remote-control-circuits
This circuit enables audio monitoring of a remote location, functioning as both a room monitor and a baby alarm. It can be powered by a 12-volt battery or a mains power supply. The interconnection utilizes three wires, allowing for the use of multi-core cable; alarm or telephone cable is suitable, with any extra wires left free. On the right side, T1 is the main transformer, with the primary winding matching the local electric supply and a secondary rating of 12V at 1 amp. The bridge rectifiers are rated for 50V peak at 1 amp and can be constructed using four 1N4001 rectifiers. Capacitor C3 smooths the supply voltage, while C4 decouples high-frequency noise. The audio amplifier is based on a single LM380 IC, which can deliver up to 2 watts into an 8-ohm speaker. Capacitor C1 provides additional supply decoupling to mitigate mains hum, and the Zobel network formed by resistor R2 and capacitor C5 prevents wideband oscillation at 10 MHz. The power supply and amplifier are connected via cable to the remote location being monitored for activity. The input circuit consists of an electret microphone insert and amplifier, connected by three wires. Alarm or telephone cable can be utilized, with any unused wires left floating. The electret microphone is amplified by a two-stage, direct-coupled preamplifier using two BC549C transistors. Electret microphones typically have two terminals, although older models may have three. Gain is adjusted using a 10k preset, while overall listening volume is controlled at the remote location with a 10k potentiometer. The preamplifier power supply is decoupled by a 1k resistor and a 200µF capacitor. The first stage operates at a low collector current to ensure a high signal-to-noise ratio, while the second stage functions as an emitter follower, providing a low output impedance for driving long cables. Due to the low output impedance, hum and noise pickup are minimized, eliminating the need for screened cable.
This audio monitoring circuit is designed for versatility and reliability in various applications, such as surveillance or infant monitoring. The choice of a 12-volt power supply makes it adaptable for both portable and stationary use. The transformer, T1, is crucial for stepping down the mains voltage to a safer level for the circuit's operation. The bridge rectifier configuration ensures that the AC input is converted to a stable DC voltage, essential for powering sensitive electronic components.
The LM380 audio amplifier is selected for its ability to deliver sufficient power while maintaining sound quality. The inclusion of decoupling capacitors, such as C1 and C4, is vital for reducing interference from external sources, particularly from the mains supply, which can introduce unwanted noise into the audio signal. The Zobel network is a critical design feature that addresses potential oscillation issues, enhancing the stability of the amplifier under varying load conditions.
The preamplifier stage, utilizing BC549C transistors, is designed for optimal performance with electret microphones. The two-stage amplification process ensures that the audio signal is sufficiently boosted before transmission, while the adjustable gain allows for fine-tuning based on the acoustic characteristics of the monitored environment. The use of a low output impedance in the second stage is particularly advantageous for long cable runs, as it minimizes the risk of signal degradation and interference.
Overall, this circuit exemplifies a well-thought-out design that balances performance, reliability, and ease of use, making it suitable for various audio monitoring applications.This circuit allows audio monitoring of a remote location and so doubles as a room monitor or baby alarm. It canbe run from a 12 Volt battery or mains power supply as shown below. Interconnect uses 3 wires, so multi core cablecan be used; alarm or telephone cable is suitable just leave any extra wires free.
From the right hand side, T1 is the main s transformer. The primary matches your local electric supply, secondaryrating 12V, 1 amp. The bridge rectifiers are rated 50V peak at 1 amp or can be made from four 1N4001 rectifiers. C3 smooths the supply and C4 decouples any high frequency noise. The audio amplifier is built around a single LM380. This IC will deliver up to 2 watts into an 8 ohm speaker. C1 provides extra supply decoupling from mains hum, whilst the zobel network formed by R2 and C5 prevent a widebandoscillation at 10MHz. (Authors note: I have once experienced the 10MHz wideband oscillation. This was on an LM380 amplifier without the zobel network; when oscillation occurs, the audio is distorted and current consumption isexcessive.
