This is a multi-part message in MIME format. ------=_NextPart_000_0187_01C6E922.D09BF740 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit slippyr4 wrote: > I need to design a circuit such that a signal from a PIC will cause a > beep signal. My definition of a beep signal is aproximately 1KHz, > close to a sine wave, and in the region of 75ms long. I need the > output signal to be audio "line level" - which although poorly defined > seems generally to be regarded at 1V peak to peak, AC, driven by a > lowish impedance. The audio signal I generate needs to connect to a > line in jack on a tape recorder. The whole circuit runs in a car - so > it's a noisy environment. I'm not looking for Hi-Fi quality audio, but > it does need to be reasonable. Drive the attached circuit from a 0-5V PIC pin. Use a 500uS periodic interrupt to toggle all the pins you want producing the 1KHz tone. Set all the pins that are supposed to be quiet to high impedence. I think the tone purity will be good enough. I haven't figured out the exact resulting amplitude, but I think it will be within acceptable range of a audio line input. ------=_NextPart_000_0187_01C6E922.D09BF740 Content-Type: image/gif; name="c.gif" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="c.gif" R0lGODlhNAIeAfcAMQAAAAEBAQICAgMDAwQEBAUFBQYGBgcHBwgICAkJCQoKCgsLCwwMDA0NDQ4O Dg8PDxAQEBERERISEhMTExQUFBUVFRYWFhcXFxgYGBkZGRoaGhsbGxwcHB0dHR4eHh8fHyAgICEh ISIiIiMjIyQkJCUlJSYmJicnJygoKCkpKSoqKisrKywsLC0tLS4uLi8vLzAwMDExMTIyMjMzMzQ0 NDU1NTY2Njc3Nzg4ODk5OTo6Ojs7Ozw8PD09PT4+Pj8/P0BAQEFBQUJCQkNDQ0REREVFRUZGRkdH R0hISElJSUpKSktLS0xMTE1NTU5OTk9PT1BQUFFRUVJSUlNTU1RUVFVVVVZWVldXV1hYWFlZWVpa WltbW1xcXF1dXV5eXl9fX2BgYGFhYWJiYmNjY2RkZGVlZWZmZmdnZ2hoaGlpaWpqamtra2xsbG1t bW5ubm9vb3BwcHFxcXJycnNzc3R0dHV1dXZ2dnd3d3h4eHl5eXp6ent7e3x8fH19fX5+fn9/f4CA gIGBgYKCgoODg4SEhIWFhYaGhoeHh4iIiImJiYqKiouLi4yMjI2NjY6Ojo+Pj5CQkJGRkZKSkpOT k5SUlJWVlZaWlpeXl5iYmJmZmZqampubm5ycnJ2dnZ6enp+fn6CgoKGhoaKioqOjo6SkpKWlpaam 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