12v relay on 3v ??

[Jonathan Kirwan]

On Tue, 06 Sep 2005 03:35:30 -0500,
ahonda55@hotmail-dot-com.no-spam.invalid (ahonda55) wrote:

i made the LM2907 tachometer circuit , and the output goes to the
transistor-relay circuit , but there is the problem of the ripple ,
the relay start bounceing before going ON or Off , i had used a 100uF
capacitor , it is ok but the reaction of the relay becomes little bit
slow , what should i do to remove that ripple.

Well, this is exactly the issue. The larger the capacitor, the longer
the reaction time. Too big and the reaction is too slow. So you must
compromise.

What I think you tried to do is go too far. In making the capacitor
really, really big you made the delay way too long. But then you have
too much ripple. The ripple causes the transistor to switch and
switch and switch way too much when the RPM is near the threshold.

So how to handle that? With the hysteresis resistor I added to the
schematic I posted. Namely, R4. By setting this properly, you can
cause the hysteresis band to be large enough to 'eat up' the ripple.
Of course, this means it switches at one threshold as the RPM rises
and the opposite at a different threshold as the RPM falls back down.
But that may be an acceptable (and even desirable) solution.

that's all about the LM2907 circuit which i will post in the bottom of
this.

Thanks for the circuit!

the second aim of my dreams is (( speed switch )) , using LM2907 to
make it open the 12v relay on a desired RPM and closes it when the
RPM becomes low.
the problems i have are...

i have the 14 pin version and i don't have the circuit for it , i just
have the 8 pin.

By this, I take it that you mean that you physically have 14-pin chips
and do not have the 8-pin chips, but that you can only find 8-pin
circuit examples and cannot find 14-pin circuit examples. Is that
right?

here is all supplies ...
Input voltage 8v or whatever below 12v will work.
the relay is a small 12v relay
i want to make the relay On when the frequency reachs 150 hertz

That helps. Can you tell me what range of switching you can accept?
In other words, if the relay came on at 150Hz, but then switched back
off only when the frequency reached 130Hz, would that be okay? If you
had to set up a rising-switch-on frequency that was different from the
falling-switch-off frequency, what would the two values be?

i want to know how to use the 14 pin instead of the 9 pin and will it
work?

and if you can help me plz send me any circuit drawings not the text
because i can't understand it and sorry for that.

The prior schematic I posted should be read with Notepad or with a
fixed-spaced font like Courier or Prestige Elite. Of course, even
then, it takes some getting used to. I included an hysteresis
resistor in it, R4, which I believe would have helped out.

here is the circuit....

http://www.niksula.cs.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho-big.gif


and the relay photo by me camera
[img:81ff149aa6]http://img386.imageshack.us/img386/5472/image12nh.jpg[/img:81ff149aa6]

Thank you very much and really sorry to ask all that help , but this
is the biginner me , need help 24/7 in something i ike to do.
Thank you again

I looked at the relay and I really do NOT know what it needs to drive
the 12V side of it. If you can point to a data sheet, I'd sure that
may help out. But since it appears you already tried driving it with
the LM2907, I think we can assume to continue that idea for now.

Jon

 

[Jonathan Kirwan]

On Tue, 06 Sep 2005 03:35:30 -0500,
ahonda55@hotmail-dot-com.no-spam.invalid (ahonda55) wrote:

here is the circuit....


http://www.niksula.cs.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho-big.gif

Oh, another problem. That schematic is for an LM2917! Not an LM2907.
Please note that the LM2907 includes an internal zener.

So... are you working with 14-pin LM2907 or a 14-pin LM2917?

Jon

 

[Jonathan Kirwan]

On Tue, 06 Sep 2005 03:35:30 -0500,
ahonda55@hotmail-dot-com.no-spam.invalid (ahonda55) wrote:

here is the circuit....


http://www.niksula.cs.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho-big.gif

Also, I should have asked -- what is your RPM sensor? Is it a
magnetic pickup? Or?

In other words, that above schematic shows three resistors, a
capacitor, and a zener all being used to condition the input signal to
the LM2907/LM2917. Did that part of the circuit work out for you?

Jon

 

[ehsjr]

Jonathan Kirwan wrote:

On Mon, 05 Sep 2005 05:40:29 GMT, ehsjr <ehsjr@bellatlantic.net
wrote:


Jonathan Kirwan wrote:

On Sun, 04 Sep 2005 05:07:57 GMT, ehsjr <ehsjr@bellatlantic.net
wrote:



snip
The single transistor circuit is no good for what you want.
Go back and read Ralph Mowrey's post of 9/2. He correctly
identified a comparator circuit, and anticipated you wanting
to adjust the voltage. Here is a schematic and explanation.
I went into a lot of details - I apologize if I mention
material you already know..


