# Op amps problem Gain Calculation

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server
Guest

Mon Jul 11, 2005 4:03 pm

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Figaro
Guest

Mon Jul 11, 2005 4:03 pm

"N" <caprice24 at no spam yahoo dot com> wrote in message
news:thvgc1d3gclelta1rmcpj1n86g1432trsh_at_4ax.com...
| Hi,
| Note to view the schematic below, change your font to fixed Courier.
|
|
| I have a problem I am trying to work out on simple Op Amps gain,
| and I am having trouble trying to prove what the gain is.
| I know what the gain is supposed to be (see below), but
| I am stumped as to how to actually go about proving it. When
| I try to setup the Kirchoff node equations I get a really
| ugly polynomial.
|
| I can put the design into a spice deck and prove it, but I want to
| understand the design from an analytical point of view.
|
| Gain = 2*R2/R1 * (1 + R2/Rg)(V2-V1) (GAIN FOR THE OP AMP BELOW)
|
| Now looking at the above equation it is obvious if you
| eliminate resistor Rg, the equation becomes a simple
| differential amplifier gain, which I can easily solve and
| prove. However when you add the positive feedback from
| the output, you get a different Beta for the loop gain
| that is hard to figure out.
|
| Anybody want to take a stab at proving this?
|
| Nick ------------
| | |
| V1---------R1-----------------------R2-------R2---| |
| | | |
| | ___ | |
| | | \ | |
| |--Vn| \ | |
| | \ Vout | Rg
| | |------------------ |
| |--Vp| / |
| | | _ / -----------
| | |
| | |
| V2----------R1-----------------------R2-------R2---|GND
|

write the loop equations, apply the following op-amp tricks:

1) currents into the inputs Vn and Vp are zero because op-amps have very
input impedance
2) Vn-Vp is zero because op-amps have very high gain

and you will get your gain equation

Dan Barlow
Guest

Mon Jul 11, 2005 4:03 pm

roll wrote:
Quote:
Hi,
does anyone knows where i can find (buy) an 2 axis potentiometer 20K?
Roland

joystick guts surplus.

http://home.labridge.com/~wnoble/forsale/Computer_HW_For_Sale.html

Dan Barlow
Guest

Mon Jul 11, 2005 4:03 pm

Synaptic Flow wrote:
Quote:
Hi, I've been given a digital camera to see if I can repair it, had a bit of
a drop. The only thing I can find wrong with it is the built in flash bulb
has become detatched at one end, looks like a bit of a tricky soldering job
but achievable. Question is, is there place I might be able to get a
replacement if this one's vacuum has been punctured/filiment damaged & if
so, how do I go about judging which rating to replace it with?

They're rated in watt-seconds, and any the same length should be a very
similar capacity. I recommend disposable cameras with flash, you can
take them apart yourself after taking all the shots. The film rolls
back into a can as you wind it, so you won't damage it. Any film place
will accept the can for processing, and then you have a free flash
assembly good for making slave flashes or strobes. Some drug store
film places will sell you the empty cameras with flash for \$0.25 each.
-Dan Barlow

Synaptic Flow
Guest

Mon Jul 11, 2005 4:03 pm

"Dan Barlow" <danbarlow_at_radix.net> wrote in message
news:3ef778ee_2_at_vienna7.his.com...
Quote:
Synaptic Flow wrote:
Hi, I've been given a digital camera to see if I can repair it, had a
bit of
a drop. The only thing I can find wrong with it is the built in flash
bulb
has become detatched at one end, looks like a bit of a tricky soldering
job
but achievable. Question is, is there place I might be able to get a
replacement if this one's vacuum has been punctured/filiment damaged &
if
so, how do I go about judging which rating to replace it with?

They're rated in watt-seconds, and any the same length should be a very
similar capacity. I recommend disposable cameras with flash, you can
take them apart yourself after taking all the shots. The film rolls
back into a can as you wind it, so you won't damage it. Any film place
will accept the can for processing, and then you have a free flash
assembly good for making slave flashes or strobes. Some drug store
film places will sell you the empty cameras with flash for \$0.25 each.
-Dan Barlow

Thanks, I've got a couple of old fixed focus units hanging around that could
act for donor

default
Guest

Mon Jul 11, 2005 4:03 pm

If the tach is supposed to help in traction control (input a signal to
the traction motors) the bike tach is useless. RPM from a bike tach
is cheap dirty and easy - as long as you don't care about absolute
values (relative values instead). It is a good solution: cheap dirty

The neatest solution to me (assuming your hobby car uses electric
motors) would be to amplify the signal produced by the motors
themselves. AC couple the signal from the motor amplify it, if
necessary, then just use it to work a tachometer IC like the National
LM2917. The tach circuit shown in the National literature shows a
circuit that biases the LM2917 so it triggers an next to nothing (like
the ripple your traction motors create)

Look at the high side motor brush with a scope. Look at the ripple.
If it is greater than .1 volts (AC coupled scope) then it is enough to
work the tack IC, directly.

