434 MHZ Jammer

By | 22. February 2016

In this tutorial we want to demonstrate how easy it is to build a small 434 MHZ jammer.

The goal is to build the jammer with the NTMF Framework. The jammer sends continuously a signal. While sending the signal continuously no other 434 MHZ transceiver can get a clear signal and can not be controlled.

The sense is not to build a jammer to harm someone! 

The intention is start to learn how frequency moduls works and how to use them for exciting projects like home control. In further tutorials we show how to decode and encode signals within the NETMF. Its usefull to controll wireless sockets.

For this tutorial we used VS 2012 with the NETMF 4.2 and the gadgeteer SDK.

Firstly we look how the operation works and after that we start to build the module.

What you need:

FEZ Spider
434 MHZ transmitters
Extender Module
Breadboard
USB Client SP Module

Lets start:

For this tutorial we used a FEZ Spider from GHI Electronics. The main reason was at the time we created this tutorial the FEZ Spider was part of the Premium Hardware from GHI Electronics.
So only with premium hardware we had access to the GHI.PEMIUM.HARDWARE assembly. This assembly provide us classes we need in this example.
The FEZ Spider is with round about 120 € not the cheapest ghi board. YOu can use the FEZ Cobra II (~50 €) too. It has a G120 Chip and this chip is part of the premium hardware too.

How to build the modul:

To work with the 434MHZ modul we need to use an Extender modul to connect it with our board.

In the next pic you see which pin is for which function.

1. GND
2. DATA IN
3. VCC
4. Antenna

With a breadboard its easy to connect the pins with the Extender modul.

  • Pin GND -> GND GHI Extender Modul
  • Pin DATA IN -> GPIO 3 GHI Extender Modul
  • Pin VCC -> 3V3 GHI Extender Modul
  • Pin Antenna -> Ýou can use a 20 cm cable increase the range

At last you connect the Extender Module with Socket 3 from the FEZ Spider board

Code:
The class we needed from the GHI.PREMIUM.HARDWARE assembly is the SignalGenerator. The SignalGenerator is a very easy way to send a specific signal to a pin. What we give to the SignalGenerator is a ByteArray. As content we can give to the ByteArray a specif signal like “on” or “off” in form of rotatory delay times. To better explain: Perhaps an “on” signal is like 10101010. So we give in the array a couple of values like be 1 for 580ms the be 0 for 400ms. If the SignalGenerator get the ByteArray from us it starts to send the signal automatic as 1 and 0.

To initalize the SignalGenrator we give a pin for the output as paramter.

private SignalGenerator sig;
void ProgramStarted()
{
Debug.Print("Program Started");
GT.Socket sender = GT.Socket.GetSocket(3, true, null, null);
sig = new SignalGenerator(sender.CpuPins[3],true,2);
}

With the “SetBlocking” function we start to send the signal. The possible arguments we can passed to paramters can be find too on the ghielectronics library documentation

public void SetBlocking(
	bool initialValue,
	uint[] timingsBuffer,
	int bufferOffset,
	int bufferCount,
	bool disableInterrupts,
	int lastBitHoldTime,
	int carrierFrequency
)

Parameters

initialValue

  • Type: System.Boolean
  • The initial value of the pin.

timingsBuffer

  • Type:System.UInt32[]
  • The timings buffer. Each entry determines how long in microseconds the pin is held in the state before transitioning.

bufferOffset

  • Type: System.Int32
  • The offset into the buffer at which to begin.

bufferCount

  • Type: System.Int32
  • The number of transitions in the buffer to make.

disableInterrupts

  • Type: System.Boolean
  • Whether or not to disable interrupts while processing the timings.

lastBitHoldTime

  • Type: System.Int32
  • How long to hold the pin in its last state before returning.

carrierFrequency

  • Type: System.Int32
  • The carrier frequency of the signal in hertz. This is generated using software and may not be fully accurate.

Example:

while (true)
{
sig.SetBlocking(true, new uint[] { 280, 541, 280, 541, 739, 250, 739, 250, 739, 250, 739, 250, 739, 250, 739, 250, 280, 541, 280, 541, 280, 541, 280, 541, 280, 541, 280, 541, 280, 541, 280, 541, 739, 250, 739, 250, 280, 541, 280, 541, 280, 541, 280, 541, 280, 541, 280, 541, 280 }, 0, 49, 1500, false);
}

Important info:

Distribution possession and use of electrical equipment that radio communication prevent (jammer), are prohibited.

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