Re: Apple ii projects for kids?

[scott@alfter.diespammersdie.us (Scott Alfter)]

In article <9a7a3e68-e48d-4d86-a382-c1ce280d5db5@e8g2000vbc.googlegroups.com>,
Kevin Dady  <kevin@hackaday.com> wrote:
>yea, you can squeeze some GPIO out of the motherboard to twiddle
>lights out other external systems, but I think you would need a card
>on the II

Only if you need more than 4 bits of output or 3 bits of input.  I
implemented a 1-Wire controller in software that uses one bit each of input
and output; source code and an ASCII-art schematic are here:

http://alfter.us/computers/apple2/software.aspx

"1-Wire Apple II Primitives" includes assembly-language code to bit-bang the
joystick port and some BASIC examples to enumerate devices and read
temperature sensors.  "Apple II Beer Fridge Controller" provides C code
(with inline assembly where needed) that you can build with cc65; in
particular, the C implementation of device enumeration is much faster than
the BASIC implementation.

(Just realized that the schematic provided with the beer-fridge controller
code doesn't mention that a relay is switched on and off by AN1 (AN0 and PB2
are used by the 1-Wire controller).  I just used a 2N3904 (or equivalent)
for this purpose.  IIRC, connect the emitter to +12V, the collector to one
end of the relay coil, and the base through a 1K resistor to AN1.  The other
end of the relay coil is connected to ground.  A small diode should be
connected in reverse bias across the relay to absorb back-EMF and keep from
frying the transistor.)

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