Agilent 34401A Serial port pints 3 (TX) 5(GND) stuck at 9V on sys (SOLVED) - Page 1
Forum section: electronics / repair

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 02, 2024, 10:42:18 pm
content: Dear All ,After finally fixing my instrument I have a new issue.THe serial port regardless of its selected on the I/O between RS232 or GPIB the device directly applies 9V on the TX pin.Is this normal ? or I am looking at another issue ?ThanksAddendum :Using wrong method to talk to the instrument

author: macboy
author_rank: Super Contributor
timestamp: October 03, 2024, 01:28:15 am
content: RS232 idles at the high voltage level, so this is normal.

author: squadchannel
author_rank: Frequent Contributor
timestamp: October 03, 2024, 05:56:01 am
content: RS-232 protocol, it would be normal operation. There is no problem.RS-232 detects "0" at positive 3-25V and "1" at nagative 3-25V, not TTL.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 03, 2024, 11:29:48 am
content: okay , but when I connect a USB to serial device seems to not be happy with said levels.Do I need so have something else in-between the instrument and the USB to serial device ?Is the first time I am encountering such issue.

author: jchw4
author_rank: Regular Contributor
timestamp: October 03, 2024, 01:27:29 pm
content: Quote from: The_Spectrum.A_idiot on October 03, 2024, 11:29:48 amhttps://www.keysight.com/us/en/lib/resources/training-materials/communicating-with-instruments-using-rs232.htmlTLDR: you need correct cable.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 03, 2024, 01:37:37 pm
content: Quote from: jchw4 on October 03, 2024, 01:27:29 pmI've made said cable as per the service and user manual and your resource. Is exactly as its shown.I have a USB to Serial but I think something is up with it. Planning to buy a new USB to serial.Let me know any more tips.Thank you in advance

author: Kleinstein
author_rank: Super Contributor
timestamp: October 03, 2024, 03:26:00 pm
content: Many of the USB to seriel adapters (especially the cheap ones) are not providing RS232 levels, but only UART at 3.3 V or 5 V CMOS levels. So one would need a level shifter like a max232 in between to get the correct levels (and AFAIK also an conversion from a +3-12 V to a low and the other way around).

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 03:42:56 pm
content: These type cheap RS232 to USB adapters based on 340 chip work fine with our HP and AG34401As, no need for a level shifter. However you do need a Null Modem Adapter between the RS232 to USB tho.https://www.aliexpress.us/item/2251832395467136.html?spm=a2g0o.order_list.order_list_main.265.54ec1802qwN5Ri&gatewayAdapt=glo2usaEdit: BTW they also work with our other RS232 instruments, like the Hioki IM3536 and Tonghui TH2830.Best

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 03, 2024, 03:51:47 pm
content: Dear All ,I managed to make it kind of work with this softwarehttps://lygte-info.dk/project/TestControllerInstalling%20UK.html#Starting_TestControllerit popped up some errors while operating in remote mode. (550 ,-101,-410,-113)I will try to get my GPIB interface and see if I get better luck with that.I will come back with more info later on.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 03, 2024, 04:00:29 pm
content: There are serial adaters for RS232 levels and other for CMOS levels. The needed driver and converter chip alone does not tell - the difference is if they include the converter in addition to the USB-serial chip.One could check the TX output of the adater to see if one gets a 5 V or more 10 V signal level. What type of adater is used (maybe a small picture) ?

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 05:05:34 pm
content: Quote from: mawyatt on October 03, 2024, 03:42:56 pmShould mention that we talk to all these instruments with these cheap adapters directly with Python using standard commands as outlined in the Instruments Manuals.Here's an example:https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/?action=dlattach;attach=1766627Best

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 03, 2024, 05:11:59 pm
content: Quote from: Kleinstein on October 03, 2024, 04:00:29 pmThe whole idea was to use Node-red and serial option to query the instrument every second to get the value.This softwarehttps://lygte-info.dk/project/TestControllerInstalling%20UK.html#Starting_TestControllerRunning on a RPI with the logging feature now logging the resistance values on the meter measuring a 1M resistor.it may show up some errors but as long as I get my data I am happy.The cable I used was a custom one and an off the shelf one.Both USB to Serial adapters worked as expected the issue was trying to use putty and ExtraPuttyTel to interrogate the instrument.With the software mentioned above all works as expected.The picture you requestedThank you everyone again for your helpP.S :My GPIB modem is NI GPIB-USB-HS As I understand is limited support outside of the NI( national instruments software )

author: mawyatt
author_rank: Super Contributor
timestamp: October 03, 2024, 05:34:44 pm
content: We started our development of the above mentioned LCR Plotting Routines on a RPI, then ported to a PC under Windows 10.Got this working, and we are not good at software, firmware and coding, so you should be able to do this without too much effort!!BTW believe the RS232 Standard is the most Non-Standard Standard ever, with all the various levels, connectors, cables and suchGood luck with your revived 34401ABest

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 04, 2024, 01:28:48 pm
content: Another question ,How long should I let the logger run ?Already the resistance started drifting downwards (initial value 995.2525K - now 995.1699K) (it's only being a day) ,Should I let it run longer ? Or rather a better question would be , when should I stop ?Thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: October 04, 2024, 05:00:24 pm
content: The warm up time for a meter like the 34401 (no fan) should be in the 2 hour range. So to capture the full warm up, from initially cold to largely stable temperature this would be some 3 or 4 hours. So 1 day is plenty for the simple thermal effect. Humitidy efffects can be slower and take a few days, but I don't hing this is where you are interested in.Ideally set up the DUT and let it settle from handling well before turning on the meter, so that the transient is from the meter and not so much the DUT.

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: October 04, 2024, 05:03:57 pm
content: The DUT was on the table for a day before on the alligator clips I just plugged the wires after dealing with the logging issueSo in essence both of your recommendations unknowingly were performed