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I know this topic has been dealt with before, but through my
searching I never found a definite solution that someone had
confirmed worked. I want to be able to read the rpm off of any
newer car with the basicx-24, does anyone know the best way to go
about this?
Thanks Alot, Jared





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Good question, though I have not seen such dealt with before. I want
to know the same thing, but I might be able to make it easier because
I can read an old fashioned coil.

-Tony --- In basicx@basi..., "jeraldin99" <jbccox@h...> wrote:
>
> I know this topic has been dealt with before, but through my
> searching I never found a definite solution that someone had
> confirmed worked. I want to be able to read the rpm off of any
> newer car with the basicx-24, does anyone know the best way to go
> about this?
> Thanks Alot, Jared





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--- In basicx@basi..., "jeraldin99" <jbccox@h...> wrote:
> I want to be able to read the rpm off of any newer car with the
> basicx-24, does anyone know the best way to go about this?

If your car has an OBD-II connector (as most newer cars do) you might
be able to get the RPM in machine readable from from that. This is
probably a more complicated solution that you were seeking but it
opens other potential avenues to explore as well.

Depending on how accuarately you need the RPM, you may be able to tap
off the ignition/injection system at the same point where a
tachometer would connect. I would expect such a signal to either be
related to the RPM by its frequency (most likely) or by its DC
level. A third possibility is that the RPM is related to the duty
cycle of the signal. Connecting a o'scope to the signal and changing
the engine speed should tell you what you need to know, including
what type of level conversion and/or signal conditioning will be
required.

A third possibility is to mount a magnetic pickup on the engine
either near the flywheel/ring gear or near a timing gear, cam gear
etc. The magnetic pickup will give you a square wave signal whose
frequency is proportional to the rate at which the gear teeth are
passing by. That frequency can be related to the RPM by a simple
ratio. This, by the way, is how tachometers on diesel engines are
often implemented. I put one on my diesel genset for which I built a
speed controller. A simple transistor clipping circuit is all that
was needed to condition the signal.

One last possibility is to mount a reed relay or photo transceiver
near a pulley (alternator, power steering, fan, etc.) and then mount
a magnet (for the reed relay) or an interrupter finger (for the photo
tranceiver) on the pulley. This mounting will have to be done with
careful consideration given to the centripetal force that it will
experience due to the pulley rotation. It might be safer to try to
mount a light source (IR for example) on one side of the pulley and
mount a receptor on the other side, drilling a hole in the pulley in
one or more places to allow the light to pass through.

Which of these methods (or others) that you might choose depends a
lot on your mechanical and electronics skills as well as your
computer knowledge and what tools you have available.

Don




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--- In basicx@basi..., "Don Kinzer" <dkinzer@e...> wrote:
>Snip
. This, by the way, is how tachometers on diesel engines are
> often implemented. I put one on my diesel genset for which I built
a
> speed controller. A simple transistor clipping circuit is all that
> was needed to condition the signal.
>
> Don
<End Snip

Don, I am planning to do this on my Onan Gas 4.5KW RV genset. The
Onan
board has failed twice since I have had the unit (3 years) and they
are
very expensive. The local Onan distributor has been, shall we say, a
bandit when it comes to repairing the genset.I think the BasicX would
handle this very well. I would appreciate any insight you would care
to
offer.

Thanks,
Craig





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--- In basicx@basi..., "wurlitzer28" <craig.whitley@a...> wrote:
> I am planning to do this on my Onan Gas 4.5KW RV genset. The
> Onan board has failed twice since I have had the unit (3 years)
> and they are very expensive.