I am curious why you think that the LM2907 doesn't already have the
necessary components for the OP's need.

I said nothing whatsoever about the LM2907.


No, you didn't. That's what confuses me. Here is a post from the op:

You quote (below) a post to which I did *NOT* reply. You
snipped my quote of the post to which I did reply. Why?

I made an RPM for my car using LM2907 , it's output is 1 to 3 volts
i need to make this output drive a 12v relay , but the main problem is
that i need to drive the relay on exactly > 3v , i mean 3v , 3.1 ,
3.2 so on.


Do you see the mention of the LM2907??


It already includes an opamp

that can be used as a comparator (with many examples provided on the
data sheet) and a 50mA floating transistor at its output.

By choosing the C and R connected to the node common to the
non-inverting input and the charge pump at pin 3, the OP can select
the desired F->V conversion desired and presented for comparison to
the opamp. By selecting the resistor divider, the inverting input can
adjusted to set the switch point. Another resistor can set the
desired hysteresis, if any. Finally, the load (relay) is connected
between the automotive supply rail and the internal floating
transistor collector (emitter tied to ground, for example.)

Under this circumstance, assuming that the transistor is capable of
handling the relay (and I don't know that it cannot, at this point,
with the data sheet specifically mentioning that it is designed to
directly drive relays), it should be done with what's already there in
the LM2907 except for a few external passives.

What do I miss, here?

Jon

I don't know what you're missing, if anything. However, I
doubt the OP can follow the datasheet and work out the
circuit without help. The OP said "i am confused cuz i am
still biginner"

I think an explicit schematic with values and description
was necessary, based on that. I think guessing about
whether the chip can drive some unnamed relay is a bad
thing, which could lead to destruction of the existing
circuit. In fact, any changes to it could do that, due
to errors that a beginner should be expected to make.
The OP already experienced a burned out pot, although
(I assume) not in the original circuit. Somebody proposed
a one transistor circuit, apparently overlooking the 3
volt requirement as the OP intended it. That is what led
eventually to the burned out pot.


Well, go back and read that post from the OP and the others and help
me understand. I think an LM2907 is being used. But?? I'm willing
to be wrong about that.

Jon

You snipped the quoted material to from my reply. My reply
addressed the quoted material. That is the source of your
confusion.

The problem I replied to:
"i have made the transistor - relay circuit , it is working
very good but there is a small problem , i wanted to
adjust the relay open volt. i mean that i need to make the
relay open on 3v or 2.5 etc." Note that the issue is in
the subject line, and has been mentioned numerous
times by the OP.

It does not matter what chip or circuit provides the varying
input voltage, the single transistor circuit described in the
thread *cannot* give him either precision or adjustability to
control the relay at a specific voltage.

Why do you think an LM2907 *MUST* be mentioned in replying
to that problem?

Ed

 

[Jonathan Kirwan]

On Wed, 07 Sep 2005 03:57:05 GMT, ehsjr <ehsjr@bellatlantic.net>
wrote:

Jonathan Kirwan wrote:
On Mon, 05 Sep 2005 05:40:29 GMT, ehsjr <ehsjr@bellatlantic.net
wrote:


Jonathan Kirwan wrote:

On Sun, 04 Sep 2005 05:07:57 GMT, ehsjr <ehsjr@bellatlantic.net
wrote:



snip
The single transistor circuit is no good for what you want.
Go back and read Ralph Mowrey's post of 9/2. He correctly
identified a comparator circuit, and anticipated you wanting
to adjust the voltage. Here is a schematic and explanation.
I went into a lot of details - I apologize if I mention
material you already know..


I am curious why you think that the LM2907 doesn't already have the
necessary components for the OP's need.

I said nothing whatsoever about the LM2907.


No, you didn't. That's what confuses me. Here is a post from the op:


You quote (below) a post to which I did *NOT* reply. You
snipped my quote of the post to which I did reply. Why?

I had been reading a number of the posts and had decided that the OP
was doing all kinds of crazy things with the LM2907. In other words,
using external transistors with it, etc. Despite the fact that it
already had one included. The central thesis I gathered was that an
LM2907 was needed to be the freq->voltage converter, as he already had
it almost working and had the parts in hand. The transistor material
in the original post, I decided, was only talking about one aspect of
some much longer experience the OP was having -- I particularly
decided this after reading the other OP post which I cited. I chose
to snip, because I wanted to focus on my question and not upon a lot
of material I was beginning to see as ancillary.

I still do see it that way, in fact.

I made an RPM for my car using LM2907 , it's output is 1 to 3 volts
i need to make this output drive a 12v relay , but the main problem is
that i need to drive the relay on exactly > 3v , i mean 3v , 3.1 ,
3.2 so on.


Do you see the mention of the LM2907??


