Happy New Year, Peter. If you get the chance, would you also have a look at the buffered 1PPS signal? I received my boards meanwhile and after mounting the LEA module I connected the 1PPS output to a scope to measure the signal rise time. I'm getting around 6ns for the 10%-90% rise and the output is not quite reaching 2.5V. That is not bad but not as fast as I'd like. I'm thinking of reducing R16/R17 to 68 Ohm to get the impedance closer to 50 Ohm. Best regards, Matthias On Mittwoch, 30. Dezember 2020 17:56:37 CET Matthias Welwarsky wrote: > Quick heads-up for everyone who might have ordered the breakout board based > on design files I uploaded to github before Dec. 28th. > > As Peter Bell found out, the voltage divider that provides VDD_USB to the > LEA module is not adequate, the impedance is way too high and since the > current drawn by the VDD_USB pin is quite variable, there is little chance > to dimension it correctly. However, it might still be possible to salvage > the boards. I suggested, and Peter verified it, that replacing R7 with a > red LED (0603 footprint), oriented such that the cathode connects to > VDD_USB, will provide an adequate supply to the pin and might even double > as an USB indicator light. > > I've updated the files on github on Dec. 28th and added a 3.3V LDO regulator > instead of the resistor divider. This is the solution recommended in the > hardware integration manual for the LEA-M8. > > My own boards still haven't arrived. > > BR, > Matthias > > On Samstag, 26. Dezember 2020 10:06:11 CET Peter Bell wrote: > > Just a quick note for anyone building these - I got my boards back and > > assembled them > > and everything works except for the USB port. This is being caused by the > > VDD_USB > > pin being fairly low-impedance and dragging down the voltage of the R7/R9 > > potential > > divider to about 700mV, at which point the module doesn't recognize it's > > connected. > > > > I guess the "proper" fix would be to add another 3.3V LDO to the board > > that > > runs from > > VBUS and generates VDD_USB - but for testing purposes I removed R7 and > > connected > > the VDD_USB pin to the 3.3V on pin 2 of U4 - after doing this, the board > > connected > > and enumerated as a virtual COM port. > > > > Regards, > > > > Pete > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow > > the instructions there.

Hi If you are looking at the “raw” output of the uBlox, it is not designed to drive a low impedance. Even if there is a buffer, it may or may not like a low impedance load. Bob > On Dec 31, 2020, at 7:39 PM, Matthias Welwarsky <time-nuts@welwarsky.de> wrote: > > Happy New Year, Peter. > > If you get the chance, would you also have a look at the buffered 1PPS signal? > I received my boards meanwhile and after mounting the LEA module I connected > the 1PPS output to a scope to measure the signal rise time. I'm getting around > 6ns for the 10%-90% rise and the output is not quite reaching 2.5V. That is > not bad but not as fast as I'd like. I'm thinking of reducing R16/R17 to 68 > Ohm to get the impedance closer to 50 Ohm. > > Best regards, > Matthias > > On Mittwoch, 30. Dezember 2020 17:56:37 CET Matthias Welwarsky wrote: >> Quick heads-up for everyone who might have ordered the breakout board based >> on design files I uploaded to github before Dec. 28th. >> >> As Peter Bell found out, the voltage divider that provides VDD_USB to the >> LEA module is not adequate, the impedance is way too high and since the >> current drawn by the VDD_USB pin is quite variable, there is little chance >> to dimension it correctly. However, it might still be possible to salvage >> the boards. I suggested, and Peter verified it, that replacing R7 with a >> red LED (0603 footprint), oriented such that the cathode connects to >> VDD_USB, will provide an adequate supply to the pin and might even double >> as an USB indicator light. >> >> I've updated the files on github on Dec. 28th and added a 3.3V LDO regulator >> instead of the resistor divider. This is the solution recommended in the >> hardware integration manual for the LEA-M8. >> >> My own boards still haven't arrived. >> >> BR, >> Matthias >> >> On Samstag, 26. Dezember 2020 10:06:11 CET Peter Bell wrote: >>> Just a quick note for anyone building these - I got my boards back and >>> assembled them >>> and everything works except for the USB port. This is being caused by the >>> VDD_USB >>> pin being fairly low-impedance and dragging down the voltage of the R7/R9 >>> potential >>> divider to about 700mV, at which point the module doesn't recognize it's >>> connected. >>> >>> I guess the "proper" fix would be to add another 3.3V LDO to the board >>> that >>> runs from >>> VBUS and generates VDD_USB - but for testing purposes I removed R7 and >>> connected >>> the VDD_USB pin to the 3.3V on pin 2 of U4 - after doing this, the board >>> connected >>> and enumerated as a virtual COM port. >>> >>> Regards, >>> >>> Pete >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow >>> the instructions there. > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.