Minimig Video output

From OpenCircuits
Jump to navigation Jump to search

My suggestion is to add copper traces to allow simple soldering of circuit to enable this.
By not assamble this by default some money can be saved.

A500 & A1000 to TV S-Video input using Analog Devices AD724:

freqmax (070731):
The minimig only have a physical VGA socket for video.

4bit/color resistor ladder D/A: Page 3/3

Resistor values 4k, 2k, 1k, 560 ohm. Method1 - Adding resistors:

R=1/(1/4000+1/2000+1/1000+1/560) = 282 ohm
U=3.3 Volt
i=U/(R+75) (impedance of VGA is defined as 75 ohm)
Output voltage max: 75*i = 0,69 Volt.

Method2 - Using Kirchhoff's law:

(3.3/(4000+75)+3.3/(2000+75)+3.3/(1000+75)+3.3/(560+75))*75 = 0,8 V (weird..)

This is all fine provided that impedance is exactly 75 ohm. However reality may not be perfect. So maybe the output should have some circuitry to handle monitors/cables that doesn't follow the 75 ohm impedance strictly?

Also the 560 ohm value seems nonlinear. See also Preferred number.

Maybe DVI/HDMI is a useful option? (no need for D/A and plugs directly into lcd-tv)