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

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

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.

>>>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...)
>
>Hadn't thought about that...I was originally going to put in just a language
>card and a Disk II controller (neither of which has $C8 ROM), but I have a
>rev. C SCSI card that's gathering dust.  Choices, choices...:-)
>
>>>While I'm at it, what would be recommended as a buffer circuit between an
>>>annunciator output and a relay with a 12VDC coil?  The relay would be used
>>>to switch the compressor on and off...since the contacts will carry 120VAC
>>>and moderate current, I'm guessing that something with a 12VDC coil would
>be
>>>needed.  I can tap power from the power supply wiring easily enough, but
>>>what would be needed to switch the relay without toasting the computer's
>>>annunciator output?
>>
>>I'd actually recommend using a small 5v or 12v relay to control a
>>larger-contact 12v relay.  Motors have fierce starting currents, and
>>compressor motors can even stall on start (if short-cycled).  The coil
>>current of a larger 12v relay can be hundreds of milliamps, so it's worth
>>choosing one with a reasonable coil resistance, to minimize arcing on the
>>small relay contacts and to reduce 12v supply loading on the Apple.
>
>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 controlled right
>now by an HVAC thermostat inside the fridge, but an intermittent
>open-circuit developed in the plugs that connect the relay and associated
>circuitry to the fridge...while I had a batch of beer in the fridge.  I
>wasn't too happy with the fairly wide temperature swings the HVAC thermostat
>was allowing anyway, so that's another reason for putting a computer in
>charge.  (Since the beer was supposed to be at lagering temperature and that
>was within range of the fridge's built-in thermostat, I simply unplugged my
>temperature controller and let the built-in thermostat take over.)
>
>The relay is powered by a simple 12VDC unregulated power supply I lashed
>together out of junkbox parts (transformer, diode, capacitor).  While I was
>planning on tapping the computer's power supply, it wouldn't be a big deal
>to reuse this power supply.
>
>>The small relay can be easily driven by a 2N2222, for example, switched by
>>the annunciator output.
>
>I was thinking it'd be something like that, with a diode reverse-biased
>across the relay to avoid toasting the transistor.  Should I also throw a
>resistor between the annunciator output and the transistor, to avoid
>overloading the annunciator output?  I'm guessing the circuit would be
>something like this:
>                                       
>                                      v--
>                                      \_______> to 120VAC
>                          +12V
>                            ^         ^-------> to compressor
>                            |___________
>                                 |      )
>                                 _    ||)
>                          1N4002 ^    ||)
>                   2N2222        |    ||)
>                         ________|______)
>            1k        | /               
>to AN0 <---/\/\/\-----|<                
>                      | \|             
>                         \__
>                          __|__
>                           _|_  gnd
>
>Would this be reasonable, or should I step up to a bigger transistor (or a
>smaller intermediate relay, though I suspect a bigger transistor would be
>cheaper and simpler)?

This looks very reasonable.  If you opt for a bigger transistor, it had better
be a Darlington pair, or the annunciator drive may be insufficient.
-michael

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