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From: Jim Thompson on 17 Mar 2010 12:43
On Wed, 17 Mar 2010 16:10:53 -0000, "markp" <map.nospam(a)f2s.com>
wrote:
[snip]
>
>You'd be better off IMO in using a high Q bandpass circuit made from two or
>more opamps. Google is your friend, here's an example:
>http://www.vidyasagar.ac.in/journal/maths/Vol11/JPS11-16.pdf
>
[snip]

Half-assed. No! I'll take that back, it's FULL-assed :-)

See the various active filter discussions on the SED page of my
website.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
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| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The only thing bipartisan in this country is hypocrisy
From: eeboy on 17 Mar 2010 12:59
>Are you using the proper emitter one that is wavelength matched to you
>TSOP?

I am using a LTE-5228A which has a peak at 940nm. The data sheet on the
TSOP part appears to have a peak at roughly the same spot.

>I agree about the optics but unless your building these in large
>quantity you likely don't have any optics.
>

I am currently using a plastic fresnel lens in front of the device.
However, the fresnel lens is being shared with another optical component
which has been given 'optical priority'... meaning the other component is
at the focal point so the TSOP device sits about .25" below. I could
probably have (and should have) pushed that device up closer to the other
device (within .100"). Perhaps I'll run some tests where I slide the
fresnel lens down to see if the situation

>Are you hammering the LED with it's max peak current are close to it?
>Keeping in mind max package power dissipation for your LED in the
>worst case ambient etc..

I believe I am currently driving it past the datasheet spec. My transmitter
is powered by a CR2032. I am utilizing a 1 ohm resistor in the path which
theoretically results in a 1.8A current for up to 80ms. The datasheets
states the maximum as 2A for 10uS. However, I am certain the small 7mil
trace width on the transmitter PCB add a good bit of resistance to the path
as well.

>
>You can adjust the duty cycle to keep the average current to
>acceptable limits. Like 10% for the carrier modulated at 40% for
>continuous transmission at 1A pulses this would be about 40mA average
>current. You could reduce this further by using discontinuous
>transmission i.e transmit intermittently in bursts .
>

I am utilizing a 50% duty cycle. I had no idea I could get away with that.
Definitely going to adjust the duty cycle downward.

---------------------------------------
Posted through http://www.Electronics-Related.com
From: eeboy on 17 Mar 2010 13:07
>
>What's the application?

This is being used as a dirt cheap remote control with 5 commands. Each
command has a different pulse length.

>
>John
>
>

---------------------------------------
Posted through http://www.Electronics-Related.com
From: John Larkin on 17 Mar 2010 13:19
On Wed, 17 Mar 2010 11:59:24 -0500, "eeboy"
<jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>>Are you using the proper emitter one that is wavelength matched to you
>>TSOP?
>
>I am using a LTE-5228A which has a peak at 940nm. The data sheet on the
>TSOP part appears to have a peak at roughly the same spot.
>
>>I agree about the optics but unless your building these in large
>>quantity you likely don't have any optics.
>>
>
>I am currently using a plastic fresnel lens in front of the device.
>However, the fresnel lens is being shared with another optical component
>which has been given 'optical priority'... meaning the other component is
>at the focal point so the TSOP device sits about .25" below. I could
>probably have (and should have) pushed that device up closer to the other
>device (within .100"). Perhaps I'll run some tests where I slide the
>fresnel lens down to see if the situation
>
>>Are you hammering the LED with it's max peak current are close to it?
>>Keeping in mind max package power dissipation for your LED in the
>>worst case ambient etc..
>
>I believe I am currently driving it past the datasheet spec. My transmitter
>is powered by a CR2032. I am utilizing a 1 ohm resistor in the path which
>theoretically results in a 1.8A current for up to 80ms. The datasheets
>states the maximum as 2A for 10uS. However, I am certain the small 7mil
>trace width on the transmitter PCB add a good bit of resistance to the path
>as well.
>
>>
>>You can adjust the duty cycle to keep the average current to
>>acceptable limits. Like 10% for the carrier modulated at 40% for
>>continuous transmission at 1A pulses this would be about 40mA average
>>current. You could reduce this further by using discontinuous
>>transmission i.e transmit intermittently in bursts .
>>
>
>I am utilizing a 50% duty cycle. I had no idea I could get away with that.
>Definitely going to adjust the duty cycle downward.

Reducing the duty cycle of the 32 KHz drive will directly reduce
equivalent transmit power. 50% is ideal; then drive it with all the
current it can stand.

John

From: eeboy on 17 Mar 2010 13:35

>3. Dump the photodiode current into a tuned LC tank and amplify that
>with a very low-noise device, probably a jfet. The 4069 will be about
>the noisiest and least gain-predictable amplifier you can buy for a
>reasonable amount of money. An LC to ground allows a lot of ambient
>light signal to get dumped without saturating any amplifier stages.
>

This sounds interesting to me. So, as I understand it with ambient light
(DC) I'll have a low impedance path to ground. However, when I am wiggling
close to the point of resonance I'll begin to see a voltage develop across
the LC tank as the impedance increases. Correct?

How is the Q of the tuned circuit adjusted?

---------------------------------------
Posted through http://www.Electronics-Related.com
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