Lock-in detectors

It is indeed a better approach for a demo to roll you own from a few parts. Otherwise the viewer sits in front of a bulky black box doing miracles. As starting point, have a look at the AD630 from Analog Devices. The datasheet shows a few examples. Add a 8038 frequency generator and a few opamps and you're there.

Rene

Hah, an ac-coupling capacitor at the input gets you a long way. :-)

The AD630 is good for square-wave demodulation. But this chip presents a bit of a black-box on its own. I like to use the signal with an inverting opamp, plus a 4053 double-throw CMOS switch, to make an inexpensive lock-in that can effectively reject room light. For example, see AoE page 1031, and here,

I often place equal small-valued resistors (2.2k) in series with the signal opamp outputs and the two HC4053 switches, to isolate the opamps from any '4053 charge injection.

I often use an AD734 multiplier with sine-wave modulation, which an 8038 nicely provides, but we're talking about square-wave demodulation, which takes the signal and its harmonics. So it's happy with square-wave modulation, which greatly simplifies the illumination drive, just switch an LED on and off from a 555 reference oscillator.

Now, arvo = afternoon? Or

I've also noticed that many/most opamps go bonkers for some microseconds if their output drives a typical cmos switch. What I usually see is a jump at the instant of switching, followed by a linear slew back to the proper level. It can be pretty big.

John

If you put a small resistor between the switch and the op amp, and a bigger one between there and the integration cap, you can make more of the injected charge go out the amp end, which is useful in reducing offsets. I'm interested in the op amp problems: I try to use 12V or

+-15V supplies when I can, to preserve dynamic range, and emitter follower outputs are pretty tough to drag around much. Does this happen mostly with R2R bipolar or CMOS parts?

MC1496 Gilbert cells make good lock-ins, if you don't need super-accurately calibrated gain--you can easily get a dc gain of 200, which can reduce the need for external circuitry.

BTW does LTC still make the LT1043 switched-capacitor block? Those things are cool, if you can afford them.

Cheers,

Phil Hobbs

Hello Win,

Just FYI: You email address seems to be non-munged this time. Might want to check that.

Regards, Joerg

I saw that but had no choice. Google makes you use a real email address to register. They hide this if one views on Google, but send it to the rest of the world. (I had to use Google for that one post.) They suggest you get a fake, real email address and use that instead. But what a crazy workaround! Anyway, I do have a few such "fake" email addresses, but I don't use them or remember where they are (Yahoo, CompuServe, Harvard, NewsGuy, etc?), or the passwords. Sigh.

--
 Thanks,
    - Win

Hello Win,

That is one reason why I don't use them. No idea if this one would be better but may be worth a look:

NGs are probably pretty far removed from spambots but s.e.d. is being copied into all kinds of web based forums and FAQ sites. From there to the spambots it's just a short hop.

Regards, Joerg

"Joerg" schreef in bericht news:VPQFf.1675$ snipped-for-privacy@newssvr27.news.prodigy.net...

Very true. But spambots also make up email adresses from domain names. Simply try to send email to snipped-for-privacy@xxxxxxxxxxxxx.com or to snipped-for-privacy@xxxxxxx.com and so on. Don't you get any spam sent to your analogconsultants domain? I'm getting email to addresses that I never created for my domains.

I'm strongly against death penalty, but for spammers I wouldn't mind if they made an exception.

--
Thanks, Frank.
(remove \'q\' and \'.invalid\' when replying by email)

Only if they are televised as a warning to other spammers.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Thanks Win & all others who replied.

Afternoon :)

Cheers, Ian Du Rieu

I've changed opamps to get me out of trouble here, bipolar to bifet as I recall, but I don't know if there's any sort of pattern. I love the LM8261, because you can hang any amount of capacitance from its output to ground and swamp this problem. It's handy for all sorts of things.

John

Hello Frank,

I don't get any to that one yet but it is also not used by friends, only by business partners. My impression is that the spam volume has increased once an email address was used by friends who could not resist that dreaded temptation to send jokes, "cool stuff" or their latest cute doggie pics to everyone in their address book. Of course some of those recipients use free mail services and since these mails contain the whole slew of other recipients in the source you can imagine what happens then. Nothing is free.

Nah, just take away their PCs and get a court order banning them from sending email to more than x people at the same time. Then if they violate that lock them up.

Regards, Joerg

Well, then, the answer is, use the one that's been revealed as your "fake" address, and stay signed up on google with it, but abandon it - I have a yahoo account that I've set to "send everything to the trash and delete it.", and another yahoo account that's real, for real email.

I'm kinda proud of myself, because the fake google-accessing yahoo email is richardgrise, so all I have to say to folks to have them unmunge it is to elide ard. ;-) Thought up that little trick all by meself, I did! %-}

Cheers! Rich

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Nah. Not death. That's too merciful.

Caning, pillorying, flogging, any kind of humane torture would be much more effective than a simple, quick, clean beheading, as far as deterrents go.

Maybe boil them in pig fat - that'd probably cut down on Islamic terrorists, too! ;-P

Cheers! Rich

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The ones that make me crazy are the spammers that take the trouble to join listservers to promulgate their trash. Given the usual method complexity (relatively hard to automate) to subscribe, they must be really driven to do so.

--
JosephKK
Gegen dummheit kampfen Die Gotter Selbst, vergebens.  
--Shiller

Hello Joseph,

It's a sign that enough people fall for spam. I was surprised when I read how much reasonably well tested email lists sell for. My real concern for society is phishing though. You and I are ok but imagine older folks who have developed early stages of memory loss. They could easily think it's a legit request from their bank.

BTW, your tag line would really go like this: Gegen Dummheit kämpfen Götter selbst vergebens! (Schiller)

I lived a block away from Schillerstrasse a while ago but must confess that I didn't read much from him.

Regards, Joerg