Homematic - Transmitter / receiver module

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Updated - August 4, 2025

The Homematic Transmitter module HM-MOD-EM is used to implement switching states, which are detected via 8 independently acting inputs by means of high or low level and forwarded to the control center by radio, while the Receive module HmIP-MOD-OC8 Switching tasks via open collector outputs (This module is the successor to the no longer available HM-MOD-Re-8 in the IP version) takes over.

Characteristics

Both modules can be operated with two AA batteries, DC 2 - 3.3 V or also 3.5 - 12 V and can therefore be used very flexibly.

The very small size allows installation in a small, waterproof housing, which can also accommodate a battery holder for the two AA batteries if required. The antenna can remain in the plastic (!) housing and does not need to be removed from it.

The receiver module also has 8 buttons that can be used to activate the assigned switching output, regardless of the actual programming on the Headquarterscan be switched, e.g. to carry out function tests on site.

Example - Recording the cistern water level

Suppose you want to remotely monitor the water level in a cistern. To do this, the cistern is fitted with a PVC pipe (e.g. installation pipe) corresponding to the depth and attached to the edge of the shaft ring with pipe clamps.

sensor

Depending on the depth of the cistern, several pipes are inserted into each other and glued together in the sockets using PVC adhesive. The end of the pipe is sealed with a PVC cap, which is also glued on.

A 12-core cable (control cable with numbered cores) is fed into the pipe. The individual wires are routed to the outside through holes drilled at intervals of one tenth of the total pipe length (= depth of the cistern).
With a very deep cistern, the cables are first pushed through the two meter pipe segments before(!) they are glued together.
For this purpose, a rigid 1.5 mm²-copper wire (e.g. Single-core installation cable), which is pushed through the relevant hole towards the upper end of the pipe, the respective cables, fixed to the copper wire with insulating tape, are pulled through the corresponding hole one after the other.

The eleventh or twelfth cable serves as an earth connection and is attached to the lower end of the tube with a stainless steel screw glued into the end cap.
The remaining ten cables are used to query the water levels in 10 % steps (10 .. 100 %) and are connected in the same way as the earth connection, to stainless steel screws (fastened using suitable cable eyelets, washers and nuts), which are then glued watertight in the borehole.

The top of the pipe should also be sealed with a watertight cable gland. Now that the pipe is sealed watertight, there is no risk of corrosion of the copper cable connections inside it.

electronics

The other end of the cable is now fed via an IP67 cable gland into a watertight PVC box containing two of the above-mentioned transmitter modules together with a battery holder (or battery with external - small - PV module).

After connecting the power supply, both transmitter modules can be taught to the control panel and set to the desired function with the appropriate programming.

Teaching the modules

Set the control panel to teach-in mode

Call up the web GUI in the alarm panel and click on "Teach-in devices" in the top right-hand corner. This starts the central unit's teach-in mode for 60 seconds.

The teach-in process can be repeated as required.

Set the transmitter module to teach-in mode

The transmitter module has a button at the bottom which, when pressed once briefly, puts the module into teach-in mode for 20 seconds.

Set the receiver module to teach-in mode

The receiver module is set to teach-in mode by pressing one of the eight buttons for at least 4 seconds.

inbox

Once the devices have been successfully programmed, they appear in the control panel's inbox, where they can be given individual names and configured.
Apart from the naming of the devices and their channels, all parameters can normally be left as standard.
The individual channels should be given descriptive names so that it is clear later which channel represents which percentage (10 .. 100 %) in the above example.

Visualization

Means AIO Creator the switching states of the inputs of both modules can be queried and graphically converted into a tank display, which provides information about the fill level of the cistern, e.g. via a bar graph (bar display).