It already includes an opamp

that can be used as a comparator (with many examples provided on the
data sheet) and a 50mA floating transistor at its output.

By choosing the C and R connected to the node common to the
non-inverting input and the charge pump at pin 3, the OP can select
the desired F->V conversion desired and presented for comparison to
the opamp. By selecting the resistor divider, the inverting input can
adjusted to set the switch point. Another resistor can set the
desired hysteresis, if any. Finally, the load (relay) is connected
between the automotive supply rail and the internal floating
transistor collector (emitter tied to ground, for example.)

Under this circumstance, assuming that the transistor is capable of
handling the relay (and I don't know that it cannot, at this point,
with the data sheet specifically mentioning that it is designed to
directly drive relays), it should be done with what's already there in
the LM2907 except for a few external passives.

What do I miss, here?

Jon

I don't know what you're missing, if anything. However, I
doubt the OP can follow the datasheet and work out the
circuit without help. The OP said "i am confused cuz i am
still biginner"

I think an explicit schematic with values and description
was necessary, based on that. I think guessing about
whether the chip can drive some unnamed relay is a bad
thing, which could lead to destruction of the existing
circuit. In fact, any changes to it could do that, due
to errors that a beginner should be expected to make.
The OP already experienced a burned out pot, although
(I assume) not in the original circuit. Somebody proposed
a one transistor circuit, apparently overlooking the 3
volt requirement as the OP intended it. That is what led
eventually to the burned out pot.


Well, go back and read that post from the OP and the others and help
me understand. I think an LM2907 is being used. But?? I'm willing
to be wrong about that.

Jon


You snipped the quoted material to from my reply. My reply
addressed the quoted material. That is the source of your
confusion.

Yes. And it is my belief that you were addressing yourself at
cross-purposes to the OP's real desire. I was merely saying so. Yes,
you correctly addressed yourself to a narrow post, but there was a
larger picture already emerging by then. That is what I was talking
about and I was trying to understand if you understood that larger
picture. Or if I was missing something important, too. Either way.

The problem I replied to:
"i have made the transistor - relay circuit , it is working
very good but there is a small problem , i wanted to
adjust the relay open volt. i mean that i need to make the
relay open on 3v or 2.5 etc." Note that the issue is in
the subject line, and has been mentioned numerous
times by the OP.

Yes, yes. And if you take a fuller view of all the posts, I am hoping
that you will see and agree with me that the OP is already having some
success with using the LM2907 for the f->v conversion and that it
would probably be better to stay with this approach. Or else tell me
why you think I'm wrong about it. Which I very well could be.

It does not matter what chip or circuit provides the varying
input voltage, the single transistor circuit described in the
thread *cannot* give him either precision or adjustability to
control the relay at a specific voltage.

yes, but the LM2907 that appears to be the source of that voltage
already includes an opamp in it. And a floating driver transistor.
Don't you think it would be better to see about using those tools in
the existing toolbox?

Why do you think an LM2907 *MUST* be mentioned in replying
to that problem?

I don't. I was only curious why you weren't looking at what the OP
later pointed out was being used. I think I understand why now, given
your answer above.

Just asking. And you've answered. Thanks.

Jon

 

[ehsjr]

ahonda55 wrote:

Hey guys , you are impressing me with your replys. you are talking as
if it is your circuit not my circuit , thank you very much thank you
, really thank you.

i made this ..
http://img326.imageshack.us/img326/7944/image28ie.jpg
----
i know that LM2907 has a comparator in it , but there is two problems
with me , the same problems with LM324 ..
1- i can't find the 8 pin version of the LM2907 here.
2- i have the data sheet of many IC's but i don't know how to realize
the circuits mentioned there.
----
i have LM741 , will it work ? if yes would anyone show me a circuit
for my usage .
i think i need so much time to "design" a circuit , so plz do it for
me.
----
special thanks to ehsjr for his great work like all of you .
but i don't understand your diagram , i am not proffeccional like you
man !
if you can plz draw a simple circuit for LM327 or LM741 the most
simple.
----



[size=18:de7a5e85d3]
Thank you[/size:de7a5e85d3]

Make sure you view this in courier font.

