DTMF 4 RELAY CONTROL OVER UTP WIRES
By: Don McClatchie
When you have an installation that requires remote control of a gate, light, or other equipment and you only have one relay to operate you can use Direct Current (DC) or Alternating Current (AC) on one pair of wires, and that is the most direct and lowest cost way to control the relay. However, if you have more than one thing to control or you need the control to work both ways then you need to use signal multiplexing. There are two basic types of signal multiplexing that you can use on a pair of wires, one type is digital, and the other type is analog.
The digital method normally uses two signal states, a high represents a 1 and the low represents a 0, so this method communicates with binary numbers to control the relays. The analog method can use many different types of signals to control the relays. Voltage level changes, low frequency or high frequency modulated signals can transmit the information to control the relays. AM Amplitude Modulation, FM Frequency Modulation, and many other types of modulation can be used including DTMF Dual Tone Multi-Frequency.
DTMF systems works by sending a set of two audio frequencies together to represent a single number. This system was used by the Bell system on pushbutton phones to dial numbers. The normal keypad had 10 numbers and two symbols for a total of 12 buttons. However, some phones had four extra buttons marked A, B, C, and D so the system was designed with 8 frequencies used two at a time for a total of 16 different dual tone combinations. This would allow for the individual control of 16 relays but only one at a time.
In order to control more than one relay at a time the system must use each of the dual tones to represent one binary 4 bit word that copies the relay conditions. This is how up to four relays can be controlled by the DTMF signal. Here is a table of the 16 dual tone combinations and the binary relay signals.
————— 1209 Hz ———- 1336 Hz ———- 1477 Hz ———- 1633 Hz
697 Hz ——— 1 —————— 2 ——————– 3 —————— A
770 Hz ——— 4 —————— 5 ——————– 6 —————— B
852 Hz ——— 7 —————— 8 ——————– 9 —————— C
941 Hz ——— * —————— 0 ——————– # —————— D
Frequencies ————— Binary ———- Number/Symbol
941 Hz/1336 Hz ———- 0000 ——————– 0
697 Hz/1209 Hz ———- 0001 ——————– 1
697 Hz/1336 Hz ———- 0010 ——————– 2
697 Hz/1477 Hz ———- 0011 ——————– 3
770 Hz/1209 Hz ———- 0100 ——————– 4
770 Hz/1336 Hz ———- 0101 ——————– 5
770 Hz/1477 Hz ———- 0110 ——————– 6
852 Hz/1209 Hz ———- 0111 ——————– 7
852 Hz/1336 Hz ———- 1000 ——————– 8
852 Hz/1477 Hz ———- 1001 ——————– 9
941 Hz/1209 Hz ———- 1010 ——————– *
941 Hz/1477 Hz ———- 1011 ——————– #
697 Hz/1633 Hz ———- 1100 ——————– A
770 Hz/1633 Hz ———- 1101 ——————– B
852 Hz/1633 Hz ———- 1110 ——————– C
941 Hz/1633 Hz ———- 1111 ——————– D
Look at the 4 bit binary number as a set of four relays each bit representing one relay you can see how control of the four relays is done with the transmission of any one of 16 dual tones. A “0” represents all relays off and a “D” represents all relays on, and every combination of binary numbers give you full control of all four relays over a single audio pair of wires.
The audio signal will go anywhere an audio signal can be sent over wires or RF transmission. This method is used for industrial control or studio to transmitter control and many other uses. This product called the IP4x4 uses this method to transmit 4 relay controls in both directions over twisted pair network cables using wire pairs 4/5 and 7/8.
The IP4x4 is a remote control system that puts two way contact relay controls onto any IP video cable without affecting the IP video. Use this to install an access control system or an emergency button out at the camera when the cost of running additional wires is prohibitive. If you have to dig a trench, break holes in walls or tear up concrete this unit can get you the remote control you need without the heavy labor and expense. Then send and receive relay control signals both ways over the same network cable used for the IP Video.
The IP4x4 can be use any twisted pair wire and does not require an IP signal to work. Say you want to have a push button at a gate to announce someone at the gate. Then you want to open the gate with a switch in the opposite direction, you can do this with as many as 4 different controls in both directions. That is a total of 8 controls on the same network cable that brings you the IP video signal.
These units have LED indicators for both the input switch signals and the relay output signals to monitor the status of all incoming and outgoing signals. The relay outputs can be set for normally open or normally closed contacts to work with any external equipment requirements. It is powered by 24 Volts AC or DC and can use the same power supply as the camera. This unit is also available in a 12 VDC version at no additional cost, use part number IP4x4-12 at time of order.
For added security the system has a two way “system alarm” relay and LED to indicate loss of communication between the two units caused by a signal disconnect or a cable failure. You get both transceivers with power supplies all included when you order the IP4x4, and you can order this unit with supervised alarm contacts for even more security at no additional cost. When ordering a supervised system, specify the loop resistance and order part number IP4x4S. The IP4x4 will pass “P.O.E. on data” when the P.O.E. is used on the Video lines 1,2 3,6. Lines 4,5 and 7,8 are terminated.
IP VIDEO INPUT SPECIFICATIONS
Standard All IP Video Standard
Impedance Hi-Z (Loop Through)
Connectors 2 8P8C (female)
IP Data Level 800 mVpp standard pass through
Baud Rate 10-100 Mbit
REMOTE CONTROL SIGNAL
RC Cable Input Impedance 100 Ohm standard
RC Cable Output Impedance 100 Ohm standard
RC Data Level 800 mVpp
Contact Input Connectors 2 Position Screw Terminal (4 inputs)
Contact Output Connectors 2 Position Screw Terminal (4 outputs)
System Alarm Connector 2 Position Screw Terminal (1 output)
RC Loop “Supervision” Optional Please Specify
Network Cable Loop though (straight)
Size 5.50″L X 3.3″W X 2.0″D
Power 24 Volts AC/DC 100mA
Power cube 24 Volts AC (2 included)