HTH's On-Line Catalog - PLM-24

PLM-24 Power Line Modem...

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Communicate over the power lines!

PLM-24 is a low cost and easy to build Power Line Modem capable to send and receive serial data
over the power lines (mains) at speed up to 2400 bps. PLM-24 lets you communicate with other devices
around the house without running any wires since it uses the wires already available in every house!

PLM-24 is designed as a small module (54 x 38 mm) to be used in new or existing designs, the picture
above shows a ready built unit. PLM-24 can easily be interfaced with any PC or microcontroller (MCU)
that are able to send and receive serial data at 2400 bps or less. Perfect for use with BASIC Stamp's, SX,
PIC, 8051, AVR, 68HC11, COP or standard PC's...

What can it be used for?

PLM-24 can be used to build your own bi-directional home automation system where you can control
lights, relays, measure temperature, measure power consumption, query status of switches, turn things on/off
or control devices like stereos etc. Since it's bi-directional you can poll your house to see what modules you
currently have available or if anyone of them isn't responding you can take proper action.

Or you can use it to send and receive messages or data (files) between personal computers and their devices
in a building without the need of cables. Use it as a low speed printer network for all in the building to share
or run a speech recognition program on your PC to "talk" with your home!

Combine both together and top it with some PLM-24 modules that have alarm sensors connected and you
will have a security system that is capable to dial up with your PC's modem and play a tune or send an fax or
e-mail if something goes wrong or your house is visited by unwanted people.

With PLM-24 you have the communication medium the rest is up to you! Below is a short list of some doable
things just to spark your imagination...

- Control lights and other devices
- Security systems
- Energy control and management
- Process control
- Environmental control
- Low speed PC networks
- Heating and air condition control
- Sprinkler/watering systems
- Sophisticated HA systems
- Help for elderly and disabled people
- Chat system for buildings
- Measure temperature in rooms
- Small info terminals in rooms
- Close blinds if sunlight is to strong
- Let your PC control your home
- Stage control in home theaters
- ...

Since PLM-24 is capable of both sending and receiving serial data over the power lines it's possible to
implement a protocol that uses checksums or CRC to ensure that received data is correct and if it isn't ask
for a re-transmission! The module itself is protocol independent so you can use how simple or complicated
protocol you want (send ASCII or binary). Since the environment on the power line isn't very friendly it is
wise to implement some way to check for errors and we recommend that you do but it's not necessary.

By being protocol independent the PLM-24 doesn't limits to any max numbers of power line modems used
in your network, it's up to you. You can have as few as two PLM-24 and our S.N.A.P network protocol
will let you have up to 16.7 millions nodes in your HA network!
Picture to the left shows a ready built PLM-24 Power Line Modem.

How do I interface to PLM-24?

PLM-24 needs +5 VDC and +10 VDC to operate and interface to the power line via a coupling
network consisting of three parts. One transient diode (D1), one small T1002 coupling transformer (TR1),
and one capacitor (C1).

The interface to the MCU or PC is very simple and requires minimum 3 I/O lines, RxD (receive data),
TxD (transmit data) and Rx/Tx control. The other I/O lines on the module may be used depending on your
application. The I/O lines are TTL/CMOS compatible. Below is a short description and they are fully
described in the manual along with examples on how to connect it to various MCU.

Name Direction Description
MCLK Output Master Clock
WD Input Watch Dog
Rx/Tx Input Rx/Tx mode select
CD Output Carrier Detect
TxD Input Transmit data in
RxD Output Received data out
RSTO Output Reset signal
CRTL Input Control input

PLM-24 Power Line Modem Kit.

We offer a complete kit (Art#: 50100) that includes everything you need to build the PLM-24 Power
Line Modem. The PLM-24 kit includes a professional made double-sided, plated through, solder masked
and silk screened printed circuit board. All required components, printed manual that contains assembling
instructions, part list, complete schematics along with examples on how to interface PLM-24 to a serial port
on a PC and to common MCU's such as BASIC Stamp, PIC and 8051. You don't need any special or
expensive development tools to get going!

Picture to the right shows two PLM-24 PCB's.


- Send and receive 110-2400 bps, half-duplex over the mains.

- At 2400 bps PLM-24 is 40 times faster than X-10.

- Works over 230 VAC/50 or 60 Hz or 110 VAC/50 or 60 Hz.

- PLM-24 is protocol independent.

- Uses FSK (more immune to noise and other interfering signals than ASK).

- Can co-exist with X-10 equipment and don't false trigger them.

- Small module, easy to embed, PCB 54 x 38 mm (2.1 x 1.5 inch).

- Simple interface to a MCU or PC.

- Easy to build and use.

- Built in watch dog function.

- Carrier detection.

- Compatible with CENELEC EN 50065-1 (EU) and FCC (US) specifications.

You can download the PLM-24 Power Line Modem leaflet in PDF-format by clicking on the link below.
To view it you will need the free Acrobat Reader from Adobe. If you don't already have it click on the
"Get Acrobat Reader" icon.

- PLM-24 Power Line Modem (115 KByte).

- Download free PLM-24 <-> TCP/IP Gateway.

- Download application notes and source code examples.

If you have any other questions please contact

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