0 + 12 V
|
+---------+----+------------+
| | | |
| | ((|| ------- <== banded end
| | ((||Relay / \ Diode
| | ((|| --- 1N4001
\ | | |
/ - |\ | +------------+
\<----2| \7 |
/50K | \ /collector
\ |741}6----/\/\/\---| TIP120
| | / 2.2K \emitter
Input-- | ----3| /4 |
| + |/ | |
| | |
+---------+-----------------+
|
Gnd

Shown above is the 741 op-amp circuit with the pin
numbers. You connect the point marked Input
to the varying 3 volt signal. The TIP120 transistor
looks like this:

------
| 0 |
|______|
/_____/|
| ||
| ||
|_____|/
| | |
| | |
b c e

Look at the datasheet at:
http://www.fairchildsemi.com/ds/TI/TIP120.pdf

For hysteresis, you add a high value resistor connected
to pin 6 and to pin 2 of the 741. Hysteresis will set the
difference between the voltage at which the relay energizes
and de-energizes in a small range, and prevent relay chatter.
The higher the value of the resistor between the pins, the
smaller the hysteresis range. Before you add the resistor,
get the circuit working. Hysteresis will be needed when the
RPM is very close to 3000. Adjust the circuit to just
energize the relay when a solid 3 volts is applied to the
input. Once you have the circuit working that way, connect
it to your RPM circuit (3 connections - Input, Gnd and +12)
and then see if you get chatter at 3000 RPM. If you
do, add the resistor. As a total guess, I'd use a 100K
resistor for hysteresis.

Later on, when you want to add adjustable on and off
voltages, you might be able to do it with a potientiometer
in the hysteresis circuit. If you use an LM324,
you'll have 3 extra op-amps. One can be used to set
the voltage at which the relay de-energizes, in conjunction
with another transistor. You can use all 4 op-amps
to control the relay, and to have 4 indicator LEDs,
like this: Led1 - idle; led2 normal working RPM;
led3 - high rpm and led4 - redline

Ed

Ed

 

[ahonda55]

Dear Jonathan you are GREAT , i never seen someone like you in a
forum.
and all of this forum are great people
and thank you mike very much

By this, I take it that you mean that you physically have 14-pin
chips and do not have the 8-pin chips, but that you can only find

8-pin

circuit examples and cannot find 14-pin circuit examples. Is that
right?

yes, that's right , i looked closely to the data sheet , and made a
comparison for the 8 pin and the 14 pin IC's here is
---------------
8pin 14pin
1 1
2 2
3 3+4
4 4
5 8
6 9
7 10
8 11+12
---------------
is tha true and will work with the speed switch circuit ??

That helps. Can you tell me what range of switching you can accept?
In other words, if the relay came on at 150Hz, but then switched
back
off only when the frequency reached 130Hz, would that be okay? If
you
had to set up a rising-switch-on frequency that was different from
the
falling-switch-off frequency, what would the two values be?

I need to make the values 150 and 146 (4500 RPM and 4400 RPM)

So... are you working with 14-pin LM2907 or a 14-pin LM2917?

I have LM2907N with 14 pin .

Also, I should have asked -- what is your RPM sensor? Is it a
magnetic pickup? Or?

If you are interested ic cars like me you know there is the destebutor
that sends a signal to the coil to make the spark . that signal is
negative , and that signal is the regular signal that any tachometer
used in cars connected to.

Thanks a lot , and here is a small video for my working LED
tachometer

http://ahonda55.8m.net/MyMovie.wmv

-----
Note that i am not the designer of the tachometer circuit , i just
build what is mentioned in this nice page ... thanks to - Paul Hill
http://www.niksula.cs.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho.html

 

[ehsjr]

ehsjr wrote:

ahonda55 wrote:

Hey guys , you are impressing me with your replys. you are talking as
if it is your circuit not my circuit , thank you very much thank you
, really thank you.

i made this ..
http://img326.imageshack.us/img326/7944/image28ie.jpg
----
i know that LM2907 has a comparator in it , but there is two problems
with me , the same problems with LM324 ..
1- i can't find the 8 pin version of the LM2907 here.
2- i have the data sheet of many IC's but i don't know how to realize
the circuits mentioned there.
----
i have LM741 , will it work ? if yes would anyone show me a circuit
for my usage .
i think i need so much time to "design" a circuit , so plz do it for
me.
----
special thanks to ehsjr for his great work like all of you .
but i don't understand your diagram , i am not proffeccional like you
man !
if you can plz draw a simple circuit for LM327 or LM741 the most
simple.
----


[size=18:ff30de3a9b] Thank you[/size:ff30de3a9b]


Make sure you view this in courier font.

0 + 12 V
|
+---------+----+------------+
| | | |
| | ((|| ------- <== banded end
| | ((||Relay / \ Diode
| | ((|| --- 1N4001
\ | | |
/ - |\ | +------------+
\<----2| \7 |
/50K | \ /collector
\ |741}6----/\/\/\---| TIP120
| | / 2.2K \emitter
Input-- | ----3| /4 |
| + |/ | |
| | |
+---------+-----------------+
|
Gnd

Shown above is the 741 op-amp circuit with the pin
numbers. You connect the point marked Input
to the varying 3 volt signal. The TIP120 transistor
looks like this:

