Back to Basics: Supervisor ICs

Posted under Back to Basics, Educational, Technology on February 12th, 2023 by

Voltage Supervisor ICs are ICs that monitor the voltage of a particular rail, (most of the time, the power supply rail) in a system. They are used to ensure that the voltage levels remain within the safe operating range and to provide a reset signal in case of an over/under-voltage event. They are especially used in microcontroller-based systems, where they monitor the voltage levels of the power supply to prevent the microcontroller from operating outside of its specification or the brownout region. If you check the datasheet of any microcontroller, you will find a lower threshold voltage, now if you feed a voltage lower than that, then the microcontroller may just stop. If it just stops working there is no problem, but most of the time, it goes into a limbo state wherein you can predict its behaviour, it starts misbehaving. This is one of the worst-case scenarios to debug as it’s random behaviour.

Voltage supervisor ICs play a crucial role in ensuring system stability. They monitor the voltage levels of a system and trigger a reset if they fall below normal limits. Essentially, they consist of a comparator with a voltage divider and a precision threshold voltage that compares the input voltage with the set limit. They can be used to trigger enable pins of LDOs, and buck converters also, not just uCs.

There are several types of voltage supervisor ICs, including fixed voltage ICs, variable threshold ICs with external resistors, and ICs with built-in watchdog timers. These ICs are essential for mission-critical systems, especially when they are battery-powered, as they prevent the system from malfunctioning due to low battery voltage. With a voltage supervisor IC in place, you can be confident that your system will perform optimally in all scenarios. Worth using if your BOM budget allows for it.

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Teardown: Doodle Pad

Posted under Educational, Product Design, Teardown, Technology on February 5th, 2023 by

These electronic writing pads have been one of the best value buys for me in the recent past. It has a large screen and you can write on it(on zero power) with any sharp object and it retains the doodle. The power is only utilised to clear the display with a press of a button. It’s excellent as a scratch pad. I really wanted to open it up and see the internals and how it works.

The PCB looks straightforward. It runs on a 3V CR2025 battery and has a delete button. When pressed, the battery powers on a single custom ASIC which I believe will put out up higher voltage with a transistor inductor circuit to drive 2 sheets Sheets are spot welded to the PCB pads with a conductive mesh. You also get a button which disables the battery which makes the screen “erase-proof”.

Started reading more about this tech and found that it was first developed by Kent displays back in 2010. The 2 sheets contain a fluid similar to the one found in LCDs called cholesteric liquid crystal display(ChLCD). In layman’s terms, I believe when pressure is applied to it with a stylus, it loses its orientation and becomes opaque which causes light falling on it to reflect back and you are able to see the line. When electricity passes through it, it reorients back and becomes transparent and no reflection happens as it’s coated on the back with a black sheet. Hence we do not need any power to write to it, only need it to erase it. It’s dirt cheap($2-$3) with so many clones out there. Worth having one around on your desk.

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