Use a gas engine and you can couple via the spark.

I tried the spark but with only one pulse per revolution the
integrating cap was so large that I only dislplayed what the RPM
average was three seconds ago - not good enough for a bike.

I just finished a tach for my motorcyle and used the signal from the
alternator. Works well (twelve pulses per revolution - puts out 30
volts I need <.1 to trigger the LM2917 / LM2907.

Output of the 2917 is a analog voltage/current suitable for a meter or
further signal and control processing.

On 24 Jun 2003 10:49:27 -0700, mlt3_at_lehigh.edu (miketinte) wrote:

Quote:
Hey everyone,

I'm trying to build a traction control system for a small (but
rideable) hobby car. I've been looking for OEM bicycle tachometers,
but haven't been too successful. I was thinking about using small
hobby motors connected to the wheels so they'll spin at the same RPMs,
then just amp that signal and run through a comparator...? Would this
work well (or at all)? If not, does anyone know where I can get some
bike tachs without all the bells and whistles.

Thanks,
Mike

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David Miller
Guest

Mon Jul 11, 2005 4:03 pm

rswww.com do a tachometer counting device, it counts the once per rev pulse
and calculates the speed.

"R. Wink" <rwwink_at_evansville.net> wrote in message
news:93mjfv4cmo09c6i6eltbelov42r9u434kg_at_4ax.com...
Quote:
Weeellll...., you could do the same thing as the BIG car makers do. Add
magnets to the axle hubs
and use a prox switch as a pick up. Run the signals through a comparisons
circuit and apply the
brake on which ever one is the higher number of pulse count/second.
You'll have a "state of the
art" traction control system just like the big guys.
R. Wink

. On 24 Jun 2003 10:49:27 -0700, mlt3_at_lehigh.edu (miketinte) wrote:

Hey everyone,

I'm trying to build a traction control system for a small (but
rideable) hobby car. I've been looking for OEM bicycle tachometers,
but haven't been too successful. I was thinking about using small
hobby motors connected to the wheels so they'll spin at the same RPMs,
then just amp that signal and run through a comparator...? Would this
work well (or at all)? If not, does anyone know where I can get some
bike tachs without all the bells and whistles.

Thanks,
Mike

petrus bitbyter
Guest

Mon Jul 11, 2005 4:03 pm

"ah" <andrew_at_hanvey82.freeserve.co.uk> schreef in bericht
news:bdjlu0\$47i\$1_at_news6.svr.pol.co.uk...
Quote:
Hi
Im beginning work on a project which I will need a RS422 to I2C Converter.
Has anyone ever done anything like this?

Andy

Andy,

I did. That's to say it was RS232 to I2C. I used a MAX232 and a PIC16F73.
For RS422 you will need differential drivers/receivers p.e. MC3487/86. For
the processor a PIC16F873 may be a better choice as it's newer. You will
need to check what protocol is used at the RS422 side. Is it asynchronous,
SDLC, HDLC or another one? You also need to look wether the I2C side has to
be master, slave or both. Unless you have a proper specification of the
protocol and the data format, you will run into a lot of problems.

pieter

Niv
Guest

Mon Jul 11, 2005 4:03 pm

I thought RS422 was an electrical protocol & I2C a data format protocol?
Niv.

"ah" <andrew_at_hanvey82.freeserve.co.uk> wrote in message
news:bdjlu0\$47i\$1_at_news6.svr.pol.co.uk...
Quote:
Hi
Im beginning work on a project which I will need a RS422 to I2C Converter.
Has anyone ever done anything like this?

Andy

Niv
Guest

Mon Jul 11, 2005 4:03 pm

Yes , that's fine, but you need to know the TTL async protocol to before it
can be converted to I2C protocol. I asume it's a UART type message or
something, but one does need to know!
Niv.