------
| 0 |
|______|
/_____/|
| ||
| ||
|_____|/
| | |
| | |
b c e

Look at the datasheet at:
http://www.fairchildsemi.com/ds/TI/TIP120.pdf

For hysteresis, you add a high value resistor connected
to pin 6 and to pin 2 of the 741. Hysteresis will set the
difference between the voltage at which the relay energizes
and de-energizes in a small range, and prevent relay chatter.
The higher the value of the resistor between the pins, the
smaller the hysteresis range. Before you add the resistor,
get the circuit working. Hysteresis will be needed when the
RPM is very close to 3000. Adjust the circuit to just
energize the relay when a solid 3 volts is applied to the
input. Once you have the circuit working that way, connect
it to your RPM circuit (3 connections - Input, Gnd and +12)
and then see if you get chatter at 3000 RPM. If you
do, add the resistor. As a total guess, I'd use a 100K
resistor for hysteresis.

Later on, when you want to add adjustable on and off
voltages, you might be able to do it with a potientiometer
in the hysteresis circuit. If you use an LM324,
you'll have 3 extra op-amps. One can be used to set
the voltage at which the relay de-energizes, in conjunction
with another transistor. You can use all 4 op-amps
to control the relay, and to have 4 indicator LEDs,
like this: Led1 - idle; led2 normal working RPM;
led3 - high rpm and led4 - redline

Ed

Ed

Duh! Applied positive feedback to the - input.
Fixing that and adding hysteresis resistor.

0 + 12 V
|
+------------+------+------------+
| | | |
| | ((|| ------- <== banded end
| | ((||Relay / \ Diode
| | ((|| --- 1N4001
| | | |
| - |\ | +------------+
Input-- | -------2| \7 |
| | \ /emitter
\ |741}6---+---/\/\/\---| TIP32C
/50K | / | 2.2K \collector
\<---+---3| /4 \ |
/ | + |/ | / 100K** |
\ | | \ |
| | | / |
| | | | |
| +------ | ----+ |
| | |
+------------+-------------------+
|
Gnd

Shown above is the 741 op-amp circuit with the pin
numbers. You connect the point marked Input
to the varying 3 volt signal. The TIP120 transistor
looks like this:

------
| 0 |
|______|
/_____/|
| ||
| ||
|_____|/
| | |
| | |
b c e

Look at the datasheet at:
http://www.fairchildsemi.com/ds/TI/TIP32C.pdf


**For hysteresis, you add a high value resistor connected
to pin 6 and to pin 3 of the 741. Hysteresis will set the
difference between the voltage at which the relay energizes
and de-energizes in a small range, and prevent relay chatter.
The higher the value of the resistor between the pins, the
smaller the hysteresis range. Before you add the resistor,
get the circuit working. Hysteresis will be needed when the
RPM is very close to 3000. Adjust the circuit to just
energize the relay when a solid 3 volts is applied to the
input. Once you have the circuit working that way, connect
it to your RPM circuit (3 connections - Input, Gnd and +12)
and then see if you get chatter at 3000 RPM. If you
do, add the resistor. As a total guess, I'd use a 100K
resistor for hysteresis.

Later on, when you want to add adjustable on and off
voltages, you might be able to do it with a potientiometer
in the hysteresis circuit. If you use an LM324,
you'll have 3 extra op-amps. One can be used to set
the voltage at which the relay de-energizes, in conjunction
with another transistor. You can use all 4 op-amps
to control the relay, and to have 4 indicator LEDs,
like this: Led1 - idle; led2 normal working RPM;
led3 - high rpm and led4 - redline

Ed

 

[ehsjr]

Jonathan Kirwan wrote:

Just asking. And you've answered. Thanks.

Jon

I snipped all but the end of your post. I assume
it means we can move on to something of substance.

How do you know that the relay he is using will
draw less than 50 mA?

Ed

 

[Jonathan Kirwan]

On Wed, 07 Sep 2005 14:34:28 GMT, ehsjr <ehsjr@bellatlantic.net>
wrote:

Jonathan Kirwan wrote:

Just asking. And you've answered. Thanks.

Jon

I snipped all but the end of your post. I assume
it means we can move on to something of substance.

Yes, I was only curious if I was mistaken in my own ability to read
the OP, comprehensively.

How do you know that the relay he is using will
draw less than 50 mA?

Ed, I've no idea at all. And I've mentioned the issue. He provided a
photograph of it and I wasn't able to find a data sheet on the unit,
given the designations I could read. So I just don't know. Also, the
output sink capability of 50mA has a minimum of 40mA, to be honest,
but it is continuous assuming dissipation issues don't get in the way.
The BJT in the LM2907 is specifically noted on the first page of the
data sheet as being appropriate for driving relays and solenoids, so
it may be able to handle short periods of higher current to start the
relay. 28V is the higher voltage allowed on the collector, relative
to ground potentials, if memory serves.

He has apparently copied a circuit, regarding the LM2907 (actually, an
LM2917), but that circuit did NOT include the use of a relay in it.
Instead, it developed a voltage that could be used elsewhere. This is
why I think the OP started out asking about comparing a voltage and
not about taking better advantage of the LM2907. But the LM2907 has
the ability to do more, that the OP didn't really know about. So, the
upshot of all this is that I think it is safe to assume that the relay
has not been tested using the LM2907 BJT.

However, it should be a simple matter to include an external BJT
tethered to the internal one and the opamp inside the package to
achieve a larger goal, if that is needed.

But I'm also only a relatively inexperienced hobbyist, Ed. So I'm
learning as I go here.

Jon

 

[ahonda55]

man you know , you have some very nice ideas , thanks a lot .
but PLEASE try to draw a simple schematis or tell me how to deal with
the text schematics ,i copied it into Notepad but it appeared same as
the Internet Explorer , i don't understand anything from the drawing


Thank you very much

 

[ahonda55]

i want to know something , what is the difference between the
inverting and non-inverting input in the 741 plz ??

thank you

 

[Jonathan Kirwan]

On Wed, 07 Sep 2005 03:35:35 -0500,
ahonda55@hotmail-dot-com.no-spam.invalid (ahonda55) wrote:

Dear Jonathan you are GREAT , i never seen someone like you in a
forum.

Oh, geez. I'm just a darned hobbyist, for gosh sake. You are
probably doing more in a short time than I do in months of playing
around. I'm just trying to read the bits and pieces and figure out
what your situation is from all that. I've been lucky.

and all of this forum are great people
and thank you mike very much

I think they are great people. Sometimes, they will spend a wonderful
amount of excellent time explaining things.

By this, I take it that you mean that you physically have 14-pin
chips and do not have the 8-pin chips, but that you can only find
8-pin
circuit examples and cannot find 14-pin circuit examples. Is that
right?

yes, that's right , i looked closely to the data sheet , and made a
comparison for the 8 pin and the 14 pin IC's here is
---------------
8pin 14pin
1 1
2 2
3 3+4
4 4
5 8
6 9
7 10
8 11+12
---------------
is tha true and will work with the speed switch circuit ??

Well, the 14-pin version is perfectly fine. I see no problem in using
it for anything the 8-pin version could do. It's just a matter of
figuring out the details of what you need to achieve and seeing if the
LM2907N can get there for you or if you need a little extra added to
it.

That helps. Can you tell me what range of switching you can accept?
In other words, if the relay came on at 150Hz, but then switched
back
off only when the frequency reached 130Hz, would that be okay? If
you
had to set up a rising-switch-on frequency that was different from
the
falling-switch-off frequency, what would the two values be?

I need to make the values 150 and 146 (4500 RPM and 4400 RPM)

Okay. So it switches the relay ON at 150Hz (4500 RPM) and can be
allowed to keep it ON until it falls back to 146 Hz (4400 RPM.)

That is tight, I suspect. And it DOES suggest a problem with using
the LM2907N.

So... are you working with 14-pin LM2907 or a 14-pin LM2917?

I have LM2907N with 14 pin .

Understood. That's what I imagined.

Also, I should have asked -- what is your RPM sensor? Is it a
magnetic pickup? Or?

If you are interested ic cars like me you know there is the destebutor
that sends a signal to the coil to make the spark . that signal is
negative , and that signal is the regular signal that any tachometer
used in cars connected to.

Thanks a lot , and here is a small video for my working LED
tachometer

http://ahonda55.8m.net/MyMovie.wmv

I'd rather not watch it on this machine -- it is my work system and I
don't run movies of any kind on it for any reason. But I may look at
it elsewhere, later on.

Note that i am not the designer of the tachometer circuit , i just
build what is mentioned in this nice page ... thanks to - Paul Hill
http://www.niksula.cs.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho.html

I see. Did you set it up with the LED bar, too? Great.

Some further questions, though:

(1) Do you need (or want) to keep that LED bargraph operating, while
at the same time having something to drive that relay at 4500 RPM?

(2) Are you currently using an 8V regulated supply, as appears to be
suggested in that web page? Do you want to keep using it?

(3) Did the circuit on Paul's web page actually work for you,
regarding your spark signal conditioning? (I gather you will say
"YES" to this, but I just want to make absolutely sure about it.)

(4) You say that 150Hz is 4500 RPM. This suggests to me that you get
2 pulses per revolution. Is this an accurate understanding of the
situation?

(5) what are the specifications for your relay? I can't find a data
sheet on it and I don't know what the required currents might be. This
is important to know, in order to guess whether or not the internal
circuitry of the LM2907 can handle it. Or we could just play it safe
and specify an external BJT, I suppose.

....

