HATs in the wild. And a unicorn.

If you’re a regular reader, you’ll recall that a month or so ago, we announced a new way of making add-on hardware for the Raspberry Pi: namely, the Raspberry Pi HAT (Hardware Attached on Top). You can read James, our Director of Hardware, explaining what they’re all about in the original blog post: in short, the HAT is a solder-less way of attaching hardware which can be auto-detected by the Pi, so GPIOs and headers are automagically configured by the Pi, without you having to do anything.

Gordon Pighat Hollingworth

The pink confection on top of Gordon is a hat, not a HAT.

(A tangentially related question: how do you pronounce EEPROM? Fights are breaking out at Pi Towers: a small majority of us rhyme the first syllable with “meep”, while the rest of us rhyme with “meh”. This is like the scone/scone thing all over again. Angry opinions in the comments, please.)

HATs are starting to appear in the wild. Adafruit are sending PCBs out for prototyping. HiFiBerry have HATs you can buy now: the Digi+, which enables you to connect an external digital-to-analogue converter; and the DAC+, a high-res all-in-one DAC. And the whimsical bearded pixies at Pimoroni have come up with my favourite so far (it’s my favourite because SPARKLES): the Unicorn HAT. I saw it in the flesh on Saturday at the Cambridge Raspberry Jam. It’s a thing of beauty. Here’s Paul, introducing the Unicorn HAT.

Are you making a HAT? Let us know in the comments: I’ll add links to this post if I’ve missed yours out here.


C Neale avatar

How do you pronounce EPROM?

Tom West avatar

“eh-prom”… the first syllable rhymes with “let”. This lets (see what I did there?) you pronoucne EEPROM as “eee-prom”, the first syllable rhyming with “eeeek!”.

u8nc avatar

when the HATS thing was announced a month ago, i dragged the picture into an art package and applied a transparency floodFill to the paper on top to see…
I decided not to divulge what i saw, that’s the foundation’s story to tell, but i just did the same trick with Gordon’s hat, and yes, he’s keeping something under his hat, and … , its the same HAT indeed as a month ago. So a reveal is imminent then.

If you don’t believe me, ask me.
( i can’t believe he keeps his sink so clean, my hats off to you old boy )

Jon Colt avatar

cf. the very first comment-question by C. Neale.

EPROM (“eee-PROM”) is an acronym for ‘eraseable programmable read-omly memory’, and was coined when Intel invented the U-V-eraseable PROM.
Then the electrically-eraseable PROM was invented, which could be erased in-place, in the circuit, by the appropriate voltage(s) applied to the device.
With the term “eee-PROM” being taken, most engineers and the electronics community in general referred to the new device as an “E”-“E”-PROM. As in “Electrcal Engineer”-PROM.

It helps to know some history of the field, and to have been, and be, there (which helps one know the history of…).

Next time you have a question such as this, I suggest you ask someone who HAS been there.

Aaron avatar

Anyone north of the Watford gap definitely says eeeeeeeeprom :-)

Got a few HATs in development and some other non HAT boards too. More on those all soon.

Liz Upton avatar

>north of the Watford gap

Are they flat HATs?

(Excuse me. I’ll get my coat.)

Andrew Gale avatar

I was just wondering: what is it that makes an add-on board a HAT? is it just the EEPROM or is it the camera/LCD cable cut-outs? Or both?!

SomrOldGuy avatar

Around here, we often pronounce EEPROM as “double-e prom.” Otherwise we’d have a confused listener think we meant EPROM.

SomeOldGuy avatar

That should have been SomeOldGuy, with fat fingers, I might add.

Dougie avatar

If “PROM” is präm (as in promenade concert at the RAH).

Then “EPROM” is ˈē-präm (ee-prom)

And “EEPROM” is ē-ˈē-präm (ee-ee-prom)

That works well anywhere Doncaster and north and south of Scotland.

Mike avatar

Pronunciation Guide for xPROM’s:

If it’s UV erased, it’s an EPROM – ep as in step!
If it’s Electronically erased, it’s an EEPROM – eep as in beep!

Simples ;)

AndrewS avatar

That’s what I’d always thought too, but I’m only a software-guy rather than a hardware-guy.

Ralph Corderoy avatar

Mike’s right, step or steep for EP or EEP. Nothing to do with scones. More likely to do with being old enough to remember waiting for UV to erase an EPROM so you could have another go at programming a BBC sideways ROM, after sticking a little price label over the window.

Andrew Gale avatar

I’m not so sure! By that argument we’d be saying “eh-mail” (as is ‘step’) rather than “e-mail” (as in ‘steep’)!

Personally, I think it’s “prom”, “e-prom” and “e-e-prom”!

