mad.scientist.jr@gmail.com wrote:
Thanks for your reply...To switch a relay on and off, I'd use an annunciator line from the joystick port. A card in an expansion slot will need at least a buffer and a latch; at the joystick port, all you'll need is an NPN transistor, a diode, and a resistor or two. You could use an expansion slot for what you want to do, but to me it sounds a bit like swatting a fly with a sledgehammer.If all you wanted to do was turn on one relay maybe, but what about 4 or 8 or more? Some things I'm looking to do * set the value of 1 or more potentiometer (control resistance from the computer) * read the value of 1 or more potentiometer (into an 8-bit number = ok) * read whether a switch (actually 8 or more switches) is closed or open, and be able to tell if several are pressed at the same time * open/close 8 or more relays (or an electronic switch such as a transistor which is faster) * control SPDP switch(es)
If you are controlling relays, speed is not an issue. So it would be possible to use two annunciator outputs on the game port to provide a data line and a clock pulse for shifting bits into a (possibly quite long) shift register, whose parallel outputs control the relay drivers. Serial in-parallel out shift registers are available with latches on the parallel side so that shifting does not disturb the outputs. Similarly, there are parallel in-serial out shift registers that can be used (with a pushbutton input for data) to read arbitrary numbers of slowly changing inputs. All of this is easily constructed on a proto board--even a soderless proto board. It's best not to build a peripheral card until you know exactly what functionality you will require and how you will program it. Using the game port and software-controlled serial input-output keeps the hardware simple and requires only short assembly language programs to control. -michael NadaPong: Network game demo for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."