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I have bought a no-brand, passive HDMI Male to VGA Female adapter, to link up a PC with a more dated monitor. It did not work.

After doing some reading, I have learned that buying such an adapter is often discouraged because in many cases it will not convert the signal from Digital to Analog, or the Motherboard/CPU on a specific computer might not be compatible with that particular adapter.

So my question is: seeing how there are so many of these passive adapters on the market, are there circumstances under which they actually do suffice to connect an HDMI output to a VGA input? Or are they generally just a rip-off?

Example of the kind of adapter I bought: https://i.stack.imgur.com/RVemq.png

  • i have gathered that buying such an adapter is discouraged From where? Appreciate your providing your sources, because I'm not sure those are valid concerns. I've used a lot of those converters with never a problem. – K7AAY May 12 at 23:00
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    Primary source of threads on the subject was tomshardware. A few examples: forums.tomshardware.com/threads/… forums.tomshardware.com/threads/… – Magikarp May 12 at 23:48
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    If your "passive HDMI Male to VGA Female adapter" is simply composed of two connectors and a cable, then it cannot possibly convert HDMI signals to VGA. Unlike oddball adapters such as HD15-to-DB9, the HDMI connector and interface is proprietary and licensed, and is rarely used with alternate (i.e. nonstandard) pinouts. That said, HDMI does have a +5VDC line, so it could be possible that some tiny electronics could be stuffed into the connector shrouds to perform active conversion. Since it didn't work, then it may be just 2 connectors and wire. – sawdust May 13 at 0:37
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are there circumstances under which they actually do suffice to connect an HDMI output to a VGA input?

There are no "passive" HDMI to VGA adapters. It requires active signal conversion. HDMI uses digital data sent over differential pairs, VGA uses analog voltage levels sent over single signal wires per colour channel.

I use a cheap plug and play, line-powered, HDMI to VGA adapter to connect a Raspberry Pi 4 to an old VGA monitor. It works well, needs no external power, no drivers, no setup, but it is not passive ("Supports output up to UXGA/1080p with 10-bit DAC").

HDMI to VGA adapter
Not much larger than a VGA connector but large enough to contain active circuitry powered from HDMI pin 18

Compare

PIN CONNECTIONS FOR TYPE A HDMI CONNECTOR

HDMI PIN NUMBER SIGNAL
1   TMDS Data 2+
2   TMDS Data 2 shield
3   TMDS Data 2-
4   TMDS Data 1+
5   TMDS Data 1 shield
6   TMDS Data 1-
7   TMDS Data 0+
8   TMDS Data 0 shield
9   TMDS Data 0-
10  TMDS Clock+
11  TMDS Clock shield
12  TMDS Clock-
13  CEC
14  HEC Data-
15  SCL (Serial Clock for DDC
16  SDA (Serial Data Line for DDC
17  DDC / CEC / HEC Ground
18  +5 V Power (50 mA max)
19  Hot Plug Detect (1.3) / HEC Data+ (1.4)

with

VGA Pinout Configuration

Pin No.  Pin Name   Description
1        RED        Red video (75 ohm, 0.7V peak-to-peak)
2        GREEN      Green video (75 ohm, 0.7V peak-to-peak)
3        BLUE       Blue video (75 ohm, 0.7V peak-to-peak)
4        ID2 / RES  Monitor ID Bit 2 / Reserved
5        GND        Ground
6        RGND       Red Ground
7        GGND       Green Ground
8        BGND       Blue Ground
9        KEY        +5V DC output from graphic card
10       SGND       Sync Ground
11       ID0 / RES  Monitor ID Bit 0 / Reserved
12       ID1 / SDA  Monitor ID Bit 1 / I2C bi-directional data line
13       HSYNC      Horizontal Sync
14       VSYNC      Vertical Sync
15       ID3 / SCL  Monitor ID Bit 3 / I2C data clock

So far as I can tell, there is nothing in common that could usefully be passed through using a passive connector.

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