Electronics

A collection of technical articles on electronics, or subjects related to electronics. Some of these articles also appear in the "application notes" section.

LED current source

2009-09-28
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

2008-09-22
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

2009-12-18
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

2006-08-14
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.

Candela, Lumen, Lux: the equations

2009-12-10
There are various measures in use for quantifying the light produced by a light source, such as a LED. This article gives a brief overview of the more important measures and how they relate.