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Magnetic-Radiation Remote-Control

Source: RED Free Circuit Designs

Short-range 35KHz operation, single-channel unit

Simple circuitry, no outer antennas required

Transmitter circuit diagram:

Magnetic-Radiation Transmitter

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 (4 to 6 AA 1.5V Cells in series, see Notes)

Receiver circuit diagram: 

          Magnetic-Radiation Receiver

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____________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)

Device purpose:

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 operated.
Circuit operation is 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.
Outstanding features for this design are as follows:

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.
Luckily, this latter snag is compensated by the fact that only a short pulse from the transmitter is needed to operate the receiver. Therefore, if the transmitter is not operated continuously, its battery should last long.

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.
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.


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