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Friday, July 18th 2003, 10:57am

Big problem to power up GM-862

Hi :)

I make PCB board to use with GM862-GPRS. This circuit has 3,6V (max 3A currency) power supply
(highly stabilized), and lines:
RXD and TXD (to communicate with GGM862-GPRS) via UART, lines ON/OFF and PWRCTL.
Everything is connected to AVR ATmega32L microprocessor.

When i switch power on, my ATmega32L starts, he sets up to HI-LEVEL (+3,6V) on ON/OFF line,
then he wait about 2 secs. and next sets ON/OFF line to LOW-LEVEL (0V) for 1 sec.
(look at GM862-GPRS_Hardware_User_Guide_issue1.pdf - page 5) and one more time sets it up to HI.
I think in this moment GM862-GPRS should self power up and then bring up PWRCTL line to HI-LEVEL (+2,8V), but it DON`T DO THIS! All the time I`ve LOW-LEVEL on line PWRCTL (0-0.29V).

I know that in normal work GM862-GPRS gives short HI-LEVEL pulse to PWRCTL line, i understand that minds he reset propabbly. but when GM862-GPRS is directly connected to my board he don`t give this pulse.

I check my PCB board, and i think everythink looks ok!

When i do simple connection "in AIR" with use Molex 52991-0508 (male) pluged into GM862-GPRS module
and connected to my board (only lines: VBATT, GND, ON/OFF), i indicate HI-LEVEL (+2,8V) on PWRCTL line) - thins mind that module power up (I think).

What can be wrong?
ATmega32L set line RXD to LOW-LEVEL (0V) and TXD to HI-LEVEL (+3,6V) before send power up 1sec signal to ON/OFF line. Is this OK?

This is possible to electromagnetic impulses indicated by ATmega32L microprocessor (clock 1,8432MHz) due to GM862-GPRS can`t power up?

Any suggestions?

Please response to my post on this forum or directly to my email:
I can send schematic and PCB layout of my circuit to any intrested peoples of my problem to priv.

Best Regards.

Krzysztof Gawrys




Sunday, July 20th 2003, 5:45pm

Big problem to power up GM-862


In the GM862 hardware userguide at page 5 it says that the ON/OFF line must only be connected in an open-collector configuration. A high level (3,6 V) or a pull-up resistor should not be connected to this line since it can cause a latch up of the GM862 internal circuit and then powering up can fail.
I`m using a transistor between my AVR and the GM862 and it works fine.
An easy way of testing the powerup function is to just connect ground (0 V) to the ON/OFF line for 2 seconds and then remove the connection so that the line is floating. This should turn it on. You can also try connecting a LED to the STAT_LED pin to see what is happening.






Thursday, August 7th 2003, 3:38pm

Big problem to power up GM-862


I`m having the same problem just like Mr.Krzysztof Gawrys. In addition, I also did what Mr.Peden have suggested. I`ve connected a LED to the STAT_LED pin. I checked the voltage coming in and out of the LT1528 and they`re OK. What could have I possibly missed? Any suggestion?





Friday, August 8th 2003, 1:41pm

Big problem to power up GM-862

I had the same problem today. The Stat-Led was pulsing whilst I was trying to ground the ON/OFF line. I soon realised that my benchtop PSU had its current limited ! SO check that your PSU is able to deliver a full 2A.




Saturday, August 9th 2003, 2:22pm

Big problem to power up GM-862

First! Sorryyyy for my English. :-(
Ok, now i exacly know how to do to power up GM862. I`ll try to describe this.
Unfornetly on this forum is not possible to attach any file to post message (Moderators think about this!), so i do that:
You need to get two N-MOSFET DMOS transistors, I connect SOURCE of first transistor to GATE of second transistor, DRAIN i need to connect to positive power supply voltage eg. +5V, and SOURCE of second N-MOSFET transistor connect to ground (0V), and than DRAIN of this transistor connect to ON/OFF pin of GM862 module.

I use this simple circuit 2xN-MOSFET based, simple 1s positive pulse to GATE of first transistor should power up GM862.

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