hz to 5khz to work on
the above. Currently we are using a gear on a drill press, which works,
but we would like a small electronic design. I was thinking about a 555
type circuit, but a 555 puts out a digital signal and the mag pickup outputs
AC. Does anyone have any simple ideas or schematics I could use for this?

Thanks.




----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Rileyesi]

I have a device which requires a signal for a tachometer. We have this
device in the training room for showing / teaching operation to mechanics.

The device gets it's normal input from a Magnetic Pickup (Inductive pickup)
used on the flywheel. It goes thru a series diode then then passes by a 5
volt Zener, then goes into a microcontroller and displays RPM as well as
other functions.

I need to make a simulator which I can adjust from 0hz to 5khz to work on
the above. Currently we are using a gear on a drill press, which works,
but we would like a small electronic design. I was thinking about a 555
type circuit, but a 555 puts out a digital signal and the mag pickup outputs
AC. Does anyone have any simple ideas or schematics I could use for this?

Thanks.

You might be able to use a diode between the common of the pickup and the
common of the 555 circuit to 'trick' the pickup to think it is seeing an AC
signal. The diode would raise the common of the pickup to a voltage potential
that is higher than the 555 circuit.

Just a thought.

 

[Richard]

Richard,
I would try first to just use the output of the 7555 (an improved C-Mos
version of the 555) with a supply of 5V the output I would capacitivly
(100uF) couple to the meter . As you have described it, the unit
apparently
only triggers on the 0-crossings, so the waveform is probably irrelevant.
If this doesn't work you either have to build a real sine generator, or
filter the 7555 output with a tracking lowpass filter. But 0Hz are not
attainable.
A simple sine generator can be made with a pic with filtered PWM output,
this can also make very low frequencies (or DC), which require
huge(infinite) capacitors when done analog.
.
Thanks.

You're welcome
--
ciao Ban
Bordighera, Italy

I think this should work directly off the 7555 because on my scope, I have
the frequency output pin used for calibration which outputs a 2khz signal
which looks like 5vdc square wave (if I remember correctly it was 5 volts)
and the tachometer did indeed pickup the signal,





----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Terry Pinnell]

"Richard" <rwskinnerATawesomenetDotnet> wrote:

I think this should work directly off the 7555 because on my scope, I have
the frequency output pin used for calibration which outputs a 2khz signal
which looks like 5vdc square wave (if I remember correctly it was 5 volts)
and the tachometer did indeed pickup the signal,

Yes, I'd certainly have expected it to. Are you confirming your
problem is now solved, and that you have a 555 astable connected
directly to your Tachometer?

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[Richard]

No, it's not solved yet because I haven't built the 555 circuit yet. I just
sent the cal. freq. from my scope to it to see if it would read a digital 5
volt pulse.


"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:jprfm0lv66okfj9et1b67l6mfg6qq0qbs1@4ax.com...

"Richard" <rwskinnerATawesomenetDotnet> wrote:

I think this should work directly off the 7555 because on my scope, I
have
the frequency output pin used for calibration which outputs a 2khz signal
which looks like 5vdc square wave (if I remember correctly it was 5
volts)
and the tachometer did indeed pickup the signal,

Yes, I'd certainly have expected it to. Are you confirming your
problem is now solved, and that you have a 555 astable connected
directly to your Tachometer?

--
Terry Pinnell
Hobbyist, West Sussex, UK

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Rich Grise]

On Saturday 09 October 2004 04:14 pm, "Richard" top-posted:

No, it's not solved yet because I haven't built the 555 circuit yet. I
just sent the cal. freq. from my scope to it to see if it would read a
digital 5 volt pulse.

Well, build the 555 circuit, and just put it to the same place you put

your 5V. pulse. Power the 555 from 5 volts, and you're done. (you did
say that it did count the 5V pulse, right?)

