jsimmonds2
Using popular Pressure, Temperature sensor LPS25H and Circuits.I2C
Seems I either don’t understand the Circuits.I2C API or don’t understand the I2C sensor device ![]()
My code has to do single-byte register transfers rather than reading 3 sequentially addressed registers to get the latest Pressure value : e.g. for device at bus address 0x5d and the LSByte of the Pressure value in Register 0x28 this is what I see :
Read each byte value seperately
iex(fb2@fb2-e53f.local)24> Circuits.I2C.write_read ph_ref, 0x5d, <<0x28>>, 1
{:ok, <<241>>}
iex(fb2@fb2-e53f.local)25> Circuits.I2C.write_read ph_ref, 0x5d, <<0x29>>, 1
{:ok, <<190>>}
iex(fb2@fb2-e53f.local)26> Circuits.I2C.write_read ph_ref, 0x5d, <<0x2a>>, 1
{:ok, "?"}
Try reading the 3 registers in one go
iex(fb2@fb2-e53f.local)28> Circuits.I2C.write_read ph_ref, 0x5d, <<0x28>>, 3
{:ok, <<241, 241, 241>>}
iex(fb2@fb2-e53f.local)29>
Thanks !
Trending in Questions
I having some trouble figuring out if I have set myself too strict of standards for my production server. Currently I can handle 75% of r...
New
Documentation
While reading the Scoped Routes section, I noticed that the documentation currently refers to a problem without explainin...
New
Hello,
I’m trying to build a basic Phoenix web-app, and I’d like to use Tailwind.
However, when I launch mix phx.server, I get an error...
New
Hi everyone,
I am toying with the idea of building a “match maker” for giving personal help to people that wants to start coding.
I sta...
New
I recently noticed that Elixir’s Logger defaults its primary log level to :debug when no :logger, :level application configuration is pre...
New
I’m working on a small exercise involving update_in/3, and I came up with this solution:
data = %{
name: "Periodic Table",
category:...
New
I’ve got trouble wrapping my head around the order in which functions are called in this snippet (from Phoenix’s authentication):
toke...
New
Other Trending Topics
Edit: 2026 May 15 - This post is archived.
Mob is alive!!
Main docs: mob v0.7.11 — Documentation
A bit of explanation for the slightly c...
New
Hey, I’m Jesse and I’m the main contributor behind Dexter, a full-featured, lightning-fast Elixir LSP optimized for large codebases. It s...
New
I am happy to introduce the very α version of the new programming language compiled to BEAM.
Welcome Cure.
It has literally three kille...
New
Hobbes is a low-level distributed database for the Elixir programming language.
Hobbes provides a simple, safe, and scalable storage lay...
New
Hi everyone!
The first release candidate for the Expert language server project is now available!
We’ve published a press release detai...
New
A little off-topic, but I feel like people here have a good head on their shoulders.
I used to be quite good at making software. Was luc...
New
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #library
- #deployment
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #elixirconf
- #channels
- #exunit
- #discussion
- #code-sync
- #podcasts
- #javascript
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #full-time-contract
- #podcasts-by-brainlid
- #ai
- #ecto-query
- #elixirconf-us
- #blog-post
- #elixir-ls
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #elixirconf-eu
- #api
- #forms
- #metaprogramming
- #hex











Showing Posts 1 to 2- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
fhunleth
Normally what you’re doing would work since I2C devices usually auto-increment the destination register on multi-byte reads. It looks like the LPS25H does something special, though. Take a look at section 5.2.1 of the datasheet. It looks like if you set the high bit of the register that you’re interested in, it will auto-increment, so try this:
jsimmonds2
@fhunleth, thanks for being my
helpful eyesonce again . . works as desired now.