looking for a timer circuit

W

Wayne

Guest
I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading. This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC. Any help is
appreciated.

Wayne
 
Wayne wrote:
I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading. This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC. Any help is
appreciated.

Wayne
Click to expand...
google on:
"sample and hold" schematic

That should bring up a fair number of results.

HTH
 
On Mar 11, 8:23 am, Randy Day <randy....@shaw.cax> wrote:
Wayne wrote:

I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading.  This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC.  Any help is
appreciated.

Wayne

google on:
"sample and hold" schematic

That should bring up a fair number of results.

HTH
Click to expand...
I have (and still am) looking through pages of google results. So
far, nothing that looks usable to me :^). I'm trying to find a
circuit that will stabilize an air/fuel ratio gauge display (a series
of LEDs). The gauge takes its input from an O2 sensor in the exhaust
header (single wire type). The o2 sensor varies it's output from 0VDC
to 1VDC based on it's reading. The problem with the gauge is it
samples too frequently and the display is almost useless. If I could
build something that takes the output from the o2 sensor and 'level'
it (only take 1 reading per second and output that reading to the
gauge until the next reading), I think it would stabilize the display
and make it more usable.

Thanks,

Wayne
 
On Tue, 11 Mar 2008 07:37:17 -0700 (PDT), Wayne
<waynelewis@gmail.com> wrote:
..
..
..

I'm trying to find a
circuit that will stabilize an air/fuel ratio gauge display (a series
of LEDs). The gauge takes its input from an O2 sensor in the exhaust
header (single wire type). The o2 sensor varies it's output from 0VDC
to 1VDC based on it's reading. The problem with the gauge is it
samples too frequently and the display is almost useless. If I could
build something that takes the output from the o2 sensor and 'level'
it (only take 1 reading per second and output that reading to the
gauge until the next reading), I think it would stabilize the display
and make it more usable.
Click to expand...
---
View in Courier:


..[O2 SENSOR]---[ADC]---[LATCH]---[DAC]---[DISPLAY]
.. | |
..[1s CLOCK]------+--------+


--
JF
 
"Wayne" <waynelewis@gmail.com> wrote in message
news:5e046560-34b8-4d22-8396-da12876bf192@m44g2000hsc.googlegroups.com...
I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading. This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC. Any help is
appreciated.

Wayne
Click to expand...

You may instead want a way to average the result. Otherwise, you end up with
the 'random' result being displayed for 1 sec, followed by another random
result, etc.

You can do this with a low pass filter, perhaps. The simplest is a resistor
from input to output, with a capacitor from output to ground. The values to
use are dependent on how much you want to smooth the output. If you want the
output to average out at 1Hz or less, then you need components so that

R * C = 0.16 = (1/(2*PI))

So, if you use a 1uF capacitor, you would need about 160k of resistance.

So, here is the circuit:

160k
sensor ---- RRR ---o---- output
|
--- 1uF
---
|
GND

Regards,
Bob Monsen
 
On Mar 11, 10:37 am, Wayne <waynele...@gmail.com> wrote:
On Mar 11, 8:23 am, Randy Day <randy....@shaw.cax> wrote:

I have (and still am) looking through pages of google results.  So
far, nothing that looks usable to me :^).  I'm trying to find a
circuit that will stabilize an air/fuel ratio gauge display (a series
of LEDs).  The gauge takes its input from an O2 sensor in the exhaust
header (single wire type).  The o2 sensor varies it's output from 0VDC
to 1VDC based on it's reading.   The problem with the gauge is it
samples too frequently and the display is almost useless.  If I could
build something that takes the output from the o2 sensor and 'level'
it (only take 1 reading per second and output that reading to the
gauge until the next reading), I think it would stabilize the display
and make it more usable.
Click to expand...
From this it sounds like the problem is that your signal is bouncing
around a lot. Many samples of a steady signal would not be an issue.
So rather than just taking snapshot samples and displaying them, you
may want to do some averaging on the input value.

Me, I'd be inclined to do the whole thing with an 8-pin micro e.g.
AVR. How much resolution does your display have?

Mike
 
On Mar 11, 11:37 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
"Wayne" <waynele...@gmail.com> wrote in message

So, here is the circuit:

              160k
  sensor ---- RRR ---o---- output
                     |
                    --- 1uF
                    ---
                     |
                    GND
Click to expand...
Yes, this is definitely the first thing to try. I got caught up in
the whole input-hold-average-output thing.

