I have assembled a diy m590e gsm gprs module kit, bought from Amazon. The seller provided image is: m590e gsm gprs diy kit

The Schematic used to assemble the kit is: Schematic used

I connected it to the Laptop using a CP2102 based USB to TTL converter: cp2102 based usb to ttl

GSM Module    CP2102 Module
 GND           GND
 RXD           TXD
 TXD           RXD
 VCC           5V

Then after opening putty, the output from the serial reads as:


+CPAS: 0










However, on powering up without sim card, the modem acts normally without getting into the loop.

The SIM Card used is Airtel Prepaid.

  • 1
    \$\begingroup\$ How are you powering that GSM module? Not from the USB port, I hope. (Just FYI, there was someone else who asked a question about the same module kit (different seller) recently - I didn't see any successful answer.) \$\endgroup\$
    – SamGibson
    Commented Dec 9, 2016 at 23:06
  • \$\begingroup\$ Yes from the usb port. Can you please send a link to the question? @SamGibson \$\endgroup\$ Commented Dec 10, 2016 at 6:50
  • \$\begingroup\$ I've explained the problem and linked to the previous question, in an answer. \$\endgroup\$
    – SamGibson
    Commented Dec 10, 2016 at 15:13

1 Answer 1


How are you powering that GSM module?

[...] from the usb port

Using a PC USB port for power is likely to be a problem, for the same reason I explained in my answer here to someone who (initially) also used a power supply with a similar current capability.

The supplier's website from that earlier question mentioned that the power supply should be capable of supplying 1A. (Actually, that GSM module's datasheet says that for a 100uF main capacitor, as shown in the photo of your kit, the power supply may need to provide up to 1.2A.)

Since a normal PC USB port is unlikely to successfully supply 1A (or 1.2A) at 5V, then when the module tries to register with a network (meaning its RF transmitter needs power), the USB port voltage will probably drop and that fits with the symptom that your GSM module appears to reboot.

This is especially true because I now see you mentioned in your question, that you connected the GSM module's power "through" the CP2102 USB to TTL adapter. The thin PCB traces on the CP2102 will cause even larger voltage drop on the 5V supply reaching the GSM module, when it tries to draw more current.

on powering up without sim card, the modem acts normally

That is because, without a SIM card installed, the module doesn't try to register on a network, therefore it doesn't enable its RF transmitter, meaning it doesn't need much current, and so it can operate with the limited current from a USB port.

If you have an oscilloscope, you can view the voltage actually on the module (pins 2 & 3) to confirm that the supply voltage to the module dips (perhaps briefly) below its absolute minimum 3.3V, during the sequence where you see the module reboot with a SIM card installed. A multimeter cannot react quickly to short dips in voltage, and so is a less reliable measurement tool in this case.

Also note that the lack of design features (like additional filtering capacitors) recommended in the module datasheet, and the use of a diode to drop the input voltage (which is specifically discouraged in the datasheet), suggest that the module is designed for low cost and not maximum reliability.


  • Power the GSM module with short, thick, ground & 5V wires from a power supply capable of provided at least 1.2A (preferably rated at 2A). Note: You need to ensure a common 0V reference is used between all the devices.


  • Increase the main capacitor from the 100uF shown in the photo of the parts kit, as explained in the module datasheet, to reduce the maximum current requirement from the external power supply:

recommended capacitor values from Neoway M590 hardware design manual


  • 1
    \$\begingroup\$ I replaced the cap with a 1000uF. It did the trick. Thanks! \$\endgroup\$ Commented Dec 10, 2016 at 16:28

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