The current into C1 is Vcc * f * C1, which itself must be less than or
equal to the minimum guaranteed current of 140uA. This means less
than 116nF at a 8V supply, or so, at 150Hz. So I generally agree with
the choice of 47nF in that circuit, which implies the need for about
56uA, which is well within the capabilities of the LM2907. It also
supports going to 11,000 RPM before reaching the analog voltage limit
of 8V. So you have a lot of range available, too.

However, and this won't exactly be clear to you right now (or me,
either) without thinking further along about the circuit (and I'll get
there), a faster response and lower ripple/hysteresis both suggest
using currents closer to the limit of 140uA, than further away. So
I'm guessing initially at recommending changing it out for 100nF
(0.1uF), instead. This will require some 120uA of the 140uA, but that
is within its ability, too. However, this will limit your maximum to
about 5200 RPM before reaching 8V. If you don't mind that limit, I'd
imagine it is better to use the 100nF capacitor as C1.

So what should R1 be? Well, smaller is better if you want a faster
response, since it the time constant is decided by R1 and the
filtering capacitor, C2 (not C1.) Since the ripple is NOT a function
of R1 but is a function of C2, you want C2 to be as big as fits your
need and you want R1 to be as small as needed to get a fast enough
response. But R1 needs to be larger in order to develop a reasonable
voltage, too. So there is some thinking to be done here.

The maximum usable value for R1 is:

R1 = 1/(f*C1)

This means about 57k ohm in the case of C1=100nF and fmax=175Hz (which
is limited by the 140uA guarantee of the LM2907.)

So let's start out with R1 = 47k ohm, which is a standard value, and
see where that takes us.

You mentioned 150Hz at 4500 RPM. And you want the hysteresis to be
only 100 RPM. So this means:

175 Hz 5250 RPM 6.58V
150 Hz 4500 RPM 5.64V
146.7Hz 4400 RPM 5.51V (or 5.49V at 146Hz)

As you can see, there is only about 0.13V-0.15V difference between one
side of the hysteresis band and the other. I'm speaking from
ignorance on this, but I'd guess that a value of 1/3rd of this amount,
or about 50mV, would make a good guess at an acceptable ripple
voltage.

The ripple calculation (the equation is in the data sheet) suggests
that C2 should be about 1uF in size. Actually, I get 1.14uF from the
calculation, but I suspect we can live with 1uF. This is good, as it
is a reasonable value. It also, taken together with R1=47k, appears
to suggest a response time in the tens of milliseconds, so this may be
fast enough for your needs. You might even be able to get by with 2uF
for C2, if you want to lower the ripple voltage a bit. You could also
lower R1 to 33k, if you wanted even faster response times.

Which gets to another question:

(6) What kind of response speed is required?

Jon

 

[Don Bowey]

On 9/7/05 9:35 AM, in article Ze2dnb6MKc9Gi4LeRVn_vQ@giganews.com,
"ahonda55" <ahonda55@hotmail-dot-com.no-spam.invalid> wrote:

man you know , you have some very nice ideas , thanks a lot .
but PLEASE try to draw a simple schematis or tell me how to deal with
the text schematics ,i copied it into Notepad but it appeared same as
the Internet Explorer , i don't understand anything from the drawing

Thank you very much

In Explorer, and maybe Notepad, go into the Preferences and change the
default font to Courier. The text schematics will display as they should.

Don

 

[Jonathan Kirwan]

On Wed, 07 Sep 2005 11:35:40 -0500,
ahonda55@hotmail-dot-com.no-spam.invalid (ahonda55) wrote:

i want to know something , what is the difference between the
inverting and non-inverting input in the 741 plz ??

When a signal moves in one direction on the non-inverting input, then
the output will move in the same direction. When a signal moves in a
particular direction on the inverting input, then the output will move
in the opposite direction. The inverting input is often used to
provide "negative feedback" for stability and setting the gain.

Jon

 

[Jonathan Kirwan]

On Wed, 07 Sep 2005 11:35:39 -0500,
ahonda55@hotmail-dot-com.no-spam.invalid (ahonda55) wrote:

man you know , you have some very nice ideas , thanks a lot .
but PLEASE try to draw a simple schematis or tell me how to deal with
the text schematics ,i copied it into Notepad but it appeared same as
the Internet Explorer , i don't understand anything from the drawing

When I get to the point of doing another schematic for you to
consider, I'll put it up as a graphic on a web page for you. Or do
you have a copy of LTSpice from Linear on your computer?

Jon

 

[ehsjr]

Jonathan Kirwan wrote:

On Wed, 07 Sep 2005 14:34:28 GMT, ehsjr <ehsjr@bellatlantic.net
wrote:


Jonathan Kirwan wrote:


Just asking. And you've answered. Thanks.

