Required parts and tools<\/h3>\n\n- Two<\/strong> Arduinos. One sends, one receives.<\/li>\n
- One transmitter and receiver pair. This is Siratek product 2661.<\/li>\n
- Two pieces of wire for antennas<\/strong>, about 17.3 cm each. See below; this matters more than anything else here.<\/li>\n
- Six jumper wires.<\/li>\n<\/ul>\n
433 or 315 MHz<\/h3>\n
The Siratek listing covers both frequencies, and the pair must match<\/strong>. A 433 MHz transmitter and a 315 MHz receiver will never hear each other, and nothing in the behaviour tells you which you have.<\/p>\nThe frequency is usually printed on the board, or implied by the colour of the resonator. If you cannot tell, the only reliable way is to test a pair that came together.<\/p>\n
In most of the world 433 MHz is the licence-free band, so prefer it unless you have a reason.<\/p>\n
The antenna, which is the whole story<\/h3>\n
These modules are sold without antennas, and without one the range is a few metres at best.<\/strong><\/p>\nA quarter-wave wire is all it takes:<\/p>\n
\n- 433 MHz: 17.3 cm<\/strong><\/li>\n
- 315 MHz: 23.8 cm<\/strong><\/li>\n<\/ul>\n
Solder a piece of solid wire that length into the ANT<\/code> hole on each board. Straight, vertical, and away from the board if you can manage it.<\/p>\nThat single change typically takes range from under five metres to fifty or more<\/strong>. If your link is unreliable, fit antennas before suspecting anything else, and before touching the code.<\/p>\nA coiled wire works less well than a straight one. Both ends vertical and parallel works better than one horizontal.<\/p>\n
The transmitter likes more volts<\/h3>\n
The transmitter accepts 3 to 12 V<\/strong>, and its output power rises with the supply.<\/p>\n\n- At 5 V from an Arduino: fine indoors, perhaps thirty metres with antennas.<\/li>\n
- At 9 or 12 V from a separate supply: considerably further.<\/li>\n<\/ul>\n
The data line is still 5 V logic<\/strong> from the Arduino regardless, so a higher supply voltage on VCC<\/code> costs nothing in complexity. The grounds must be joined, as always.<\/p>\nThe receiver is 5 V only.<\/strong> These superregenerative receivers do not work properly at 3.3 V, so an ESP32 needs either a 5 V supply for the receiver and a divider on the data line, or a different radio altogether.<\/p>\nWhat it cannot do<\/h3>\n\n- One way.<\/strong> The transmitter cannot receive and the receiver cannot send. Two-way needs two pairs on different frequencies, which is usually the point at which an NRF24L01 becomes the better choice.<\/li>\n
- Shared band.<\/strong> Car remotes, doorbells, weather stations and garage doors all use 433 MHz. Your receiver hears all of them, which is why the library\u2019s addressing and checksums matter.<\/li>\n
- No real security.<\/strong> Anything transmitted can be received by anyone with a module. Do not use it to unlock anything.<\/li>\n
- Slow.<\/strong> Two thousand bits a second is typical, so a short message takes tens of milliseconds.<\/li>\n<\/ul>\n
Pin reference<\/h2>\n
