TruePosition GPSDO troubleshooting - Page 1
Forum section: electronics / projects

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 25, 2018, 05:26:56 pm
content: I am currently working with one of the TruePosition GPSDO boards, and having a communication issue.I have the later Rev C board with the CTS OCXO.I have the board working fine with the RS232 connected to the 6 pin header.But I would like to eventually use an Arduino to connect to the board, and not use a PC.If I connect a USB-TTL board to the 15 pin header to bypass RS232, I can receive data, but not transmit to it.So, I can't break it out of the boot loop when it powers up.I am a little concerned that the USB-TTL board may have damaged the TruePosition.I don't believe those TTL ports can handle more than 3.3v.I have a CP2102 USB board, but I just found out it was one of the flawed ones that put out 4.2v.It wouldn't control my uBlox Neo 7M board either.I corrected that and it now works with the Neo.But not with the TruePosition.Can someone else here who has a Rev C TruePosition board take some voltage readings for me to compare??With nothing connected to the headers, I measure 3.3v on pins 7 and 8, which is the transmit out.When I measure pins 3 and 4, I measure 1.5v. That is the receive in.I know that pin 5 on the RS232 header needs grounded for it to work, and if it's grounded, then the TTL doesn't accept commands.But mine will not accept commands even with pin 5 of the RS232 header open.I didn't realize that my TTL board was a flawed one, so now I'm concerned I damaged something.Thanks for any help!

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 27, 2018, 02:47:26 pm
content: I think my only option now may be to use a MAX232 or 233 chip from the Arduino and connect to the main RS232 header.The Arduino is 5v anyway, so I'd have to use a level shifter if I did get the TTL port to work, at least on the RX in.My guess is that the RX input on pins 7 and 8 of the TruePosition is either damaged, or not enabling properly when removing the enable jumper from the RS232 port.

author: texaspyro
author_rank: Super Contributor
timestamp: February 28, 2018, 07:28:27 am
content: Check the Packrat docs on this GPSDO. There is a jumper that needs to be installed to use RS-232 and removed for Arduino. You can get 3.3V Arduino Nano boards...

author: Squiddaddy
author_rank: Regular Contributor
timestamp: February 28, 2018, 02:16:14 pm
content: Thanks pyro.I do know about the jumper. I had installed it to get the RS232 DB9 to work. But when I remove the jumper, I still cannot get the TTL section to receive data from the PC. It transmits fine. So, on TTL, I get stuck in the BOOT loop. On RS232, I can get past it.When I measure pins 7 and 8, there is 3.3v on them. Scope shows the data stream. When I measure pins 3 and 4, there is about 1v and it either floats around that, or it drops over time, like it's discharging a cap. Same result whether or not the enable/disable jumper is installed.That's why I'm concerned that the 3.3v TTL-USB board being faulty may have damaged that RX in with overvoltage, even though it was only 4.2v. But that may have exceeded the pin. And I didn't try it very long. I now have a USB-TTL 3.3v board that works.The RS232 DB9 works fine to the PC, I just wanted to get the TTL going with a microcontroller, to save having to use a MAX233.And the Packrat docs are wrong. They show 3-4 and 5-6, but 5-6 are GND. It should be 3-4 RX and 7-8 TX, and 11-12 for 1PPS.Not sure what exactly enables/disables the TTL pins when the jumper is installed/removed, but mine appears to not function.

author: TWMIV
author_rank: Contributor
timestamp: April 19, 2018, 05:55:04 pm
content: I am having the same issue with this version of the board currently. I haven't tested the rs232 port as of yet, but on the TTL port I can receive but not transmit anything to the board.I also have the older version of the board coming in the mail to compare it to the newer version which I already have.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 19, 2018, 06:47:34 pm
content: Quote from: TWMIV on April 19, 2018, 05:55:04 pmIf the TTL <-> RS232 converter chip is connected to the TTL RX port it will hold the input either high or low and you will not be able to transmit to the board if you can't break the connection or make the converter go high impedance/tristate.

author: texaspyro
author_rank: Super Contributor
timestamp: April 19, 2018, 06:55:47 pm
content: Quote from: PA0PBZ on April 19, 2018, 06:47:34 pmIsn't there a jumper that you have to move in order to use the logic level serial port? It is mentioned in the Packrat documentation.

author: TWMIV
author_rank: Contributor
timestamp: April 19, 2018, 07:59:29 pm
content: Quote from: texaspyro on April 19, 2018, 06:55:47 pmOn the 2010 boards I am not sure how the jumper functions on the RS232 interface, however I now have it working.I removed and reattached the usb-TTL adapter and changed power supplies and it began responding to commands over TTL. I had been powering it from a 66312A which went into CC mode at 10.7 V 0.25 A and figured that may have been an issue, so now I am feeding it 12 V from an E3630A and it is still drawing 0.25 A but now I am able to get past the boot mode.

author: Squiddaddy
author_rank: Regular Contributor
timestamp: April 22, 2018, 02:30:58 am
content: I have always powered mine by 12v, and it pulls between 200 and 250mA, but I still cannot get the TTL to work. I have 2 different USB/TTL adapters, a CP2102 and a CHG340, both capable of 3.3v operation. Maybe I'm having that issue where it's holding the state wrong. Did you still need to leave the jumper off of the RS232 port to get the TTL to work??I still think my board may have been damaged by the TTL adapter exceeding 3.3v.