The controller that I built (several years ago) uses the BasicStamp.
If I were to do it today, I'd use the BX-24. (I had to add external
RAM to the Stamp to be able to implement the controller.) I have a
page that describes what I did including the schematics and Stamp
code. It could be adapted to a BX-24 fairly easily, I would think.
The most difficult part would be trying to translate the Stamp code to
BasicX. It might be easier to start fresh and just use some core ideas
from the Stamp code.

http://www.kinzers.com/don/GenSet


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Electronic Tachometer circuitI found this website that I believes explains a good way to read in the rpm, let me know what everyone thinks. And if they think it would work. Thanks, Jared.
Electronic Tachometer Circuit

--------------------------------------------------------------------------------

This circuit gives a voltage that corresponds the the current RPM. The advantage over a analogue meter is a reading that is more accurate since the "needle" is much quicker to react. In fact since the output is a voltage you could connect it to a moving needle if you require.
Background information

--------------------------------------------------------------------------
The RPM can be converted to a frequency quite easily. There are two sparks per rotation and we are working in seconds so simply devide the RPM by 30! (thus 8000rpm is actually 266 Hertz).
The frequency input to the circuit can be taken from the -Ve terminal of the coil. You would expect the voltage to swing by about 12 volts since the contact breakers simply switch the battery to the coil. Unfortunately the coil is an inductor and the condensor is a capacitor thus we have a highly resonant circuit which can hit over 40 volts. Protection is shown in the circuit diagram.

Circuit design

--------------------------------------------------------------------------
The conversion from frequency to voltage is done by the LM2917 chip which is a fairly simple 14 pin device. Only a few components are required to make it perform. The formula is shown below:
Vout can be found by using the formula: Vout = Vcc * R1 * C1 * Fin

Where Vcc is the supply, Fin is the frequency input.

It is a good idea to make R1 a variable resistor. On making the circuit you may find that the output of the chip isn't quite right, twiddling the value of R1 helps to get the right output.

If you choose values of Vcc=8, R1=40K, C1=47nF and Fin=266 then the output is 4 Volts.

Therefore if the output is linear then we have 1V for every 2000rpm.

The ripple voltage has to be considered but for this design the ripple is 33mV at 2000rpm (or a swing of 66hertz around ideal voltage). The circuit is shown below:
Now that we have the output corresponding to the input frequency we need some way of showing it. Below is a circuit that I have found to be very simple and reliable... This is a somewhat simplified version only showing 10 leds but my final version will have around 40!

Siililand note: you can buy one of those LED bars ready from an electronic shop for next to nothing. Make it back-lit, and you have a real-cool looking bar graph right next to all your other wiggits on the dashboard.
an accurate Tachometer ready for some serious testing :-).

Disclaimer!

--------------------------------------------------------------------------
I apologise if the above circuits are not shown correctly. I have checked my design both with the made circuit and the data sheet of the LM2917. If you have any problems then please mail me, but you may find the answers are in the LM2917 data sheet. I was planning on showing the output verses input graph but my circuit doesn't want to work today - the chip seems very easy to blow up and I have had a long day :-(. I'll put up the results when I have obtained them. --------------------------------------------------------------------------
by Paul Hill
Northavon Mini Drivers Club [Non-text portions of this message have been removed]

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--- In basicx@basi..., "Jared Cox" <jbccox@h...> wrote:
> [...] conversion from frequency to voltage ...

After you go to the trouble of adding external components to convert
frequency to (analog) voltage, you then have to convert it to back to
digital. It's simpler to just determine the frequency of the signal
directly by measuring its period. The only external components you
might need is simple transistor to clip the voltage to acceptable
levels. You might even be able to do that satisfactorily with two
diodes and a resistor.

Don



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Thanks Don for the link! Great implementation. This gives me a great
head start into using the BasicX for my Onan genset.
Craig
--- In basicx@basi..., "Don Kinzer" <dkinzer@e...> wrote:
>
> --- In basicx@basi..., "wurlitzer28" <craig.whitley@a...>
wrote:
> > I am planning to do this on my Onan Gas 4.5KW RV genset. The
> > Onan board has failed twice since I have had the unit (3 years)
> > and they are very expensive.
>
> The controller that I built (several years ago) uses the BasicStamp.
> If I were to do it today, I'd use the BX-24. (I had to add external
> RAM to the Stamp to be able to implement the controller.) I have a
> page that describes what I did including the schematics and Stamp
> code. It could be adapted to a BX-24 fairly easily, I would think.
> The most difficult part would be trying to translate the Stamp code
to
> BasicX. It might be easier to start fresh and just use some core
ideas
> from the Stamp code.
>
> http://www.kinzers.com/don/GenSet





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To clip the voltages, Not being that great on electronic design (thus
another queston to come on the message board), how would you connect
those diodes and resistor?