Mike
 
Wayne wrote:

I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading. This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC. Any help is
appreciated.

Wayne
Well, using a simple RC type padding will slow down the movement
Click to expand...
of the signal for you how ever, if this sensor is connected to another
device in the car like your car's ignition computer, you may want to
isolate the signal before altering it to suit your needs.
Passing the signal into the + input of an op-amp and on the output
of the op-amp you apply the padding RC filtering.


http://webpages.charter.net/jamie_5"
 
"Wayne" <waynelewis@gmail.com> wrote in message
news:5e046560-34b8-4d22-8396-da12876bf192@m44g2000hsc.googlegroups.com...
I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading. This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC. Any help is
appreciated.

Wayne
Click to expand...
How about a kit from Jaycar Electronics
http://www.jaycar.com.au/

Kit number KC5195

http://tinyurl.com/39w7w4 should take you to the page

I think it does exactly what you want and there are loads more toys to buy
to make ordering from Australia worth while.
 
On Tue, 11 Mar 2008 08:37:56 -0700, "Bob Monsen" <rcmonsen@gmail.com>
wrote:

"Wayne" <waynelewis@gmail.com> wrote in message
news:5e046560-34b8-4d22-8396-da12876bf192@m44g2000hsc.googlegroups.com...
I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading. This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC. Any help is
appreciated.

Wayne


You may instead want a way to average the result. Otherwise, you end up with
the 'random' result being displayed for 1 sec, followed by another random
result, etc.

You can do this with a low pass filter, perhaps. The simplest is a resistor
from input to output, with a capacitor from output to ground. The values to
use are dependent on how much you want to smooth the output. If you want the
output to average out at 1Hz or less, then you need components so that

R * C = 0.16 = (1/(2*PI))

So, if you use a 1uF capacitor, you would need about 160k of resistance.

So, here is the circuit:

160k
sensor ---- RRR ---o---- output
|
--- 1uF
---
|
GND

Regards,
Bob Monsen
Click to expand...
I'll also add my vote for the filter approach as a first step.

But if you ultimately decide you do need a sample/hold,
it can be done in a fairly straightforward manner without
going digital. You have a buffer amp that charges a
capacitor through a switch (4016, etc). The capacitor
voltage is monitored by another buffer that feeds your display
circuit. A timer closes the switch for a brief interval, once
per second, to charge up the cap to the present input
voltage.

The input impedance of the op-amp output buffer will be
very high, so it won't draw down the capacitor voltage
between samples. In general you need a low input bias
current op-amp for this, but I'll bet a TL082 or LF351
will be OK. You will need to experiment with the cap
if dielectric absorption or leakage gives you problems,
but I suspect a big mylar will be fine since this is not
really a critical issue for your application.

The timer is totally non-critical. I prefer simple CMOS
gate timers, but you could probably use the popular (though
I could never understand why) 555 series here if you don't
mind all the extra parts and the supply current spikes.

Best regards,


Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
Science with your sound card!
 
On Mar 11, 11:37 am, "Bob Monsen" <rcmon...@gmail.com> wrote:
"Wayne" <waynele...@gmail.com> wrote in message

news:5e046560-34b8-4d22-8396-da12876bf192@m44g2000hsc.googlegroups.com...

I need a circuit that will read an input voltage once every second,
and output that same voltage on the output side until the next
reading.  This will be used in a vehicle (12VDC) and the input voltage
that is being 'sampled' will vary from 0 - 1.0VDC.  Any help is
appreciated.

Wayne

You may instead want a way to average the result. Otherwise, you end up with
the 'random' result being displayed for 1 sec, followed by another random
result, etc.

You can do this with a low pass filter, perhaps. The simplest is a resistor
from input to output, with a capacitor from output to ground. The values to
use are dependent on how much you want to smooth the output. If you want the
output to average out at 1Hz or less, then you need components so that

 R * C = 0.16 = (1/(2*PI))

So, if you use a 1uF capacitor, you would need about 160k of resistance.

So, here is the circuit:

              160k
  sensor ---- RRR ---o---- output
                     |
                    --- 1uF
                    ---
                     |
                    GND

Regards,
 Bob Monsen
Click to expand...
Bob,

I tried your suggestion today, and it did help some. You can
definitely see a difference in the display, especially at idle.
Thanks.
 
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