Transmitter<\/strong>, three pins:<\/p>\n\n\n\nPin<\/th>\n Connect to<\/th>\n Notes<\/th>\n<\/tr>\n<\/thead>\n \n\nVCC<\/code><\/td>\n5 V, or a higher separate supply<\/td>\n More volts, more range<\/td>\n<\/tr>\n \nDATA<\/code><\/td>\nUno D12<\/code><\/td>\n5 V logic either way<\/td>\n<\/tr>\n \nGND<\/code><\/td>\nUno GND<\/code><\/td>\nJoin the grounds if using a separate supply<\/td>\n<\/tr>\n \nANT<\/code><\/td>\n17.3 cm of wire<\/td>\n Not optional<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nReceiver<\/strong>, four pins. The two middle pins are both data; use either.<\/p>\n\n\n\nPin<\/th>\n Connect to<\/th>\n Notes<\/th>\n<\/tr>\n<\/thead>\n \n\nVCC<\/code><\/td>\nUno 5V<\/code><\/td>\n5 V only<\/td>\n<\/tr>\n \nDATA<\/code><\/td>\nUno D11<\/code><\/td>\nEither middle pin<\/td>\n<\/tr>\n \nDATA<\/code><\/td>\nNot used<\/td>\n The duplicate<\/td>\n<\/tr>\n \nGND<\/code><\/td>\nUno GND<\/code><\/td>\n<\/td>\n<\/tr>\n \nANT<\/code><\/td>\n17.3 cm of wire<\/td>\n Not optional<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n![\"A](\"http:\/\/siratek.net\/wp-content\/uploads\/2026\/11\/rf-433mhz-wiring.svg\")
Three wires each. The antenna is what takes the range from five metres to fifty.<\/figcaption><\/figure>\nWiring steps<\/h2>\n
On the sending board:<\/strong><\/p>\n\n- Transmitter
VCC<\/code> to 5V<\/code>, GND<\/code> to GND<\/code>, DATA<\/code> to D12<\/code>.<\/li>\n- Solder 17.3 cm of wire to the antenna pad.<\/li>\n<\/ol>\n
On the receiving board:<\/strong><\/p>\n\n- Receiver
VCC<\/code> to 5V<\/code>, GND<\/code> to GND<\/code>, one middle DATA<\/code> pin to D11<\/code>.<\/li>\n- Solder 17.3 cm of wire to its antenna pad.<\/li>\n<\/ol>\n
Keep the two boards at least a metre apart for the first test. Closer than that, the receiver can be overloaded, which is the same trap as the NRF24L01.<\/p>\n
Software and libraries<\/h2>\n
Install RadioHead<\/strong> by Mike McCauley through Library Manager. It supersedes the older VirtualWire and handles the framing, addressing and checksums these bare modules do not.<\/p>\nWriting to the modules directly is possible and a poor idea: without framing you get a stream of noise with your data somewhere inside it.<\/p>\n
Minimal working example<\/h2>\nTransmitter<\/h3>\n\/\/ Siratek: send a reading every two seconds.\n\n#include <RH_ASK.h>\n#include <SPI.h> \/\/ RadioHead needs this even though we are not using SPI\n\n\/\/ speed, receive pin, transmit pin\nRH_ASK radio(2000, 11, 12);\n\nstruct Message {\n uint8_t id; \/\/ which sender this is\n uint16_t count;\n int16_t valueTenths;\n};\n\nMessage message = {1, 0, 0};\n\nvoid setup() {\n Serial.begin(9600);\n if (!radio.init()) {\n Serial.println(\"Siratek: radio init failed\");\n }\n}\n\nvoid loop() {\n message.count++;\n message.valueTenths = 243; \/\/ 24.3, as tenths\n\n radio.send((uint8_t*) &message, sizeof(message));\n radio.waitPacketSent();\n\n Serial.print(\"sent \");\n Serial.println(message.count);\n\n delay(2000);\n}<\/code><\/pre>\nReceiver<\/h3>\n\/\/ Siratek: receive, and ignore everything that is not ours.\n\n#include <RH_ASK.h>\n#include <SPI.h>\n\nRH_ASK radio(2000, 11, 12);\n\nstruct Message {\n uint8_t id;\n uint16_t count;\n int16_t valueTenths;\n};\n\nuint16_t lastCount = 0;\n\nvoid setup() {\n Serial.begin(9600);\n if (!radio.init()) {\n Serial.println(\"Siratek: radio init failed\");\n }\n Serial.println(\"listening.\");\n}\n\nvoid loop() {\n Message message;\n uint8_t length = sizeof(message);\n\n if (!radio.recv((uint8_t*) &message, &length)) {\n return;\n }\n\n \/\/ The band is busy. Check the length and the id before believing anything.\n if (length != sizeof(message) || message.id != 1) {\n return;\n }\n\n if (message.count != lastCount + 1 && lastCount != 0) {\n Serial.print(\" missed \");\n Serial.print(message.count - lastCount - 1);\n Serial.println(\" packet(s)\");\n }\n lastCount = message.count;\n\n Serial.print(\"count \");\n Serial.print(message.count);\n Serial.print(\" value \");\n Serial.println(message.valueTenths \/ 10.0, 1);\n}<\/code><\/pre>\nThree things here are the difference between a link that works and one that drives you mad.<\/p>\n