) The power supply and amplifier are connected by cable to a remote location (the room you want to monitor foractivity). The input circuit is built around an electret mic insert and amplifier and is connected by threewires.
Alarm or telephone cable can be used, if the cable has more than three cores, just leave the unused wiresfloating. The electret mic is amplified by a two stage, direct coupled preamp comprising two BC549C transistors.
Electret mics have two terminals, older types may have three terminals. Gain is controlled by the 10k preset, once set for a particular room environment listening volume is controlled atthe remote location using the 10k potentiometer. The preamp power supply is decoupled by the 1k and 200u capacitor, the first stage is run at a low collector current to ensure a high signal to noise ratio.
The second stage is anemitter follower which ensures a low output impedance for driving long cables. As the output impedance is low, humand noise pickup are minimum and therefore screened cable is not required. 🔗 External reference
This audio monitoring circuit is designed for versatility and reliability in various applications, such as surveillance or infant monitoring. The choice of a 12-volt power supply makes it adaptable for both portable and stationary use. The transformer, T1, is crucial for stepping down the mains voltage to a safer level for the circuit's operation. The bridge rectifier configuration ensures that the AC input is converted to a stable DC voltage, essential for powering sensitive electronic components.
The LM380 audio amplifier is selected for its ability to deliver sufficient power while maintaining sound quality. The inclusion of decoupling capacitors, such as C1 and C4, is vital for reducing interference from external sources, particularly from the mains supply, which can introduce unwanted noise into the audio signal. The Zobel network is a critical design feature that addresses potential oscillation issues, enhancing the stability of the amplifier under varying load conditions.
The preamplifier stage, utilizing BC549C transistors, is designed for optimal performance with electret microphones. The two-stage amplification process ensures that the audio signal is sufficiently boosted before transmission, while the adjustable gain allows for fine-tuning based on the acoustic characteristics of the monitored environment. The use of a low output impedance in the second stage is particularly advantageous for long cable runs, as it minimizes the risk of signal degradation and interference.
Overall, this circuit exemplifies a well-thought-out design that balances performance, reliability, and ease of use, making it suitable for various audio monitoring applications.This circuit allows audio monitoring of a remote location and so doubles as a room monitor or baby alarm. It canbe run from a 12 Volt battery or mains power supply as shown below. Interconnect uses 3 wires, so multi core cablecan be used; alarm or telephone cable is suitable just leave any extra wires free.
From the right hand side, T1 is the main s transformer. The primary matches your local electric supply, secondaryrating 12V, 1 amp. The bridge rectifiers are rated 50V peak at 1 amp or can be made from four 1N4001 rectifiers. C3 smooths the supply and C4 decouples any high frequency noise. The audio amplifier is built around a single LM380. This IC will deliver up to 2 watts into an 8 ohm speaker. C1 provides extra supply decoupling from mains hum, whilst the zobel network formed by R2 and C5 prevent a widebandoscillation at 10MHz. (Authors note: I have once experienced the 10MHz wideband oscillation. This was on an LM380 amplifier without the zobel network; when oscillation occurs, the audio is distorted and current consumption isexcessive.
) The power supply and amplifier are connected by cable to a remote location (the room you want to monitor foractivity). The input circuit is built around an electret mic insert and amplifier and is connected by threewires.
Alarm or telephone cable can be used, if the cable has more than three cores, just leave the unused wiresfloating. The electret mic is amplified by a two stage, direct coupled preamp comprising two BC549C transistors.
Electret mics have two terminals, older types may have three terminals. Gain is controlled by the 10k preset, once set for a particular room environment listening volume is controlled atthe remote location using the 10k potentiometer. The preamp power supply is decoupled by the 1k and 200u capacitor, the first stage is run at a low collector current to ensure a high signal to noise ratio.
The second stage is anemitter follower which ensures a low output impedance for driving long cables. As the output impedance is low, humand noise pickup are minimum and therefore screened cable is not required. 🔗 External reference