Maybe one to the device thru a resistor. The other diode....to ground
somehow? I might have thought of a Zener to ground to clamp the
upper voltage limit. Clearly I do not even have enough info to get
myself in trouble!!!

-Tony

--- In basicx@basi..., "Don Kinzer" <dkinzer@e...> wrote:
>
> --- In basicx@basi..., "Jared Cox" <jbccox@h...> wrote:
> > [...] conversion from frequency to voltage ...
>
> After you go to the trouble of adding external components to convert
> frequency to (analog) voltage, you then have to convert it to back to
> digital. It's simpler to just determine the frequency of the signal
> directly by measuring its period. The only external components you
> might need is simple transistor to clip the voltage to acceptable
> levels. You might even be able to do that satisfactorily with two
> diodes and a resistor.
>
> Don





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Okay, been there, done that.

Voltage clipping worked best with a 5.1 volt zener through a 10k resistor.
That remaining pulse is fed into a comparator to get rid of the small
transients. This effectively limits the pulses to transitions that are over
2.5 volts (the floor voltage for the comparator) and the max voltage left
by the clipping zener. ( I use a 0-5V control voltage that is adjusted by a
potentiometer for the control voltage in the comparator.)

(Don, I used to use a transistor for voltage clipping until I ran into a
Mazda with serious transient problems that was burning up the clipping
circuit. The zener seems to be more robust.)

The transitions are fed into a D-type flip-flip and the duration of either
the high ff output or the low ff output is timed. Simple math gives the RPM.

Now having said all this, my advice is to use OBDII if available and the
project permits the relatively slow update rate. Mucking about in auto
ignitions systems can be very messy, expensive and frustrating. Pulses from
coils can be impossible to work with. (TTL voltage maxs require just a bit
of signal conditioning of coil pulses.) Ignitor pulses can be just as bad.
Ignition pulses from an ECU to the ignitors can be good pulse sources as
are fuel injectors pulses in cars with electronic fuel injection.

Most newer cars have the rpm (and speedometer) circuitry in the dash which
are fed by a conditioned pulse stream generated in the ECU. Often these are
square waves where each transition is actually the pulse. Measuring the
rising transition actually gives freq/2.

I tried the LM2917 (anybody want a hand full cheap?) and never got reliable
results. The data sheet for the LM2917 has a perfectly good schematic for
an auto rpm circuit right in the doc. I could never get it to give a
reliable output. Yes, they are very easy to toast. Try them with
marshmallows. A big problem is getting the circuit to give the maximum
possible voltage range for the maximum rpm range. The ideal circuit would
give 0 volts for the min rpm and +5V for the max rpm. in order to give the
max resolution with a 10 bit ADC. This isn't trivial in reality.

Measuring pulse frequency can present another set of problems. What's the
minimum rpm that you' be measuring? How many cylinders - 4, 5 (Audi), 6, 8,
10 (Viper), 12 (Ferrari)? What's the maximum rpm (5000 Mustang GT), 9000
(racing Acura V-TEC), 18000 (McLaren-Mercedes F1 car)?

An interesting aside: the rpm data that is shown on screen during an F1
broadcast is actually determined using an audio transducer. I guess it's
obvious that the engineers who control an F1 car wouldn't allow the tv guys
to tap into their ignition systems for data. Rather, the audio transducer
converts the audio pulses from the exhaust to electronic pulses which are
then period measured and converted to the displayed rpm figures. This was
patiently explained during the Shanghai F1 race last fall by announcer
Steve Matchett (a retired F1 engineer/mechanic) when one of the data
displays show a car developing just a tick over 20,000 rpm? Do that with a
BX-24!! Let's see: that's 1 / 20000 = .00005 secs... what was that max
timer resolution again?

Many applications can not suffer the native timer resolution in the BX24 of
1.95 ms. Using the PulseIn command fouls the RTC for pulses longer that
1.05 ms which most rpm period measurements are. Of course that problem can
be ameliorated by not using PulseIn and using a chain of flip-flops to
lengthen the apparent period and then dividing the resulting period by the
number of FF's in the chain.

