Magnetic Radiation Remote Control

This circuit is useful as a short-range, single-channel remote-control. This circuit is work based on a non-modulated 35KHz frequency carrier transmitter, and on a high-gain two-stage 35KHz amplifier receiver, followed by a frequency-voltage converter and DC load driver. This is the figure of the circuit.


This circuit is consists of two part, transmitter and receiver. In the transmitter, Q1 and Q2 are wired as a Darlington pair to obtain the highest possible output from a Hartley type oscillator. C2 must be trimmed to obtain the highest sine wave output (best viewed on oscilloscope). In the prototype the sine wave amplitude measured across C1 leads reached 800V peak-to-peak at 9V supply and 450mA current.

In the receiver circuit, Q1 and Q2 form a two-stage linear amplifier. Therefore, the small 35 KHz signal picked-up by L1 is highly amplified by these devices and feds Q3 wired as a pulse-to-DC converter. When the input signal reaches Q3, the collector voltage of this transistor goes low, thus activating the LED D1 (or the optional beeper or relay) by means of Q4. Stand-by current is only 100µA. Current drawing is about 10mA when the LED is on and about 20mA when a relay is activated.

Transmitter parts:
R1_____________68K 1/4W Resistor
C1______________4n7 630V Ceramic or Polyester Capacitor
C2__________60-80pF 63V Ceramic Trimmer
C3____________100µF 25V Electrolytic Capacitor
Q1____________BC337 45V 800mA NPN Transistor
Q2____________BD139 80V 1.5A NPN Transistor
L1_________________ 500 turns on a 10mm. diameter, 10cm. long ferrite rod.
Enameled wire diameter: 0.2mm.
The tap is made after 200 turns, ground side
P1_____________SPST Pushbutton
B1_____________6-9V Battery

Receiver parts:
R1,R3___________1M 1/4W Resistors
R2,R4__________47K 1/4W Resistors
R5____________330K 1/4W Resistor
R6,R7__________68K 1/4W Resistors
R8____________180R 1/4W Resistor
R9____________100R 1/4W Resistor
C1____________470pF 63V Ceramic Capacitor (See Notes)
C2_____________10nF 63V Polyester or Ceramic Capacitor
C3____________100µF 25V Electrolytic Capacitor
C4,C5_________100nF 63V Polyester or Ceramic Capacitors
C6______________1µF 63V Polyester, Ceramic or Electrolytic Capacitor
D1_____________5 or 3mm. Red LED
Q1,Q2,Q3______BC549C 25V 100mA NPN High-gain Low-noise Transistors
Q4____________BC328 30V 800mA PNP Transistor
L1_________________ 700 turns on a 10mm. diameter, 10cm. long ferrite rod.
Enameled wire diameter: 0.2mm.
The tap is made after 350 turns, i.e. at the center
of the winding
BZ1___________Piezo sounder (incorporating 3KHz oscillator, optional, see Notes)
RL1______________5V DIL Reed-Relay SPDT or DPDT (Optional, see Notes)
B1_______________3V Battery (2 x 1.5V AA, AAA or AAAA Cells in series
or 1 x 3V Lithium Cell)