v4.2 designed by Peter JAKAB in 2004-2005
old version in December, 1999

NOTE for beginners: PICs are general purpose microcontrollers which have to be programmed before you can use them in the actual circuit! Check out this link to learn more.

If you are looking for walkie-talkie or RF circuits, please check here (this page has nothing to do with walkie-talkie circuits).

RF transmitter, built-in antenna	same RF transmitter with external antenna
RF receiver, 4 channels	same receiver PCB with IR module

description

This is a general purpose remote control project with using programmable PIC microcontrollers. Schematics are shown for using infrared (RF) or radio (RF) media. If you are not familiar with microcontroller programming, you can use fixed encoder and decoder integrated circuits instead. Well-known such IC-s are Holtek HT-12D, HT-12E and Motorola MC145026, MC145027, MC145028. Remote controls usually consist of encoder/decoder parts connected to a transmitter/receiver module which takes care of the transmission of digital signals by radio or infra waves. The format of this project's signal is designed to be ideal even for the cheapest ASK RF modules (using 50% signal/silence ratio), and it is similar to the Philips RC-5 format used in infrared remote controls. The transmitter has a varying number of buttons and sends the states of these inputs to the receiver. The receiver device decodes the message and sets the outputs accordingly.

general schematic for remote controls

encoder methods

There are two different methods for encoding/decoding channel information:

• for remote control - this page is about remote control. The information about which key is pressed is encoded and sent.
  You can press at most one key at a time on the encoder, and only the code for the pressed key is sent to the decoder. This is an efficient method for general remote control
  
  
• parallel channels - please see older codecs for such designs. The state of all inputs are encoded and sent.
  The input to the encoder is the state of buttons or TTL inputs. Every input channel state is encoded into each message sent to the decoder (one bit per channel), so TTL inputs can change asynchronously, and any number and combination of buttons can be pressed and encoded, the same state is reproduced on the decoder outputs. This method is suitable for modeling AND remote control, but messages are longer. Analog channels would also be possible, but are not yet implemented
  

remote control

Current devices have 4 or 8 channels - it means they are capable of controlling the state of 4 or 8 switched outputs. Each transmitter and receiver has an address, and the transmitter address must match the address of the receiver to control the channels. The transmitters are capable of sending three different types of codes for the available channels:

• transmitting simple code indicating that the button for a channel is pressed - it can be used for momentary or toggled channel outputs
  
• transmitting channel ON codes - it is used for turning on latched channel outputs
  
• transmitting channel OFF codes - used for turning off latched channel outputs

All the receivers have an indicator LED showing that a valid packet was received. Receivers can have different type outputs for each channel:

• momentary output - the channel output is turned ON while the corresponding transmitter button is pressed
  
• latched output - the last received state is kept. The channel output can be toggled on/off by a momentary button press, or the output can be turned on or off by specific ON/OFF-type transmitter codes

Combining different code-type transmitters with receivers with different type channels, great versatility is achieved. The possible combinations are described below.

transmitter channel type code	receiver channel type	resulting behaviour
simple code	momentary	the channel output is turned ON while the corresponding transmitter button is pressed, and turned OFF when the button is released
simple code	latched	the channel output state is toggled each time its button is pressed: when the corresponding transmitter button is pressed, the output is turned on. By pressing the same button again, the channel output is turned off
channel ON	latched	the channel output is turned on when the corresponding transmitter button is pressed
channel OFF	latched	the channel output is turned off when the corresponding transmitter button is pressed

Current choice of devices:

name	channels and types	addresses	source code
4-channel RF/IR transmitter	4 channels, 8 buttons - each channel has 2 buttons: ON and OFF (for latched receiver operation)	16 (4-bit)	4-ch RF 4-ch IR
8-channel RF/IR transmitter	8 channels, 8 buttons (for toggle or momentary receiver operation)	16 (4-bit)	8-ch RF 8-ch IR
8-channel RF/IR receiver	8 channels: each channel can be latched or momentary	16 (4-bit)	8-ch RF 8-ch IR
4-channel RF/IR receiver	4 channels: each channel has both momentary AND latched outputs (2 outputs per channel)	16 (4-bit)	4-ch RF 4-ch IR

4/8-channel V4.2 RF transmitter

The transmitter has 8 buttons. The 8-channel transmitter can be used for controlling 8 channels by sending simple codes, the 4-channel transmitter can be used with four ON and four OFF buttons for 4 channels. The diode wires (J1-J4) determine the transmitter address. The number of channels (and button functions) depends on the PIC code used.

