Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Controlling Equipment Remotely

Not open for further replies.


Member level 2
Jun 1, 2002
Reaction score
Trophy points
Queensland Australia
Activity points
elektor gprs

Controlling Equipment Remotely

I'm asking for your help.
I will first explain what I want to do and why, and what I have come up with so far.
I live in Australia on a small Properity, there is no mains power supply.
Power is supplied by generator and solar system. What I want to do, is control equipment remotely over a large area Pumps on Dams (petrol driven electric start), Generator (240vac electric start), Lighting (low voltage solar powered) ETC.
I am not able to control this equipment with low voltage control circuits, due to voltage drop, especially over a one kilometre distance.
What I have come up with, is running telephone cable to these remote pieces of equipment (which are solar powered) controlling them using switching TONES back and forward down a pair of telephone cables.
I have attached a circuit using discreet conponents that I have started working on, but I,m sure there is many better ways of doing it with out a huge cost, and still have a wide band of tones for switching many oieces of equipment in each direction.
EG Pump Start
Pump running
Tank Full
Pump Stop
Fuel Level Low


I think a good way to control devices in large distances is by using gsm modems.Elektor had an artilce about it few months ago.

Hi thisthat!

You can use DTMF receivers and transmitters. Or simply adapt old telephone sets with tone dialing - you will have quick construction with nice looking design. :)

But do not forget to use balanced circuit to separate input and output signals. So you will have a dozen of combination on each direction.

Best Wishes! Klug.

dirace Elektor artilce

dirace can I get a copy of this artilce on gsm modems from Elektor mag,
can provide somewhere to upload it.


dirace said:
I think a good way to control devices in large distances is by using gsm modems.Elektor had an artilce about it few months ago.

I have attached GSM SMS part 1 as required.

have attached part 2 of the GMS SMS.

Enjoy !

Due to the size of the file, I have to split them up into serveral volumes in order to be accepted by elektroda. Altogether 6 parts for Part II

Last 2 parts of Part II

Thank You ayeong for uploading GSM files, you went to alot of trouble for me.

Doesn't look to useful for what I want to do unfortunately,
dirace must of miss read what I wanted to do. Interesting artilce thu, you can only use siemens phone.

Must be something better out there using tone switching system or alike system for this purpose.


Just in case take a look here
**broken link removed**

Nowadays, the GSM-SMS style is disappearing in favour to GPRS (at least here in Europe). GPRS permits a true TCP/IP connection at a fraction of the cost of SMS.

You need at the receiver end:
-a cellular phone GPRS capable.
-a PIC with a TCP/IP stack (there are free one on the net) and your control program.

It would be like having your own network.

I forgot saying that it was just a comment to the SMS-GPRS issue. Not an easy alternative to your tone system.

I suppose it had been understood... But just in case. Sometimes I get a bit crazy while writing in a foreign language and write a not-so-clear text.

Anyway. Good luck with your project.

Ever considered using RS485 on a low cost twisted pair or even on a telephone wire that you already have installed. You cant beat the cost / performance ratio.

DTMF Decoding...

Hi there,

I would do it the easy way.
1. Use a telephone set as the sender.
2. Use a DTMF decoder chip at each station to decode the sent number,
e.g. if you press #1 digit the decoder would output the binary
code of that digit, then latch the output. You can use the same digit to
de-activate your device.

Good luck and keep us informed on you progress.



It depends if you have a point - to - point connection or multipoint connection.
If it is a two point connection is very easy to use DTMF sigals, transmitted with a good amplifier, a line transformer and a balanced line you can reach easily 2 Km.
You can set the receiver to decode pairs of tones ( one for the ON command and the desecond for the OFF command, caried to the S/R of a D type flip-flop.( for the connection base to remote )
For the connection ( remote to base ) you can use the same signals ( but in total you must use 4 wires, two for the up and two for the down ) and use each tone for every alarm.
Transmit each alarm for few tenths of a second ( to avoid more commands at the same time ) and on the receiver memorize all teh alarms received.


The idea is have as few a cables running over large distance. Send a different tones down the single pair to different pieces of remote equipment.
Different tones back to say that something has operated. (say tank full pump off)

All help welcome thisthat

some ideas

Here are a few ideas.

1a. Run the power over the control cable to power the remote control units.

1b. Route the control cable daisy chain for the shortest possible total path. It is good to use a hot loop and return the far end back to the central control unit. This guards against breaks shutting the system down.

2a. Use two signalling frequencies. One for command one for response.

2b. Use ordinary low frequency PLL and oscillator chips.

3. Use UARTs for the data. You can get some that are 16 bits long.

4. Part of the 16 bit word is the remote unit address when the command is sent out and when responding.

5. Remotes only transmit after they have been polled.

6. This way every unit has the same design of transmitter and receiver.

Not open for further replies.

Part and Inventory Search

Welcome to