Timing measurements require a good deal more code than you might think to
produce moving averages or multiple samples for averaging. All this stuff
causes the program update rate to suffer and to eat up a lot of scarce RAM.
There are a lot of trade offs to consider.

Again, if the conditions permit, use OBDII. There's a ton of info at
http://OBD-2.com or Elm Electronics, both OBDII interface chip suppliers.

Paul

At 01:34 AM 3/27/2005, you wrote:
>--- In basicx@basi..., "Jared Cox" <jbccox@h...> wrote:
> > [...] conversion from frequency to voltage ...
>
>After you go to the trouble of adding external components to convert
>frequency to (analog) voltage, you then have to convert it to back to
>digital. It's simpler to just determine the frequency of the signal
>directly by measuring its period. The only external components you
>might need is simple transistor to clip the voltage to acceptable
>levels. You might even be able to do that satisfactorily with two
>diodes and a resistor.
>
>Don >
>
>Yahoo! Groups Links ===========================================================
"We have the power to do any damn fool thing we want to do,
and we seem to do it about every ten minutes."
J. William Fulbright , quoted in Time (New York, Feb. 4, 1952).
===========================================================

[Non-text portions of this message have been removed]



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--- In basicx@basi..., "arhodes19044" <spamiam@c...> wrote:
> To clip the voltages, how would you connect those diodes and
> resistor?

Connect the diodes in series, aligned in the same direction. That
is, the anode of one to the cathode of the other. Now connect the
free cathode to the +5 supply and the free anode to ground. Connect
one end of the resistor to the anode-cathode junction and the other
to the signal of interest. Also, connect a wire from the anode-
cathode junction to the BX input pin.

Note: the cathode of a diode is the end corresponding to the bar of
the diode symbol, the banded end of the diode package. Conventional
current flows alphabetically, from anode to cathode but not in the
reverse direction.

This works because if you apply, say, a 10V signal to the input end
of the resistor, it attempts to move the BX pin to around 10V.
However, when the level gets to about 5.6V or so the diode whose
cathode is connected to +5 begins to conduct, effectively clamping
the BX pin at 5.6V. The same type of thing occurs with the other
diode if the input voltage goes below ground.

You select the resistor value to limit the current flow at the
expected voltage extremes: V=I*R. Assuming that the input signal is
symmetrical around ground, the worst case will occur with the
negative excursion. Let's assume a 10V negative excursion. The
voltage across the resistor will be about 9.4V. A 1K resistor will
limit the current flow to 9.4ma.

The inputs of the AVR chip have their own clamping diodes so, to some
extent, using external ones is over-kill. I think that it is cheap
insurance.

A transistor clipper works similarly but also inverts the signal and
provides some gain to square up the signal (provide faster
transitions from low to high, and vice versa). Use any common small-
signal NPN, transistor (2N2222A, 2N3904, etc.), connecting the
emitter to ground. Connect the collector to the BX input and either
enable the input's pull-up resistor or add an external pull-up
resistor (or both). Then connect a resistor from the input signal to
the base and also connect a diode from the base to ground with the
anode grounded.

This diode will conduct if the input signal goes more negative than
about 0.6V, protecting the base-emitter junction of the transistor.
You choose the resistor value to limit the current at the maximum
expected input voltage. Whether positive or negative, the drop
across the resistor is going to be the input voltage minus about
0.6V. A 1K input resistor would yield about 9.4mA with a 10V signal
applied. If the resistor is too large, it won't allow enough current
to flow to cause the transistor to saturate but there's not much risk
of that unless you get really carried away and use a really big
resistor. I'd probably opt for something around 10K.

Common small signal diodes will serve for these purposes. I
generally use 1N914 because I have dozens of them in my parts drawers.

Another term that is used to describe diodes working in this way
is "clamping".



