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I trying to drive the rs232 interface, so I can send and receive data to the device am controlling.

I want to know why you need the two transistors on its comms line. Why not just one?

enter image description here

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  • \$\begingroup\$ Nobody in her/his right mind would follow some weird link. Add the information to the question. \$\endgroup\$ – Oldfart Dec 21 '18 at 10:26
  • \$\begingroup\$ its samsung cloud... its not the usual imgur, but its not anything malicious either. \$\endgroup\$ – Thefoilist Dec 21 '18 at 11:03
  • \$\begingroup\$ Plus I am a beginner asking for help. wouldn't be my best interest to infect ppl pc with a virus or malware \$\endgroup\$ – Ageis Dec 21 '18 at 11:06
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When comms is low, T2 is closed and T1 is open, T2 is needed to provide the path to ground, and brings Rx active through T2. When comms is high, T2 is open and T1 is closed the opposite occurs.

You need 2 transistors to get this switching action in this case. 1 could work in a theoretical application, but the amount of other passives involved would probably degrade the signal past the point of no return. The same transistor is likely used to allow for higher baud rates, as the switching time will be constant for each.

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  • \$\begingroup\$ I think I understand now basically when comms is high, the base for T2 is pulled low hence it's off. I don't know why I didnt see that. You use pull ups everywhere in the digita domain. \$\endgroup\$ – Ageis Dec 21 '18 at 11:29

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