Summary of Inside the ALU of the first ARM microprocessor
### Summary This article describes a low-cost, isolated USB-to-UART converter designed to protect computers from hardware failures. The author recounts an incident where a faulty device destroyed a computer's USB port, highlighting the need for isolation. Using a SparkFun breakout board, the project prevents ground loops and shields expensive laptops from high-voltage faults or excessive current during development of battery-powered devices.
Parts used in the Isolated USB-to-UART Converter:
- Sparkfun USB-to-UART breakout board (BOB)
- Isolation circuit components
I stood in stunned silence at the smoke billowing up from the hardware on the workbench. Just moments before, it had been operating as expected, before self-destructing with a sound that can only be compared with a gunshot. The failure of the hardware under test had an unexpected consequence: the computer that had been using a USB-to-UART converter to communicate with the hardware experienced a USB fault that was not recoverable. The computer was now damaged and worthless.
A simple isolation circuit that costs only a few dollars could have been used to protect the USB port on the computer. Embedded system developers get used to plugging strange hardware and components into their computers on a daily basis and rarely consider the consequences of what their actions might bring.
This Design Idea documents a low-cost, isolated USB-to-UART converter using the Sparkfun USB-to-UART breakout board (BOB).
There are a number of times when an isolated USB-to-UART converter can come in handy. For example, during development of battery powered devices, there is a tendency to leave the USB-to-UART converter attached to the device, which, without isolation, will connect it through the host’s ground to an Earth ground. The device may work perfectly, but when detached from the computer, it doesn’t work at all. The isolated converter will keep the device and host grounds separate, allowing any grounding issues to be found early on rather than later.
The most important use of an isolated USB-to-UART converter is of course in fault conditions. Consider the consequences of connecting an untested electronic board to an expensive laptop such as a MacBook Pro. The USB specification and hardware layer does have protection circuits, but they may not be rated for devices operating at hundreds of volts DC. When a device fails on the USB bus and has the potential to put more than 5V, or significant current, onto the bus, it is a wise decision to spend $20 and isolate the two devices.
For more detail: Inside the ALU of the first ARM microprocessor
- Why is isolation important when testing new hardware?
Isolation protects the computer from damage if the tested hardware self-destructs or sends high voltage onto the USB bus. - What happens if you connect an untested board without isolation?
The computer may experience an unrecoverable USB fault and become damaged or worthless. - How does isolation help with battery-powered devices?
It keeps the device and host grounds separate, preventing grounding issues that cause devices to fail when detached. - Can standard USB protection circuits handle hundreds of volts DC?
No, standard protection circuits are not rated for devices operating at hundreds of volts DC. - When should you spend $20 to isolate two devices?
You should isolate them when connecting a device that could put more than 5V or significant current onto the bus. - What component is used to build this isolated converter?
The project uses the Sparkfun USB-to-UART breakout board.
