In search of 4B3A Microswitch Keyswitches (for a restoration, not a keyboard collector!)

Brent Hilpert bhilpert at
Fri Jul 10 14:29:44 CDT 2020

On 2020-Jul-10, at 11:27 AM, Ian Finder via cctalk wrote:
> On Fri, Jul 10, 2020 at 11:06 AM Al Kossow via cctalk <cctalk at>
> wrote:
>> Since it isn't very fancy, I wonder if you could make a new board with a
>> modern Hall
>> effect sensor? You just need a contact closure.

> Yeah Al, that's a great suggestion. I was looking at the AH1815 last night.
> The challenge is getting the whole assembly as thin as the original, which
> presents a not insignificant challenge-
> Even using the SOT553 package of this:
> - I'd have to do some
> trickery, like have it mount into a hole into the center of the board.

Reading that datasheet, it appears that to reduce power consumption those sensors employ pulsed sleep/wake operation, presenting up to a 1/8 second delay in response time. Probably not very good for use in a keyboard, and something to watch out for if looking for a modern replacement sensor.

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