Uplift Desk Automation

Message Syntax

Transmit

A transmitted message has the following syntax.

0xF1, 0xF1, <cmd>, 0x00, <crc>, 0x7E

0xF1, 0xF1 indicates the message start cmd is one of:

0x01 - Up 0x02 - Down 0x2B - Stop 0x03 - Save sitting height 0x04 - Save standing height 0x05 - Recall sitting height 0x06 - Recall standing height 0x06 - Sync crc is the sum of the bytes at index 2 and 3. 0x7E indicates the end of message.

Receive

A received message has the following syntax.

0xF2, 0xF2, <cmd>, <len>, <data...>, 0x0F, <crc>, 0x7E

0xF2, 0xF2 indicates the message start cmd is one of:

0x01 - Height value 0x25 - Unknown 0x26 - Unknown 0x27 - Unknown 0x28 - Unknown len indicates how many messages will be sent next, excluding the CRC and EOT. data will contain the incoming data values, explained for height readings below. 0x0F - Unknown crc will be the sum of bytes at index 2 up to the CRC. 0x7E indicates the end of message.

Received Height Message

When a new height value comes in, the message will look something like this:

0xF2, 0xF2, 0x01, 0x03, 0x01, 0x1B, 0x0F, 0x2F, 0x7E

In this case, the desk was at 28.3". Here is how we can calculate that.

First off, the command is 0x01, so we know we're about to receive height data. The next byte tells us to listen for 3 data bytes. The relevant data comes in as 0x01, 0x1B. This will be converted to a height value later. Then, we add all of the previous bytes (other than the header) to verify the CRC is correct.
0x01 + 0x03 + 0x01 + 0x1B + 0x0F = 0x2F

Height Calculation

To do. For now, see https://embedded-elixir.com/post/2019-01-18-nerves-at-home-desk-controller/.