RF transmitter schematic

4/8-channel V4.2 IR transmitter

The transmitter has 8 buttons. The 8-channel transmitter can be used for controlling 8 channels by sending simple codes, the 4-channel transmitter can be used with four ON and four OFF buttons for 4 channels. The diode wires (J1-J4) determine the transmitter address. The number of channels (and button functions) depends on the PIC code used.

IR transmitter schematic

8-channel V4.2 IR/RF receiver

The receiver has 8 relay-switched NO/NC outputs for 8 channels. Each channel can be set to momentary or latched operation. The address is set by switch S1. The schematic shows the RF version of the receiver, the IR version differs only in the receiver module - a 3-pin IR receiver IC, like TSOP1738 is used

8-channel RF receiver schematic

4-channel V4.2 IR/RF receiver

The receiver has 4 or 8 relay-switched NO/NC outputs for 4 channels. Each channel has both momentary AND latched outputs (2 outputs per channel). LM[0-3] outputs are latched outputs of channels, and LM[4-7] outputs are momentary outputs of channels. The 4-relay PCB can be re-wired to select momentary or latched output for the four relays. The address is set by switch S1. The schematic shows the RF version of the receiver, the IR version differs only in the receiver module - a 3-pin IR receiver IC, like TSOP1738 is used
4/8-channel RF receiver schematic, decoder part	4-channel RF/IR receiver schematic, relays

4-channel V4.2 monitoring IR/RF receiver

The receiver is to display received packets and communication errors on a 2x16 character LCD display. The display is connected through a special 3-wire serial interface which is described here.

RF transmitter/receiver modules

It is possible, but not easy to construct a working RF transmitter or receiver. High frequency circuits need special expertise and equipment so I recommend that you buy a working RF module. I used the following devices: HX1000 transmitter, RX1010 receiver from RFM and small PCB panels: RF-EZ transmitters, RX-3302 super-regenerative receiver, Telecontrolli sup-reg and super-heterodyne receivers. The RF modules are available from a lots of companies. Here is a list of companies from Oricom: Laipac, Linx, IMST, Glolab, Semelab, Sage, Axonn, Lincast, Abacom, Ramsey, Orbit, Innomedia, RF Innovations, Radiometrix, OKWElec, Temic, Telecontrolli, Lemos, Unilink, TrueBlue, Parallax, Computronics, VideoComm, Rentron (schematics), RFM

434M RF transmitter modules: RF-EZ STM series, TM01DS, 15-980TX

434M RF receiver modules: RX-3302, Telecontrolli RR8-434

hardware

The RF transmitter modules can use a wide range of input voltages, so transmitter V+ varies by module specs. Higher RF module voltages usually result in greater transmission distances. IR diodes start working at 2.2VDC, so at least 3V should be applied to the IR version devices. The microcontrollers can work on voltages 2-5.5VDC, lower voltages result in smaller current consumption and longer battery life.  The receiver modules (RF and IR) usually take fixed +5VDC, this is already shown on the RF/IR schematics. The relay driver part can use a higher voltage, depending on the relay ratings. Standard voltages for receiver V+ are 12VDC, 6VDC.

software

All the devices use new, FLASH-based microcontrollers, this means that they can be re-programmed many times. You can experiment with the source code settings to fit your needs. The code can be compiled under MPLAB v5 or v6, but a linked project is required. Please check FAQ at the PIC page.