The length check.<\/strong> RadioHead\u2019s checksum catches corruption, but a neighbour\u2019s doorbell can still produce a frame that passes. Comparing the length against your own struct discards almost all of it.<\/p>\nThe id field.<\/strong> One byte, and it means your receiver ignores every other 433 MHz device in the street. Without it, a car remote going past produces a reading.<\/p>\nThe sequence count.<\/strong> It tells you what you are losing. At the edge of range a link does not fail cleanly; it starts dropping packets, and without a counter that is invisible.<\/p>\nSending something only occasionally<\/h3>\n
For a doorbell or an alarm, sending once is unreliable: a single packet lost means nothing happened. Send it several times.<\/p>\n
for (int i = 0; i < 5; i++) {\n radio.send((uint8_t*) &message, sizeof(message));\n radio.waitPacketSent();\n delay(50);\n}<\/code><\/pre>\nThe receiver then needs to ignore repeats, which the sequence count makes easy: act only when count<\/code> is new.<\/p>\nExpected result<\/h2>\n
With antennas fitted, a packet every two seconds across a house, and the count arriving unbroken nearby.<\/p>\n
Walk away until packets start being missed. That distance, with the antennas you fitted, is your real range, and it will be several times what you get without them.<\/p>\n
Troubleshooting<\/h2>\n
\n\n\nSymptom<\/th>\n Likely cause<\/th>\n Check or fix<\/th>\n<\/tr>\n<\/thead>\n \n\nRange of a few metres<\/td>\n No antennas<\/strong><\/td>\n17.3 cm of wire on each board<\/td>\n<\/tr>\n \nNothing received at all<\/td>\n 433 against 315 MHz<\/td>\n The pair must match<\/td>\n<\/tr>\n \nNothing received, frequency matches<\/td>\n DATA<\/code> pins, or the receiver at 3.3 V<\/td>\nThe receiver is 5 V only<\/td>\n<\/tr>\n \nWorks far away, fails adjacent<\/td>\n Receiver overloaded<\/td>\n A metre apart for testing<\/td>\n<\/tr>\n \nRandom nonsense received<\/td>\n Other 433 MHz traffic<\/td>\n Check the length and an id byte<\/td>\n<\/tr>\n \nPackets missed intermittently<\/td>\n At the edge of range<\/td>\n Expected; a sequence count shows it<\/td>\n<\/tr>\n \nTransmitter range poor at 5 V<\/td>\n Power rises with supply<\/td>\n Try 9 or 12 V on VCC<\/code> only<\/td>\n<\/tr>\n\nReceiver output noisy with no sender<\/td>\n Normal for this receiver type<\/td>\n The library\u2019s framing discards it<\/td>\n<\/tr>\n \nWorks indoors, not between buildings<\/td>\n Walls and distance<\/td>\n Raise the antennas; keep them vertical<\/td>\n<\/tr>\n \nTwo-way needed<\/td>\n These are one-way parts<\/td>\n Use an NRF24L01<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nNext steps<\/h2>\n\n- Easier first:<\/strong> Digital and Analog, and When Each Applies<\/em>, which is all the theory needed.<\/li>\n
- Related:<\/strong> Board-to-Board Radio with NRF24L01<\/em>, for two-way links with acknowledgements.<\/li>\n
- Next project:<\/strong> a tank-level sensor in the garden reporting to a display indoors.<\/li>\n<\/ul>\n
Sources and attribution<\/h2>\n
All text, wiring guidance and code in this tutorial are original Siratek work.<\/p>\n
\n- RadioHead library documentation for the
RH_ASK<\/code> interface.<\/li>\n- Quarter-wave antenna lengths are calculated from the wavelength at 433 and 315 MHz.<\/li>\n
- The four-pin receiver with its tuning adjustment and the frequency pairing were read from the Siratek product listing and photographs for item 2661.<\/li>\n<\/ul>\n
Range figures depend entirely on antennas, supply voltage and surroundings, and the tutorial gives a procedure for measuring your own. The statement that these links provide no security follows from their having no encryption or authentication. No third-party tutorial text, diagrams, photographs or code has been reproduced here.<\/p>\n
<\/p>\n<\/body>","protected":false},"excerpt":{"rendered":"
The cheapest radio link there is. A transmitter the size of a postage stamp, a receiver slightly bigger, and a few lines of code gets a message from one Arduino to another across a building.<\/p>\n","protected":false},"featured_media":0,"template":"","siratek_tutorial_level":[],"class_list":["post-52338","siratek_tutorial","type-siratek_tutorial","status-publish","hentry"],"yoast_head":"\n
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433 or 315 MHz<\/h3>\n
The Siratek listing covers both frequencies, and the pair must match<\/strong>. A 433 MHz transmitter and a 315 MHz receiver will never hear each other, and nothing in the behaviour tells you which you have.<\/p>\n The frequency is usually printed on the board, or implied by the colour of the resonator. If you cannot tell, the only reliable way is to test a pair that came together.<\/p>\n In most of the world 433 MHz is the licence-free band, so prefer it unless you have a reason.<\/p>\n These modules are sold without antennas, and without one the range is a few metres at best.<\/strong><\/p>\n A quarter-wave wire is all it takes:<\/p>\n Solder a piece of solid wire that length into the That single change typically takes range from under five metres to fifty or more<\/strong>. If your link is unreliable, fit antennas before suspecting anything else, and before touching the code.<\/p>\n A coiled wire works less well than a straight one. Both ends vertical and parallel works better than one horizontal.<\/p>\n The transmitter accepts 3 to 12 V<\/strong>, and its output power rises with the supply.<\/p>\n The data line is still 5 V logic<\/strong> from the Arduino regardless, so a higher supply voltage on The receiver is 5 V only.<\/strong> These superregenerative receivers do not work properly at 3.3 V, so an ESP32 needs either a 5 V supply for the receiver and a divider on the data line, or a different radio altogether.<\/p>\n Transmitter<\/strong>, three pins:<\/p>\n Receiver<\/strong>, four pins. The two middle pins are both data; use either.<\/p>\n On the sending board:<\/strong><\/p>\n On the receiving board:<\/strong><\/p>\n Keep the two boards at least a metre apart for the first test. Closer than that, the receiver can be overloaded, which is the same trap as the NRF24L01.<\/p>\n Install RadioHead<\/strong> by Mike McCauley through Library Manager. It supersedes the older VirtualWire and handles the framing, addressing and checksums these bare modules do not.<\/p>\n Writing to the modules directly is possible and a poor idea: without framing you get a stream of noise with your data somewhere inside it.<\/p>\n Three things here are the difference between a link that works and one that drives you mad.<\/p>\n The length check.<\/strong> RadioHead\u2019s checksum catches corruption, but a neighbour\u2019s doorbell can still produce a frame that passes. Comparing the length against your own struct discards almost all of it.