How to program this radio breakout

Short question before I solder speaker to my radio module: the datasheet speaks of a programming of the module via TTL (38400).
Now I had tried it out, with 3 options:
a.) the photon with wires directly to the radio (TX<>RX, RX<>TX, GND+3V3) and the code snippet here:

void setup()

void loop()
  if (Serial1.available())
    //int inByte =;

b.) with a USB2Serial module and
c.) with a YP-05 FDDI module and send AT commands via Arduino IDE/Serial Monitor

Am I on the right track, because I failed with all options?
For example, via AT-Command to set a new station frequency.

I didn’t read anything about that module emulating a serial modem and so using AT command doesn’t make sense. nevermind… farther down all the commands start with AT.

TTL stands for Transitor-Transistor-Logic… Or simply, it uses 0-5V signaling. Since the Particle devices only output 3.3V max, you need a logic-level shifter between the Particle device and the radio module (and that also implies needing a 5V supply).

The radio module can be operated between 3 and 5.5V. Even if I switch from the Photon 3V3 to V from the radio, it starts. Do you think that a logical level shifter is necessary? I have one in the office with 2x 4 PINs here (vcc, scl, sda, gnd) - Can I take that to shift only the voltage (I tested this without success :wink:

Perhaps not. But since you were having issues, it was logical to interpret TTL as requiring 5V signals. 3.3v signaling is referred to as CMOS logic if I remember correctly.

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Thanks so far, I have to organize an LLS.