3 ms·

> But some environments are notoriously noisy. Many years ago I put a system using several Z80s and a PDP-11 in a steel mill. A motor the size of a house drawin

by nickcw 2y ago

> But some environments are notoriously noisy. Many years ago I put a system using several Z80s and a PDP-11 in a steel mill. A motor the size of a house drawing thousands of amps drove the production line. It reversed direction every few seconds. The noise generated by that changeover coupled everywhere, and destroyed everything electronic unless carefully protected. We optocoupled all cabling simply to keep the smoke inside the ICs, where it belongs. All digital inputs still looked like hash and needed an astonishing amount of debounce and signal conditioning. :-) I had a similar experience with a elevator motor and a terminal. The electronics worked absolutely fine, but when someone operated the elevator it occasionally produced phantom keypresses on the capacitive keypad. This was perhaps understandable, but what really confused the users was that these phantom keypresses sometimes pressed the not fitted debug buttons (which weren't on the production keypad) which stuck the device into debug mode! We learnt not to include the debug code in the production firmware and beefed up the transient suppression hardware and the debouncing firmware to fix.

HeyLaughingBoy 2y ago
My favorite noise story is from just a couple years ago. Our controller would run fine for hours or days and then reset for no apparent reason. Looking at the debug output, I could tell that it wasn't a watchdog or other internal reset (e.g., system panic) and there had been no user input. The debug log basically said that someone pushed the reset button, which clearly wasn't happening. The EE and I were standing around the machine and he happened to be in front of the UI when it reset and I mentioned that I heard a soft click just before he said that it reset, but we had no hardware in the region where I thought the noise came from. Finally, we put two and two together and realized that the system included a propane heater with an automatic controller and the noise I heard was probably the propane igniter. The high voltage from the igniter was wirelessly coupling into one of the I/O lines going to the controller board. The reason that the problem had suddenly started happening after months of trouble-free development was that the customer had rerouted some of the wiring when they were in the machine fixing something else and moved it closer to the heater. In 30 years of doing this, I can count on one hand the number of times I've had to deal with noise that was coupling in through the air!
- throwup238 2y ago
  I’ve worked with electron microscopes and in silicon fabs and it’s super fun being on the teams hunting for sources of noise during construction and bringup. In fabs there are multiple teams because it’s so specialized, the HVAC team being the most interesting one because they’ve got tons of mechanical and electronic sources all over the buildings. They were also the long tail for problems with yield (which was expected and budgeted for). I think the EM startup I worked for failed in part due to not taking the issue seriously enough. I can’t tell any specific stories but poorly shielded USB ports were the bane of our existence in the 2000s. Every motherboard would come with them and the second a random floor worker would plug something in it’d take down a section of the fab or all of the microscopes even if it were on the other side of the building. For some god forsaken reason all the SBC manufacturers used by tons of the bespoke equipment were also adding USB ports everywhere. We ended up glueing all of them shut over the course of the several months it took to discover each machine as floor workers circumvented the ban on USB devices (they had deadlines to meet so short of gluing them shut we couldn’t really enforce the ban).
- ikiris 2y ago
  Only time I’ve ever run into this was: - an am radio station nearby coupling into a pbx - when some genius thought it would be a good idea to run Ethernet down the elevator shaft, right next to the lines feeding its truck sized motor.
fsckboy 2y ago
>Many years ago I put a system using several Z80s and a PDP-11 many years ago I wired up my own design for an 8080 system, but i was a self taught beginner and not very good at stuff like a capacitive RC debounce circuit so I couldn't get my single-step-the-CPU button to work. I was reading the spec sheet for the processor and I realized I could kluge it with signals. There was something like a "memory wait" pin, and another one called something like "halt", but one fired on the leading edge of the clock, and the other on the trailing edge, so I was able to use a SPDT push button and a flip flop to single step halt/memory wait on the first bounce, and then restart only on the first bounce when the button was released.

by nickcw 2y ago

HeyLaughingBoy 2y ago

My favorite noise story is from just a couple years ago. Our controller would run fine for hours or days and then reset for no apparent reason. Looking at the debug output, I could tell that it wasn't a watchdog or other internal reset (e.g., system panic) and there had been no user input. The debug log basically said that someone pushed the reset button, which clearly wasn't happening. The EE and I were standing around the machine and he happened to be in front of the UI when it reset and I mentioned that I heard a soft click just before he said that it reset, but we had no hardware in the region where I thought the noise came from. Finally, we put two and two together and realized that the system included a propane heater with an automatic controller and the noise I heard was probably the propane igniter. The high voltage from the igniter was wirelessly coupling into one of the I/O lines going to the controller board. The reason that the problem had suddenly started happening after months of trouble-free development was that the customer had rerouted some of the wiring when they were in the machine fixing something else and moved it closer to the heater. In 30 years of doing this, I can count on one hand the number of times I've had to deal with noise that was coupling in through the air!

throwup238 2y ago
I’ve worked with electron microscopes and in silicon fabs and it’s super fun being on the teams hunting for sources of noise during construction and bringup. In fabs there are multiple teams because it’s so specialized, the HVAC team being the most interesting one because they’ve got tons of mechanical and electronic sources all over the buildings. They were also the long tail for problems with yield (which was expected and budgeted for). I think the EM startup I worked for failed in part due to not taking the issue seriously enough. I can’t tell any specific stories but poorly shielded USB ports were the bane of our existence in the 2000s. Every motherboard would come with them and the second a random floor worker would plug something in it’d take down a section of the fab or all of the microscopes even if it were on the other side of the building. For some god forsaken reason all the SBC manufacturers used by tons of the bespoke equipment were also adding USB ports everywhere. We ended up glueing all of them shut over the course of the several months it took to discover each machine as floor workers circumvented the ban on USB devices (they had deadlines to meet so short of gluing them shut we couldn’t really enforce the ban).
ikiris 2y ago
Only time I’ve ever run into this was: - an am radio station nearby coupling into a pbx - when some genius thought it would be a good idea to run Ethernet down the elevator shaft, right next to the lines feeding its truck sized motor.

fsckboy 2y ago

>Many years ago I put a system using several Z80s and a PDP-11 many years ago I wired up my own design for an 8080 system, but i was a self taught beginner and not very good at stuff like a capacitive RC debounce circuit so I couldn't get my single-step-the-CPU button to work. I was reading the spec sheet for the processor and I realized I could kluge it with signals. There was something like a "memory wait" pin, and another one called something like "halt", but one fired on the leading edge of the clock, and the other on the trailing edge, so I was able to use a SPDT push button and a flip flop to single step halt/memory wait on the first bounce, and then restart only on the first bounce when the button was released.