Free Electronic Circuits & 8085 projects

Electronic projects with circuit diagram and 8085 microprocessor projects.

Three FM wireless microphone production

Published on Mar 14 2011 // DIY Telephone Circuits

Printed circuit board as shown in Figure 3, printing plate size can be scaled according to need. Transistors, resistors, capacitors, microphone according to the data used in Figure 2; battery 9V laminated battery available; L1, L2, L3 can F0.33 enameled wire around the system, the antenna can skin about 20cm long flexible cord; K with a button sub-switch. By the following steps when debugging 1. Check the solder circuit board, to ensure that equipment connected in order. First measure the static resistance between positive and negative power short-circuit or open circuit. 2. Total current measured. Power measurement of the total current is about 50mA or so, clamp the short T1, b, e pole or short-circuit C3, the current should be significant changes, and then short T2 and T3, b, e should have a very obvious change. 3. Measuring the carrier frequency. Measured by ultra-high frequency mV Table T2 in the b pole and ground should be a few volts between the high-frequency voltage, with digital frequency meter observation, adjustment is adjustable to C3 carrier frequency of around 45MHz. The same method to test T3 base, adjusting the C7 should be able to get the carrier frequency of 90MHz. Then the frequency meter and voltmeter placed across the UHF antenna on the ground, adjust C10 so that the frequency 90MHz, maximum voltage can be. In this way, the carrier frequency on the adjustment is completed. 4. Modulation voltage measurement. First short-circuit C3, with the R4 mV across both ends of the table, aligned microphone propaganda, ac voltage should be instructed that the microphone and T1 working. If no instrument can also be the above steps, try receiving side, while repeatedly adjust the C3, C7, C10, until the receiver distance, the sound until the minimum distortion.

The microphone uses direct frequency modulation, center frequency 90MHz, transmitter power of about 0.5W, the maximum deviation ± 50kHz, firing distance of not less than 50 meters.
  Block Diagram
  The block diagram and schematic diagram shown in Figure 1,2. Electret microphone generated audio signal is applied to the modulator for modulation of T1’s emitter voltage. The voltage is directly changing the size of the transistor emitter junction capacitance, junction capacitance circuit parameters as part of its fo about 45MHz or so, after doubling the output frequency up to 90MHz or so, the FM signal is amplified by the high-frequency amplifier, out by the antenna.

Three FM wireless microphone production circuit 1

Modulation signal from the microphone M (CRZ-22) by the C1 coupled to the base of the modulator, R1 for the M microphone load resistor. Modulator from the T1, R2, R3, C2, C3, C4, C6 and L1 composition of common base power
Capacity three-point oscillator circuit. The circuit is connected with the base C2, is the base of the high ground, the audio is grounded collector (the collector power supply is via L1), collector junction capacitance Cc is actually in the oscillator circuit in parallel at both ends, so, with the the audio signal changes, a corresponding change in oscillation frequency, resulting in FM signals.
  Circuit Features
  1. Direct FM modulator method, the frequency is stable and reliable.
  2. With electret condenser microphone. The microphone has a built-form emitter follower FET, and its high sensitivity, wide frequency response, using the microphone audio amplifier can be obtained from time to increase the modulation rate of the appropriate voltage.
  3. Adjust the levels of both components, debugging. C3 adjustable to change the frequency of T1, T2 adjustable to obtain the harmonic frequency of C7, T3 adjustable C10 for maximum output.
  Production debugging

Three FM wireless microphone production circuit 2

Printed circuit board as shown in Figure , printing plate size can be scaled according to need. Transistors, resistors, capacitors, microphone according to the data used in Figure 2; battery 9V laminated battery available; L1, L2, L3 can F0.33 enameled wire around the system, the antenna can skin about 20cm long flexible cord; K with a button sub-switch.
  By the following steps when debugging
  1. Check the solder circuit board, to ensure that equipment connected in order. First measure the static resistance between positive and negative power short-circuit or open circuit.
  2. Total current measured. Power measurement of the total current is about 50mA or so, clamp the short T1, b, e pole or short-circuit C3, the current should be significant changes, and then short T2 and T3, b, e should have a very obvious change.
  3. Measuring the carrier frequency. Measured by ultra-high frequency mV Table T2 in the b pole and ground should be a few volts between the high-frequency voltage, with digital frequency meter observation, adjustment is adjustable to C3 carrier frequency of around 45MHz. The same method to test T3 base, adjusting the C7 should be able to get the carrier frequency of 90MHz. Then the frequency meter and voltmeter placed across the UHF antenna on the ground, adjust C10 so that the frequency 90MHz, maximum voltage can be. In this way, the carrier frequency on the adjustment is completed.
  4. Modulation voltage measurement. First short-circuit C3, with the R4 mV across both ends of the table, aligned microphone propaganda, ac voltage should be instructed that the microphone and T1 working.
   If no instrument can also be the above steps, try receiving side, while repeatedly adjust the C3, C7, C10, until the receiver distance, the sound until the minimum distortion.