A few years ago, Elektor published a buffer board for the unprotected 40-pin Raspberry Pi HAT connector. As this board was intended for use with the normal Raspberry Pi boards, it doesn’t fit on the ‘400, and so it was decided to remodel it. Let's take a look at the Elektor Raspberry Pi 400 Buffer Board.

A Buffer Board for the 400

The Raspberry Pi 400 is a Raspberry Pi 4 built into a keyboard and it is all you need to surf the Internet with or play games on (if you connect a monitor and a mouse to it, of course). But that’s not all that you can do with it. On its backside the Raspberry Pi 400 also features an extension connector to control other equipment with and for experimenting. This connector is the well-known 40-pin Raspberry Pi HAT connector found on “normal” Raspberry Pi boards.

Like on the other Raspberry Pi boards, the HAT connector on the ‘400 has no protection against electrostatic discharges (ESD). Plugging (or unplugging) things on it without taking the necessary precautions – powering off the Raspberry Pi first comes to mind – may result in unrecoverable damage to the board. A standard Raspberry Pi board is easy enough to replace, but a broken ‘400 is good for the bin, and you don’t want that, do you?

A few years back, we published a buffer board for the HAT connector. The board was intended for use with the normal Raspberry Pi boards, so it does not fit on the ‘400. Thus the decision to remodel it.

Elektor Raspberry Pi 400 Buffer Board
Elektor's Raspberry Pi 400 Buffer Board (210320).

ESD Protection & Fuses

Based on TI’s TXS0108E 8-bit bidirectional, level-shifting, voltage translator for open-drain and push-pull applications, the Raspberry Pi 400 buffer board allows interfacing with both 3.3 V and 5 V external logic for all the 26 GPIOs and adds ESD protection to them. Two 0.5 A PPTC resettable fuses protect the +5 V and +3.3 V power supplies of the Raspberry Pi 400.

The buffer board can be connected to external circuits with a short 40-way ribbon cable (not included) in case you need all 40 signals, or just jumper wires to a breadboard or so (not included either). Note that the board can also be used with other Raspberry Pi boards.

Always Add Common Sense

The Elektor Buffer Board for the Raspberry Pi 400 greatly reduces the risk of damage during experiments. However, even though it adds protection, it doesn’t protect your Raspberry Pi 400 against yourself doing dumb things. So, always switch off the ‘400 before (un)plugging the buffer board and avoid any mechanical stress that may damage the HAT connector inside the ‘400. (I highly recommend sticking one or two rubber standoffs on the bottom of the buffer board.)