Electronics: Circuit design

A few simple & useful circuits.

LED current source

2015-03-07
This article presents a circuit for a "constant current source", for example to drive LEDs. The circuit allows the current flow to be switched on and off, with 5V TTL-logic. One way to use the on-off switching capability is to dim the LEDs with pulse-width modulation.

A MIDI to RS232 converter

2024-12-02
The MIDI protocol is a serial data communications protocol using on a "current loop" physical layer, and using a Baud rate of 31250 bps. This article shows the electronics needed to convert between current loop and the RS232 signal levels. The circuit can be connected directly to the RS232 port of the H0420 MP3 player. In the second part, the article covers the "software protocol" of MIDI and develops a simple script to send and receive MIDI commands.

An RS232 "spy" cable

2024-12-02
The RS232 norm defines a one-on-one communication link between two devices. With a special cable, though, it is possible to have a third device (a PC) "listen in" on the data —a useful trick in debugging serial protocols or for deciphering an unknown protocol.

A voltage inverter circuit

2015-03-07
Sometimes you need to generate a negative voltage when you only have a positive power supply. The circuit in this application note does just that. The circuit was built to drive LCDs that require a negative LC-driving voltage.