current calculation problem in a project

[balvendrajat]

i have a problem that how can i calculate a current consumed by a circuit in which component like ATMEGA16 MCU, L293D driver, 12 volt DC relay, GSM SIM900 Module etc.
please help me

 

[Batang]

Use a multimeter.

Cheers.

 

[balvendrajat]

i mean which current rating transformer i use how can i decide it

 

[jiripolivka]

i mean which current rating transformer i use how can i decide it

Assuming that the primary power source for yor circuitry is DC, say 5 or 12V, then your combination of digital circuits and relays can consume a wide range of current OVER TIME.
Use a DVM or an analog meter to record current peaks, then you must decide if the peaks are short (duty cycle <10%) or longer, then use a large capacitor to cover the peaks while a lower-current can be supplied from a larger internal-resistance supply.
For AC primary, use rather a higher-power supply to be sure larger current peaks do not affect the DC voltage needed for the digital circuits. Best of all, use separate power supplies for low-power circuits and "power" circuits like relays, etc.