It was not vacuum tubes. They dd have transistors then, you know!

 

OMG, lie detector with vacuum tubes. one should start sweating at the thought of being hooked up to such circuit

I found a photo of the lie detector being prepared for testing:

 

The things John Carpenter could do with this as a remake:

I pulled this post up before donning my reading glasses.
As a Canadian I read THE DAY OF THE TARRIFS. !!

 

I've searched for old articles before, there are archive sites.

But saying "70s or 80s" mean potentially 240 distinct issues to search.

Try to narrow the window, like do you recall anything else in the magazine, some other article perhaps, any recollection of the cover image?

To be honest, I didnt think this would be so difficult

 

To be honest, I didnt think this would be so difficult

The problem is that I dont think it was part of the typical "splash" artwork on the cover, as the main projects get.
Dont worry about it, I just thought it world be a fun project from my past that would be fun to make after all the years. The other project I never ,made, but always wanted to was a V.L.F. Receiver, I could never make it at the time because it required a TRIPLE Gang 365 pf tuning capacitor....which I couldnt find at the time.

 

The problem is that I dont think it was part of the typical "splash" artwork on the cover, as the main projects get.
Dont worry about it, I just thought it world be a fun project from my past that would be fun to make after all the years. The other project I never ,made, but always wanted to was a V.L.F. Receiver, I could never make it at the time because it required a TRIPLE Gang 365 pf tuning capacitor....which I couldnt find at the time.

Some of the old UK magazines have some excellent receivers and I recall some were VLF. There was a guy named F.G. Rayer, he dabbled in science fiction but also designed some impressive receivers in the 60s/70s, he was an early user of the 40673 dual gate MOSFET.

Not sure about a VLF project, I'm sure I saw then back in the day though...

See:

Page 288 of this 1975 issue

This is a great site - World Radio History

Their brute force search page.

 

Back in high school, we actually did this project. I had seen a similar circuit, but I believe it was POPULAR ELECTRONICS, which used differential amplifiers and narrow band filters to extract a plant’s electrical signals.

Rather than building PE’s crude circuit, we were fortunate that one of the team member’s dad was a professor at a local medical school.
He would allow us to use (supervised and assisted by a licensed technician) the lab’s ECG machine, a professional multi-channel device with boatloads of CMRR and all sorts of filters and adjustments, which were able to discern the valid electrical signals in much larger values of electrical noise.

The raw collected data was fed to a PDP-8 mini computer for further digital processing. Furthermore, the technician understood whether we had recorded was valid or spurious data. And he knew how to perform blind A-B comparisons and apply statistics to prevent bias.

Even then with all the professional assistance, the results we got were inconclusive.
But it was still a very fun and engaging project.
If anything, you will learn the art and science of extracting minute electrical signals on a sea of random and periodic noise.

 

I believe you are not after soil/environment monitoring, but plants themselves. If not successful locating the article, perhaps other modern places after the first below :

¿? mentions polygraph, [ - 0 + ] meter... ----> https://borderlandsciences.org/project/bio-icomm/lg.lawrence/Electronics_and_the_Living_Plant.html

----> https://duino4projects.com/plant-communicator/

----> https://www.science.org/doi/10.1126/sciadv.1501136

----> https://www.researchgate.net/publication/284277313_Electronic_plants

----> https://www.sciencedirect.com/science/article/pii/S1872204022001669

----> https://www.nature.com/articles/s41528-022-00177-5

----> https://www.researchgate.net/figure...PWS-for-plant-pulse-monitoring_fig6_361258035

Or somewhere here ----> https://search.brave.com/search?q=+...summary=1&conversation=6faa78b7741efbd6ee59d8

----> https://search.brave.com/search?q=monitoring+plants&source=web

 

Looking for a very old magazine article, could be around the 70s/80s. It was an article about communicating with your plants, and was basically a lie detector circuit, with an output to a 50/0/50 meter. Could be either elementary Electronics or Popular Electronics Magazine

1970-1980's spans about 20 years. Let's try to narrow down the years. How old are you now? How old were you at at time when you saw this article?

 

If you can recall the exact article title then you could search for that.
I just happened to be examining my archives and there were a stack of construction articles from Popular Electronics, about 1968 thru 1974 that I had torn out and saved. No luck. So it may not have been a project article. Or more recent than 1974.

 

Popular Electronics June 1971 has an article similar to what you describe, although their circuit has a 1mA meter rather than 50-0-50uA

 

What's the actual meaning of 50-0-50uA in this context? Polarity?

 

What's the actual meaning of 50-0-50uA in this context? Polarity?

An old-style analogue meter with center-zero and +/- 50uA deviation to FSD either side:

 

They were also called nulling meters, very useful for balancing Wheatstone or similar impedance bridges.

 

Or "centre zero" ammeters.

 

Elementary Electronics:
https://www.worldradiohistory.com/A...cs/1970/Elementary-Electronics-1972-11-12.pdf
https://www.worldradiohistory.com/A...cs/1970/Elementary-Electronics-1974-03-04.pdf
https://www.worldradiohistory.com/B...als/Electronics-Hobbyist-1974-Fall-Winter.pdf
https://en.wikipedia.org/wiki/Cleve_Backster

 

Page 25 of the third link shows a schematic.

 

It was not vacuum tubes. They dd have transistors then, you know!

I remember 741 amps in the old "Metal Can" style

 

https://www.worldradiohistory.com/B...als/Electronics-Hobbyist-1974-Fall-Winter.pdf
Bassbindevil has found it!!!!!!!!!!
I am sane (in relative terms!!!!!)
Thank you everyone, and especially bassbindevil.

 

https://www.worldradiohistory.com/B...als/Electronics-Hobbyist-1974-Fall-Winter.pdf
Bassbindevil has found it!!!!!!!!!!
I am sane (in relative terms!!!!!)
Thank you everyone, and especially bassbindevil.

Took awhile but I now remember that article.