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I have a problem in the UART communication between NRF52832 and SIM868 module.

The problem is the data sent by NRF doesn't be interpreted by SIM868.

To see that i did tow tests:

First one, I added an Usb to Serial module (TTL) between NRF52832 and SIM868 as shown below in picture enter image description here

When I send "ATD+phoneNumber" from NRF i got it in the TTL module but the SIM868 doesn't execute the command.

Then i did another test as shown below: enter image description here

Now i send the same Command form TTL Module directly to SIM868 "ATD+PhoneNumber" and it was executed, and received the response in the NRF and TTL module

I think the problem can be Logic level difference between NRF and SIM868.

could anyone help in this problem?

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  • \$\begingroup\$ have you connected the SIM868 to the TTL module alone? \$\endgroup\$ – jsotola Feb 14 at 17:16
  • \$\begingroup\$ do not connect the TX pin on the TTL module when NRF is connected ... if you have a second TTL module, then use it to monitor the second data line \$\endgroup\$ – jsotola Feb 14 at 17:17
  • \$\begingroup\$ @jsotola yes i did a test with just TTL module and SIM868 and it was working properly. \$\endgroup\$ – Hakraf Feb 14 at 17:23
  • \$\begingroup\$ @jsotola i'm getting the respense of SIM868 in the NRF, the issue is just when i want to send commands from NRF to SIM868, the module doesn't interpret it. \$\endgroup\$ – Hakraf Feb 14 at 17:25
  • \$\begingroup\$ what are the signal voltage levels of the three modules? \$\endgroup\$ – jsotola Feb 14 at 17:35
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You can't connect the TX lines from two modules together. If you want to use your "TTL module" to monitor the communication then you can only connect the RX line. So, you can only monitor one direction of data transmission at a time.

Of course, you must also have compatible voltage levels for the serial interfaces in all three devices. You haven't provided enough information to answer that, so I'll just have to trust that you have verified this.

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