"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:jprfm0lv66okfj9et1b67l6mfg6qq0qbs1@4ax.com...
"Richard" <rwskinnerATawesomenetDotnet> wrote:

I think this should work directly off the 7555 because on my scope, I
have
the frequency output pin used for calibration which outputs a 2khz
signal which looks like 5vdc square wave (if I remember correctly it was
5
volts)
and the tachometer did indeed pickup the signal,

Yes, I'd certainly have expected it to. Are you confirming your
problem is now solved, and that you have a 555 astable connected
directly to your Tachometer?

Cheers!
Rich

 

[Richard]

Built a 555 circuit and tested it by hooking it up to my scope. The 555 is
working fine however
I do not get a RPM reading on the device. So I gues it is expecting a zero
crossing.

BTW, my calibration frequency on the scope was 0.5vpp and it does not
trigger the device consistently either.

Anymore ideas?

Richard



"Rich Grise" <null@example.net> wrote in message
news:ei2ad.199$MY.80@trnddc03...

On Saturday 09 October 2004 04:14 pm, "Richard" top-posted:

No, it's not solved yet because I haven't built the 555 circuit yet. I
just sent the cal. freq. from my scope to it to see if it would read a
digital 5 volt pulse.

Well, build the 555 circuit, and just put it to the same place you put
your 5V. pulse. Power the 555 from 5 volts, and you're done. (you did
say that it did count the 5V pulse, right?)

"Terry Pinnell" <terrypinDELETE@THESEdial.pipex.com> wrote in message
news:jprfm0lv66okfj9et1b67l6mfg6qq0qbs1@4ax.com...
"Richard" <rwskinnerATawesomenetDotnet> wrote:

I think this should work directly off the 7555 because on my scope, I
have
the frequency output pin used for calibration which outputs a 2khz
signal which looks like 5vdc square wave (if I remember correctly it
was
5
volts)
and the tachometer did indeed pickup the signal,

Yes, I'd certainly have expected it to. Are you confirming your
problem is now solved, and that you have a 555 astable connected
directly to your Tachometer?

Cheers!
Rich

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

 

[Ban]

Richard wrote:

Built a 555 circuit and tested it by hooking it up to my scope. The
555 is working fine however
I do not get a RPM reading on the device. So I gues it is expecting
a zero crossing.

BTW, my calibration frequency on the scope was 0.5vpp and it does not
trigger the device consistently either.

Anymore ideas?

Richard

Put the capacitor between the input and the timer, like I had described in
my first post, this will shift the DC-level, so the input signal goes below
0, even when the timer is fed from only +5V.
--
ciao Ban
Bordighera, Italy

 

[Ban]

Richard wrote:

I have a device which requires a signal for a tachometer. We have
this
device in the training room for showing / teaching operation to
mechanics.

The device gets it's normal input from a Magnetic Pickup (Inductive
pickup)
used on the flywheel. It goes thru a series diode then then passes
by a 5
volt Zener, then goes into a microcontroller and displays RPM as well
as
other functions.

I need to make a simulator which I can adjust from 0hz to 5khz to
work on
the above. Currently we are using a gear on a drill press, which
works,
but we would like a small electronic design. I was thinking about a
555
type circuit, but a 555 puts out a digital signal and the mag pickup
outputs
AC. Does anyone have any simple ideas or schematics I could use for
this?

Richard,
I would try first to just use the output of the 7555 (an improved C-Mos
version of the 555) with a supply of 5V the output I would capacitivly
(100uF) couple to the meter . As you have described it, the unit apparently
only triggers on the 0-crossings, so the waveform is probably irrelevant.
If this doesn't work you either have to build a real sine generator, or
filter the 7555 output with a tracking lowpass filter. But 0Hz are not
attainable.
A simple sine generator can be made with a pic with filtered PWM output,
this can also make very low frequencies (or DC), which require
huge(infinite) capacitors when done analog.
..

Thanks.

You're welcome

--
ciao Ban
Bordighera, Italy