Hi
I am using L89 gps for one of my product and i am connecting an LED with 330 ohm resistor for the PPS.
Is that ok or do i compulsory need to use a transistor to drive that LED.
Also some of the clients compliant that there is no output sometimes but after few hours/days its started giving the data out. Confused.
also i am just using the TXD, IPPS, VCC, Vbackup, Ground pin and keep all other in open condition.
i am using 4.2v battery at Vbackup and 3,3v from 5v using AMS1117, guide me please
Edit: my power supply module can deliver 200ma in which the vbackup charger ic is tunned for 50ma and hc05 Bluetooth module needs 40ma. Is there any problem here.
Hi Binu_Johnson,
About PPS indicator, the EVB SCH is shown below. Please take a reference.
Is there any problem when i connect a LED with a 330 ohm resistor?
Also sometimes the L89 does not give out any NMEA sentences on the output. But once i remove the Vbackup and then switch on the module then it start giving the output.
what is the problem?
i am just connecting the Vbackup, VCC, GND and TXD pins, all other pins are open connected.
Do i need to connect any other pins?
since this problem occurs at customer side its difficult for us to remove the vbackup and reconnect it.
Hi Binu_Johnson,
Can you show me the LED with a 330ohm resistor SCH design? Cause I’m not sure about the circuit.
About the no output problem:
- Is it useful to turn off and on VCC (or reset the module)without disconnect VBCKP, when the problem occurs?
- Does the customer strongly need the backup mode?
- What’s the firmware version that currently used? Query by sending $PSTMGETPAR,1500
Best regards.
Hi Binu_Johnson,
Please note that the V_BCKP must be powered simultaneously with the VCC or before it.
Best regards.

This is the schematic for LED
About the no output problem:
- No even i reconnect the VCC and reset the module nothing at the output, only after removing the Vbackup and Connect Vcc again it starts giving output.
- It would be fine, if they get the fix soon. but not so critical
- Havent checked it.
- The Vbackup is connected to battery always.
Also can i connect the Pin7(Wakeup) to ground, is it necessary?
Hi Binu_Johnson,
About the schematic for LED. PPS output voltage is always lower than 3.3v . And in your schematic, PPS pin is pulled high externally. Please use a transistor to drive and refer to Reference Design.
Hi Binu_Johnson,
There is no need to pull down Wakeup pin externally.
Hi Binu_Johnson,
Can you try to connect VBCKP with VCC? That means VCC power supply to the two pin. And see whether the problem reappears or not.
Best regards.
Yes, i tried that. most time it works fine. But only one time it happen again and then i switched off the gps and switched on few minutes later and then its started giving nmea at the output.
i think better remove the vbackup battery and connect the Vcc and VBCKP. only disadvantage is it take 1 to 2 mins to get the FIX, since my product is a Bluetooth GPS and not time critical i am going to use this method.