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I have a random device: GT MEDIA V8 Finder Pro. I would like to communicate over its console port.

Here are some pictures of its mainboard. Here is the area around the console connector:

enter image description here

I have no idea if I should connect my RS232 adapter or my TTL USB adapter to it. I know that their previous model V8 Finder used RS232 levels, and also all their other boxes (Freesat V7, Freesat V7 MAX, Freesat V7Combo, V8 Series) use that, but am not sure about this one. I realy don't want to eather fry my TTL adapter or my Finder if I assume wrongly. Is there a good way to check?

I did check the TX pin with a multimeter, but it hardly moved, not much to see.

Now, if I knew what chipset this device uses it would be easier, but the only thing I know is that it's probably made by Ali

I know it's not an M3602, because my box can decode H265 and supports DVB-S2/S2X so it has to be a recent chipset (but because the heatsink is in the way, I can't check).

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  • \$\begingroup\$ Use a oscilloscope to measure the levels. Or make a voltage divider to lower the RS232 to what your TTL serial device can tolerate. \$\endgroup\$
    – MatsK
    Dec 27, 2022 at 10:28
  • \$\begingroup\$ TTL is 0-5, RS232 is +- 25V, Using a voltmeter measure ex and ground, if either is negative you have RS232 or if over +5. This is not 100 % as many did not follow the spec. \$\endgroup\$
    – Gil
    Dec 27, 2022 at 13:18
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    \$\begingroup\$ @Gil Don't know if it is a typo, but I think RS232 most commonly uses +/- 15 V or +/- 12 V. AFAIK 25 V is out of spec, although specs are often ignored in practice wrt RS232. \$\endgroup\$ Dec 27, 2022 at 15:30
  • \$\begingroup\$ You are correct as you stated most not all. The maximum open-circuit voltage specified by the RS232 standard is 25 V, but signal levels are normally 12V, 5 V, 10 V, 12 V, and 15 V. According to the RS-232 standard, all data is bipolar. \$\endgroup\$
    – Gil
    Dec 27, 2022 at 20:49
  • \$\begingroup\$ "Normally" is a bit of a misstatement. +/- 5V or +/- 10V are commonly found according to the Wikipedia page, but I wouldn't imply they're standard RS232, which is +/- 12V or 15V. However, +/- 5V is RS423/EIA423, which is compatible aside from the voltage. \$\endgroup\$
    – Sotto Voce
    Dec 28, 2022 at 5:58

2 Answers 2

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From the parts (complementary BJT transistors and discretes near the connector) I think it's a non-standard RS-232 port that idles at 0V rather than -9 or whatever.

That will work with most RS-232 receivers- they typically have a threshold of + 2-3V.

The measurement of 0V idle would tend to confirm that.

That said, it's hard to be 100% sure, so there is some risk.

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  • \$\begingroup\$ I used a multimeter at the end and the device did idle at 0V most of the time (multimeter said DC when I mesured (multimeter always says DC if there is any voltage, or red light lights up in AC if there is any voltage) I did want to find an apropriate connector thought, to connect, since none of my breadboard wires would fit inside it, it looks like 3 pin JST but am not sure. Sadly this junk device, broke on me (it does not charge anymore, nor work from battery, it only works if its plugged in the wall) so this project sadly came to an end \$\endgroup\$
    – LimetaPeta
    Dec 28, 2022 at 12:23
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The idle level of asynchronous serial communication is logical "1". Unless the device is constantly sending a lot of "0" bits, you can use this fact.

If the wires transport so-called TTL levels, the idle level will be a positive voltage near the digital supply voltage. Commonly this is 5 V or 3.3V.

If the wires transport RS232 levels, the idle level will be a negative voltage, commonly between -3 V and -15 V. Many interfaces only provide about -5 V, so be prepared.

So measure the TX output in reference to Ground, you can use a simple multimeter. If it is some positive voltage between 2 and 5 V, most probably it is "TTL" level. If it is some negative voltage between -2 and -15 V, most probably it is RS232 level.

If you happen to have an oscilloscope, even better. Measure the TX output and look at the levels: TTL levels "swing" between near-positive-digital-supply and near-ground; RS232 levels "swing" between positive and negative voltages of similar magnitude.

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