I have a SIM800C module mounted on a PCB with peripheral circuitry, like this:
except the pin adjacent to the 5V pin is labelled EN instead of V_TTL. V_TTL is supposed to select between 3.3 and 5V signal levels
Firstly, is the function of the EN pin the same, if not what does it do?
Secondly, the PWK pin I understand to be connected to the SIM800C PWRKEY pin and should be held low for 1 second to switch the modem on or off. What is less certain from information I have found on the web is whether a low pulse is required after power up to turn the module on (claimed by Hardware build | Details | Hackaday.io), and having powered off using the PWK pin whether a 1 second pulse will turn it back on (one source said a 30s LOW was required).
Thirdly, the same source (Hardware build | Details | Hackaday.io) claimed that the voltage regulation ciruirty on these boards is screwy and the diodes should be removed and the input voltage reduced to 3.8V.
TBH I'm tempted to just get another SIM800L EVB which I have used successfully in the past and has a reset pin which is useful to me.