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RX-5 4-Bit Remote Control RF Receiver Interface With 2 Relay

2015-03-02 21:03  
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RX-5 4-Bit Remote Control RF Receiver Interface With 2 Relay & 2 Digital Outputs

The RX-5 receiver board is designed for use with the TX-4-PC RF transmitter board shown HERE, but can be used with any RF transmitter operating at the same frequency as the RF receiver module used with the RX-5. The transmitter must also use the Holtek HT-12E or equivalent 4-bit series encoder IC such as the Ming TX-99 K2, 2-button, key-chain type transmitters.

The RX-5 receiver board is designed for use with three popular & inexpensive RF receivers.

bulletRWS-434 RF transmitter module
bulletMing RE-99 RF transmitter module
bulletMing RE-66 RF transmitter module

Just plug-in one of these three RF receiver modules for instant remote control.

The RX-5 receiver boards are designed for operation with the RWS-434, Ming RE-99 or RE-66 RF receiver modules. As shown below, female headers are provided for mounting RWS-434 & Ming RF receivers on the RX-5.

RX-5 With RWS-434 RF Receiver Module

RX-5 With Ming RE-99  RF Receiver Module

Note:The antenna wire for the RWS-434 photo was coiled to include the wire antenna in the picture. You'll want to extend the antenna straight up without coiling it for optimum range.

Mounting Antennas:

The RX-5 circuit board includes a gold single-pin socket for the RWS-434 antenna wire, and a solder pad for whip antenna ground connections. The RWS-434 RF receiver requires a solid 6 1/2" piece of 22 gauge insulated wire for a 1/4 wave antenna. Just insert the end of the 6 1/2" 22 gauge wire into the gold pin socket as shown below.

Installing 22 Gauge Wire Antenna For RWS-434

For the whip style 434MHz antennas, solder the center conductor of the whip antenna coax wire to the gold pin socket marked ANT, and solder the shield to the pad marked AGND [antenna ground].

The Ming RE-99 and RE-66 RF receiver modules require a 9.06" 22 gauge wire for a 1/4 wave antenna. Solder the antenna wires directly to the Ming RF receiver modules as described in the documentation for the specific receiver module used. The gold pin socket is used only for the RWS-434 wire or whip antenna connections.

No Antenna Required For 30-50 Foot Operation:

One benefit of using the Ming RF receiver modules is the loop antenna designed into the RF module. The loop antenna allows operation between 30-50' [or more] without the addition of the external wire antenna. The RWS-434 receiver modules require a minimum 6 1/2" antenna wire, or the 434MHz whip antenna.


RX-5 schematics in Adobe .PDF format HERE.


RX-5 full documentation & schematics HERE

The RX-5 Board:

The RX-5 uses an 18-pin ULN2803A high-current darlington transistor driver IC to control the two mechanical relays, provide two digital outputs for controlling solid state relays, and to drive the LEDs used as output status indicators. The ULN2803 has internal fly-back protection diodes that cancel the kick-back voltage spikes produced when relay coils are de-energized. The ULN2803A simplifies the design by reducing the number of components required for the relay drive, digital outputs, LED drives, and inductive spike protection circuits to a single IC.

Note:Unlike most equipment with ICs soldered directly to the PCB, the RX-5 ULN2803A driver, and HT-12D decoder ICs are in dual-leaf DIP sockets for easy replacement.

Relay & Digital Output Connections:

RX-5 Relay & Digital Output Connections

Connections [shown above] to the RX-5 relay contacts are made via the two 3-position screw terminals marked D0 and D3. The TX2.5 relays used on the RX-5 have normally open & normally closed contacts. Each connection is marked on the RX-5 PC board. C = common, NO = normally open, and NC = normally closed.

The remaining two 2-position screw terminals [ D1 & D2 ] are the digital outputs. The ULN2803A outputs connect directly to the D1 & D2 screw terminals marked "-" providing a switched ground to each screw terminal as shown above, and in the schematics. The D1 & D2 screw terminal connections marked "+" connect directly to the RX-5 +5V power supply.

Note:The ULN2803A outputs are capable of driving 500mA per output. The 7805 +5V regulator on the RX-5 limits the amount of current available to 1A total. Do not exceed 200mA per digital output to avoid shutting down the regulator or possible damage. The digital outputs are primarily designed for solid state relay control outputs, but can be used for direct control of DC powered equipment that requires less than 200mA.

Each output terminal has a green  output "status" LED directly above the terminal connection. Status LEDs' indicate the ON or OFF state of each relay & digital output.

Note:The relay contacts at screw terminals marked D0 & D3 do not provide power. These are dry contacts used to switch external power. The digital outputs provide +5 at the screw terminals marked "+", and "switched ground" at the screw terminals  marked "-" as shown above for D1 & D2.

Example Relay & Digital Output Connections:

Solid State Relay / Digital Output

Relay Contact / External Power Control

Important Note:Use the digital outputs with solid state relays for controlling AC powered equipment, and locate the AC powered equipment away from the RF receiver.

