Early in my engineering profession, I labored with a few colleagues on an outdoor mission. We had an idea for a safety system for gaming arcades. On the time, arcades had been very fashionable, internet hosting video games like Pac-Man, House Invaders, and Pinball. One of many enterprise issues, although, was the theft of cash from the gaming machines. Apparently, when workers members had been emptying the coin containers, they might pocket a handful of cash. Theft in these arcades was stated to be round 25%.
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Our idea for stopping these thefts was a tool that consisted of two components. One micro-based system was put in in every of the arcade video games. This counted the cash as they entered the slot. Then, periodically, the entire coin depend and recreation ID had been transmitted, by way of the ability line, to the again workplace. Within the again workplace was the receiver. It monitored the ability line and picked up all of the transmissions from the varied video games. This back-office system was additionally linked to a phone landline, and as soon as a day, the central workplace would name into the back-office system to have the each day information despatched to it. The hand depend of cash might then be reconciled with the digital coin depend from all of the machines.
My colleagues and I divided up the work, with one doing the schematic and PCB prototypes. One other did the enclosures, labeling, and many others. I did the firmware for the 2 items of kit. After many months of night work, we had a system that carried out simply as we anticipated. We additionally acquired a check web site recognized to put in an entire system. Because the arcade was greater than 1000 miles away, we had somebody on the different finish set up the system. After a couple of days, we acquired a name from the arcade operator telling us the workplace system wouldn’t reply the cellphone name into it. The {hardware} design was rechecked to see if the opto-isolator, signaling the firmware of a excessive voltage on the ring line, was designed accurately to consider lower-level ring voltages—no problem there. This problem fell on me because it seemed to be a firmware problem. I examined my firmware dozens of occasions with numerous adjustments utilizing an precise landline—it all the time labored. After many days of testing, I introduced that I couldn’t discover any points.
As a final resort, we had the {hardware} engineer fly to the arcade web site with a raft of check gear. After only some hours, he known as and stated he had discovered the difficulty. The usual for ringing for a landline is outlined by ANSI T1.401-1988 part 5.4.2, which I adopted for the firmware. In line with this customary, the ring cadence consists of two seconds of ringing adopted by 4 seconds of silence. The cellphone system, within the city the place the arcade was, adopted this…type of. In the course of the ring, there was a brief dropout ( about 80 ms, if I keep in mind accurately). So, what the firmware noticed was about 1 second of ring, no ring for 80 ms, then 920 ms of ring, after which 4 seconds of silence. The firmware, noting that the ring was just one second lengthy, decided that it wasn’t a sound ring and subsequently wouldn’t reply. The invention of the difficulty was lengthy, troublesome, and costly. The repair was simple to implement in firmware. After updating the firmware, the arcade system labored very properly (we by no means acquired wealthy off it, although…one other, non-technical, story).
The takeaway right here isn’t methods to assemble landline cellphone answering firmware; these days are lengthy gone. However the lesson right here is that when you might have a problem, suspect all the pieces. We continued to have discussions on why the system wouldn’t reply the cellphone after we knew it was sensing the ring. We by no means thought that perhaps the cadence, outlined by an ANSI customary, wouldn’t be appropriate. Why the city’s phone ring system had an 80 ms hole was by no means found, however it clearly didn’t meet the spec. So, if you happen to can’t discover an issue in your system, perhaps it’s the opposite system(s) you’re connecting to. And at that time, the opposite system must be checked towards its specs.
Damian Bonicatto is a consulting engineer with many years of expertise in embedded {hardware}, firmware, and system design. He holds over 30 patents.
Phoenix Bonicatto is a contract author.
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