desk-control

Take control of your height adjustable desk!

Several brands for height adjustable desks like Uplift and Ergotopia use components made by Jiecang Linear Motion. Among them is the JCB35N2 or a variant thereof as the control box, in combination with one of their control panels, for example the JCHT35K9.

Documentation on this system basically does not exist and thus custom controllers are not available. This obviously has to change.

Note: The information in this project is made with the best of intentions. However, we are tinkering with expensive components. You are solely responsible for your stuff and when things break, it is your problem. Please don't try anything without double checking this information and knowing what you do.

JCB35N2 Control Box

The JCB35N2 control box is designed for standard desks with 2 motors, with soft-start/soft-stop and anti-collision protection. It has a power port AC, two motor ports M1 & M2 and two control ports F & HS. (JCB35N[3,4] are very similar in their design, except for the number of motor ports and missing F port; the HS control port might be exactly the same, but this is not tested!)

The JCHT35K9 control panel has buttons to raise ▲ and lower ▼ the desk, four memory buttons 1-4 to set the height to predefined positions and a setup button M, which is used for different settings. A three-digit 7-segment display shows the current height of the desk (probably with configurable units; the Ergotopia Desktopia Pro shows the height in cm).

HS Port

The HS port is used by the control panels with support for memory buttons. It uses a standard 8 pin RJ45 connector with 5V logic. Pins are active low.

Pinout

            RJ45 Jack

      1   2   3   4   5   6   7   8
    +-+---+---+---+---+---+---+---+-+
    | |   |   |   |   |   |   |   | |
    | +   +   +   +   +   +   +   + |
    |                               |
    |                               |
    |                               |
    +--------+-------------+--------+
             |             |
             +-------------+

Pin	Function
1	M button
2	Height output (UART)
3	GND
4	?
5	VCC (+5V)
6	Memory buttons
7	Raise + memory buttons
8	Lower + memory buttons

The function of pin 7 and 8 depends on the input. They can be used alone to manually raise and lower the desk. If they are used in one of the combinations shown below, the respective memory slot is triggered.

Pulling pin 4 low just activates the display of the control panel. Might be the intended function, but it might not be?

Memory Buttons

Button	Pin 6	Pin 7	Pin 8
1		x	x
2	x
3	x		x
4	x	x

While the box can report the current height, it seems like it is not used by the panel to set the height for the memory slots. The memory function is therefore entirely managed by the control box. Unfortunately, this also means that the soft-start/soft-stop feature is not controllable from the outside.

UART height output

The control box can report the current height for the control panel to show. It uses a one-directional UART connection with 9600 baud rate, 8 data, 1 stop, no parity.

• The control box starts a transmission whenever a button is pressed. It begins with two bytes, 0x81 and 0xF5.
• Data is constantly sent for 10 s with a delay of 15 ms between updates. One update consists of four bytes: the first two are always 0x01, the remaining encode the height in a 16-bit value. (This applies specifically to the Ergotopia Desktopia Pro, which shows the value in cm on the display. The value given by the control box is provided in mm.)
• Transmission ends with two bytes, 0x01 and 0x05.

This example shows one update. The last two bytes combined to a 16-bit value result in a height of 1093 mm, or 109.3 cm.

F Port

?

Missing / ToDo

• Analyze F port
• Find out all options (anti-collision sensitivity, min/max height, ...)
• Document error codes (missing motor, ...)