Magnetic-Radiation Remote-Control Short-range 35KHz operation, single-channel
unit Simple circuitry, no outer antennas
Short-range 35KHz operation, single-channel unit
Simple circuitry, no outer antennas required
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 (4 to 6 AA 1.5V Cells in series, see Notes)
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____________BD328 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)
This unit can be useful as a short-range, single-channel remote-control. When
the pushbutton in the transmitter circuit is briefly activated, the LED D1 in
the receiver illuminates and an optional beeper or relay can be
Snags are: the short-range
operation (about a medium-sized apartment), the high number of windings for the
coils and the high current drawn by the transmitter.
Transmitter circuit operation:
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 sinewave output (best viewed on oscilloscope). In the prototype the sinewave amplitude measured at C1 leads reached 800V peak-to-peak at 9V supply and 450mA current.
Receiver circuit operation:
Q1 and Q2 form a two-stage linear amplifier. Therefore, the small 35KHz
signal picked-up by L1 is highly amplified by these devices and feds Q3 wired as
a pulse-to-DC converter.