<\/p>\n The id field.<\/strong> One byte, and it means your receiver ignores every other 433 MHz device in the street. Without it, a car remote going past produces a reading.<\/p>\n The sequence count.<\/strong> It tells you what you are losing. At the edge of range a link does not fail cleanly; it starts dropping packets, and without a counter that is invisible.<\/p>\n For a doorbell or an alarm, sending once is unreliable: a single packet lost means nothing happened. Send it several times.<\/p>\n The receiver then needs to ignore repeats, which the sequence count makes easy: act only when With antennas fitted, a packet every two seconds across a house, and the count arriving unbroken nearby.<\/p>\n Walk away until packets start being missed. That distance, with the antennas you fitted, is your real range, and it will be several times what you get without them.<\/p>\n All text, wiring guidance and code in this tutorial are original Siratek work.<\/p>\n Range figures depend entirely on antennas, supply voltage and surroundings, and the tutorial gives a procedure for measuring your own. The statement that these links provide no security follows from their having no encryption or authentication. No third-party tutorial text, diagrams, photographs or code has been reproduced here.<\/p>\n <\/p>\n<\/body>","protected":false},"excerpt":{"rendered":" The cheapest radio link there is. A transmitter the size of a postage stamp, a receiver slightly bigger, and a few lines of code gets a message from one Arduino to another across a building.<\/p>\n","protected":false},"featured_media":0,"template":"","siratek_tutorial_level":[],"class_list":["post-52338","siratek_tutorial","type-siratek_tutorial","status-publish","hentry"],"yoast_head":"\nThe antenna, which is the whole story<\/h3>\n
\n
ANT<\/code> hole on each board. Straight, vertical, and away from the board if you can manage it.<\/p>\nThe transmitter likes more volts<\/h3>\n
\n
VCC<\/code> costs nothing in complexity. The grounds must be joined, as always.<\/p>\nWhat it cannot do<\/h3>\n
\n
Pin reference<\/h2>\n
\n\n
\n \nPin<\/th>\n Connect to<\/th>\n Notes<\/th>\n<\/tr>\n<\/thead>\n \n VCC<\/code><\/td>\n5 V, or a higher separate supply<\/td>\n More volts, more range<\/td>\n<\/tr>\n \n DATA<\/code><\/td>\nUno D12<\/code><\/td>\n5 V logic either way<\/td>\n<\/tr>\n \n GND<\/code><\/td>\nUno GND<\/code><\/td>\nJoin the grounds if using a separate supply<\/td>\n<\/tr>\n \n ANT<\/code><\/td>\n17.3 cm of wire<\/td>\n Not optional<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \n\n
\n \nPin<\/th>\n Connect to<\/th>\n Notes<\/th>\n<\/tr>\n<\/thead>\n \n VCC<\/code><\/td>\nUno 5V<\/code><\/td>\n5 V only<\/td>\n<\/tr>\n \n DATA<\/code><\/td>\nUno D11<\/code><\/td>\nEither middle pin<\/td>\n<\/tr>\n \n DATA<\/code><\/td>\nNot used<\/td>\n The duplicate<\/td>\n<\/tr>\n \n GND<\/code><\/td>\nUno GND<\/code><\/td>\n<\/td>\n<\/tr>\n \n ANT<\/code><\/td>\n17.3 cm of wire<\/td>\n Not optional<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Wiring steps<\/h2>\n
\n
VCC<\/code> to 5V<\/code>, GND<\/code> to GND<\/code>, DATA<\/code> to D12<\/code>.<\/li>\n\n
VCC<\/code> to 5V<\/code>, GND<\/code> to GND<\/code>, one middle DATA<\/code> pin to D11<\/code>.<\/li>\nSoftware and libraries<\/h2>\n
Minimal working example<\/h2>\n
Transmitter<\/h3>\n
