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Sample Project 2: Drive-thru Loop Interface


The Problem:

The client wanted to track the progress of a drive-thru system. This consisted of a series of loop sensors that would sense the position of a vehicle as it passed from the order board, payment window, pick-up window and exit the drive through. They wanted this information to be fed to a PC so this information could be logged, and traced with a database.

The solution:

I designed a small PCB using a PIC processor that read the status of the loop sensors and report events to the PC via a serial port. First the protocol was defined. This allows the clients software developed to begin work immediately.

I designed the circuit that consisted of the single-chip processor and some small interface logic. I built a prototype and wrote and tested the software. My entire development time was about 3 days. The prototype was delivered to the client and worked as specified. The client then developed the production board from the schematic I provided.

The Second version:

The Drive-Thru Timer had worked well. Apparently too well as users began to unplug them because they showed how bad they were perfoming.

The client wanted to improve the system. The PC-based software was not perfoming well. It was decided to move some of the functionality to the box. One of the requirements was a network interface.

A full TCP/IP stack is way to much for the PIC processor to handle. So the timer box was redesigned using a Z-World Rabbit module with built-in ethernet. The Z-World module also allowed development in the 'C' language.

The new system was developed in a few weeks. It has worked well. The client decided to move more functions from the PC to the box as the box was much more reliable. I also wrote a service for NT/2k that communicates with the box and stores the information in a database. This greately simplified the clients software as all it had to do was process the database data. All data collection is done via the box and my service.

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