■ BY JON MCPHALEN
ADVENTURES IN PROPELLER PROGRAMMING
PICK A CARD OR ... ABORT!!!
Around Christmas time, I helped a friend
with a reverse geocache project that he
was building as a gift. Jeff hasn't had a lot
of time with the Propeller yet, and I'm
always happy to encourage anyone
willing to give it a go. Part of the project
involved "backdoor" access to the box in
the event the number of attempts were
exceeded by the user. We kept things
simple — or so we thought — by using a
magnetically-tripped reed switch inside
the box. We did get it working, but the
original switch was a bit of a problem.
Not long after, I was looking through a parts drawer
and came across a surplus magnetic card reader that I’d
picked up at All Electronics. I immediately smiled, thinking
this would have been a very cool “backdoor” access point
for our project since we could have coded the box to
open only for Jeff’s credit card, while displaying all kinds
of “Thank you for the cash!” messages if the user inserted
their own card.
Long-time followers may remember that I wrote some
code for a reader in SX/B about five years ago. The
program worked just fine, but wasn’t terribly sophisticated.
With the resources of the Propeller and the ability to
create object libraries, it makes good sense to connect the
reader and write some new code.
Figure 1 shows the basic connections to the
Propeller; for my initial experiments, I connected to a
■ FIGURE 1. The ISO2 reader