The digital volume control published in Elektor Electronics October 1997 can be used either with an RC5 remote control or with two pushbuttons (louder/softer). If for whatever reason you cannot do without the feeling of turning a real potentiometer, then with a little effort it is possible to add a shaft encoder to provide rotational[…]
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Electrically Isolated RS232 Adapter Schematic Circuit Diagram
This circuit represents an interface converter between the UART pins of a microcontroller (with TTL levels) and a ‘standardised’ RS232 port with symmetric ±15- V levels. In contrast to the commonly used IC solutions such as the MAX232, it also provides electrical isolation between the two sides of the converter. This interface converter inverts the[…]
Read more2.5-GHz Signal Source Schematic Circuit Diagram
More and more communications systems are operating in the 2.4-GHz ISM (Industrial, Scientific, and Medical) band, including Bluetooth, various WLAN (Wireless Local Area Network) and Home-RF systems. A simple test oscillator for the frequency band between 2.4 GHz and 2.5 GHz can prove useful in testing receivers. Such an oscillator is available from Maxim[…]
Read moreSwitching Amplifier for Analogue Signals Schematic Circuit Diagram
If analogue signals have to be switched, a bilateral switch such as the 4066 is often utilized. Because this IC can be powered from single-ended supply only, all the associated components are usually connected to the same asymmetrical supply (typically 8 V). The disadvantage of this is that the opamp runs on only half the[…]
Read moreSerial-to-Parallel Converter Schematic Circuit Diagram
This converter may help if just the serial port on a personal computer is free, whereas the printer needs a parallel (Centronics) port. It converts a serial 2400 baud signal into a parallel signal. The TxD line, pin 3, CTS line, pin 8 and the DSR line, pin 6, of the serial port, are used[…]
Read moreOptical S/PDIF Output Schematic Circuit Diagram
This little circuit is intended to be used to provide external access to an unused digital output of a CD or DVD drive in a PC. It provides an electrically isolated interface. In addition, this circuit is also handy for connecting a (portable) MD recorder, since these devices usually only have optical digital inputs. The[…]
Read more0 – 44 dB RF attenuator Schematic Circuit Diagram
Anyone who has to reduce the amplitudes of RF signals in a controlled manner needs an attenuator. Linearly adjustable attenuation networks using special PIN diodes are available for this, but they require quite intricate control circuitry. A simpler solution is to use an integrated attenuator that can be switched in steps. The RF 2420 is[…]
Read moreAdapter for SB Live! Player 1024 Schematic Circuit Diagram
In the December 1999 issue, we published a design for a digital extension for the Sound Blaster Live! Value Player (circuit board #990079-1). This sound card has a 12-pin Audio Extension connector. The successor to this card is the Live! Player 1024, which has a 40-pin connector that includes the same inputs and outputs (plus[…]
Read moreTelephone gong
Those of you who like the telephone hell louder may find this circuit of interest. It uses the telephone bell signal to actuate an oscillator, which in turn drives a relay that operates a standard door gong. The oscillator is an RC type based on a 4093 Schmitt trigger. Both the charging and discharge times[…]
Read moreReal-time switch debounce
Most debounce circuits shorten or lengthen the time a switch is pressed to obviate interference pulses. The present circuit does not affect that time: the pulse at the output is exactly in accordance with the time elapsed between the depressing and the releasing of the switch. When switch S1 is pressed. monostable IC1a is triggered[…]
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