Mike avatar

Oh, and why have you disabled Pinch-to-Zoom on your website – some of us have visual impairments, but still browse with a tablet from time to time and find PtZ invaluable … Have you never heard of accessibility and the Equality Act? (You did ask for angry comments – off topic though this may seem, I can assure you it’s both important and quite angry!!)

Liz Upton avatar

Working fine for me. What device are you using, what OS, and what browser?

Michael avatar

Android on an original Nexus 7. I have had an exchange with Ben about this because your updated site is indeed very clever but the font colour and size used in the blog combined with the inability to zoom makes it difficul to read for those of us with even slightly reduced visual acuity. We normally just zoom and live with any overspill of text.
Since you ask.

Michael avatar

Firefox btw.

Richard avatar

Same problem on an iPad – version 3, os 7.1.2 using safari. No pinch zoom.

Hove avatar

Phoebe, my autonomous pure-Python Quadcopter will soon be wearing her own design of a HAT when she moves to a model B+ from a model A. Her custom HAT lacks the EEPROM (pronounced like eee-baa-gum in Yorkshire) and camera cable slot as the HAT design hadn’t been released when she came up with her design – and she does like to do things her own way!

Howard avatar

It appears that none of the boards from ABelectronics are real HATs!

They look like HATs but none have the EEPROM that no-one seems to know how to pronounce.

So they are only conform to the mechanical spec. but by being included in Liz’s list folks will think they are the real McCoy.

Gordon avatar

If they do not have an EEPROM then you are right they are not HATs


Brian avatar

The boards to fit the B+ from AB Electronics UK are not advertised as being HATs, they only conform to the mechanical spec so they can be fitted using the 4 mounting points. Our boards are also stackable so you can use more than one expansion board at a time and HATs cannot be stacked so you are restricted to one add-on board at a time. Please can you remove the link above so it dosnt confuse people?

Hemal Chevli avatar

I’m selling a proto HAT on tindie.

Michael Horne avatar

That’s not a HAT either. No EEPROM from the looks of it and requires soldering a header.

Stephen avatar

When I worked in hardware R&D back in the day (early-90s) we used :

Prom (as in the concerts) for PROM
Ee-Prom (ee as in cheese) for EPROMS (which were wiped with UV)
Ee-Ee-Prom (with a repeated ee) for EEPROMs (which could be electrically erased)

Neil avatar

It’s E-E-prom, dudes. Anything else is just plain wrong. First there was ROM, then there was PROM, then there was EPROM (E-prom), now there is EEPROM (E-E-prom). I’m old enough to remember them all.

Barry W Christie avatar

So why no mention of the IQAudio DAC+ ?


All the best … Barry

Gordon avatar


Usual problem, we don’t know about everything everyone is working on!!!

What we could probably do with is a web registration interface so people can register their GUIDs for their HAT EEPROM. Then in future we may also be able to add other things like a documentation website link and source download links to Raspbian


Gordon Garrity avatar

I’ve even heard “Ee squared Prom” recently. E-E-prom get’s my vote – that’s what we used way back…

Anyway, HATs….
We’ve got one too :-)
Pi-DAC+ full HD Audio with headphone support too. Information via Tindie.com

Will there be a HAT logo please? We need one of those to allow additional branding and stop any non-HAT confusion.

[email protected]

Hamish Cunningham avatar

Howdy hatters,

The next version of MoPi will be a HAT!


Mobile power for the Pi all in a cute woolly format. (I think.)

Have a good one,


Ben Nuttall avatar

Great! I like the scope for a new set of puns! We’ve got plans for a chef’s HAT, we’ve seen the unicorn HAT, the concept of a top-of-the-stack one being called a top HAT – yours can be woolly HAT!

I suppose an early version of a HAT could be a CAP – a Crude Attempt Prototype?

Hove avatar

Now CAP, I like! That’s definitely what I have because it’s a precursor created prior to the publishing of the true HAT design. Phoebe will be wearing a CAP from now on!

Mark B avatar

My tendency is to use “double-E PROM” but I’ve heard “E E PROM” as well. Either is consistent with the convention (in my experience) of spelling out the first couple letters as in calling UVEPROM “You Vee EPROM” or NV-RAM “N V RAM”.

Using “‘eep’ PROM” vs “‘ep’ PROM” seems like an invitation to misinterpretation.

Of course one can just go with “Flash” if that’s the EEPROM technology and be done with it.

Tom avatar

Let’s call the whole thing off!

Rob S avatar

Being a chap who grew up with the good ol’ Speccy and Beeb, an EPROM was (and still is) pronounced using an ‘e’ as in Eccles (cake).
Whereas an EEPROM had/has an ‘e’ sound as in Tea (a cup of).

Hope this helps.

Scot avatar

That unicorn thing looks pretty cool, but then again I’m a sucker for anything with colorful lights.

Comments are closed