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Dok, Ok. Excellent explanation, both physically, and
electronically I can see the way it works, But I have no
instinctive feel for it. I will have to play with it a little to
see and understand how it really works!
-Tony

--- In basicx@basi..., "Don Kinzer" <dkinzer@e...> wrote:
>
> --- In basicx@basi..., "arhodes19044" <spamiam@c...> wrote:
> > To clip the voltages, how would you connect those diodes and
> > resistor?
>
> Connect the diodes in series, aligned in the same direction. That
> is, the anode of one to the cathode of the other. Now connect the
> free cathode to the +5 supply and the free anode to ground.
Connect
> one end of the resistor to the anode-cathode junction and the
other
> to the signal of interest. Also, connect a wire from the anode-
> cathode junction to the BX input pin.
>
> Note: the cathode of a diode is the end corresponding to the bar
of
> the diode symbol, the banded end of the diode package.
Conventional
> current flows alphabetically, from anode to cathode but not in the
> reverse direction.
>
> This works because if you apply, say, a 10V signal to the input
end
> of the resistor, it attempts to move the BX pin to around 10V.
> However, when the level gets to about 5.6V or so the diode whose
> cathode is connected to +5 begins to conduct, effectively clamping
> the BX pin at 5.6V. The same type of thing occurs with the other
> diode if the input voltage goes below ground.
>
> You select the resistor value to limit the current flow at the
> expected voltage extremes: V=I*R. Assuming that the input signal
is
> symmetrical around ground, the worst case will occur with the
> negative excursion. Let's assume a 10V negative excursion. The
> voltage across the resistor will be about 9.4V. A 1K resistor
will
> limit the current flow to 9.4ma.
>
> The inputs of the AVR chip have their own clamping diodes so, to
some
> extent, using external ones is over-kill. I think that it is
cheap
> insurance.
>
> A transistor clipper works similarly but also inverts the signal
and
> provides some gain to square up the signal (provide faster
> transitions from low to high, and vice versa). Use any common
small-
> signal NPN, transistor (2N2222A, 2N3904, etc.), connecting the
> emitter to ground. Connect the collector to the BX input and
either
> enable the input's pull-up resistor or add an external pull-up
> resistor (or both). Then connect a resistor from the input signal
to
> the base and also connect a diode from the base to ground with the
> anode grounded.
>
> This diode will conduct if the input signal goes more negative
than
> about 0.6V, protecting the base-emitter junction of the
transistor.
> You choose the resistor value to limit the current at the maximum
> expected input voltage. Whether positive or negative, the drop
> across the resistor is going to be the input voltage minus about
> 0.6V. A 1K input resistor would yield about 9.4mA with a 10V
signal
> applied. If the resistor is too large, it won't allow enough
current
> to flow to cause the transistor to saturate but there's not much
risk
> of that unless you get really carried away and use a really big
> resistor. I'd probably opt for something around 10K.
>
> Common small signal diodes will serve for these purposes. I
> generally use 1N914 because I have dozens of them in my parts
drawers.
>
> Another term that is used to describe diodes working in this way
> is "clamping".





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--- In basicx@basi..., Paul Dubinsky <pdubinsky@f...> wrote:
> That remaining pulse is fed into a comparator to get rid of the
> small transients. This effectively limits the pulses to transitions
> that are over 2.5 volts (the floor voltage for the comparator)
> and the max voltage left by the clipping zener.

Such comparator circuits generally utilize hysteresis, especially
with input signals that are slowly changing or subject to noise.
Hysteresis is implemented by adding positive feedback around the
comparator so that once the threshold is crossed, the threshold is
adjusted so that the input signal is well beyond it. That way, a
slight perturbation of the input signal won't cause the comparator to
switch back to the opposite state again.

> I used to use a transistor for voltage clipping until I ran into a
> Mazda with serious transient problems that was burning up the
> clipping circuit. The zener seems to be more robust.

You can, of course, use a zener to protect the transistor. One of
the benefits of using a transistor is that the gain squares up the
signal. This may or may not be needed depending on the nature of the
input signal.

