SparkFun Forums

[biscuit]

Hello,

I bought the Venus GPS (gps-11058) and a usb to TTL converter, which has a regulated 3.3v output, (dev-08531) and I thought should be sufficient. I've wired the 3.3v output from the usb-mb5 to the venus along with the tx and rx to the tx0 and rx0 on the venus. And they are crossed -- tx -> rx0, rx -> tx0.

The venus is definitely getting power (the LED lights up). And my laptop saw the usb-mb5 and I installed the drivers. The com port is configured to 9600 and the SkyTraq GPS Viewer is set to the right com port and baud. But the gps viewer cannot communicate with the Venus itself.

Can somebody point me in the right direction as to what I'm doing wrong?

Thank you,
Rich

[teekay_tk]

Do you have a multi-meter and can you cheack voltage on the TX and RX lines. It may be that these two lines need pullups to work. in that case do you have , say, 10K or 100K resisitors to use as pulls ups to 3.3V on these lines?

[teekay_tk]

Working with electronics you will need the right tools. May be good idea to invest in a low cost oscilloscope like the http://www.seeedstudio.com/depot/index. ... es&x=0&y=0

[biscuit]

I will check that out. I've got a nice multimeter but not an oscilloscope yet...althought I have been looking for an excuse to get one. I'll let you know what I find out, thanks for the suggestion!

[biscuit]

Alright, my voltages seem okay.

USB-MB5 Outputs:
3.3v is a steady 3.393v
TX0 is 3.258v
RX0 is 3.393v (I guess this is technically output from the Venus)

One thing I've noticed is that the led on the Venus seems very...dull. It's lit up but it's just not very bright at all. I wired an LED to the PPS and I'm getting flashes out of it about once every 4 seconds instead of once every second.

3.258v on TX0 seems a reasonable level to me. Can anybody confirm this? Or have any other ideas?

Thanks,
Rich

[teekay_tk]

ok

try this.. if you have a capacitor like 100uF can you put this across the GPS power lines as close to the GPS connector as possible. Sometime the Skytraq GPS doesn't start very well. Also, can you stick a the multimeter in current mode inline with the power line to GPS to see how much current it is drawing.

If its a startup problem it will be drawing very less. If its some other problem it should be around the 60-70mA .

[biscuit]

Tried the cap but it didn't have any impact.

The current draw stays right around 24.6-24.7mA. So based on what you said it sounds like a startup problem.

[biscuit]

Another interesting note is that if I connect up an LED to the NAV output on the venus board the LED on the venus board gets very bright -- more along the level I would expect it to be normally.

Also noticed that when I attempt to send a command to the venus through the gps viewer I see the activity light blink on the usb-mb5. So it's sending the command...it just never receives anything from the venus.

[biscuit]

Still not having any luck. Let me ask one more question... If there is no antenna connected (and therefore no satellites picked up) will the venus output anything? I would assume that I should still be able to query the software version and such.

At this point I'm thinking the venus I received is defective.

[teekay_tk]

Hi
yes the gps should be saying something. Assuming TX0 is output from GPS and TX0 is 3.258v instead of 3.39 this may mean that there is data on the line, just your multimeter is averaging it out and showing a lower voltage. Have you considered that the USB converter can be faulty as well. As you dont have oscilloscope, you cant tell exacly what is and what is not working. I have a feeling if you return the GPS device and get another one in and find it doesnt change anything?

[biscuit]

Well, I threw an LED on the data lines. When I sent a command from GPS Viewer the LED on the USB converter flashed and the LED on the TX line coming off the USB converter flashed. So the converter definitely got the command and forwarded it out of it's own TX output.

However, the LED attached between TX0 on the Venus and the RX line on the USB converter never flashed at all. And if the Venus were outputting any data it should at least trigger a flicker in the LED I would expect.

[teekay_tk]

can you upload a picture of your setup?