Adding Continuity to old DMMs with GPIB? - Page 1
Forum section: electronics / projects

author: agentrob95
author_rank: Newbie
timestamp: January 30, 2022, 02:46:09 pm
content: Forgive me as I know very little about GPIB or Continuity test circuits.I have an HP 3457A and Fluke 8520A that I use quite frequently, and I enjoy using them but it would be nice If these old meters had a continuity function. Since both meters are basically built around their GPIB interfaces from what I understand, an idea struck:Continuity, from what I understand is basically:While (mode == Resistance && measuredResistance <= someThreshold){BEEP}...ideally latched for some time. Would it be possible to build a small board that does such a thing by monitoring the mode and measured value over GPIB?I know the real answer to this question is "buy a newer meter" but it seemed like it might be an interesting project to learn GPIB

author: Kleinstein
author_rank: Super Contributor
timestamp: January 30, 2022, 02:53:15 pm
content: In theory this can work, with a small µC to operate the GPIB. The tricky part is than however that GPIB is not easy with mulitple masters, especially if the interface is not full featured at the µC side. There is a GIPB with an AVR µC projet around that could be used as a basis for this (just add the SW and maybe a beeper).Still it would be easier to build a small stand along continuity tester with just a beep, no display of ADC needed.

author: inse
author_rank: Super Contributor
timestamp: January 30, 2022, 07:55:17 pm
content: I expect the response time would render it useless

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 30, 2022, 08:15:53 pm
content: Quote from: inse on January 30, 2022, 07:55:17 pmI mean... could be better than some products.Whether those count as "useful" though...Yeah, would be easy enough to take a typical GPIB project and run it as a dedicated master, with a built-in monitor function like that, assuming you don't need to share the port with anything else.Tim

author: Hydron
author_rank: Super Contributor
timestamp: January 30, 2022, 08:41:52 pm
content: Take a look here, seems to do what you want, albeit for a 3478A (possibly somewhat compatible with your HP though!):https://www.eevblog.com/forum/projects/project-extending-hp3478a-functionality/?all

author: agentrob95
author_rank: Newbie
timestamp: January 31, 2022, 12:49:13 am
content: Quote from: Hydron on January 30, 2022, 08:41:52 pmThis looks like exactly what I was thinking, and an oppourtunity get get my hands dirty with GPIB. Thanks!

author: free_electron
author_rank: Super Contributor
timestamp: January 31, 2022, 01:27:23 am
content: tricky. when you switch the machine to gpib you lose front panel control. so you would have to switch the machine to remote , check range , if resistance : trigger a reading , and figure out the beep function, then switch back to local ... it will be slow as hell....

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: May 01, 2022, 05:17:08 pm
content: I have a Yokogawa 7563 meter that has hi/low test output as a separate digital line. So I hooked up a buzzer directly on that line and it works well as a continuity tester. The only problem is that I have to program hi/low resistance limits each time I turn on the meter because I don't have an external memory card for it.On HP3457 there is a math pfail function that allows one to set limits. When test fails, it activates the SRQ line of the GPIB bus. One could make a buzzer respond directly to pin 10 on GPIB connector. The only problem is that the SRQ is not automatically cleared, one has to issue CSB command. So it probably still requires an external GPIB controller to clear.