Don

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At 01:13 PM 3/27/2005, you wrote:
>--- In basicx@basi..., Paul Dubinsky <pdubinsky@f...> wrote:
> > That remaining pulse is fed into a comparator to get rid of the
> >.....<

> Mazda with serious transient problems that was burning up the
> > clipping circuit. The zener seems to be more robust.
>
>You can, of course, use a zener to protect the transistor. One of
>the benefits of using a transistor is that the gain squares up the
>signal. This may or may not be needed depending on the nature of the
>input signal.

I agree. Actually, I used the transistor first and added the zener after
the Mazda episode. These apps didn't really need squaring - they did start
out as pulses with rapid rising edges. The clipping was more of the concern.

Paul >Don >
>
>Yahoo! Groups Links ===========================================================
"We have the power to do any damn fool thing we want to do,
and we seem to do it about every ten minutes."
J. William Fulbright , quoted in Time (New York, Feb. 4, 1952).
===========================================================

[Non-text portions of this message have been removed]



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Oh, ok, I see what your saying, so just use the count transition function and sample over a certain amount of time and then you can determine the rpm that way. Thanks, Jared
----- Original Message -----
From: Don Kinzer
To: basicx@basi...
Sent: Saturday, March 26, 2005 10:34 PM
Subject: [BasicX] Re: Measuring RPM off a car into the BasicX-24
--- In basicx@basi..., "Jared Cox" <jbccox@h...> wrote:
> [...] conversion from frequency to voltage ...

After you go to the trouble of adding external components to convert
frequency to (analog) voltage, you then have to convert it to back to
digital. It's simpler to just determine the frequency of the signal
directly by measuring its period. The only external components you
might need is simple transistor to clip the voltage to acceptable
levels. You might even be able to do that satisfactorily with two
diodes and a resistor.

Don Yahoo! Groups Sponsor
ADVERTISEMENT ------------------------------------------------------------------------------
Yahoo! Groups Links

a.. To
[Non-text portions of this message have been removed]



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This is a very interesting topic and i too have a
question on this subject. I have a race car that i
would like built a little black box for. Basicly I
want to keep track of time and rpm after each run.
It's a 80's model car with s 350 motor in it. I'm
assuming i can tap into the wire that going from
distrubutor to the tach? I'll have to reread some of
the emails a few more times to see what will work for
my applaction.

thanks,
t
--- Paul Dubinsky <pdubinsky@pdub...> wrote:
>
> At 01:13 PM 3/27/2005, you wrote: >
> >--- In basicx@basi..., Paul Dubinsky
> <pdubinsky@f...> wrote:
> > > That remaining pulse is fed into a comparator to
> get rid of the
> > >.....<
>
> > Mazda with serious transient problems that was
> burning up the
> > > clipping circuit. The zener seems to be more
> robust.
> >
> >You can, of course, use a zener to protect the
> transistor. One of
> >the benefits of using a transistor is that the gain
> squares up the
> >signal. This may or may not be needed depending on
> the nature of the
> >input signal.
>
> I agree. Actually, I used the transistor first and
> added the zener after
> the Mazda episode. These apps didn't really need
> squaring - they did start
> out as pulses with rapid rising edges. The clipping
> was more of the concern.
>
> Paul > >Don
> >
> >
> >
> >
> >
> >
> >
> >Yahoo! Groups Links
> >
> >
> >
> ===========================================================
> "We have the power to do any damn fool thing we want
> to do,
> and we seem to do it about every ten minutes."
> J. William Fulbright , quoted in Time (New
> York, Feb. 4, 1952).
>
=========================================================== > [Non-text portions of this message have been
> removed] >
>
> Yahoo! Groups Links > basicx-unsubscribe@basi...
__________________________________



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--- In basicx@basi..., "arhodes19044" <spamiam@c...> wrote:
> I will have to play with it a little to
> see and understand how it really works!

Here is a link to an image of a schematic that contains the transistor
clipper circuit that I used to condition the signal from the magnetic
pickup on my diesel generator. The circuit is in the lower left
corner. The upper diode is probably not needed but doesn't hurt
anything. If the base-emitter junction would fail in the open state ,
it would keep the collector clamped to +5 protecting the circuit
connected to it.

http://www.kinzers.com/don/GenSet/GenSet_Sch_2.jpg





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