Re: Anything like a No-Slot Clock for a II+?

[mjmahon@aol.com (Michael J. Mahon)]

Scott Alfter replied:

>The new paint is drying on the fridge...finally got around to digging
>through the catalogs to see what the new electronics will cost.
>
>In article <20030120190031.19058.00000240@mb-fp.aol.com>,
>Michael J. Mahon <mjmahon@aol.com> wrote:
>>Scott Alfter replied:
>>>In article <20030120054747.14490.00000200@mb-fc.aol.com>,
>>>Michael J. Mahon <mjmahon@aol.com> wrote:
>>>>Scott Alfter wrote:
>>>>>I'm thinking of taking a II+ that's currently gathering dust and putting
>>>>>it to work controlling my beer fridge...
>>>>>
>>>>>I figure that the joystick connector has the necessary I/O...a
>>>>>thermistor on a joystick input and a relay on an annunciator output
>>>>>(along with whatever buffering electronics might be needed) would do the
>>>>>job.  Since I'll want to change temperatures slowly (maybe 1�F/hr) and
>>>>>I'll want to periodically log the temperature (maybe once per minute), a
>>>>>real-time clock of some sort will be necessary.
>>>>
>>>>A thermistor will work fine.  You may have to fiddle a bit or use signal
>>>>conditioning to get 1 degree resolution over your desired temperature
>>>>range with the Apple paddle circuitry.
>>>
>>>I can write a routine that'll read a paddle input with greater resolution
>>>than the one that's in ROM.  If that's not sufficient, it shouldn't be much
>>>to lash up a circuit around a 555 that would do the job...if that ends up
>>>being necessary, a button input would be used instead of a paddle input.
>>
>>That should do it.  Just be sure that the thermistor you choose can
>>easily provide the needed resolution near room temperature, since
>>thermistor response is nonlinear.
>
>Since I was already thinking of putting in a SmartWatch (more on that
>later), I figured I'd see what else is available from Dallas.  It turns out
>that there's a temperature sensor (the DS18B20) available.  It uses their
>one-wire interface (should be able to lash something compatible together
>that'll work through the game port) and offers 0.5�C accuracy from -10�C to
>+85�C...more than a wide-enough range for the beer fridge.  It's available
>in a TO-92 package, so all it'd need is a three-wire cable to carry power
>and signal to it.

Sounds like fun--perhaps you could publish your "1-wire" interface code
for the rest of us to try.  ;-)  I expect you'll have to use a PB input and
an annunciator output, tied together.

>>>>>I could wait for a clock card to show up on eBay or in
>>>>>comp.sys.apple2.marketplace, but that'd be too easy.  I know the No-Slot
>>>>>Clock was a variant of the Dallas SmartWatch that would work in a ROM
>>>>>socket in a IIe or IIc (which use 8K ROMs), but is there a version that
>>>>>would work in the 2K ROM sockets of a II+?  If there isn't, would it be
>>>>>feasible to build an "interposer" that would enable the clock to work in
>>>>>a 2K socket?
>>>>
>>>>It will take an adapter, as you describe.  An alternative is to put it
>under
>>>>any standard (27xx) slot ROM, if you have any such card(s) in the
>computer.
>>>>(For example, a 3.5" disk controller...)
>
>The DS1216E would be the most likely candidate...but DigiKey wants over
>$38.00 for one of these.  I might spring for one of these for my IIe, but
>it's a bit more than I want to put into this project.
>
>As it turns out, though, there are other timekeeper chips available.  The
>DS2417 uses the same interface as the aforementioned temperature sensor. 
>It's basically a 32-bit counter that gets bumped once every second.  I'd
>have to write a driver for it if I want ProDOS 8 to recognize it, but it
>costs less than $3.  A crystal, backup battery, and diode should be all it'd
>take to make a RTC out of it that would keep running while the computer is
>shut off.
>
>>>I already have a relay with contacts rated for either 5A or 10A...don't
>>>remember which offhand, but 10A seems more likely.
>>
>>The starting current could easily exceed 10A, but since it has held
>>up OK controlling this motor, it should be fine.
>>
>>The critical question, then, is what is its coil current?  You may
>>be able to get by with a 2N2222 driven hard, but you may need
>>a Darlington pair.
>
>It's Radio Shack #275-218:
>
>http://support.radioshack.com/support_supplies/doc9/9525.htm
>
>Coil current is 75 mA.  Here's a 2N2222 datasheet I found after a quick
>google:
>
>http://www.semiconductors.philips.com/acrobat/datasheets/2N2222_CNV_2.pdf
>
>Looks like a 2N2222 should easily be up to the task.  Even if the coil
>current at turn-on is 10x nominal, that would still be within the limit, and
>it would quickly settle down to less than that.

I agree--that relay looks great.  And, FWIW, coil currents tend to rise
gradually, not spike (it's the voltage across the coil that spikes).  Of 
course, "gradually" in this case is several microseconds.  ;-)

BTW, at 75 ma., you shouldn't have any problem using the Apple II
12v supply.
-michael

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