My QLG1 is built.? After a few start-ups, the behaviour is as follows: Red LED lights immediately upon power up and yellow LED starts flashing at about 50% duty cycle once per second.? After a few seconds the green LED lights, almost continously.? If I look at the green LED carefully I can see that it is dimming briefly once per second, just before the yellow LED turns on.? Current drain is about 50 mA at 5.0V supply.

Is this the correct behaviour (i.e. the PPS output from the board is at 5V 90% of the time) ?

Unfortunately, I don't have an oscilloscope, or a suitable interface to allow reading the NMEA messages, that could tell me better what is going on.

73,
Steve VE3SMA

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Hi Steve,

The red and yellow LED's behaviour seems normal, but the green PPS LED should remain off until a lock/fix is obtained, then only wink on briefly once per second ... just before the yellow LED turns on.

Seems like something is 'upside down' or 'back to front' in the PPS circuitry ... ???


73, Bob? ZL1RS

P.S. today it is taking about 30 seconds from power up to obtain a fix with the external active GPS antenna.

Hi Steve,?
Bobs' description is how it should work but you obviously are not seeing this.
What have to got connected to the QLG1 (U3S etc)?
Can you isolate the PPS line?? It could be you are feeding volts into the the PPS output line?

You could build a simple transistor inverter and feed this into a PC to look at the GPS DATA coming out using a terminal programmme.

73 Ken G4APB

Hi Steve,?
I had a problem where suddenly one of my qlg1 developed a problem where the green led was constantly lit. I traced it to a bad 74ACT08.
Check that on pin 1and 2 you have a varying voltage, basically on, off. If so do you have a voltage, again varying on pin 3.
if yes check pins 4 and 5 for a varying voltage, if yes do you have an output on pin 6.
Good luck?
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

Forgot to say, an analogue volt meter would show this best.
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

Thanks for all your comments and suggestions.? I have nothing connected to the QLG1 at this point other than a few feet of 3-wire shielded cable from the 4-pin terminals.? I have done some probing with an analogue voltmeter- pins 1 & 2 are around 3 volts and dropping briefly every second (but I can't tell how far the voltage drops as the voltmeter responds too slowly).? As it seems it should be the other way around, I am suspicious of the 74ACT08 (IC1a), and hoping the problem is not in the GPS module.

73,
Steve VE3SMA

The green LED indicates an active lock on the satellites. Are you where you have good access to the sky? Do you have a metal roof, perhaps? Or are you in a basement? It does need to have a fair view of the sky to work. Which way is the antenna facing? It should be up or toward the sky.
My unit is mounted in a plastic case sitting on a windowsill (without a metal screen) and looks out at an open patch of sky. I acquire a PPS lock (flashing green) in a minute from cold start (without backup battery). It is very sensitive compared to my hand-held location GPS but they are all hampered by heavy vegetation, metal roofs, foil-backed insulation, and such. It is a QRP microwave signal from outer space. It needs all the help that it can get.
You could use an LED with a 470 ohm resistor on one leg as a probe. The other lead of the LED would go to ground. Pin 6 of IC1 should flash it.

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On 14/03/2019 1:08 AM, Steve Kavanagh via Groups.Io wrote:

... I have done some probing with an analogue voltmeter- pins 1 & 2 are around 3 volts and dropping briefly every second (but I can't tell how far the voltage drops as the voltmeter responds too slowly).? As it seems it should be the other way around ...

?
Indeed Steve, Pin 1 and 2 on IC1a should be low and have positive going pulses after the GPS has obtained a fix/lock.? Confirmed on the QLG1 here which is operating correctly.?

Just pulling at straws, but would there happen to be a solder bridge/whisker/un-etched PCB along the PC track from Pin 3 of the GPS module (near the zero in "R10" printed on the board) to Pin 1 and 2 of IC1a, particularly around the through-holes and PC track 'jumper' near C4 (the regulator 3V3 output smoothing capacitor)?? If everything along there appears clean, and if it were mine, I'd then cut that PC track and see what is coming out of pin 3 on the GPS module.? Brutal, and ugly when later repaired, but ...

73, Bob? ZL1RS

Yes, Bob...I was thinking along the lines of maybe cutting pins 1 & 2, but it would require removing a capacitor to get at them, so maybe cutting the trace would be easier, though it will require a fine soldering iron tip and a steady hand to repair it!

73,
Steve VE3SMA

Before you do that Steve,?
What is the output of pin 6? It should vary from 0 to around 3v, does it?
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

Andy

Not having an oscilloscope, it's hard to say.? An analogue meter shows pin 6 close to 5V but dropping briefly (how far, I can't tell) each second.? This is the same as the LED appears to be doing, as it should be.? Pins 1 & 2 are doing something similar near 3V.??

I am trying to devise a more meaningful test method and thinking about breaking down and ordering a cheap 'scope.

73,
Steve VE3SMA

Hi Steve,?
You shouldn't be seeing 5v, looks like 3v would be right dropping to 0.
I had a problem with a qlg1 where the output pins showed a constant voltage, cut all the IC pins, unsoldered the pin stubs left, put a socket in with replacement ic1 and problem was sorted.?
Hope you fix it,
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

I think your green LED is in backwards, and other than that it is working correctly.

I built two QLG1s, the first one has a blinking green LED when a fix is acquired, the second one will not blink the green LED with a fix. I know #2 QLG is working fine because it's hooked up to a U3S. Maybe one of these days I'll troubleshoot the problem.
--
John, WB5THT

Ok. I have made a small step forward. In lieu of an oscilloscope I made a simple circuit with an LM111 comparator and an LED. It is set up so the LED will turn on whenever the input voltage is below a reference voltage, which is set with a pot.

When the input is connected to IC1 pin 1 (1PPS output from GPS module) the test circuit LED flashes briefly once per second for a reference voltage as low as 0.5 V. Above about 3 V reference the LED stays on. So it seems Pin 1 really is sitting at about 3 V 90 percent of the time and about 0 V 10 percent of the time.

I wonder if the GPS module is designed somehow to produce an upward 1PPS pulse into a pull-down load or a downward pulse into a pull-up load.

I guess the next step is to break the connection at the GPS module output and see if it does the same thing when isolated from the 74ACT08.

73,
Steve VE3SMA

I see from looking at the (still woefully incomplete) data sheet for the MediaTek MT3339 or MT3337 GPS chip used in the QLG1's YIC5 GPS modules that the duty cycle of the PPS pulse is programmable (doesn't say within what limits) - I wonder if the latest batch from YIC are different from the earlier ones?? The negative-going 1PPS pulse is not uncommon in GPS receivers, as I understand it (though I am far from knowledgeable on this subject).

73,
Steve VE3SMA

Hi Steve,?
I don't know how long you have had the kit, there were some sent out with the wrong firmware installed at factory,?

?

After this was discovered Hans flashed some chips to sort the problem out.?
Andy

The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

Thanks for pointing that out, Andy.? But mine was ordered just a few weeks ago, so it should be immune from that particular problem.

73,
Steve VE3SMA