Difference between revisions of "Minimig Video output"
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My suggestion is to add copper traces to allow simple soldering of circuit to enable this.<br> | My suggestion is to add copper traces to allow simple soldering of circuit to enable this.<br> | ||
By not assamble this by default some money can be saved. | By not assamble this by default some money can be saved. | ||
| + | |||
| + | A500 & A1000 to TV S-Video input using [http://www.analog.com Analog Devices] AD724:<br> | ||
| + | http://eab.abime.net/showthread.php?t=30752<br> | ||
| + | |||
| + | freqmax ([http://www.amiga.org/modules/newbb/viewtopic.php?topic_id=38888&post_id=461218&order=0&viewmode=flat&pid=0&forum=8#forumpost461218 070731]):<br> | ||
| + | The minimig only have a physical VGA socket for video. | ||
| + | |||
| + | 4bit/color resistor ladder D/A: | ||
| + | :http://home.hetnet.nl/%7Eweeren001/downloads/minimig1_schematics.pdf 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 [http://en.wikipedia.org/wiki/Preferred_number Wikipedia.org Preferred number]. | ||
| + | |||
| + | Maybe DVI/HDMI is a useful option? (no need for D/A and plugs directly into lcd-tv) | ||
Latest revision as of 08:24, 31 July 2007
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:
http://eab.abime.net/showthread.php?t=30752
freqmax (070731):
The minimig only have a physical VGA socket for video.
4bit/color resistor ladder D/A:
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 Wikipedia.org Preferred number.
Maybe DVI/HDMI is a useful option? (no need for D/A and plugs directly into lcd-tv)