Jon

I snipped all but the end of your post. I assume
it means we can move on to something of substance.


Yes, I was only curious if I was mistaken in my own ability to read
the OP, comprehensively.


How do you know that the relay he is using will
draw less than 50 mA?


Ed, I've no idea at all. And I've mentioned the issue. He provided a
photograph of it and I wasn't able to find a data sheet on the unit,
given the designations I could read. So I just don't know. Also, the
output sink capability of 50mA has a minimum of 40mA, to be honest,
but it is continuous assuming dissipation issues don't get in the way.
The BJT in the LM2907 is specifically noted on the first page of the
data sheet as being appropriate for driving relays and solenoids, so
it may be able to handle short periods of higher current to start the
relay. 28V is the higher voltage allowed on the collector, relative
to ground potentials, if memory serves.

He has apparently copied a circuit, regarding the LM2907 (actually, an
LM2917), but that circuit did NOT include the use of a relay in it.
Instead, it developed a voltage that could be used elsewhere. This is
why I think the OP started out asking about comparing a voltage and
not about taking better advantage of the LM2907. But the LM2907 has
the ability to do more, that the OP didn't really know about. So, the
upshot of all this is that I think it is safe to assume that the relay
has not been tested using the LM2907 BJT.

However, it should be a simple matter to include an external BJT
tethered to the internal one and the opamp inside the package to
achieve a larger goal, if that is needed.

But I'm also only a relatively inexperienced hobbyist, Ed. So I'm
learning as I go here.

Jon

How did you view the relay? When I click the link he posted,
I get to what I presume is the home page for ImageShack, but
I can't figure out how to get to the image from there.

Regarding the transistor, I usually include something like
a TIPxxx with "muscle" when I don't know what a poster is
using for the relay. I hope we're all learning as we go.
I suppose the only ones who don't are those who think they
know it all already.

Ed

 

[Jonathan Kirwan]

On Thu, 08 Sep 2005 04:23:36 GMT, ehsjr <ehsjr@bellatlantic.net>
wrote:

How did you view the relay? When I click the link he posted,
I get to what I presume is the home page for ImageShack, but
I can't figure out how to get to the image from there.

Try:
http://img386.imageshack.us/img386/5472/image12nh.jpg

It works for me.

Jon

 

[Terry Pinnell]

ehsjr <ehsjr@bellatlantic.net> wrote:

Jonathan Kirwan wrote:

How did you view the relay? When I click the link he posted,
I get to what I presume is the home page for ImageShack, but
I can't figure out how to get to the image from there.

Ed: He mentioned it in this follow up post:
news:utidnRKx0bVfD4beRVn_vQ@giganews.com
as follows:
"and the relay photo by me camera
[img:81ff149aa6]http://img386.imageshack.us/img386/5472/image12nh.jpg[/img:81ff149aa6]"

--
Terry Pinnell
Hobbyist, West Sussex, UK

 

[ahonda55]

(1) Do you need (or want) to keep that LED bargraph operating, while

at the same time having something to drive that relay at 4500 RPM?

it doesn't matter , i fact i made anothe freq.>voltage circuit like
the one in paul's page.

2) Are you currently using an 8V regulated supply, as appears to be

suggested in that web page? Do you want to keep using it?

I use it now , but i can use anything else , electronic parts are
cheap here!!

3) Did the circuit on Paul's web page actually work for you,
regarding your spark signal conditioning? (I gather you will say
"YES" to this, but I just want to make absolutely sure about it.)

YES

(4) You say that 150Hz is 4500 RPM. This suggests to me that you get

2 pulses per revolution. Is this an accurate understanding of the
situation?

i got that from Paul's page , and it is logically true.

5) what are the specifications for your relay? I can't find a data
sheet on it and I don't know what the required currents might be.
This
is important to know, in order to guess whether or not the internal

circuitry of the LM2907 can handle it. Or we could just play it safe

and specify an external BJT, I suppose

i still can't find any info. about it , but it is safe to play.

6) What kind of response speed is required?

i have tested the LM2907 circuit with the transistor - relay circuit
in my car yesterday , i got that the response should be slow to let
the engine RPM go down.

In Explorer, and maybe Notepad, go into the Preferences and change
the
default font to Courier. The text schematics will display as they
should.

thanks , i have tryed it but nothing happenned.

When I get to the point of doing another schematic for you to
consider, I'll put it up as a graphic on a web page for you. Or do
you have a copy of LTSpice from Linear on your computer?

thank you very much , i don't have it but i will try to search for
it.

i have now in my car 20 LED's tachometer ,, here is a photo for the
circuit....


http://img146.imageshack.us/img146/868/dsc044706zn.jpg

Thanks a lot , your answers are more that my expectations, really
thanks , i know that i have asked too many questions but i have
learned so many things from you.