SparkFun Forums 

Where electronics enthusiasts find answers.

Tips and questions relating to the GPS modules from SFE
By molex
Hey Guys,

I'm using a GM862 Quad and I bought a 50 pin breakout board for it. I have connected
the three GND pins to ground and the four VBATT pins to 3.8V. The 3.8 V is provided by
the LT1528 regulator. RXD, TXD lines are connected to T1IN, R1OUT lines respectively of a Max232 which is powered using 2.8V.

The PWRMON signal is connected to an LED in series with a 560 Ohms resistor which goes to ground, and the STAT_LED pin of the GM862 is connected to the -ve side of an LED which is connected in series with a 220 Ohms resistor which is in turn connected to 3.8V.

RST is connected to ground and ON/OFF to a debounced switch which ties the ON/OFF pin to ground when pressed.

Problem is the PWRMON LED doesn't turn on when I apply power to the circuit. Consequently, the status LED doesn't blink.

In fact, I expected that if I test the ON/OFF signal with an oscilloscope, it would be at around 3.8V when the switch isn't pressed down but that's not the case.

Could there be something that I could be doing wrong? By the way, is connecting VBATT to 3.8V and GND to ground enough for the module to power on (i.e for the PWRMON pin to go high).

This is very urgent guys. I would really appreciate anyone's help.

Thanks alot,

User avatar
By leon_heller
You don't need a debounced switch for ON/OFF, your circuit probably isn't pulling it right down to ground. Try grounding it directly.

Make sure you have a 100 uF tantalum directly across the supply pins.

By molex
Ok. Thanks, I will do that. I'm trying to avoid reconnecting rx and tx signals at this moment. Is it ok to assume that the module will power on without connecting these signals?

Also, I assume that since we're pulling ON/OFF to ground, it must originally be at some high voltage. However, when I connect the ON/OFF pin to the oscilloscope, it shows zero volts. So perhaps something is wrong with the module/my connection because even before I pull it to ground to turn it on, the ON/OFF pin should probably be at some high voltage like 3.8V. Or am I wrong?

User avatar
By leon_heller
I've only used the GE863, but it's similar. It should power up OK without RxD and TxD connected.

I've just checked the ON/OFF pin on one of my prototypes, it is at 3.9V. Perhaps you have something wrong with your module.

By falingtrea
molex wrote:Hey Guys,

I'm using a GM862 Quad and I bought a 50 pin breakout board for it.

RST is connected to ground .

That's your problem, right there. RESET# is active low. Here is a quote from the data sheet.

"NOTE: don't use any pull up resistor on the RESET# line nor any totem pole digital output. Using pull up resistor may bring to latch up problems on the GM862-QUAD / PY power regulator and improper functioning of the module. The line RESET# must be connected only in open collector configuration."

So Reset needs to be floating and then pulld to ground by some sort of circuitry when a Reset is required.
By molex
sorry! I mean RTS and RST. Reset **is** hanging, but RTS is connected to ground.
By spenk
Hi, I have same problem! have you solve the problem? I use an adapter with 12v output (1.5A max) , a 7808 and a lm317 with 3.8v. on pin on/off I have 0V and the status led doesn't turn on. RTS is ground and reset is floating.
I try with 2 different gm862 and 2 GM862 Evaluation Board - Basic 50-Pin.
help please!!!!
By molex
What I needed to do was urgent so I did not solve the problem and abandoned the project for a while. If you end up solving the problem, I am interested in knowing what you did. Can't help, sorry...
By spenk
now I try to contact the telit support. I hope!!!
By spenk
ahhhhh! I have solved the problem. the problem was the plastic label in the molex connector of the boad. I have removed that label and now the status led blink
I hope you have the some problem!!!