\/\/ Siratek: send a reading every two seconds.\n\n#include <RH_ASK.h>\n#include <SPI.h> \/\/ RadioHead needs this even though we are not using SPI\n\n\/\/ speed, receive pin, transmit pin\nRH_ASK radio(2000, 11, 12);\n\nstruct Message {\n uint8_t id; \/\/ which sender this is\n uint16_t count;\n int16_t valueTenths;\n};\n\nMessage message = {1, 0, 0};\n\nvoid setup() {\n Serial.begin(9600);\n if (!radio.init()) {\n Serial.println(\"Siratek: radio init failed\");\n }\n}\n\nvoid loop() {\n message.count++;\n message.valueTenths = 243; \/\/ 24.3, as tenths\n\n radio.send((uint8_t*) &message, sizeof(message));\n radio.waitPacketSent();\n\n Serial.print(\"sent \");\n Serial.println(message.count);\n\n delay(2000);\n}<\/code><\/pre>\nReceiver<\/h3>\n
\/\/ Siratek: receive, and ignore everything that is not ours.\n\n#include <RH_ASK.h>\n#include <SPI.h>\n\nRH_ASK radio(2000, 11, 12);\n\nstruct Message {\n uint8_t id;\n uint16_t count;\n int16_t valueTenths;\n};\n\nuint16_t lastCount = 0;\n\nvoid setup() {\n Serial.begin(9600);\n if (!radio.init()) {\n Serial.println(\"Siratek: radio init failed\");\n }\n Serial.println(\"listening.\");\n}\n\nvoid loop() {\n Message message;\n uint8_t length = sizeof(message);\n\n if (!radio.recv((uint8_t*) &message, &length)) {\n return;\n }\n\n \/\/ The band is busy. Check the length and the id before believing anything.\n if (length != sizeof(message) || message.id != 1) {\n return;\n }\n\n if (message.count != lastCount + 1 && lastCount != 0) {\n Serial.print(\" missed \");\n Serial.print(message.count - lastCount - 1);\n Serial.println(\" packet(s)\");\n }\n lastCount = message.count;\n\n Serial.print(\"count \");\n Serial.print(message.count);\n Serial.print(\" value \");\n Serial.println(message.valueTenths \/ 10.0, 1);\n}<\/code><\/pre>\nSending something only occasionally<\/h3>\n
for (int i = 0; i < 5; i++) {\n radio.send((uint8_t*) &message, sizeof(message));\n radio.waitPacketSent();\n delay(50);\n}<\/code><\/pre>\ncount<\/code> is new.<\/p>\nExpected result<\/h2>\n
Troubleshooting<\/h2>\n
\n\n
\n \nSymptom<\/th>\n Likely cause<\/th>\n Check or fix<\/th>\n<\/tr>\n<\/thead>\n \n Range of a few metres<\/td>\n No antennas<\/strong><\/td>\n 17.3 cm of wire on each board<\/td>\n<\/tr>\n \n Nothing received at all<\/td>\n 433 against 315 MHz<\/td>\n The pair must match<\/td>\n<\/tr>\n \n Nothing received, frequency matches<\/td>\n DATA<\/code> pins, or the receiver at 3.3 V<\/td>\nThe receiver is 5 V only<\/td>\n<\/tr>\n \n Works far away, fails adjacent<\/td>\n Receiver overloaded<\/td>\n A metre apart for testing<\/td>\n<\/tr>\n \n Random nonsense received<\/td>\n Other 433 MHz traffic<\/td>\n Check the length and an id byte<\/td>\n<\/tr>\n \n Packets missed intermittently<\/td>\n At the edge of range<\/td>\n Expected; a sequence count shows it<\/td>\n<\/tr>\n \n Transmitter range poor at 5 V<\/td>\n Power rises with supply<\/td>\n Try 9 or 12 V on VCC<\/code> only<\/td>\n<\/tr>\n\n Receiver output noisy with no sender<\/td>\n Normal for this receiver type<\/td>\n The library\u2019s framing discards it<\/td>\n<\/tr>\n \n Works indoors, not between buildings<\/td>\n Walls and distance<\/td>\n Raise the antennas; keep them vertical<\/td>\n<\/tr>\n \n Two-way needed<\/td>\n These are one-way parts<\/td>\n Use an NRF24L01<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Next steps<\/h2>\n
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Sources and attribution<\/h2>\n
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RH_ASK<\/code> interface.<\/li>\n