Teacher Needs Electronics Help

eBETH

I need some help - I took 1 class in basic linear/digital electronics when I was in highschool so I am not a total dummy but that was over 15 years ago and since then I haven't done any serious electronics projects. I am OK with BASIC programming so I won't need much help there.

I am trying to automate a classroom training device that currently requires manual operation requiring the teacher to monitor a readout while a student works and to turn a rotary switch depending on various criteria in order to get the student to modify their behaviour. I think the PROP1 is part of the solution (for outputs) but not sure how to do the inputs ... any advice is welcome.

OUTPUTS:

Need to create the digital equivalent of an 6 position rotary switch carrying between 5VDC-12VDC load (external power supply) ... the **critical** thing here is that like a rotary switch each of the 6 switch circuits **MUST NEVER** be active in combination with the others. One-at-a-time or else damage will happen to the controlled device!

How to safeguard this ?

INPUTS:

(A) Need to input 4 numbers, two are 4-digit and two are 2-digit. These numbers need to be loaded before the primary control function starts and worked with by the software to determine outputs. These numbers also need to be easy to enter so I am thinking maybe thumbwheel switches with binary/bcd outputs ? A keypad option with a display might work if not too expensive.

(B) Need following trigger (momentary pulse) signals: Start, Stop, Reset, Next.
* Reset can be used to reset software and to "load" the numbers from inputs A1-A4
* Start & Stop can share the same signal as in Start/Resume & Stop/Pause.
* Next must be a stand alone signal.

Philip Gamblin

Well hardware wise If a rotary switch will work, and you need higher current capacity, you could use the swwitch to select 1 of six relay coils.
The BCD thumbwheels shouldn't be too expensive. If you could use a PC you could probably do your project in the debug screen with the stamp doing your controlling Stamp==>> transistor driver ==> relay. I 'll offer all the help I can. I owe that much to some of the excellent teachers I had.
Good luck!

Jon Williams

With eight I/O lines you could read four BCD switches pretty easily. Four of the pins would be used as outputs to (one at a time) drive the common of a given BCD switch, then use four inputs (use the nature INx groupings on the BASIC Stamp) to grab the state of the switch. Two more output pins could be used to tell the user which number is being loaded -- of course, you'll also want an Enter button, and maybe even and advance button. You could drive six loads through a ULN2x03. If you run short of I/O pins, the outputs could be run through a 74hc595 prior to the ULN; this would reduce the relay output pin count from six to three. To prevent possible output problems you could always clea all the outputs before setting a new state -- kind of an electronic version of the wiper "floating" between two sets of contacts.

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Jon Williams
Applications Engineer, Parallax