"Gary Tait" <taitg_at_hurontel.on.ca> wrote in message
news:d7utfvo2r4joarjoti10gdfpam8nv8gi53_at_4ax.com...
Quote:
On Sat, 28 Jun 2003 19:48:54 +0100, "Niv" <niv_at_ntlworld.com> wrote:

I thought RS422 was an electrical protocol & I2C a data format protocol?
Niv.

It is, hence the need for a two staged process. 1: to convert RS422 to
TTL and the other way round. and 2: to convert the TTL Async to I2C,
in a manner you can access either any I2C device, or a particular one
"ah" <andrew_at_hanvey82.freeserve.co.uk> wrote in message
news:bdjlu0\$47i\$1_at_news6.svr.pol.co.uk...
Hi
Im beginning work on a project which I will need a RS422 to I2C
Converter.
Has anyone ever done anything like this?

Andy

Allan
Guest

Mon Jul 11, 2005 4:03 pm

What a Champ!!!
But what a cool site....
:>

"A Friend" <..> wrote in message news:3f029277\$1_at_clear.net.nz...
Quote:

Michael Munroe
Guest

Mon Jul 11, 2005 4:03 pm

mlt,
If you are an electronics hobbyist then you could do something really cool.
You could get a \$40 rotary optical encoder and mount it to a shaft, and with
some microcontroller work you could make a superb very high resolution
traction control system (and even an energy control system).

-mike

"miketinte" <mlt3_at_lehigh.edu> wrote in message
Quote:
Hey everyone,

I'm trying to build a traction control system for a small (but
rideable) hobby car. I've been looking for OEM bicycle tachometers,
but haven't been too successful. I was thinking about using small
hobby motors connected to the wheels so they'll spin at the same RPMs,
then just amp that signal and run through a comparator...? Would this
work well (or at all)? If not, does anyone know where I can get some
bike tachs without all the bells and whistles.

Thanks,
Mike

Michael Munroe
Guest

Mon Jul 11, 2005 4:03 pm

Miketinte,

When you want to use an electric motor as a taco-meter are you wanting to
a) place the shaft of the electric motor so that its axis is parallel to the
axis of the tire, but the surface of the shaft touches the surface of the
wheel
b) use the motor that drives the wheel as its own tachometer?

-mike

Bob Eager
Guest

Mon Jul 11, 2005 4:03 pm

On Wed, 9 Jul 2003 16:07:58 UTC, Blake Patterson
<bwpatter_at_bellatlantic.net> wrote:

Quote:
I had to take apart my SGI 1600SW flatscreen monitor to clean it out
with distilled water becuase it had been rained on from a leaking duct
with mineralized water. I had to cut through some metal shielding tape
that was used on some internal metal parts to get the screen out. I
want to replace this with some new tape, but Radio Shack does not seem
to carry this thin tape. It's like a strip of adhesive aluminum foil.

What is this stuff actually called and where can I order some online?

You don't say how wide. If not very, look at using the self adhesive
foil used in burgalr alarm systems to stretch across windows...it's
conductive but breaks the circuit when the foil breaks.

--
Bob Eager
rde at tavi.co.uk
PC Server 325*4; PS/2s 9585, 8595, 9595*2, 8580*3,
P70, PC/AT..

Tony 'Nicoya' Mantler
Guest

Mon Jul 11, 2005 4:03 pm

In article <bwpatter-4AF545.12075809072003_at_news.bellatlantic.net>,
Blake Patterson <bwpatter_at_bellatlantic.net> wrote:

: I had to take apart my SGI 1600SW flatscreen monitor to clean it out
: with distilled water becuase it had been rained on from a leaking duct
: with mineralized water. I had to cut through some metal shielding tape
: that was used on some internal metal parts to get the screen out. I
: want to replace this with some new tape, but Radio Shack does not seem
: to carry this thin tape. It's like a strip of adhesive aluminum foil.
:
: What is this stuff actually called and where can I order some online?

You should be able to get aluminum foil tape at any hardware store or home
center, it's usually used for sealing ductwork (as opposed to using ductape,
which is most definatley not good for sealing ductwork - the adhesive on
aluminum foil tape should last much longer).

Cheers - Tony 'Nicoya' Mantler :)

--
Tony "Nicoya" Mantler - Renaissance Nerd Extraordinaire - nicoya_at_apia.dhs.org