Use the mechanical relays for DC powered equipment. Connecting AC power directly to any of the screw terminals will decrease the overall operating range due to the interference generated by the AC power lines and or the device being powered by the AC voltage. Connection of AC power to the screw terminals is also not recommended due to the exposed screw terminals, and danger of contact with the exposed terminals.

Locate the AC powered device and solid state relays away from the RF receiver as far as possible to remove the AC power as a source of interference. The digital outputs can easily drive the solid state relay even when located several feet from the RX-5 board. Locate any motors away from the RX-5 also to avoid interference from the magnetic field generated by the motor when turned ON.

A common symptom would be: You can turn the motor ON from a good distance, but need to get very close to the receiver to turn the motor back OFF. This is caused by interference generated by the motor when it's ON - resulting in a decreased overall operating range. When the motor is OFF, there is no interference, hence the longer range until you turn it ON.

How it Works:

The RX-5 receiver uses the Holtek HT-12D decoder IC digital output pins to control the NPN darlington transistor array ULN2803A driver. A logic 1 on the NPN ULN2803A input switches ON the transistor drive output. A logic 0 on the input turns OFF the output driver. As shown below, each of the HT-12D outputs connect/control two inputs/outputs of the ULN2803A.

The RX-5  uses the additional drive outputs of the ULN2803A to drive four green output "status" indicator LEDs. Each of the four HT-12D data output pins has a corresponding green LED output status indicator. The HT-12D D0 output pin controls the relay marked as D0 on the RX-5 board, and the D0 status LED. When the D0 relay is energized, the D0 status LED is ON. This same arrangement is used for the remaining outputs & status LEDs.

HT-12D to ULN2803A Schematic

The D3 relay can be operated in "momentary" or "latched" mode. Momentary mode is selected by placing the shorting jumper in the "M" position connecting the HT-12D VT output to the ULN2803A IN1 & IN2 input pins. Latched mode is selected by moving the jumper to connect the HT-12D D3 output to IN1 & IN2 of the ULN2803A. Below is a close up photo of the D3 mode option jumper set for momentary operation of the D3 relay --

D3 Mode Option Jumper


ULN2803A to Relays & Digital Outputs Schematic

Each of the ULN2803A outputs are open collector type. When an output is ON, it will sink current to the relay coils, digital outputs, and status LEDs. The digital outputs will easily drive solid state relays for controlling AC loads. The mechanical relays [D0 & D3 screw terminals] can be used for DC control with a limit of 30 VDC at 2A max. For details on the mechanical relays used on the RX-5, please download the datasheetHERE.

Address Feature:

The RX-5 receiver has an 8-position DIP switch [shown below] used for setting the receiver/decoder address. Addresses from 0 to 255 are possible, allowing control of up to 256 individually addressed receivers, or combinations with multiple receivers set to the same address.

A7    A6    A5    A4    A3    A2    A1    A0

As shown above, all of the HT-12D decoder IC address pins are at ground with each DIP switch in the ON position for an address of "0". Switches in the down position represent a logic "1". In the up or ON position at logic "0".

Close-up Photos:

The first photo shown below gives a close-up view of the RWS-434 RF receiver module mounted in the female header sockets, and the 3-pin header socket provided for the optional Ming series RE-99 or RE-66 RF receivers. You might want to trim the RWS-434 pins down as shown in the photo to seat the RWS-434 into the header securely, and to help protect the module. The Ming RF receiver modules mount in the 3-pin header socket shown just to the left of the RWS-434. The RX-5 works equally well with either the RWS-434 or Ming RE-99 and RE-66 series RF receivers.

The RX-5 board D2 and D3 outputs can also be controlled with the Ming TX-99 K2 2-button transmitter when using the RE-99 receiver module with the RX-5.

Photos are reduced to thumb-nail size. Just click one to view the larger picture.

Mounting RF Receiver Modules

Assembled RX-5 With RWS-434

The Power Supply:

The LM7805 +5V regulator is used on the RX-5 receiver board to handle the larger current requirements of the mechanical relays, and provide ample current for the four status LEDs' and two solid state relay drive outputs. As shown above in the picture, a PC mount female power jack is used. The jack size is 2.1 x 5.5 mm center positive. The LM7805 regulator requires an input voltage of at least 7V minimum, and can handle up to 35V input voltages.


Power Supply & +5V Regulator Schematic

We recommend a DC power supply between 9 & 12 VDC input to the 7805 regulator. There is no gain in performance by using a larger supply input voltage, and lower inputs reduce the amount of heat generated by the regulator.

To complete the TX-4-PC & RX-5 RF remote control system, we have a PC software application that allows you to set the time of day, receiver address, and receiver data output states to control RX-5 receivers directly from your PC serial port at specific times. We also have a tutorial showing how to create your own custom remote control software for use with the TX-4-PC & RX-5 remote control boards on the TX-4-PC details page HERE