[sdiy] THAT 2155 on sale

Oren Leavitt obl64 at ix.netcom.com
Fri Apr 10 15:38:28 CEST 2020


I have an idea for "quick matching" photo cells.

Basically one op-amp - a comparator with hysteresis (like that of a 
basic LFO)

1) Put the photo cell side in a resistor divider and connect to the 
comparator input.

2) Connect comparator output to to LED side thru appropriate current 
limit resistor.

The circuit should self oscillate at an amplitude/frequency determined 
by the LDR's light/dark resistance and lag time characteristics. Plug 
different photocells into same circuit and sort them by matches in 
amplitude/frequency shown on oscilloscope.

An idea..

On 4/10/20 5:52 AM, john slee wrote:
> Also interested in this, as I, too, have a bunch of unsorted 
> single-cell vactrols. Possibly from my last (successful) Goldmine order!
>
> John
>
> On Fri, 10 Apr 2020 at 15:38, Laughing Man <laughingman647 at gmail.com 
> <mailto:laughingman647 at gmail.com>> wrote:
>
>     This might be off topic, but I've been trying to test photocells
>     myself recently in order to make up some vactrols for a 208. What
>     kind of circuit would you use to test to the spec of the
>     datasheet? Putting 10mA through a resistance of 1 megohm produces
>     a ridiculous voltage drop, so I'm not sure how I'm supposed to
>     'bias' the photocell so I can test if it's response matches the
>     datasheet.
>
>     On Thu, Apr 9, 2020 at 8:18 PM Crys <crystals at sonic.net
>     <mailto:crystals at sonic.net>> wrote:
>
>         yeah, me too. i got quite a few hundred, then i bought a box
>         of envelopes and tested out a big pile of them and made
>         envelopes full of matching units.
>
>         crystal chris
>
>         On 4/9/2020 8:22 PM, Kylee Kennedy wrote:
>>         Post came through fine.
>>         Interesting I'll have to find that Vactrol. Electronic
>>         Goldmine is well know for selling out of spec Vactrols in the
>>         past. A lot of the stuff here is surplus from manufacturers
>>         that's why they can sell them so cheaply. I still have a few
>>         hundred dual leg Vactrols from their blow out sales...All
>>         with different responses.
>>
>>         Kylee
>>
>>
>>
>>         On Thursday, April 9, 2020, Laughing Man
>>         <laughingman647 at gmail.com <mailto:laughingman647 at gmail.com>>
>>         wrote:
>>
>>             First time posting, so I'm not sure if I'm sending this
>>             out right, but I also stumbled across a 3-lead photocell
>>             on their site as well. Sounds like an easy way to make
>>             some home-baked 5c3/2's.
>>
>>             On Thu, Apr 9, 2020 at 2:27 PM john slee
>>             <indigoid at oldcorollas.org
>>             <mailto:indigoid at oldcorollas.org>> wrote:
>>
>>                 Interesting. I tried to order some. Unfortunately
>>                 their payment processor is rejecting my cards due to
>>                 (incorrectly) failing AVS checks, and they
>>                 inexplicably don't allow Paypal for Australia.
>>                 Infuriating.
>>
>>                 They need to bring their site forward at least 20
>>                 years. Limiting people to 10-character passwords is
>>                 awful (see: NIST guidelines) and also while I don't
>>                 have proof of this, based on the way their form flow
>>                 works, I suspect they're being very naughty and
>>                 storing credit card CVV info. This is absolutely not
>>                 allowed
>>
>>                 Thanks for the heads-up, anyway.
>>
>>                 John
>>
>>                 On Fri, 10 Apr 2020 at 01:44, David G Dixon
>>                 <dixon at mail.ubc.ca <mailto:dixon at mail.ubc.ca>> wrote:
>>
>>                     Hey SDIY Team,
>>
>>                     Electronic Goldmine has a stash of THAT 2155 VCAs
>>                     on sale for $1.99 each, if you’re interested.
>>
>>                     Cheers,
>>
>>                     Dave Dixon
>>
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