Easy Build RF Receiver / Transmitter Pair (27 MHz)
Easy Build RF Receiver / Transmitter Pair (27 MHz)
In this article we will build a simple rf receiver module that works at 27 mhz and turns on an LED anytime the signal from the transmitter is detected. A very simple idea, but as you will soon find out, a lot goes into making it a reality. We'll be making our own PCB for this circuit, so get out the ferric chloride and copper clad PC board.
Purpose and Overview Of This Project
The goal of this project is to make an RF receiver front end to capture the 27 MHz signal that we're expecting, connect that to two amplifier stages and then to use the originally transmitted signal to turn an LED on. This processs is very much the opposite of how the transmitter worked.
The front end receiver will be a very old regenative design that has been used for decades. The amplifier stages will be single transistor amplifiers that basically rail the signal between power and ground. The final part is a 555 timer which will be used as a comparator which will tell us whether our signal has made it through or not by lighting up a green LED.
Parts
PC Board
Toroid Core (AL=25)
3x 2N2222 Transistors
1x 555 Timer
2x 2.2MΩ Resistor
2x 180kΩ Resistor
2x 100kΩ Resistor
4.3kΩ Resistor
560Ω Resistor
2x 100Ω Resistor
100uF Capacitor
4.7uF Capacitor
3x 0.1uF Capacitor
2.2nF Capacitor
47pF Capacitor
27pF Capacitor
1x 5mm Red LED
1x 5mm Green LED
Magnetic Wire (AWG 24/26)
Antenna Wire (AWG 26/28)
+9v Battery Connector
Ferric Chloride
Clothing Iron
Solder
Soldering Iron
Parts List Details
Most of the parts in this project are discrete passive componenets, however the few active components are described in more detail below.
PC Board
We will make our own PCB for the receiver so that we can have exact control over all the connection lengths and parts used. 27 MHz is pretty low frequency so there's actually not too too much to worry about in terms of performance degradation.
6 Turn Inductor Toroid Core
The toroid core and magnetic wire will be used to make a small inductor. It's very important that your ferrite core is AL=25 otherwise the inductance will be off and the receiver won't work.
2N2222 Transistors
We will use 2N2222 general purpose transistors as part of our front-end for the receiver and for the amplifier stages.
555 Timer
The 555 timer will be used as a comparator and LED driver. The input voltage from the receiver will get compared using the 555 timer's input pins and the green LED will either be driven or not. The red LED driven by the 555 timer tells you the 555 timer is on and functioning.
Schematic Overview
The schematic for this project flows naturally from left to right. Beginning at the antenna and the regenerative receiver front-end, then flowing through the amplification stages and then into the 555 timer.
Schematic Specifics
Front-End Regenative Receiver
This is a very common regenerative receiver front-end that you can find in circuits all over the web. I tailored the parts used to what I had laying around, generally you can tweak part values a little bit, with the exception of L2 and C2 which are your tuning circuit (tank circuit) for 27.145 MHz.
Amplifier Stages
Two amplifier stages exist in the middle of the schematic. They are used to 'rail' the signal back to its square-wave digital form of either +5v or +0v. I'm pretty sure that these amplifiers could be tweaked to get better performance, however the current design should work well enough for our requirements.
555 Timer Receiver Comparator
The amplified signal makes its way to the 555 timer in the form of its original square wave where this 555 timer uses the voltage detected with internal comparators to create an output that turns on the green LED.
The video below shows the circuit in action:
In this article we will build a simple rf receiver module that works at 27 mhz and turns on an LED anytime the signal from the transmitter is detected. A very simple idea, but as you will soon find out, a lot goes into making it a reality. We'll be making our own PCB for this circuit, so get out the ferric chloride and copper clad PC board.
Purpose and Overview Of This Project
The goal of this project is to make an RF receiver front end to capture the 27 MHz signal that we're expecting, connect that to two amplifier stages and then to use the originally transmitted signal to turn an LED on. This processs is very much the opposite of how the transmitter worked.
The front end receiver will be a very old regenative design that has been used for decades. The amplifier stages will be single transistor amplifiers that basically rail the signal between power and ground. The final part is a 555 timer which will be used as a comparator which will tell us whether our signal has made it through or not by lighting up a green LED.
Parts
PC Board
Toroid Core (AL=25)
3x 2N2222 Transistors
1x 555 Timer
2x 2.2MΩ Resistor
2x 180kΩ Resistor
2x 100kΩ Resistor
4.3kΩ Resistor
560Ω Resistor
2x 100Ω Resistor
100uF Capacitor
4.7uF Capacitor
3x 0.1uF Capacitor
2.2nF Capacitor
47pF Capacitor
27pF Capacitor
1x 5mm Red LED
1x 5mm Green LED
Magnetic Wire (AWG 24/26)
Antenna Wire (AWG 26/28)
+9v Battery Connector
Ferric Chloride
Clothing Iron
Solder
Soldering Iron
Parts List Details
Most of the parts in this project are discrete passive componenets, however the few active components are described in more detail below.
PC Board
We will make our own PCB for the receiver so that we can have exact control over all the connection lengths and parts used. 27 MHz is pretty low frequency so there's actually not too too much to worry about in terms of performance degradation.
6 Turn Inductor Toroid Core
The toroid core and magnetic wire will be used to make a small inductor. It's very important that your ferrite core is AL=25 otherwise the inductance will be off and the receiver won't work.
2N2222 Transistors
We will use 2N2222 general purpose transistors as part of our front-end for the receiver and for the amplifier stages.
555 Timer
The 555 timer will be used as a comparator and LED driver. The input voltage from the receiver will get compared using the 555 timer's input pins and the green LED will either be driven or not. The red LED driven by the 555 timer tells you the 555 timer is on and functioning.
Schematic Overview
The schematic for this project flows naturally from left to right. Beginning at the antenna and the regenerative receiver front-end, then flowing through the amplification stages and then into the 555 timer.
Schematic Specifics
Front-End Regenative Receiver
This is a very common regenerative receiver front-end that you can find in circuits all over the web. I tailored the parts used to what I had laying around, generally you can tweak part values a little bit, with the exception of L2 and C2 which are your tuning circuit (tank circuit) for 27.145 MHz.
Amplifier Stages
Two amplifier stages exist in the middle of the schematic. They are used to 'rail' the signal back to its square-wave digital form of either +5v or +0v. I'm pretty sure that these amplifiers could be tweaked to get better performance, however the current design should work well enough for our requirements.
555 Timer Receiver Comparator
The amplified signal makes its way to the 555 timer in the form of its original square wave where this 555 timer uses the voltage detected with internal comparators to create an output that turns on the green LED.
The video below shows the circuit in action: